Acids, Bases and Salts
Multiple Choice Questions
- A solution turns red litmus blue. Its pH is likely to be
(b) 4 (d) 10.
- An element common in all acids is
- Which acid is present in sting of a honey bee?
(a) Hydrochloric acid
(b) Acetic acid
(c) Sulphuric acid
(d) Methanoic acid.
- Olfactory indicator is
(d) Rose petals.
- Dissolution of acid or base in water is.
(d) None of these.
- An indicator is what type of compound?
(a) Reducing agent
(c) Strong base or acid
(d) Weak base or acid.
- The organic acid present in tomato is
(a) Tartaric acid
(c) Lactic acid
(b) Oxalic acid
(d) Malic acid.
- HCI reacts with NaOH to form salt and water. This reaction is called
(a) Redox reaction
- A solution reacts with crushed egg-shells to give a gas that turns lime wate milky. The solution contains
- Which one of the following types of medicines is used for treating in digestion?
Ans. 1. (d), 2. (c), 3. (d), 4. (c), 5. (b), 6. (d), 7. (d), 8. (c), 9. (b), 10. (c).
Fill in the Blanks
- The acid present in lemon is
- The chemical name of plaster of Paris is…………..
- Chemical name of baking soda is…………
- Egg shell is made up of ………….
- If the pH of a solution is greater than 7, the solution will be.
- Mixing of concentrated acid or base with water is a highly ……………reaction.
- Tooth enamel corrodes if the pH of mouth is less than……………
- pH of a neutral solution is…….
- Litmus is a……….. indicator. 10…………. changes blue litmus to red.
- Acids and bases neutralise each other to form corresponding salt and ……….. (2021)
Ans. 1. Citric acid, 2. Calcium sulphate hemihydrate, 3. Sodium hydrogen carbonat (NaHCO3), 4. Calcium Carbonate, 5. basic, 6. exothermic, 7. 5.5, 8. 7, 9. natural
- Acid, 11. water.
- Distilled water does not conduct electricity.
- Acidity is cured by analgesic.
- pH of a solution can range from 0-14.
- HCI is a weak acid.
- NaOH is a strong base,
- When the pH of rain water becomes less than 5-6, it is called acidic rain.
- Reactivity of a solution is determined by its pH value.
- Turmeric turns dark brown in colour in basic medium
Ans. 1. True, 2. False, 3. True, 4. False, 5. True, 6. True, 7. False, 8. True.
Match the Columns
Column ‘A’ Column ‘B’
- Vinegar. (a) Plaster of Paris.
- Magnesium hydroxide. (b) Baking soda
- Moisture proof container. (c) Acetic acid
- Fire extinguisher (d) Milk of Magnesia
- Sodium carbonate (e) Wood pulp in Paper
- Bleaching powder. (f) Permanent hardness
Ans. 1. → (c), 2. → (d), 3. → (a). 4. (b), 5. (f), 6. → (e).
Answer in one Word/Sentence
- What is the pH value of pure water?
- Which acid is produced in our stomach ?
- Which acid is present in Nettle leaves ?
Ans. Methanoic acid.
- What is the chemical formula of washing soda?
Ans, Sodium carbonate, Na₂CO3.10H₂O
- What are the products formed in chlor-alkali process?
Ans. Chlorine (chlor), Sodium hydroxide (alkali), and hydrogen.
- What is brine?
Ans. Aqueous solution of sodium chloride.
- What is water of crystallisation?
Ans. Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.
- What is the effect of an acid and a base on the smell of an onion ?
Ans. Smell of an onion remains as such in the presence of an acid and it diminishes or fades away in the presence of a base.
Very Short Answer Type Questions
- 1. Why does an aqueous solution of an acid conduct electricity ?
Ans. The presence of hydrogen ions (H+) or hydronium ions (H3O+) in the aqueous solution of an acid are responsible for conducting electricity.
- 2. Why does dry HCl gas not change the colour of dry litmus paper ?
Ans. The separation of H +ions from HCI molecules cannot occurs in the absence of
water. Hence, dry HCI has no hydrogen ions. Therefore, dry HCI gas does not change the colour of dry litmus paper because it has no hydrogen ions (H+) in it.
Q.3. How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted ?
Ans. When an acid is diluted, the concentration of hydronium ions (H3O+) per unit volume decreases. This means that the strength of the acid decreases. When water is added, the H+ ions of acid react with hydroxyl ions (OH-) of water to form water molecule.
Hence, concentration of (OH-/H3O+)in acid decreases, on dilution with water.
Q.4. How is the concentration of hydroxide ions (OH-) affected when excess base is dissolved in a solution of sodium hydroxide?
Ans. The concentration of hydroxide ions (OH-) would increase when excess base is dissolved in a solution of sodium hydroxide. Water soluble bases produce OH- ions on dissolving in water. Thus, when NaOH is dissolved in NaOH solution, the concentration of
OH- ions increases.
NaOH(s) ——–Na (aq) + OH (aq).
- 5. Do basic solutions also have H+ (aq) ions? If yes, then why are these basie? Ans. Yes, basic solution also has H+ ions. However, their concentration is less as compared to the concentration of OH- ions that makes the solution basic.
- 6. What is the common name of the compound CaOCH₂ ?
Ans. Bleaching Powder.
- 7. Name the substance which on treatment with chlorine yields bleaching powder.
Ans. Calcium hydroxide [Ca(OH)₂].
- 8. Name the sodium compound which is used for softening hard water.
Ans. Washing soda (Na₂CO3.10H₂O).
- 9. What will happen if a solution of sodium hydrocarbonate is heated ? Give the equation of the reaction involved.
Ans. When sodium hydrogen carbonate is heated then sodium carbonate and water is formed along with the evolution of carbon dioxide gas.
2NaHCO3———Na₂CO3 + H₂O + CO₂
- 10. Write an equation to show the reaction between plaster of Paris and water.
- 11. Write the importance of pH in daily life. (Any two importance)
Ans. (1) Living organisms can survive only in a narrow range of pH change.
(2) Plants require a specific pH range for their healthy growth.
Short Answer Type Questions
- 1. Why should curd and sour substances not be kept in brass and copper vessels? Ans. Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thus spoiling the food.
- 2. Why do HCI, HNO3 etc. show acidic characters in aqueous solutions, while solutions of compounds like alcohol and glucose do not show acidic character?
Ans. When HCI or HNO3 are mixed with water, they dissolve in water to form H* or
H3O+ ions which shows their acidic character. For e.g.,
When alcohol or glucose are mixed with water, they do not dissolve to form ions. Hence, they do not show acidic character.
Q.3. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
Ans. The process of dissolving an acid in water is exothermic, hence it is always recommended that acid should be added to water. If water is added to acid then it is possible that because of large amount of heat generated, the mixture splashes out and causes burns.
- 4. What effect does the concentration of H* (aq) ions have on the nature of the solution ?
Ans. If the concentration of H* (aq.) ions is increased (>10-7) then the solution will become acidic and if the concentration of H* (aq) ions is decreased (<10-7) then the solution will become basic in nature.
- 5. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk calcium carbonate)?
Ans. If the soil is acidic and improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with quick lime or slaked lime or chalk, because these salts are basic in nature. Hence, it will be used to neutralise the acidic nature of soil as the reaction of acid and base is neutralisation reaction.
- 6. Why does distilled water not conduct electricity, whereas, rain water does ?
Ans. Distilled water is pure and does not contain dissolved salts hence, it cannot conduct electricity because it does not contain ions, while rain water conducts electricity as it contains ions due to the presence of dissolved salts in it.
- 7. Why do acids not show acidic behaviour in the absence of water?
Ans. Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions in an acid takes place only in presence of water.
- 8. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd ? Explain your answer.
Ans. The pH of milk is 6. When the milk changes into curd, its pH will reduce because
curd is acidic in nature. The acids present in it will decrease the pH. Conversion of milk into curd produces lactic acid due to which the curd is acidic and pH value of acids is low, Therefore, pH of curd will reduce.
- 9. A milkman adds a very small amount of baking soda to fresh milk:
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline ?
(b) Why does this milk take a longer time to set as curd ?
Ans.(a) The milkman shifts the pH of the fresh milk from 6 to slightly alkaline because in this condition milk does not set as curd easily.
(b) Since this milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base. Thus, this milk takes a longer time to set as curd.
- 10. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Write its equation.
Ans. Plaster of Paris should be stored in a moisture-proof container because it absorbs moisture and turns into a hard substance (Gypsum). The following equation represents
- 11. Define neutralization reaction with example.
Ans. A reaction in which an acid and a base react together to give salt and water is termed as neutralization reaction, e.g.
(i) NaOH + HCI →→→→ NaCl + H₂O
(ii)HNO3 +KOH →→→→KNO3 + H₂O
- 12. Write two important uses of washing soda and baking soda. Ans. Uses of washing soda : (1) It is used for removing permanent
(2) It is used as a cleaning agent for domestic purposes.
Uses of baking soda: (1) It is used in making of baking powder.
(2) It is also used in soda-acid fire extinguishers.
- 13. Write the chemical formula and one use of baking soda.
Ans. Chemical Formula: NaHCO3.
Use: See Q. 12.
- 14. Write the chemical formula of the following: (1) Bleaching powder, (2) Plaster of Paris.
Ans. (1) CaOCI2, (2) CaSO4 H₂O.
- 15. Write the chemical name, formula and two uses of bleaching powder.
Ans. Chemical name of bleaching powder : Calcium oxy-chloride.
Formula of the bleaching powder : CaOCl₂
Uses of bleaching powder :
(1) For bleaching clothes and papers.
(2) As an insecticide.
Long Answer Type / Analytical Questions
- 1. What is the chemical name of Bleaching powder ? How is it prepared ? List its uses.
Ans. Chemical name of bleaching powder is calcium oxychloride with chemical formula
(1) As a bleaching agent in the textile industry for bleaching cotton and linen.
(2) As an oxidising agent in many chemical industries.
(3) To make drinking water free from germs.
(4) In paper industry for bleaching wood pulp.
- 2. Tooth enamel is one of the hardest substances in our body. How does it undergo damage due to eating of chocolates and sweets? What should we do to prevent it?
Ans. Tooth decay starts when the pH of mouth is lower than 5-5. Tooth enamel made of calcium phosphate is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH of mouth is below 5-5. Bacteria present in the mouth produce acids by degradation of sugar, due to chocolates and sweets, and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food.
Using toothpastes, which are generally basic, for cleaning the teeth, can neutralise the excess acid and prevent tooth decay.
Q.3. 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?
Ans. Hydrogen gas is liberated when an acid reacts with a metal. Take few pieces of zinc (Zn) granules in a delivery tube. Add 5 ml of hydrochloric acid (HCI). White fumes will evolve. Pass the gas to a soap solution or collect it in a balloon. The gas collected is hydrogen. Since hydrogen gas has low density in comparison to air, the balloon will float in air.
Zn(s) + 2HCl(aq)→→→→ ZnCl₂(s) + H₂(g)
The evolved gas is hydrogen, this can be tested by bringing a burning candle near it. The gas burns with a pop sound.
- 4. Differentiate between acids and bases. Name a strong acid and a base. Difference between Acids and Bases