Unit Test | Acids Bases And Salts | Class 10 Science

MG SCHOOL SCIENCE

UNIT TEST – 02

ACIDS, BASES AND SALTS

Class 10 | Science | Chemistry

25 MARKS

Board Exam Preparation

Maximum Marks
25

Time Duration
50 Minutes

Total Questions
15

Student Name: ______________________________

Class & Section: ______________ Roll No: __________

Date: ______________________________

GENERAL INSTRUCTIONS

1. All questions are compulsory.
2. Read every question carefully.
3. Write balanced chemical equations wherever necessary.
4. Use appropriate chemical formulae and symbols.
5. Marks are indicated against each question.

SECTION A – MULTIPLE CHOICE QUESTIONS (5 × 1 = 5 Marks)

1. Which of the following is a natural indicator? 1 Mark

Phenolphthalein Methyl orange Litmus Universal indicator

Answer: (C) Litmus

2. The pH value of a neutral solution at 25°C is: 1 Mark

0 7 10 14

Answer: (B) 7

3. Which gas is produced when an acid reacts with a metal carbonate? 1 Mark

Hydrogen Oxygen Carbon dioxide Nitrogen

Answer: (C) Carbon dioxide

4. Which of the following is the chemical formula of baking soda? 1 Mark

Na₂CO₃ NaHCO₃ CaCO₃ NaCl

Answer: (B) NaHCO₃

5. Which substance is used for disinfecting drinking water? 1 Mark

Washing soda Baking soda Bleaching powder Plaster of Paris

Answer: (C) Bleaching powder

SECTION B – ONE MARK QUESTIONS (4 × 1 = 4 Marks)

6. What is an acid? 1 Mark

An acid is a substance that produces H⁺ ions (more accurately H₃O⁺ ions) in aqueous solution.

7. What is the pH range of an acidic solution? 1 Mark

The pH of an acidic solution is less than 7 at 25°C.

8. Name the acid present in lemon juice. 1 Mark

Citric acid.

9. Write the chemical formula of Plaster of Paris. 1 Mark

CaSO₄·½H₂O

SECTION C – TWO MARK QUESTIONS (3 × 2 = 6 Marks)

10. Why does dry HCl gas not change the colour of dry blue litmus paper? 2 Marks

HCl produces H⁺ ions only in the presence of water. Dry HCl gas does not ionise to produce these ions, so dry blue litmus paper shows no colour change.

11. Write two uses of baking soda. 2 Marks

1. It is used in baking powder to make bread and cakes soft and fluffy.
2. It is used as an antacid to relieve acidity.

12. What happens when an acid reacts with a metal? Write a balanced chemical equation. 2 Marks

An acid reacts with a suitable metal to form a salt and hydrogen gas.

Zn + 2HCl → ZnCl₂ + H₂↑

SECTION D – THREE MARK QUESTIONS (2 × 3 = 6 Marks)

13. Explain the importance of pH in everyday life. Give any three examples. 3 Marks

1. Digestion: Excess stomach acid is neutralised by antacids.
2. Tooth decay: Tooth decay starts when the pH of the mouth falls below 5.5. Basic toothpaste helps neutralise acids.
3. Soil: Plants grow well in a suitable soil pH. Farmers add lime to acidic soil.

14. Explain the preparation of washing soda from sodium chloride. Write the relevant chemical equations. 3 Marks

Sodium chloride (brine) is used to prepare sodium carbonate through the Solvay process. Sodium carbonate is heated with water and then crystallised to obtain washing soda.

2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O

Washing soda is sodium carbonate decahydrate.

SECTION E – FOUR MARK QUESTION (1 × 4 = 4 Marks)

15. Answer the following questions about salts: 4 Marks

(a) What is a salt? (1 Mark)

(b) Write the chemical formula of bleaching powder. (1 Mark)

(c) Write one use of washing soda. (1 Mark)

(d) Write the chemical equation for the preparation of bleaching powder. (1 Mark)

(a) A salt is an ionic compound formed when the replaceable hydrogen ion of an acid is replaced by a metal or ammonium ion.

(b) CaOCl₂ (commonly represented as bleaching powder).

(c) Washing soda is used for removing permanent hardness of water.

(d)

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

YOUR TEST RESULT

0 / 5

Automatic evaluation covers the five MCQs (5 marks). Descriptive answers require teacher evaluation (20 marks).

COMPLETE ANSWER KEY – TEACHER'S REFERENCE

Section A – MCQ Answers
1. C – Litmus
2. B – 7
3. C – Carbon dioxide
4. B – NaHCO₃
5. C – Bleaching powder

Section B – One Mark Answers

1. Acids produce H⁺ ions in aqueous solution.
2. Less than 7.
3. Citric acid.
4. CaSO₄·½H₂O.

Section C – Two Mark Answers

10. HCl requires water to ionise and produce H⁺ ions.
11. Baking and as an antacid.
12. Salt and hydrogen gas are formed. Zn + 2HCl → ZnCl₂ + H₂.

Section D – Three Mark Answers

13. Importance of pH in digestion, tooth decay and agriculture.
14. Washing soda is obtained by crystallisation of sodium carbonate with water. Equations are given above.

Section E – Four Mark Answer

Refer to the four sub-answers given under Question 15.

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Class 10 Science – Acids, Bases and Salts