CLASS
XTH
NOTES
AND PRACTISE QUESTIONS
CHAPTER-2
ACIDS,
BASES AND SALTS
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On the
basis of there chemical properties, all the compounds can be classified into
three groups.
Definition of acids, bases and salts:
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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
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Indicators can be natural or synthetic.
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Neutral colour
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Colour with acids
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Colour
with base
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Litmus
paper
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purple
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red
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blue
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Turmeric
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Red
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Red
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Green
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Methyl
orange
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orange
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red
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Yellow
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phenolphthalein
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colourless
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colourless
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pink
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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.
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Olfactory
indicators: These
are those indicators whose odour changes in acidic or basic medium. Example:
onion, Vanilla essence.
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Onion:
Smell of onion diminishes in a base and remains as it is in an acid.
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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.
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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?
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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.
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Thus, basic solution can be
easily identified.
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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.
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If either of them changes colour
to blue, then it is basic. Therefore, out of three, one is eliminated.
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Out of the remaining two, any one
can be acidic or neutral.
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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.
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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.
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This is because acidic and basic
solutions neutralize each other.
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Hence, we can distinguish between
the three types of solutions.
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ACIDS
Acids are those substances which have a
sour taste. Acids change the color of blue litmus to red.
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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.
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Strong Acids and Weak Acids
All the
acids are divided into two groups: strong acids and weak acids.
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.
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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.
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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.
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DILUTING ACIDS
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PROPERTIES OF ACIDS
The important characteristic of acids is:
1.
Reaction of acids and
bases with water:
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Acids
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Bases
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Release
H+ or H3O+ ions in water
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Release
OH- ions in water
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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.
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Metal + Acid
à
Salt + Hydrogen gas
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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.
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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?
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.
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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?
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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.
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3. Reaction
of acids and bases with metal carbonates:
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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
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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.
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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
(d) 16 mL of HCl solution will be required.
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Which one
of the following types of medicines is used for treating indigestion?
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5. Reaction of acids with metallic oxides:
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Acids react with metal oxides to
form salt and water.
Metal oxide +
Acid à Salt +
Water
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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.
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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
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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
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- Acids have a sour taste
- Acids turns blue litmus to red.
3. Acids have corrosive nature.
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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.
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Acids are never stored in metal
container because they gradually corrode and eat up metal container so they
stored in glass and ceramics container.
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The strong bases (or alkali)
such sodium hydroxide are also very corrosive, and attack and destroy our skin.
- Acids solutions conduct electricity
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Why does an aqueous solution of acid conduct electricity?
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Answer Acids
dissociate in aqueous solutions to form ions. These ions are responsible for
conduction of electricity.
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Why does distilled water not conduct electricity, whereas rain
water does?
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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.
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WHAT DO ALL ACIDS HAVE IN
COMMON
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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.
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Acids Do Not Show Acidic
Behavior in the Absence of Water
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Why do acids not show acidic
behaviour in the absence of water?
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.
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Why does dry HCl gas not change the colour of the dry litmus
paper?
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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.
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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.
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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)
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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.
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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)
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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.
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How is the
concentration of hydroxide ions (OH−) affected when excess base is
dissolved in a solution of sodium hydroxide?
The concentration of hydroxide ions
(OH−) would increase when excess base is dissolved in a solution
of sodium hydroxide.
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Properties of Bases
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All the metal does not react with bases to form salts and
hydrogen gas.
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)
+
Non-metal + Base
à
Salt + Water
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STRENGH OF ACID AND BASE SOLUTIONS: pH SCALE
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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.
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§ 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.
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According to pH scale: ---
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A
solution turns red litmus blue, its pH is likely to be
(a) 1 (b)
4 (c) 5 (d) 10
(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.
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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.
(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
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§ 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.
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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?
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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.
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Question 3:
Do
basic solutions also have
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Answer Yes,
basic solution also has
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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.
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IMPORTANCE
OF PH IN OUR DAILY LIFE
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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.
§ 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.
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Living organisms are pH sensitive. Human body
works within a pH range of 7.0 to 7.8.
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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.
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.
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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.
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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.
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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.
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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.
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Fresh
milk has a pH of 6. How do you think the pH will change as it turns into
curd? Explain your 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.
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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?
(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.
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SALTS
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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.
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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’.
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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
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COMMON
SALT (SODIUM CHLORIDE)
·
The chemical name of common
salt is sodium chloride (NaCl).
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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.
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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)
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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:
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
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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.
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Name the sodium
compound which is used for softening hard water.
Washing soda (Na2CO3.10H2O)
is used for softening hard water
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What will happen
if a solution of sodium hydrocarbonate is heated? Give the equation of the
reaction involved.
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Answer When a
solution of sodium hydrocarbonate (sodium hydrogencarbonate) is heated,
sodium carbonate and water are formed with the evolution of carbon dioxide
gas.
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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
Heat
2NaHCO3 ----------- > Na2CO3 +
CO2 + H2O
Uses of sodium hydrogen carbonate
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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.
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BLEACHING POWER
Bleaching power is calcium oxychloride and
the formula is CaOCl2.
|
|
|
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
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|
Properties
of bleaching power
CaOCl2
+ H2SO4 à
CaSO4 + Cl2 +
H2O
|
|
Uses of
Bleaching Power
|
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
Uses of plaster of Paris
|
|
Write an equation
to show the reaction between Plaster of Paris and water.
|
|
Plaster
of Paris should be stored in a moisture-proof container. Explain why?
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.
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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
- Which gas is usually liberated when an
acid reacts with a metal?
- While diluting an acid, why is it
recommended that the acid should be added to water and not water to acid?
- What happens when an acid reacts with
a metal carbonate?
- What happens when an acid reacts with
a metal hydrogen carbonate?
- What happens when an acid reacts with
a base? Give equation of the reaction involved. What is the special name
of this reaction?
- What happens when an acid reacts with
a metal oxide? Write the equation of the reaction involved.
- 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.
- 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
- What are organic acids and mineral
acids? Give examples of each.
- Which element is common to all acids?
- 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?
- Why does dry HCl gas not change the
color of the dry litmus paper?
- Why does distilled water not conduct
electricity whereas rain water does?
- Give the name and formulae of two
strong acids and two weak acids.
- Fill in the following statement with a
suitable word:
Substances do not show their acidic properties
without……..
- 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?
- Two solutions X and Y have pH=4 and
pH=8, respectively. Which solution will give alkaline reaction and which
one acidic.
- The pH of a cold drink is 5. What will
be its action an blue and red litmus solution?
- A solution turns red litmus blue, its
pH is like to be:
(a) 1 (b) 4 (c) 5 (d) 10
- (a) Which is more acidic, pH = 2 or pH
= 11?
(b) Which is more basic pH = 8 or pH = 11?
- Fresh milk has a pH of 6. How do you
think the pH would change a it turns into curd? Explain your answer.
- What effect does the concentration of
H+(aq) ions have on the nature of the solution?
- Name the indicator which can give us
an idea of how strong or weak an acid or base is?
- How does a universal indicator work?
- 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?
- Under what soil conditions do you
think a farmer would treat the soil of his fields with quicklime or slaked
lime or chalk?
- How does an antacid work? Name two
antacid.
- Explain the pH change as the tooth
decay. How can tooth decay caused by pH change be prevented?
- What happens during a bee sting? What
is its remedy?
- 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?
- A salt X when dissolved in distilled
water gives a clear solution which turns red litmus blue. Explain the
phenomenon.
- Explain why, an aqueous solution of
sodium chloride is neutral but an aqueous solution of sodium carbonate is
basic.
- 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.
- What is meant by a family of salts?
Explain with examples.
- Write the chemical name and formula of
common salt.
- Name the major salt present in
sea-water?
- Name three chemicals made from common
salt.
- Give any two uses of common salt.
- Name the salt which is used as a
preservative in pickle, and in curing meat and fish.
- What happens when a concentrated solution
of sodium chloride is electrolyzed? Write the equation of the reaction
involved.
- The electrolysis of an aqueous
solution of sodium chloride gives us three products. Name them.
- Explain why, chlorine is used for
sterilizing drinking water supply.
- Name the product formed when Cl2 and
H2 produced during the electrolysis of brine are made to
combine.
- Write the chemical formula of sodium
carbonate.
- Name a metal compound which has
detergent properties.
- Name a sodium compound used for
softening hard water.
- What is the common name Na2CO3.10H2O?
- Name the metal whose carbonate is known
as washing soda.
- What is the chemical name of baking
soda?
- What is the chemical formula of baking
soda?
- What is the common name of sodium
hydrogen carbonate?
- Name an acid which is present in
baking powers.
- What happens when a solution of sodium
hydrogen carbonate is heated? Write equation of the reaction involved.
- Give the chemical formula of washing
soda and baking soda.
- What is the chemical name of bleaching
power?
- What is the chemical formula of
bleaching power?
- What are the materials used for the
preparation of bleaching power?
- Name the substances obtained by the
action of chlorine on solid slaked lime.
- Name one compound of calcium which is
used for bleaching cloth.
- Which is the real bleaching agent
present in bleaching power?
- What is plaster of Paris? Write the
chemical composition of plaster of Paris.
- Name the raw material used for the
preparation of plaster of Paris.
- What is the commercial name of calcium
sulphate hemi-hydrate?
- What will happen if heating is not
controlled while preparing plaster of Paris?
- State two important uses of plaster of
Paris.
- What is meant by ‘water of
crystallization’
- What is meant by ‘hydrated’ and
‘anhydrous’ salts? Explain with an example.
- What happens when a copper sulphate
crystal are heated strongly/ explain with the help of an equation.
- Write the names, formula and colors of
any two hydrated salts.
- What happens when copper sulphate
crystals are added to anhydrous copper sulphate? Explain with the help of
an equation.
|
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?
If
you think feymans, Irodov & Resnick-Halliday
are
the bibles of Physics
Think
Again
Redefining
education in physics
TRANSITION
TRANSIÇÃO
{Striving singularity, Exploring
Excellence}
La physique pure, rien d'autre
(Pure physics, nothing else)
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