Question 1

A substance that changes its colour to show whether something is an acid or a base is called a/an:

Accepted Answer

Indicator. An indicator changes colour in acids and bases, so we use it to tell them apart.

Question 2

Litmus, a common natural indicator, is taken from a plant-like living thing called:

Accepted Answer

Lichen. Litmus is extracted from lichens, which grow on rocks and tree bark.

Question 3

When blue litmus paper is dipped in an acid, its colour changes to:

Accepted Answer

Red. Acids turn blue litmus red. That is the simple test for an acid.

Question 4

Red litmus paper is dipped in a base. Its colour changes to:

Accepted Answer

Blue. Bases turn red litmus blue, which is the test for a base.

Question 5

Acids usually have a ___ taste.

Accepted Answer

Sour. Acidic foods like lemon and tamarind taste sour, which is a common sign of an acid.

Question 6

The acid found in lemon and orange is:

Accepted Answer

Citric acid. Citrus fruits such as lemon and orange contain citric acid.

Question 7

Vinegar, used in cooking and pickles, contains:

Accepted Answer

Acetic acid. Vinegar is a dilute solution of acetic acid, which gives it a sour taste and smell.

Question 8

Which of these is an acidic substance?

Accepted Answer

Lemon juice. Lemon juice is acidic (sour). Soap, baking soda and lime water are all basic.

Question 9

Bases usually have a ___ taste.

Accepted Answer

Bitter. Bases such as soap taste bitter. (We should never taste chemicals to check this.)

Question 10

To the touch, bases usually feel:

Accepted Answer

Soapy / slippery. Bases like soap solution feel slippery or soapy on the skin.

Question 11

Which of these is a base?

Accepted Answer

Baking soda. Baking soda is basic, while lemon juice, vinegar and curd are all acidic.

Question 12

When red litmus paper is dipped in soap solution, it turns:

Accepted Answer

Blue. Soap solution is basic, and bases turn red litmus blue.

Question 13

When an acid and a base are mixed so that they cancel each other out, the reaction is called:

Accepted Answer

Neutralization. In neutralization an acid and a base react and remove each other’s effect.

Question 14

When an acid reacts with a base, it usually forms:

Accepted Answer

Salt and water. Neutralization gives salt and water: acid + base → salt + water.

Question 15

After an acid and a base have exactly neutralised each other, the mixture is:

Accepted Answer

Neutral. When the acid and base cancel out, the leftover mixture is neutral (neither acid nor base).

Question 16

Toothpaste is basic. It protects our teeth by neutralising the ___ made by bacteria in the mouth.

Accepted Answer

Acid. Bacteria produce acid that harms teeth; the basic toothpaste neutralises this acid.

Question 17

A drop of lemon juice is placed on yellow turmeric paper. What is most likely to happen?

Accepted Answer

It stays yellow. Turmeric only changes colour with a base. Lemon juice is an acid, so the paper stays yellow.

Question 18

Which statement about litmus is completely correct?

Accepted Answer

An acid turns blue litmus red, and a base turns red litmus blue. Acids change blue litmus to red; bases change red litmus to blue. Litmus does not turn green.

Question 19

A strip of blue litmus paper is dipped into orange juice. What will happen?

Accepted Answer

It turns red. Orange juice is acidic (citric acid), so it turns blue litmus red.

Question 20

A fizzy cold drink (soda) is acidic mainly because it contains:

Accepted Answer

Carbonic acid. Carbon dioxide gas dissolved in the drink forms carbonic acid, making it fizzy and acidic.

Acids, Bases and Neutralization — Homi Bhabha Class 6 Chemistry MCQs with Solutions

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Sample questions with solutions