CLASS XTH

NOTES AND PRACTISE QUESTIONS

CHAPTER-2

ACIDS, BASES AND SALTS

On the basis of there chemical properties, all the compounds can be classified into three groups. Acids, Bases, and Salts Definition of acids, bases and salts: Acids Bases Salts Sour in taste Bitter in taste & Acid + Base →   Salt soapy to touch + Water Give H+ or H3O+ Give OH- ions in ions in aqueous aqueous solutions solutions

ACID-BASE INDICATORS: (FOR TESTING ACIDS AND BASES) 1.       DEFINATION: - acid-base indicators are those chemical substances that indicate the presence of acid or base in a solution by a change in their colour or smell. 2.       Indicators behave differently in acidic and basic medium thus it is help in determining the chemical nature of the substance. Acid base indicators indicate the presence of an acid or a base

Indicators can be natural or synthetic.

	Neutral colour	Colour with acids	Colour with base
Litmus paper	purple	red	blue
Turmeric	Red	Red	Green
Methyl orange	orange	red	Yellow
phenolphthalein	colourless	colourless	pink

The three common indicators to test for acids and bases are: Litmus, Methyl orange and Phenolphthalein. (i)                 Litmus: -- Litmus can be used in the form of litmus solution or in the form of litmus paper (Blue litmus and Red litmus). Litmus is natural indicator extracted from ‘lichen’ plant. The natural color of lichen is purple. ->An acid turns blue litmus to red. ->A base (or alkali) turns red litmus to blue. (ii)                Turmeric:-Turmeric is also a natural indicator. It contains a yellow dye. It turns red in basic solution. The red cabbage extract (obtain from red cabbage leaves) is also a natural indicator. It is red in acidic solution but turns green on adding to basic solutions. (iii)             Methyl orange:  -- Methyl orange is synthetic indicator. The natural color of methyl orange is orange. ->Methyl orange indicator gives red color in acid solution. ->Methyl orange indicator gives yellow color in basis solution. (iv)             Phenolphthalein: -- Phenolphthalein is synthetic indicator. The natural color of phenolphthalein is colorless. ->Phenolphthalein indicator is colorless in acid solution ->Phenolphthalein indicator gives pink color in basic solution.

Olfactory indicators: These are those indicators whose odour changes in acidic or basic medium. Example: onion, Vanilla essence. ·         Onion: Smell of onion diminishes in a base and remains as it is in an acid. ·         Vanilla essence: The odour of vanilla essence disappears when it is added to a base. The odour of vanilla essence persists when it is added to an acid.

You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube? ·         Answer ·         If the colour of red litmus paper gets changed to blue, then it is a base and if there is no colour change, then it is either acidic or neutral. ·         Thus, basic solution can be easily identified. ·         Let us mark the three test tubes as A, B, and C. A drop of the solution in A is put on the red litmus paper. Same is repeated with solution B and C. ·         If either of them changes colour to blue, then it is basic. Therefore, out of three, one is eliminated. ·         Out of the remaining two, any one can be acidic or neutral. ·         Now a drop of basic solution is mixed with a drop of each of the remaining two solutions separately and then the nature of the drops of the mixtures is checked. ·         If the colour of red litmus turns blue, then the second solution is neutral and if there is no change in colour, then the second solution is acidic. ·         This is because acidic and basic solutions neutralize each other. ·         Hence, we can distinguish between the three types of solutions.

ACIDS

Acids are those substances which have a sour taste. Acids change the color of blue litmus to red.

On the basis of origin, acids are classified as: a.    Organic acids: Acids derived from living organisms like plants and animals are called organic acids. They are weak acids and are not harmful for living organisms. For example: citric acid is present in fruits, acetic acid present in vinegar, oxalic acid present in tomato, tartaric acid present in tamarind, lactic acid present in sour milk and curd.Formic acid (methanoic acid) in ants. b.    Mineral acids: They are also called inorganic acids. They are dangerous and corrosive. Special precautions have to be taken while handling them. For example: sulphuric acid (H2SO4), hydrochloric acid (HCl) and Nitric acid etc.

Strong Acids and Weak Acids All the acids are divided into two groups: strong acids and weak acids. On the basis of their strength, acids are classified as: a.    Strong acids: Strong acids are those acids which completely dissociate into its ions in aqueous solutions. Example: nitric acid (HNO3) ,sulphuric acid (H2SO4), hydrochloric acid (HCl). §  Strong acid is completely ionised in water and produce s a large amount of hydrogen ions is called a. Hydrochloric acid is completely ionized in water, so it is a strong acid. §  Strong acids react very rapidly with other substance (such as metals, metal carbonates and metal hydro carbonates). b.    Weak acids: Weak acids are those acids which do not completely dissociate into its ions in aqueous solutions. For example: carbonic acid (H2CO3), acetic acid (CH3COOH). §  weak acid is partially ionized in water and thus produces a small amount of hydrogen ions is called a. Acetic acid (CH3COOH) is partially ionized in water to produce only small amount of hydrogen ions, so it is weak acid. §  When a concentrated solution of acid is diluted by mixing water, then the concentration of hydrogen ions, H+ (aq) [or hydronium ions, H3O+ ] per unit volume decreases.

Note:- (i)All the mineral acids are strong acids except carbonic acid. Hydrochloric acid, sulphuric acid and nitric acid are strong acids. (ii)The organic acids are weak acids. Acetic acid, formic acid, tartaric acid and carbonic acid are weak acids.

Concentrated and dilute acids On the basis of their concentration, acids are classified as: a.    Dilute acids: Have a low concentration of acids in aqueous solutions. A dilute acid is one which contains much more of water in it. b.    Concentrated acids: Have a high concentration of acids in aqueous solutions. A concentrated acid is one which contains the minimum possible amount of water in it.

DILUTING ACIDS

While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid? ·         Answer :  ·         The dilution of concentrated acid should always be done by adding concentrated acid to water gradually with string and not by adding water to concentrated acid. ·         Since the process of dissolving an acid in water is exothermic, it is always recommended that acid should be added to water. ·         If it is done the other way, then it is possible that because of the large amount of heat generated, the mixture splashes out and causes burns.

PROPERTIES OF ACIDS

The important characteristic of acids is:

1.   Reaction of acids and bases with water:

Acids

Bases

Release H+ or H3O+ ions in water

Release OH- ions in water

Question: How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted? ·         Answer When an acid is diluted, the concentration of hydronium ions (H3O+) per unit volume decreases. This means that the strength of the acid decreases .

2.   Reaction of acids and bases with metals:

Metals displace hydrogen from the acids and form salt and hydrogen gas. This is a displacement reaction. So, acids react with only those metals which are placed above hydrogen in the reactivity series so that metals can displace hydrogen from acids.

Acids react with metals to form hydrogen gas.

Metal    +    Acid     à    Salt   +   Hydrogen gas Zn + H2SO4 →   ZnSO4 + H2 Metal  Acid Salt Hydrogen gas

Note:- 1.    Bases react with some metals to form salt and hydrogen gas. Zn + 2 NaOH → Na2ZnO2 + H2 2.    Bases do not react with all the metals to form salt and water. 3.    Most of the acids react with metals to form salts and evolve hydrogen gas. Hydrogen is common to all acid.

Question:    Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas? ·         Answer Hydrogen gas is usually liberated when an acid reacts with a metal. Take few pieces of zinc granules and add 5 ml of dilute H2SO4. Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas. We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.

Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why? ·         Answer The fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added. This is because HCl is a stronger acid than CH3COOH and therefore produces hydrogen gas at a faster speed due to which fizzing occurs.

Why should curd and sour substances not be kept in brass and copper vessels? Answer Curd and sore food stuffs should not be kept in metal vessels because curd and other food stuffs contain acids which can reacts with metal of the vessel to form poisonous metal compounds which can cause food poisoning.

3.    Reaction of acids and bases with metal carbonates:

Acids react with metal carbonate (and metal hydrogen carbonates) to form salt, water and release carbon dioxide. Metal carbonate   +   Acid    à    Salt    +   Carbon dioxide   +    Water Na 2 CO3   + 2HCl  →  2 NaCl + CO2   + H 2 O NaHCO3   + HCl  →  NaCl + CO2   + H2 O

Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride. ·         Answer

A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains (a) NaCl (b) HCl (c) LiCl (d) KCl ·         Answer  (b) The solution contains HCl

4.  Acids react with bases (or alkali) to form salt and water.

Acid   +Base     à    Salt     +    Water

The reaction between an acid and base to form salt and water is called a netralisation reaction.

QWhat is a neutralization reaction? Give two examples. ·         Answer A reaction in which an acid and base react with each other to give a salt and water is termed as neutralization reaction. In this reaction, energy is evolved in the form of heat. For example: (i) (ii) During indigestion (caused due to the production of excess of hydrochloric acid in the stomach), we administer an antacid (generally milk of magnesia,which is basic in nature). The antacid neutralizes the excess of acids and thus gives relief from indigestion.

10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be(a) 4 mL (b) 8mL (c) 12 mL (d) 16 mL ·         Answer  (d) 16 mL of HCl solution will be required.

Which one of the following types of medicines is used for treating indigestion? Answer  (c) Antacid is used for treating indigestion.

5.   Reaction of acids with metallic oxides:

·         Acids react with metal oxides to form salt and water. Metal oxide   +   Acid   à   Salt   +   Water ·         Metallic oxides are basic. Therefore, acids react with metallic oxides to form salt and water. HCl + CuO →   CuCl2 + H2O The acids also react with metal hydroxides to form salt and water.

Reaction of bases with non-metallic oxides: Non – metallic oxides are acidic in nature. Bases react with non- metallic oxides to form salt and water. Example: CO2 Ca(OH)2 + CO2 →   CaCO3 + H2O

Neutral oxides: Oxides which are neither acidic nor basic are called neutral oxides. Example: CO Amphoteric oxides: Oxides which show acidic as well as basic properties. For example: ZnO, Al2O3 HCl + ZnO →   ZnCl2 + H2O Zn + 2 NaOH →   Na2ZnO2 + H2O

1. Acids have a sour taste
2. Acids turns blue litmus to red.

3.       Acids have corrosive nature.

·         The mineral acids cause severe burns on the skin and attack and eat up materials like cloth, wood, metal structures and stonework, so they are said to be corrosive.

·         Acids are never stored in metal container because they gradually corrode and eat up metal container so they stored in glass and ceramics container.

·         The strong bases (or alkali) such sodium hydroxide are also very corrosive, and attack and destroy our skin.

4. Acids solutions conduct electricity

Why does an aqueous solution of acid conduct electricity? ·         Answer Acids dissociate in aqueous solutions to form ions. These ions are responsible for conduction of electricity.

Why does distilled water not conduct electricity, whereas rain water does? ·         Answer Distilled water is a pure form of water and is devoid of any ionic species. Therefore, it does not conduct electricity. Rain water, being an impure form of water, contains many ionic species such as acids and therefore it conducts electricity.

WHAT DO ALL ACIDS HAVE IN COMMON

1.       An acid is a substance which dissociates (or ionizes) on dissolving in water to produce hydrogen ions [H+(aq)ions]. HCl(aq)    à    H+(aq)    +    Cl-(aq) 2.       A common thong in all the acids is that they produce hydrogen ions [H+(aq)ions] when dissolved in water. 3.       The aqueous solution of acid conducts electricity due to the presence of charge particles called ions in it. 4.        Due to the absence of ions, glucose solution do not conducts electricity. Distilled water dose not conducts electricity because it does not contain any ionic compound (like acids, bases of salts) dissolved in it. 5.       Due to the presence of carbonic acid (which provides ions to rain water), the rain water conducts electricity.

Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character? ·         Answer The dissociation of HCl or HNO3 to form hydrogen ions always occurs in the presence of water. Hydrogen ions (H+) combine with H2O to form hydronium ions (H3O+). The reaction is as follows: Although aqueous solutions of glucose and alcohol contain hydrogen, these cannot dissociate in water to form hydrogen ions. Hence, they do not show acidic character.

Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it. ·         Answer Two nails are fitted on a cork and are kept it in a 100 mL beaker. The nails are then connected to the two terminals of a 6-volt battery through a bulb and a switch. Some dilute HCl is poured in the beaker and the current is switched on. The same experiment is then performed with glucose solution and alcohol solution. Observations: It will be observed that the bulb glows in the HCl solution and does not glow in the glucose solution. Result: HCl dissociates into H+ and Cl− ions. These ions conduct electricity in the solution resulting in the glowing of the bulb. On the other hand, the glucose solution does not dissociate into ions. Therefore, it does not conduct electricity. Conclusion: From this activity, it can be concluded that all acids contain hydrogen but not all compounds containing hydrogen are acids. That is why, though alcohols and glucose contain hydrogen, they are not categorised as acids.

Acids Do Not Show Acidic Behavior in the Absence of Water

Why do acids not show acidic behaviour in the absence of water? ·         Answer In the absence of water, a substance will not form hydrogen ions and will not show its acidic behavior. It is the hydrogen ions that are responsible for the acidic behaviour. Dry HCl gas dose not change the color of dry litmus paper because it has no hydrogen ions [H+(aq)ions] in it.

Why does dry HCl gas not change the colour of the dry litmus paper? ·         Answer ·         Dry HCl gas dose not change the color of dry litmus paper because it has no hydrogen ions [H+(aq)ions] in it. The HCl gas turns ‘wet’ blue litmus paper red because it dissolves in the water present in wet litmus paper to form hydrogen ions, which can turns blue litmus paper to red. Colour of the litmus paper is changed by the hydrogen ions. Dry HCl gas does not contain H+ ions. It is only in the aqueous solution that an acid dissociates to give ions. Since in this case, neither HCl is in the aqueous form nor the litmus paper is wet, therefore, the colour of the litmus paper does not change.

BASES

Bases are those chemical substances which have bitter taste. It changes the color of red litmus blue. Bases are chemical opposite of acids. Base is a chemical substance which can neutralize an acid.

Water Soluble Bases: Alkalis Most bases do not dissolve in water but some dissolve in water with out any chemical reaction. A base which dissolves in water is called an alkali. Alkalies: Water soluble bases are called alkalies. For example: Sodium hydroxide (NaOH), potassium hydroxide(KOH)

What do All the Bases have in Common? A common property of all the bases (or alkali) is that they all have a tendency to produce hydroxide ions (OH- ions) when dissolved in water. NaOH, KOH, Mg(OH)2, NH4OH are all bases.

On the basis of their strength, bases are classified as: a.    Strong bases: Strong bases are those bases which completely dissociate into its ions in aqueous solutions. Example: sodium hydroxide (NaOH), potassium hydroxide (KOH) b.    Weak bases: Weak bases are those bases which do not completely dissociate into its ions in aqueous solutions. For example: ammonium hydroxide (NH4OH)

On the basis of their concentration, bases are classified as: a.    Dilute bases: Have a low concentration of alkali in aqueous solutions. b.    Concentrated bases: Have a high concentration of alkali in aqueous solutions.

How is the concentration of hydroxide ions (OH−) affected when excess base is dissolved in a solution of sodium hydroxide? ·         Answer The concentration of hydroxide ions (OH−) would increase when excess base is dissolved in a solution of sodium hydroxide.

Properties of Bases Bases have bitter taste Bases feel soapy to touch Bases turn red litmus to blue Bases conduct electricity in solution(They are electrolytes): Acids and bases conduct electricity because they produce ions in water. There is a flow of electric current through the solution by ions.

Bases react with some metals to form hydrogen gas All the metal does not react with bases to form salts and hydrogen gas. Bases react with acids to form salts and water. When an acid and base combine then real the neutralization reaction occurs due to combination of hydrogen ions present in acid and hydroxide ions presents in base to form water.                   H+(aq)     +     OH-(aq)                  à              H2O(l) Bases react with non metal oxide to form salt and water Non-metal    +       Base    à    Salt    +   Water

STRENGH OF ACID AND BASE SOLUTIONS: pH SCALE

pH: §  A scale for measuring hydrogen ion concentration in a solution is called pH scale. §  It is used to find out the strength of acids and bases i.e., how strong or weak the acid or a base is. p in pH stands for ‘potenz’ in German. §  The strength of acids and bases depends on the number of H+ ions and OH- ions produced respectively.

§  Acidic solution has excess of hydrogen ions but it also contains hydroxide ions. §  Basic solution has excess of hydroxide ions but it also contains hydrogen ions. §  Both acidic solutions as well as basic solution contain hydrogen ions. In 1909 Sorenson devised a scale (Known as pH scale) on which acid solutions as well as basic solutions could be represented by making use of the hydrogen ion concentration in them. §  The pH of a solution is inversely proportional to the concentration of hydrogen ions in it. §  The strength of an acid or base is measured on a scale of numbers called the ph scale. The pH scale has values from 0 to 14, pure number, no units.

On pH scale, we measure pH from 0 to 14. pH value:   pH Type of solution Less than 7 Acidic Equal to 7 Neutral More than 7 Basic

According to pH scale: --- Neutral substances have a pH of exactly 7. Acids (or acidic solution) have a pH pf less than 7. Lower the pH, the stronger the acid. Bases (or basic solution) have a pH of more than 7. Higher the pH, the stronger the base (or alkali).

A solution turns red litmus blue, its pH is likely to be (a) 1 (b) 4 (c) 5 (d) 10 ·         Answer  (d) Bases turn red litmus blue and acids turn blue litmus red. Basic solution has a pH value more than 7. Since the solution turns red litmus blue, its pH is likely to be 10.

Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is (a) neutral? (b) strongly alkaline? (c) strongly acidic? (d) weakly acidic? (e) weakly alkaline? Arrange the pH in increasing order of hydrogen-ion concentration. ·         Answer  (a) Neutral → Solution D with pH 7 (b) Strongly alkaline → Solution C with pH 11 (c) Strongly acidic → Solution B with pH 1 (d) Weakly acidic → Solution A with pH 4 (e) Weakly alkaline → Solution E with pH 9 The pH can be arranged in the increasing order of the concentration of hydrogen ions as: 11 < 9 < 7 < 4 < 1

Variation in pH:

§  Acids which produce more hydrogen ions are said to be strong acids and acids which produce less hydrogen ions are said to be weak acids. In other words, strong acids have a lower pH value than weak acids. §  Bases which produce more hydroxyl ions are said to be strong bases and bases which produce less hydroxyl ions are said to be weak bases. In other words, strong bases have a higher pH value than weak bases.

Question 1: You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic? ·         Answer A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Therefore, the solution with pH = 6 is acidic and has more hydrogen ion concentration than the solution of pH = 8 which is basic.

Question 2: What effect does the concentration of ions have on the nature of the solution? ·         Answer Concentration of can have a varied effect on the nature of the solution. With an increase in H+ ion concentration, the solution becomes more acidic, while a decrease of H+ ion causes an increase in the basicity of the solution.

Question 3: Do basic solutions also have ions? If yes, then why are these basic? ·         Answer Yes, basic solution also has ions. However, their concentration is less as compared to the concentration of OH− ions that makes the solution basic.

Universal Indicator §  To obtain the idea of how acidic or basic substance is, universal indicator is used. §  Universal indicator is a mixture of many different indicators (or dyes) which gives different color in different pH values of the entire pH scale. Like litmus which can be produced in the form of solution or paper. §  Water will produce green color with universal indicator.

IMPORTANCE OF PH IN OUR DAILY LIFE pH of our digestive system: ·         Our stomach produces hydrochloric acid for digestion of food. But during indigestion, excess of acid is produced in the stomach and therefore, the pH decreases. This causes pain and irritation. ·         So, to neutralise this excess acid, a mild base is used. This mild base works as an antacid. An antacid is any substance, generally a base or basic salt, which counteracts stomach acidity. ·          Dilute hydrochloric acid helps in digesting our food. Excess acid in the stomach    causes indigestion. Being basic in nature, antacids react with excess in stomach and neutralize it. ·         Magnesium hydroxide (milk of magnesia) and sodium hydrogen carbonate (baking soda) are used as antacids. pH change as the cause of tooth decay: §  The bacteria present in our mouth breaks down the sugar to form acids. Tooth decay starts when the pH of acid formed in the mouth falls 5.5. §  The best way to prevent tooth decay is to clean the mouth thoroughly after eating food. Prints and Animals are Sensitive to pH Changes ·         Living organisms are pH sensitive. Human body works within a pH range of 7.0 to 7.8. ·         pH is also significant as it is used in self defence by animals and plants. Bees use acids in their sting. To neutralise the effect a mild base like baking soda can be used. self defense by Animals Plants by through Chemical Warfare An ant’s string injects methanoic acid into the skin of a person causing burning pain. When a person happens of a nettle plant accidentally, the stinging hair leaves injects methanoic acid into the skin of the person causing burning pain. 5.   Soil pH and Plant Growth. ·         Most of the plants grow best when pH of the soil is close to 7. If the soil is too acidic or too basic, the plant grows too badly or do not grow at all. ·         If the soil is too acidic, then it is treated with materials like quicklime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate). Plants also require a specific pH range of soil for their healthy growth. 6.   pH Change and Survival of Animals. ·         Our body works well within a narrow range of 7.0 to 7.8. If this pH range gets disturbed in the body, then many ailments can occur. ·         Rain water with a pH less than 5.6 is called acid rain. This acid rain if it flows into river water makes the survival of aquatic life difficult. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)? ·         Answer If the soil is acidic and improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with quick lime or slaked lime or chalk.

Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer. ·         Answer The pH of milk is 6. As it changes to curd, the pH will reduce because curd is acidic in nature. The acids present in it decrease the pH.

A milkman adds a very small amount of baking soda to fresh milk. (a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline? (b) Why does this milk take a long time to set as curd? ·         Answer  (a) The milkman shifts the pH of the fresh milk from 6 to slightly alkaline because in alkaline condition, milk does not set as curd easily. (b) Since this milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base. Therefore, it takes a longer time for the curd to set.

SALTS

A salt is a compound formed from an acid by the replacement of hydrogen in the acid by a metal. Salts are formed when acids reacts with bases. Just like acids and bases, solutions of salts in water conduct electricity. Salts are ionic compounds.

Family of salts The salts having the same positive ions (or same negative ions) are said to belong to the family of salts. For example sodium chloride (NaCl) and sodium sulphate (Na2SO4) belong to the same family of salts called ‘sodium salts’.

The pH of Salt Solutions Though the aqueous solutions of many salts are neutral (having a ph of 7), some salts produce acidic or basic solutions when dissolve in water The acidic nature and basic nature of some salt solutions can be explained on the basis of hydrolysis of salts. (i)                 The salts of strong acid and strong bases give neutral solutions (ii)               The salts of strong acid ands and weak bases give acidic solution (iii)             The salts of weak acids and strong bases give basis basic solutions

COMMON SALT (SODIUM CHLORIDE) ·         The chemical name of common salt is sodium chloride (NaCl). ·         Sodium chloride can be prepared by the combination of sodium hydroxide and hydrochloric acid: NaOH(aq)     +    HCl(l)    à    NaCl(aq)     +      H2O(l) How Common Salt is obtained (i)                 Common Salt from Sea-water – Common salt obtains from sea-water by the process of evaporation. (ii)               Common Salt from Underground Deposits – Rock is mined from the underground deposits just like coal.      Uses of Common Salt (i)                 Common salt is used as a raw material for making chemicals like: sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, hydrochloric acid , hydrogen chlorine, and sodium metal. (ii)               Common salt is used in cooking food. (iii)             Common salt is used as a preservative. (iv)             Common salt is used in the manufacturing of soap. (v)               Common salt used to melt ice which collects in the roads during winter in cold countries. Chemicals from Common Salt SODIUM HYDROXIDE Sodium hydroxide is commonly known as caustic soda. ·         When electricity is passed through a concentrated solution of sodium chloride, it decomposes to form sodium hydroxide, chlorine and hydrogen. 2NaCl (aq)     +      2H2O(l)     à   2NaOH(aq)      +       Cl2(g)      H2(g) ·         Chlorine gas is produced at the anode and hydrogen gas is produced at the cathode. Sodium hydroxide solution formed near the cathode. The process of sodium chloride solution is called chlor-alkali process. The three very useful products obtained by the electrolysis of sodium chloride solution called brine (or chlor-alkali process) are sodium hydroxide, chlorine and hydrogen  Sodium hydroxide (NaOH) Preparation: Chlor Alkali process: In this process, electricity is passed through an aqueous solution of Sodium chloride (called brine). Sodium chloride decomposes to form sodium hydroxide. Chlorine gas is formed at the anode, and hydrogen gas at the cathode. Sodium hydroxide solution is formed near the cathode. 2NaCl(aq) + 2 H2O (l) →   2NaOH(aq) + Cl2(g) + H2(g) Uses of Sodium Hydroxide 1.       Sodium hydroxide is used for making soaps and detergents 2.       Sodium hydroxide is used for making artificial textile fibers 3.       Sodium hydroxide is used in the manufacturing of paper 4.       Sodium hydroxide is used in purifying bauxite ore from aluminum metal is extracted 5.       Sodium hydroxide is used de-greasing metals, oil refining, and making dyes and bleaches Uses of Chlorine 1.       Chlorine is to used to sterilize drinking water 2.       Chlorine is used in the production of bleaching powder 3.       Chlorine is used in the production of hydrochloric acid 4.       Chlorine is used to make plastics 5.       Chlorine is used for making solvents for dry-cleaning     Uses of Hydrogen 1.       Hydrogen is used in the hydrogenation of oils to obtain solid fats 2.       Hydrogen is used in the production of hydrochloric acid 3.       Hydrogen is used to make ammonia for fertilizers 4.       Hydrogen is used to make methanol 5.       hydrogen is used as a fuel for rockets     Uses of Hydrochloric acid 1.       Hydrochloric acid is used for cleaning iron sheets before tin-plastic or galvanization 2.       Hydrochloric acid is used in the preparation of chlorides such as ammonium chloride 3.       Hydrochloric acid is used in medicines and cosmetics 4.       Hydrochloric acid is used is textile, dyeing and tanning industry 5.       Hydrochloric acid is used in making plastics

 

WASHING SODA      Washing is produced from sodium chloride in following three steps (i)                 A cold and concentrated solution of sodium chloride is reacted with ammonia and carbon dioxide to obtain sodium hydrogen carbonate.      NaCl     +     NH3    +   H2O    CO2       à    NaHCO3       +    NH4Cl (ii)               On heating sodium hydrogen carbonate decomposes to form sodium carbonate      2NaHCO3    à     Na2CO3   +     CO2    +    H2O (iii)             Anhydrous sodium carbonate is dissolved in water and recrystallised to get washing soda crystals containing 10 molecules of water of crystal satin.    Na2CO3    +     10H2O    à    Na2CO3.10H2O Properties of washing soda 1.      Washing soda is a transparent crystalline solid 2.      Washing soda is one of the metal carbonates which are soluble in water 3.      The solution of washing soda in water is alkaline which turns red litmus to blue 4.      Detergent properties (or cleansing properties) Use of sodium carbonate 1.      Sodium carbonate is used as a “cleansing agent” for domestic proposes. 2.      Sodium carbonate is used for removing permanent hardness of water. 3.      Sodium carbonate is used in the manufacturing of glass, soap and paper. 4.      Sodium carbonate is used in the manufacturing of sodium compounds such as borax.

Name the sodium compound which is used for softening hard water. ·         Answer Washing soda (Na2CO3.10H2O) is used for softening hard water

What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved. ·         Answer When a solution of sodium hydrocarbonate (sodium hydrogencarbonate) is heated, sodium carbonate and water are formed with the evolution of carbon dioxide gas.

BAKING SODA         The chemical name of backing soda is sodium hydrogen carbonate and the formula is NaHCO3. Baking soda: Sodium hydrogen carbonate (NaHCO3) Preparation: NaCl + H2O + CO2+ NH3 →   NH4Cl + NaHCO3 Production of sodium hydrogen carbonate Sodium carbonate is produced by reacting a cold and concentrated solution of sodium chloride with ammonia and carbon dioxide NaCl     +    NH3      +     H2O       +      CO2    à   NaHCO3        +      NH4Cl Properties of sodium hydrogen carbonate Sodium hydrogen carbonate consists of white crystals which are sparingly soluble in water. Sodium hydrogen carbonate is a mild, non-corrosive base and water is mildly alkaline. When solid hydrogen carbonate is heated, then it decomposes to give sodium carbonate and carbon dioxide.                                   Heat 2NaHCO3          ----------- >      Na2CO3     +    CO2       +    H2O Uses of sodium hydrogen carbonate Sodium hydrogen carbonate is used as an antacid in medicine to remove acidity of the stomach. Sodium hydrogen carbonate is used in making baking power Sodium hydrogen carbonate is used in fire extinguishers.

Give two important uses of washing soda and baking soda. Answer Two important used of washing soda and baking soda are as follows: (1) Washing soda: (a) It is used in glass, soap, and paper industries. (b) It is used to remove permanent hardness of water. (2) Baking soda: (a) It is used as baking powder. Baking powder is a mixture of baking soda and a mild acid known as tartaric acid. When it is heated or mixed in water, it releases CO2 that makes bread or cake fluffy. (b) It is used in soda-acid fire extinguishers.

BLEACHING POWER

Bleaching power is calcium oxychloride and the formula is CaOCl₂.

What is the common name of the compound CaOCl2? ·         Answer :The common name of the compound CaOCl2 is bleaching powder.

Name the substance which on treatment with chlorine yields bleaching powder? ·         Answer :Calcium hydroxide [Ca (OH)2], on treatment with chlorine, yields bleaching powder.

Preparation of bleaching power Bleaching powder: Bleaching powder is represented as CaOCl2, though the actual composition is quite complex. Preparation: Bleaching powder is produced by the action of chlorine on dry slaked lime. Ca(OH)2        +       Cl2        à      CaOCL2      +     H2O

Properties of bleaching power Bleaching power is a white power which gives a strong smell of chlorine. Bleaching power is soluble in cold water. Bleaching power reacts with dilute acids to produce chlorine. CaOCl2      +       H2SO4    à     CaSO4       +      Cl2      +     H2O

Uses of Bleaching Power Bleaching power is used for bleaching cotton and linen in textile industry Bleaching is used for disinfectant drinking water. Bleaching power is used for the manufacturing of chloroform (CHCl3). Bleaching power is used for making wood unshrinkable. Bleaching power is used as an oxidizing agent in many chemical industry.

PLASTER OF PARIS

Plaster of Paris is calcium sulphate hemi hydrate (calcium carbonate half-carbonate) and the formula is CaSo4.1/2H2O. Preparation of Plaster of Paris Plaster of Paris is prepared by heating gypsum (CaSO4.2H2O calcium sulphate dihydrate) to a temperature of 100o C. CaSO4.2H2O      à    CaSO4.1/2H2O     +     1/2H2O

Properties of Plaster of Paris Plaster of Paris is a white power. Plaster of Paris has a very remarkable property of setting into a hard mass on wetting in water. Plaster of Paris should be stored in a moister proof container. Uses of plaster of Paris Plaster of Paris is used in hospitals for setting fractured bones in the right position. Plaster of Paris is used in making toys, decorative materials, cheap ornaments, black-board chalks and cast for statues. Plaster of Paris is used as a fire-proofing material. Plaster of Paris is used in chemical laboratories for sealing air-gaps in apparatus. Plaster of Paris is used for making surfaces smooth before painting them.

Write an equation to show the reaction between Plaster of Paris and water. ·         Answer The chemical equation for the reaction of Plaster of Paris and water can be represented as

Plaster of Paris should be stored in a moisture-proof container. Explain why? Answer Plaster of Paris (POP) should be stored in a moisture-proof container because Plaster of Paris, a powdery mass, absorbs water (moisture) to form a hard solid known as gypsum.

WATER OF CRYSTALISATION

Water of crystallisation: It is the fixed number of water molecules present in one formula unit of a salt. ·         The water molecules which form part of the structure of a crystal (of a salt) are water of crystallization. ·         The salt contain water of a crystallization are called hydrated salt. ·         Every hydrated salt has a “fixed number” of molecule of water of crystallization in its one formula unit ·         Water of crystallization is a part of ‘crystal structure’ of a salt. Since water of crystallisation is not free water, it does not wet the salt. ·         The water of crystallization gives the crystals of the salts their ‘shape’ and, in some cases, imparts them ‘color’. ·          For example copper sulphate crystal contain 5 molecules of water of crystallization per formula unit and hence written as CuSO4.5H2O.

ACTION OF HEAT ON HYDRATED SALTS

When hydrated salts are heated strongly, they lose their water of crystallization. The salts which have lost their water of crystallization are called anhydrous salts.

QUESTION FOR PRACTISE

1. Which gas is usually liberated when an acid reacts with a metal?
2. While diluting an acid, why is it recommended that the acid should be added to water and not water to acid?
3. What happens when an acid reacts with a metal carbonate?
4. What happens when an acid reacts with a metal hydrogen carbonate?
5. What happens when an acid reacts with a base? Give equation of the reaction involved. What is the special name of this reaction?
6. What happens when an acid reacts with a metal oxide? Write the equation of the reaction involved.
7. What happens when carbon dioxide gas passed through lime water: (a) for a short time, and (b) for a considerable time? Write equations of the reactions involved.
8. Complete and balance the following chemical reactions:

(a) Zn(s)   +   HCl(aq)   à

(b) Na₂CO₃(s)    +   HCl(aq)    à

(c) NaHCO₃(s)    +    HCl(aq)    à

(d) NaOH(aq)      +     HCl(aq)   à

(e) CuO(s)      +     HCl(aq)   à

9. What are organic acids and mineral acids? Give examples of each.
10. Which element is common to all acids?
11. Why do HCl, H₂SO₄, HNO₃ etc... show acidic character in aqueous solution while solutions of compounds like glucose and alcohol do not show acidic character?
12. Why does dry HCl gas not change the color of the dry litmus paper?
13. Why does distilled water not conduct electricity whereas rain water does?
14. Give the name and formulae of two strong acids and two weak acids.
15. Fill in the following statement with a suitable word:

Substances do not show their acidic properties without……..

16. What does pH of a solution signify? Three solutions A, B, and C have pH value of 6, 4 and 10 respectively. Which of the solution is highly acidic?
17. Two solutions X and Y have pH=4 and pH=8, respectively. Which solution will give alkaline reaction and which one acidic.
18. The pH of a cold drink is 5. What will be its action an blue and red litmus solution?
19. A solution turns red litmus blue, its pH is like to be:

(a) 1 (b) 4 (c) 5 (d) 10

20. (a) Which is more acidic, pH = 2 or pH = 11?

(b) Which is more basic pH = 8 or pH = 11?

21. Fresh milk has a pH of 6. How do you think the pH would change a it turns into curd? Explain your answer.
22. What effect does the concentration of H⁺(aq) ions have on the nature of the solution?
23. Name the indicator which can give us an idea of how strong or weak an acid or base is?
24. How does a universal indicator work?
25. Two solutions X and Y are tasted with universal indicator. Solution X turns orange where as solution Y turns red. Which of the solution is a stronger acid?
26. Under what soil conditions do you think a farmer would treat the soil of his fields with quicklime or slaked lime or chalk?
27. How does an antacid work? Name two antacid.
28. Explain the pH change as the tooth decay. How can tooth decay caused by pH change be prevented?
29. What happens during a bee sting? What is its remedy?
30. The pH of a soil A is 7.5 while that of soil B is 4.5. Which of the two soils, A or B, should be treated with powered chalk to adjust its to adjust its pH and why?
31. A salt X when dissolved in distilled water gives a clear solution which turns red litmus blue. Explain the phenomenon.
32. Explain why, an aqueous solution of sodium chloride is neutral but an aqueous solution of sodium carbonate is basic.
33. What is a salt? Give the names and formulae of any two salts. Also name the acids and bases from which these salts may be obtained.
34. What is meant by a family of salts? Explain with examples.
35. Write the chemical name and formula of common salt.
36. Name the major salt present in sea-water?
37. Name three chemicals made from common salt.
38. Give any two uses of common salt.
39. Name the salt which is used as a preservative in pickle, and in curing meat and fish.
40. What happens when a concentrated solution of sodium chloride is electrolyzed? Write the equation of the reaction involved.
41. The electrolysis of an aqueous solution of sodium chloride gives us three products. Name them.
42. Explain why, chlorine is used for sterilizing drinking water supply.
43. Name the product formed when Cl₂ and H₂ produced during the electrolysis of brine are made to combine.
44. Write the chemical formula of sodium carbonate.
45. Name a metal compound which has detergent properties.
46. Name a sodium compound used for softening hard water.
47. What is the common name Na₂CO₃.10H₂O?
48.  Name the metal whose carbonate is known as washing soda.
49. What is the chemical name of baking soda?
50. What is the chemical formula of baking soda?
51. What is the common name of sodium hydrogen carbonate?
52. Name an acid which is present in baking powers.
53. What happens when a solution of sodium hydrogen carbonate is heated? Write equation of the reaction involved.
54. Give the chemical formula of washing soda and baking soda.
55. What is the chemical name of bleaching power?
56. What is the chemical formula of bleaching power?
57. What are the materials used for the preparation of bleaching power?
58. Name the substances obtained by the action of chlorine on solid slaked lime.
59. Name one compound of calcium which is used for bleaching cloth.
60. Which is the real bleaching agent present in bleaching power?
61. What is plaster of Paris? Write the chemical composition of plaster of Paris.
62. Name the raw material used for the preparation of plaster of Paris.
63. What is the commercial name of calcium sulphate hemi-hydrate?
64. What will happen if heating is not controlled while preparing plaster of Paris?
65. State two important uses of plaster of Paris.
66. What is meant by ‘water of crystallization’
67. What is meant by ‘hydrated’ and ‘anhydrous’ salts? Explain with an example.
68. What happens when a copper sulphate crystal are heated strongly/ explain with the help of an equation.
69. Write the names, formula and colors of any two hydrated salts.
70. What happens when copper sulphate crystals are added to anhydrous copper sulphate? Explain with the help of an equation.

Write word equations and then balanced equations for the reaction taking place when − (a) dilute sulphuric acid reacts with zinc granules. (b) dilute hydrochloric acid reacts with magnesium ribbon. (c) dilute sulphuric acid reacts with aluminium powder. (d) dilute hydrochloric acid reacts with iron filings. ·         Answer (a) Sulphuric acid + Zinc → Zinc sulphate + Hydrogen (b) Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen (c) Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen (d) Hydrochloric acid + Iron → Ferric chloride + Hydrogen

QUESTIONS TOPIC ARRANGED

ACID, BASES AND SALTS

INDICATORS

1.        You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

2.        What is the colour of litmus in a solution of ammonium hydroxide.

3.        What would be the colour of litmus in a solution of sodium carbonate.

ACID (PHYSICAL PROPERTIES)

4.        While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

5.         How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?

6.        Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

7.        Why does an aqueous solution of an acid conduct electricity?

8.        Why does dry HCl gas not change the colour of the dry litmus paper?

9.        Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.

10.     Why does distilled water not conduct electricity, whereas rain water does?

11.     Why do acids not show acidic behaviour in the absence of water?

ACID (CHEMICAL PROPERTIES)

12.     Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence ofthis gas?

13.     Write word equations and then balanced equations for the reaction taking place when –

(a) dilute sulphuric acid reacts with zinc granules.

(b) dilute hydrochloric acid reacts with magnesium ribbon.

(c) dilute sulphuric acid reacts with aluminium powder.

(d) dilute hydrochloric acid reacts with iron filings.

14.     Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?

15.     Why should curd and sour substances not be kept in brass and copper vessels?

16.     Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

17.      A solution reacts with crushed egg-shells to give a gas that turns lime-water milky.The solution contains which acid

BASE (PHYSICAL PROPERTIES)

18.     What is an alkali.

19.     How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?

20.     Do basic solutions also have H+(aq) ions? If yes, then why are these basic?

BASE  (CHEMCIAL PROPERTIES)

BASE (USES)

21.    Why antacid is considred as medicines for treating indigestion?

PH

22.    You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?

23.    What effect does the concentration of H+(aq) ions have on the nature  or pH of the solution?

24.    Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

25.    Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

26.    Why does 1 M HCl solution have a higher concentration of H+ ions than 1 M CH3Cooh solution.

27.    A milkman adds a very small amount of baking soda to fresh milk.

(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?

(b) Why does this milk take a long time to set as curd?

APPLICATION OF PH IN DAILY LIFE

28.    Why does tooth decay start when the pH of mouth is lower then 5.5 ?

SALTS

29.    What is a neutralisation reaction? Give two examples.

30.    10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will be (a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL

SOLVAY PROCESS

31.    Name the product formed  if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

32.    Give two important uses of washing soda and baking soda.

33.    Name the sodium compound which is used for softening hard water.

HANSCLEVER’S PROCESS

34.    What is the common name of the compound CaOCl₂

35.    Write the name and chemical formula of the calcium compound used for disinfecting drinking water. How is this compound manufactured.

36.    Name the substance which on treatment with chlorine yields bleaching powder.

PLASTER OF PARIS

37.    Write an equation to show the reaction between Plaster of Paris and water.

38.    Plaster of Paris should be stored in a moisture-proof container. Explain why?

WATER  OF CRYSTALLISATION

1.       What is meant by water of crystallization of a substance? Describe an activity to show that blue copper sulphate crystals contain water of crystallization.

2.       Crystals of copper sulphate are heated in a test tube for some time.

a.        What is the colur of copper sulphate crystals before and after heating.

b.        What is the source of liquid droplets seen on the inner upper side of the test tube during the heating process?

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