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TRANSITION
{Striving singularity, Exploring Excellence}
:TRANSITION by Rajeev Sharma
EM-133, Deen Dayal Nagar, Gwalior
Ph:9993696297, 9329837149
e-mail: raji_greymatter@rediffmail.com
login: transitionarena.blogspot.com
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CHEMICAL EQUATION AND REACTIONS+ACID, BASES AND
SALTS
Time: 2½ Hours
Max. Marks: 60
General Instructions
1. The question paper comprises of two sections A and B. You
have to attempt both the sections.
2. All questions are compulsory.
3. There is no overall choice.
4. All questions of section A and all questions of section B
to be attempted separately.
5. Questions 1 to 6 in section A and 19 to 21 in section B
are very short answer type questions and carry one mark each.
6. Questions 7 to 12 in section A and 22 to 24 in section B
are short answer type questions and carry two marks each.
7. Questions 13 to 16 in section A and 25 and 26 in section
B are also short answer type questions and carry three marks each.
8. Questions 17 and 18 in section A and question 27 in
section B are long answer type questions and carry five marks each.
SECTION-A
1.
A
substance ‘M’ reacts violently with water with the evolution of heat to form a
compound ‘N’ which is also used in white washing. When carbon dioxide is passed
through the aqueous solution of ‘N’, a solid compound ‘X’ is obtained as white
precipitate. Compound ‘X’ on heating strongly gives compound ‘M’ with the
liberation of carbon dioxide. Identify the compounds M, N, and X and write the
reactions involved.
2.
Can
we store zinc sulphate solution in a copper vessel? Why or why not?
3.
What
is the meaning of “available chlorine”. Why it is important.
4.
What
would you observe when a test tube full of SO2 gas is inverted in a
beaker containing water with few drops of blue litmus paper solution?
5.
Calcination
of lime stone (CaCO3) yields quick lime (Cao) and carbon dioxide.
What mass of CaCO3 should be calcinated to obtain 112 Kg of quick lime?
6.
Why
is FeCl2 formed instead of FeCl3 when iron reacts with
dilute HCl.
7.
A
compound ‘X’ on electrolysis in aqueous solution produces a strong base ‘Y’
along with 2 gases ‘A’ and ‘B’. ‘B’ is used in the manufacture of bleaching
power. Identify ‘X’, ‘Y’, ‘A’ and ‘B’ and write chemical equation.
8.
Compound
‘X’ forms enamel of teeth. It is the hardest substance of the body. It does not
dissolve in water but it is corroded when pH in the mouth is below 5.5. Write
the chemical reactions involved. How does tooth paste prevent dental decay?
9.
What
will be the colour produced on pH paper if lemon juice is poured over it? What
will be the change in colour if excess of soap solution is added over it?
10.
A
colourless compound ‘X’ obtained from sea water used in daily meals is taken in
test tub. Conc. H2SO4 was added to the test tube. A
pungent smelling gas ‘Y’ comes out which does not affect dry litmus paper but
turns moist blue litmus paper red. Identify ‘X’ and ‘Y’. Write the chemical
reaction involved.
11.
When
CO2 (g) is passed through saturated solution of ammonical brine, 2
compound ‘X’ and ‘Y’ are formed. ‘Y’ is used as an antacid an decomposes to
form another solid ‘Z’. Identify ‘X’,’Y’,’Z’ and write chemical reactions.
12.
A
housewife wanted her house to be whitewashed. She bought 10 KG of quick lime
from the market and dissolved it in 30 litres of water. On adding lime to
water, she noticed that the water started boiling even when it was not being
heated. Give reason for her observation. Write the corresponding chemical
equation and name the product formed.
13.
35.62 mL of NaOH is neutralized with 25.2 mL of
0.0998 M HCl by titration to an equivalence point. What is the concentration of the NaOH?
14.
You have a stock bottle of hydrochloric acid, which
is 12.1 M. You need 400 mL of 0.10 M
HCl. How much of the acid and how much
water will you need? Identify the chemical reaction involved.
15.
If
all bases do not donate OH- ion on dilution, then which is the best
method to describe bases. Explain in 3 suitable points.
16.
pH
of a solution changes from 3 to 4. What is the change in concentration of H+
ions in the solution? How many times do you expect a change in hydrogen ion concentration?
17.
(i)
How can a farmer raise the pH of soil in the fields?
(ii)
Fresh milk has a pH of 6. How do you think the pH will change as it turns into
curd? Explain your answer.
(iii)
A housewife found that the cake prepared by her is hard and small in size.
Which ingredient has she forgotton to add that would have made the cake fluffy?
Give reason.
18.
Explain
the solvay process and chlor-alkali process of production of different
categories of salts.
OR
What
is the meaning of salt hydrolysis? give reactions each for the preparation of
neutral, acidic and basic salts.
SECTION-B
19.
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.
20.
Why
do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions
of compounds like alcohol and glucose do not show acidic character?
21.
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?
22.
(I)
what is the colour of litmus in a solution of ammonium hydroxide.
(II)
What would be the colour of litmus in a solution of sodium carbonate?
23.
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?
24.
What
is observed when a solution of potassium iodide is added to a solution of lead
nitrate taken in a test tube? What type of reaction is this.
25.
Distinguish
between exothermic and endothermic reactions by giving examples. Amongst the
following reactions, identify the exothermic reaction and endothermic reaction.
a.
Heating coal in air to form carbon dioxide.
b.
Heating
limestone in a lime kiln to form quick lime.
c.
Decomposition
of vegetable matter into compost.
26.
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?
27. Give
answer according to the narrated story:
According to the website of the
Hungarian Central Bank, the silvery white Hungarian 2 forint coin is composed
of an alloy containing only copper and nickel. A curious chemist (who did not
know that it is illegal to destroy money in Hungary) weighed a 2-Ft coin
(3.1422 g) and dissolved it completely in concentrated nitric acid in
about 4 hours under a fume hood. A brown gas was produced during this process
and no other gaseous products were formed.
a) What are
the chemical equations for the dissolution reactions?
Our hero diluted the solution to
100.00 cm3 in a volumetric flask. To determine the composition of
the coin, he devised a clever plan. First, he prepared a Na2S2O3
solution by dissolving 6 g
of Na2S2O3·5H2O in 1.0 dm3
of water. Then he weighed 0.08590
g KIO3, dissolved it in water and prepared
100.00 cm3 stock solutions in a volumetric flask. He measured 10.00
cm3 of this stock solution, added 5 cm3 20 % hydrochloric
acid and 2 g
solid KI. The solution turned brown immediately. Then he titrated this sample
with the Na2S2O3 solution. In a number of parallel
measurements the average for the equivalence point was 10.46 cm3.
b) Write down
the equations of all the reactions that have taken place and determine
the concentration of the Na2S2O3 solution. What could our hero have used as an indicator?
When our hero began to wash up,
he noticed that some white precipitate appeared in the first sample. He
remembered clearly that he added more Na2S2O3
solution to this sample than was necessary to reach the end point.
Next, our hero returned to the
greenish blue stock solution he prepared first. He measured 1.000 cm3
of this solution into a titration flask, added 20 cm3 of 5 % acetic
acid and 2 g
solid KI. He waited about 5 minutes. The solution became brown and a
light-colored precipitate appeared.
d) What is
the chemical equation of the process producing the colored species and the
precipitate? Why did our hero have to wait? Why would it have been a mistake to wait hours rather than
minutes?
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