Chapter: Acids, Bases and Salts
Class: X | Subject: Science (Chemistry)
Time Allowed: 40 minutes Maximum Marks: 20
General Instructions:
(i) All questions are compulsory.
(ii) Questions 1–3 are Multiple Choice
Questions (1 mark each).
(iii) Questions 4–5 are Assertion–Reason type
(1 mark each).
(iv) Questions 6–7 carry 2 marks; 8–9 carry 3
marks; Question 10 carries 5 marks.
(v) All questions are based on
real-life/competency-based scenarios — read each carefully before answering.
Section A — Multiple Choice
Questions (1 × 3 = 3 marks)
1. A student spills a few drops of a colourless liquid on the lab bench.
On testing with blue and red litmus paper, the blue litmus turns red but the
red litmus shows no change. The liquid is most likely:
(a) A basic solution such as dilute NaOH
(b) An acidic solution such as dilute HCl
(c) A neutral solution such as common salt
solution
(d) Distilled water
2. Ravi adds a pinch of baking soda to a test tube containing dilute
acetic acid. He observes brisk effervescence. When he passes the gas produced
through freshly prepared lime water, it turns milky. The gas evolved is:
(a) Hydrogen gas
(b) Oxygen gas
(c) Carbon dioxide gas
(d) Sulphur dioxide gas
3. A farmer is advised to treat his acidic soil before sowing crops.
Which of the following would he most appropriately add to the soil to
neutralise its excess acidity?
(a) Quick lime (calcium oxide)
(b) Gypsum
(c) Common salt
(d) Sulphuric acid
Section B — Assertion–Reason Type
(1 × 2 = 2 marks)
For questions 4 and 5,
two statements are given — one labelled Assertion (A) and the other labelled
Reason (R). Choose the correct option:
(a) Both A and R are true, and R is the
correct explanation of A.
(b) Both A and R are true, but R is not the
correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
4. Assertion (A): Dilute acids are generally stored and transported in
plastic containers rather than metal containers.
Reason (R): Acids react with reactive metals
to liberate hydrogen gas, which can corrode a metal container over time.
5. Assertion (A): While diluting a concentrated acid, the acid should
always be added slowly to water, and not water to acid.
Reason (R): The process of dissolving an acid
in water is highly exothermic, and adding water to concentrated acid can cause
the mixture to splash out due to sudden local heating.
Section C — Short Answer Type I
(2 × 2 = 4 marks)
6. A shopkeeper stores an antacid tablet on his shelf to treat acidity. A
customer complains of a burning sensation in the stomach after a heavy meal and
asks how the tablet works.
Explain, with a chemical equation, how an
antacid tablet (containing milk of magnesia) relieves acidity. Name the type of
reaction involved.
7. Two test tubes, A and B, contain colourless solutions. A student adds
a few drops of phenolphthalein to test tube A and it turns pink; the same
indicator added to test tube B shows no colour change.
Identify the nature (acidic/basic/neutral) of
the solution in each test tube. Justify your answer using the property of
phenolphthalein.
Section D — Short Answer Type II
(3 × 2 = 6 marks)
8. A milkman adds a very small amount of baking soda to fresh milk before
storing it for a few hours in summer, to prevent it from turning sour quickly.
(a) State whether baking soda is acidic, basic
or neutral in nature.
(b) Explain how adding it shifts the pH of
milk and helps delay souring. (c) Write the chemical name and formula of baking
soda.
9. During an experiment, a student takes dilute sulphuric acid in a test
tube and drops a few pieces of zinc granules into it. She observes bubbles of a
gas forming, and on bringing a burning matchstick near the mouth of the test
tube, it burns with a 'pop' sound.
(a) Identify the gas evolved and write a
balanced chemical equation for the reaction.
(b) Why does the gas burn with a pop sound?
(c) Name one metal that would NOT show this
reaction with dilute acids, and give a reason.
Section E — Long Answer Type (5 ×
1 = 5 marks)
10. A water-treatment plant supervisor needs to make chlorine-free
drinking water safe for a village that primarily has hard, slightly acidic
water. He plans to use bleaching powder for disinfection and lime for treating
the acidity of water and soil around the reservoir.
(a) Name the chemical compound used as
bleaching powder, and write the chemical equation for its preparation from
slaked lime.
(b) Explain why bleaching powder is used for
disinfecting drinking water.
(c) Name the type of lime used to reduce
soil/water acidity and write its chemical formula.
(d) A student says, 'Plaster of Paris and bleaching powder are
prepared from the same raw material.' Justify whether this statement is
correct, identifying the common raw material.
(e) State one precaution that should be taken
while storing bleaching powder.
— End
of Question Paper —
