QUESTIONS - ACIDS BASES AND SALTS

1/2 Mark Questions

1. What is the colour of methyl orange indicator in acidic medium ?

Ans: Red

2. What is the colour of phenolphthalein indicator in basic solution ?

Ans: Pink

3. What is the colour of methyl orange in alkali conditions?

Ans: Yellow

4. What is the colour of phenolphthalein indicator in acidic solution ?

Ans: Colour less

5. If a base dissolves in water by what name is it better known?

Ans: Alkali

6. What colour would hydrochloric acid (pH=1) turn universal indicator ?

Ans: Red

7. What gas is produced when magnesium is made to react with hydrochloric acid ?

Ans: Hydrogen

8. What happens when the pH of the mouth is lower than 5.5 ?

Ans: Tooth decay starts.

9. Which gas is produced when metals react with acids ?

Ans: Hydrogen (H2)

10. Which chemical is present in antacid tablet ?

Ans: Magnesium hydroxide (MgOH2)

11. Which acid does honey bee sting leaves in our body ?

Ans: Methanoic acid (formic acid)

12. Which acid is injected by stinging hair of nettle plant?

Ans: Methanoic acid (formic acid)

13. Which one of the following types of medicines is used for treating indigestion ?

 A) antibiotic B) analgesic C) antacid D) antiseptic

Ans: C) antacid

14. Which of the following is not an olfactory indicator ?

 A) Onion B) Vanilla essence C) Groundnut D) Clove oil

Ans: C) Groundnut

15. Ravi added acid to the metal hydrogen carbonate and observed the gas evolved. The evolved gas is

 A) O2 B) N2 C) H2 D) CO2

Ans: D) CO2 

1 Mark Questions

1. What are olfactory indicators?

Ans: There are some substances whose odour changes in acidic or basic media. These are called olfactory indicator.

 Ex: onion, vanilla essence clove oil ...etc.

2. Is the substance present in antacid tablet acidic or basic?

Ans: The substance present in antacid tablet is basic.

3.What is a pH scale?

Ans: A scale for measuring hydrogen ion concentration in a solution is called pH scale.

 pH = - log [H+]

4. What type of reaction takes place in stomach when an antacid tablet is consumed?

Ans: A neutralization reaction takes place in stomach when an antacid tablet is consumed.

5. Which gas is usually liberated when an acid reacts with a metal? How will you test for the presence of this gas?

Ans: 1. Hydrogen gas is usually liberated when an acid reacts with a metal.

 Ex: 2 HCl + Zn → ZnCl2 + H2

 2. Bring a burning candle near the gas filled test tube.

 3.The gas evolved put off the burning candle with a pop sound and burns with blue colour flame indicating H2.

6. Why does not distilled water conduct electricity?

Ans: 1. Distilled water didn't have ions (H3O+/OH-) to conduct electricity.

 2. That's why it does not conduct electricity.

7. What will happen if the pH value in our body increases?

Ans: 1. Our body works well within a narrow pH range of 7.0 to 7.8.

 2. If due to some reason this pH range gets disturbed in the body of a person, then many ailments can occur.

8. A compound of a calcium reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle; turns lime water milky. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Ans: CaCO3 + 2 HCl → CaCl2 + CO2 + H2O

9. Under what soil conditions a farmer would treat the soil of his fields with quicklime (calcium hydroxide) or calcium carbonate?

Ans: Under Acidic soil conditions a farmer would treat the soil of his fields with quicklime (calcium hydroxide) or calcium carbonate.

10. Why pure acetic acid does not conduct electricity ?

Ans:1. Pure acetic acid didn't have ions (H3O+).

 2. That's why it does not conduct electricity.

2 Mark Questions

1. What is a neutralization reaction? Give two examples.

Ans: Neutralization reaction: The reaction of an acid with a base to give a salt and water is called a neutralization reaction.

 Acid + Base → Salt + Water

 Ex: HCl + NaOH → NaCl + H2O

 H2SO4 + 2 NaOH → Na2SO4 + 2 H2O

2. Why does tooth decay start when the pH of mouth is lower than 5.5?

Ans: 1. Tooth decay starts when the pH of the mouth is lower than 5.5.

2. Tooth enamel, made of calcium phosphate is the hardest substance in the body.

3. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5.

4. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth.

5. Using tooth pastes, which are generally basic neutralize the excess acid and prevent tooth decay.

3. Write any two properties of acids.

Ans: 1. Acids react with metals and evolve Hydrogen gas.

 2HCl + Zn → ZnCl2 + H2

2. Acids react with bases to give saltd and water. This reaction is called neutralization.

 Base + Acid → Salt + Water

 NaOH + HCl → NaCl + H2O

3. Acids react with metal carbonates and hydrogen carbonates to give corresponding salts, carbon dioxide and water.

Na2CO3 + 2HCl → 2NaCl + H2O + CO2

NaHCO3 + HCl → NaCl + H2O + CO2

4. How does the flow of acid rain into a river make the survival of aquatic life in a river difficult?

Ans: 1. Living organisms can survive only in a narrow range of pH change.

2. When pH of rain water is less than 5.6, it is called acid rain.

3. When acid rain flows in to the rivers, it lowers the pH of the river water.

4. Then the survival of aquatic life in such rivers becomes difficult.

5. Why pickles and sour substances are not stored in brass and copper vessels?

Ans: 1. pickles and sour substances are contain weak acids.

2. If these substances are stored in brass and copper vessels, the weak acids react with vessels and form corresponding salts.

3. These salts are toxic and injurious to health.

4. That's why pickles and sour substances are not stored in brass and copper vessels.

6. Why do living organism have narrow pH range?

Ans: 1. Living organisms can survive only in a narrow range of pH.

2. pH of gastric juices in the stomach is important for the process of digestion. 

3. Living beings carry out their metabolic activities within an optimal pH range.

4. But if the pH range is change then many ailments can occur.

5. That is why they have narrow range of pH.

7. What is Universal indicator ? What is it’s use?

Ans: Universal indicator is a mixture of several indicators.

Uses: 1.The universal indicator can be used to know the strength of acid or base.

 2. It shows different colours at different concentrations of hydrogen ions in a solution.

8. a) If someone in the family is suffering from a problem of acidity, which of the following would you suggest as a remedy? Lemon juice, vinegar or baking soda solution.

 b) Which property do you think of while suggesting the remedy?

Ans: a) I will suggest Baking Soda solution as a remedy.

 b) Baking Soda can neutralize the acidity.

9. You are provided with three test tubes containing distilled water, an acid and a base solution respectively. If you are given only blue litmus paper, how do you identify the contents of each test tube?

Ans:1. Dip the blue Litmus Paper in three test tubes one by one.

2. Identify the test tube where blue Litmus changes to red, it is acid.

3. The colour changed (red) litmus is dipped in remaining two test tubes.

4. Identify the test tube in which red litmus changes to blue, it is base.

5. Remaining test tube contains water.