CBSE Class 10 Science HOTs Acids Bases And Salts

CASE STUDY TYPE QUESTIONS

Salt of a strong acid and strong base is neutral with a pH value of 7. NaCl common salt is formed by a combination of hydrochloric acid and sodium hydroxide solution. This is the salt that is used in food. Some salt is called rock salt which was formed when seas of bygone ages dried up. The common salt thus obtained is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, and bleaching powder.

Question. Which of the following does not form an acidic salt?
(a) Phosphoric acid
(b) Carbonic acid
(c) Hydrochloric acid
(d) Sulphuric acid
Answer : B

Question. Which of the following salts has no water of crystallization?
(a) Copper sulphate
(b) Washing soda
(c) Baking soda
(d) Gypsum
Answer : C

Question. The formula of baking soda is
(a) NaCl
(b) KHCO₃
(c) NaHCO₃
(d) Na₂CO₃
Answer : C

Question. Which of the following is treated with chlorine to obtain bleaching powder
(a) Ca SO₄
(b) Ca (OH)₂
(c) Mg (OH)₂
(d) KOH
Answer : B

VERY SHORT ANSWER TYPE QUESTIONS

Question. Write the chemical name and formula of the compound which is used as an antacid
Answer : Sodium bicarbonate, NaHCO₃

Question. Acidic and basic solutions in water conduct electricity. Why?
Answer : Because they produce hydrogen and hydroxide ions respectively.

Question. Which bases are called alkalies?
Answer : Soluble bases are called alkalies.

Question. The pH of a salt used to make tasty and crispy pakoras is 14. Identify the salt and write a chemical equation for its formation
Answer : Baking soda (Sodium Hydrogen Carbonate)

Question. The pH of three solutions A, B and C are 4, 9 and 6 respectively. Arrange them in increasing order of acidic strength.
Answer : The increasing order of acidic strength is : B < C < A.

Question. Name the hardest substance in the body.
Answer : Tooth enamel (Calcium phosphate).

Question. Kazi and priyam want to prepare dil H₂SO₄ .Kazi added conc.H₂SO₄ to water slowly with constant stirring& cooling whereas Priyam added water to conc.H₂SO₄.Name the student who was correct and why?
Answer: Kazi was correct. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

SHORT ANSWER TYPE QUESTIONS

Question. A compound X is bitter in taste. It is a component of washing powder& reacts with dil.HCl to produce brisk effervescence due to colourless, odourless gas Y which turns lime water milky due to formation of Z. When excess of CO₂ is passed, milkiness disappears doe to formation of P. Identify X, Y, and Z & P.
Answer :

Question. Compound P forms enamel of teeth. It is the hardest substance of the body. It does not dissolve in water but it is corroded when pH in the mouth is below 5.5. How does tooth paste prevent dental decay?
Answer : P = C_a3 (PO₄)₂. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. Using toothpastes, which are generally basic, for cleaning the teeth can neutralize the excess acid and prevent tooth decay.

Question. The oxide of a metal M was water soluble when a blue litmus strip was dipped in this solution, it did not go any change in colour. Predict the nature of oxide
Answer : The Metal oxide (MO) is of basic in nature. It dissolves in water to form metal hydroxide as MO + H₂O → M (OH)₂ B lu e litmus does not undergo any change in colour in the basic medium.

Question. A first aid manual suggests that vinegar should be used to treat wasp sting and baking soda for bee stings.
(i) What does this information tell you about the chemical nature of the wasp stings
(ii) If there were no baking soda in the house, what other household substance could you use to treat bee stings?
Answer : (i) Since vinegar (acetic acid) is used to heal or neutralize the effect of wasp stings this means that the chemical present in the stings must be some base.
(ii) NH₄OH

Question. `A` is a soluble acidic oxide and `B` is a soluble base. Compared to pH of pure water. What will be the pH of (a) solution of A (b) solution of B?
Answer : pH of A will be less than 7 and that of B will be more than 7.

Question. A road tanker carrying an acid was involved in an accident and its contents spilled on the road. At the side of the road, iron drain covers began melting and fizzing as the acid ran over them. A specialist was called to see if the acid actually leaked into the nearby river.
(a) Explain how the specialist could carry out a simple test to see if the river water contains some acid or not.
(b) The word melting is incorrectly used in the report. Suggest a better name that should have been used.
(c) Explain why drain covers began fizzing as the acid rain over them.
Answer : (a) By dipping a strip of blue litmus paper in to the sample of river water. If the colour changes to red this means that some acid has gone in to the river.
(b) Corrosion.
(c) Iron reacts with acid to evolve hydrogen gas.

Question 8. A compound `X` on electrolysis in aqueous solution produces a strong base. `Y` along with two gases `A` and `B`. `B` is used in manufacture of bleaching powder. Identify X, Y, A and B. Write chemical equations.
Answer :

Question 9. A yellow powder X gives a pungent smell if left open in air. It is prepared by the reaction of dry compound Y with chlorine gas. It is used for disinfecting drinking water. Identify X and Y. and write the reaction involved.
Answer :

Question 10. When CO2 gas pass through saturated solution of ammonical brine, two compound `X` and `Y` are formed. `Y` is used as antacid and decomposes to form another solid `Z`. Identify `X`,`Y`, `Z` and write chemical equations.
Answer :

Question 11.A compound `A on heating at 370 K gives `B` used as plaster for supporting fractured bones in the right position. `B` on mixing with water changes to `A`. Identify `A` and `B` and write the chemical reaction.
Answer :

Question 12. A few drops of phenolphthalein indicator were added to an unknown solution A. It acquired pink colour. Now another unknown solution B was added to it drop by drop and the solution becomes colorless. Predict the nature of A & B.
Answer : `A` is basic in nature as phenolphthalein has imparted pink colour to it. Sol `B` is an acid it has made solution A colourless by neutralizing by its basic effect.

Question. A student heated a few crystals of copper sulphate in a dry boiling tube.
(a) What will be the color of the copper sulphate after heating?
(b) Will you notice water droplets in the boiling tube?
(c) Where have these come from?
Answer :
(a) White
(b) Yes
(c) Copper sulphate crystals which seem to be dry contain water of crystallization.

Question. A substance `X` used in the kitchen for making tasty crispy pakoras.and is also an ingredient of antacid. Name the substance `X`.
(i) How does `X` help to make cakes and bread soft and spongy.
(ii) Is the pH value of solution of `X` is lesser than or greater than 7.0?
Answer :

(i) When CO2 gas escapes as bubbles it leaves behind pores which make the cake or bread soft and spongy.
(ii) It is a salt of strong base so the pH of the solution will be more than 7.0

Question : Kazi and priyam want to prepare dil H2SO4 .Kazi added conc.H2SO4 to water slowly with constant stirring& cooling whereas Priyam added water to conc. H2SO4.Name the student who was correct and why?
Answer : Kazi was correct. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

Question : Compound P forms enamel of teeth. It is the hardest substance of the body. It does not dissolve in water but it is corroded when pH in the mouth is below 5.5. How does tooth paste prevent dental decay?
Answer : P = Ca3 (PO4)2. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. Using toothpastes, which are generally basic, for cleaning the teeth can neutralize the excess acid and prevent tooth decay.

Question : The oxide of a metal M was water soluble when a blue litmus strip was dipped in this solution, itmdid not go any change in colour. Predict the nature of oxide
Answer : The Metal oxide (MO) is of basic in nature. It dissolves in water to form metal hydroxide as MO + H2O -> M (OH) 2 B lue litmus does not undergo any change in colour in the basic medium.

Question : A first aid manual suggests that vinegar should be used to treat wasp sting and baking soda for bee stings.
(i) What does this information tell you about the chemical nature of the wasp stings
(ii) If there were no baking soda in the house, what other household substance could you use to treat bee stings?
Answer : (i) Since vinegar (acetic acid) is used to heal or neutralize the effect of wasp stings this means that the chemical present in the stings must be some base.
(ii)NH4OH

Question. To a solution of sodium hydroxide in a test tube, two drops of phenolphthalein are added.
(i) State the colour change observed.
(ii) If dil HCl is added dropwise to the solution, what will be the colour change?
(iii) On adding few drops of NaOH solution to the above mixture the colour of the solution reappears. Why?
Answer : (i) On adding phenolphthalein to NaOH solution, the colour becomes pink.
(ii) On adding dilute HCl solution dropwise to the same test tube, the pink colour disappears and the solution again becomes colourless.
(iii) On again adding NaOH to the above mixture, pink colour reappears because the medium becomes basic again.

Question. A gas X reacts with lime water and forms a compound Y which is used as bleaching agent in the chemical industry. Identify X and Y. Give the chemical equation of the reaction involved.
Answer : X is chlorine Y is CaOCl₂ (calcium oxy chloride) used as bleaching agent.
Ca (OH) ₂+ Cl₂ -------------- CaOCl₂ +H₂O

Question. You are given two solutions A and B. The pH of solution A is 6 and pH of solution B is 8.
(i) Which solution is acidic and which is basic?
(ii) Which solution has more H+ ion concentration?
(iii) Why is HCl a stronger acid than acetic acid?
Answer : (i) The solution with pH 6 is acidic while the solution with pH 8 is basic.
(ii) The solution with pH 6 has more H₊ ion concentration.
(iii) HCl is a stronger acid than CH₃COOH since its degree of dissociation
(α) is more or it releases more H₊ ions in solution than acetic acid.

Question : A road tanker carrying an acid was involved in an accident and its contents spilled on the road. At the side of the road,  ron drain covers began melting and fizzing as the acid ran over them. A specialist was called to see if the acid actually leaked into the nearby river.
(a) Explain how the specialist could carry out a simple test to see if the river water contains some acid or not.
(b) The word melting is incorrectly used in the report. Suggest a better name that should have been used.
(c) Explain why drain covers began fizzing as the acid rain over them.
Answer : (a) By dipping a strip of blue litmus paper in to the sample of river water. If the colour changes to red this means that some acid has gone in to the river.
(b) Corrosion.
(c) Iron reacts with acid to evolve hydrogen gas.

Question : A few drops of phenolphthalein indicator were added to an unknown solution A. It acquired pink colour. Now another unknown solution B was added to it drop by drop and the solution becomes colorless. Predict the nature of A & B.
Answer : Sol `A` is basic in nature as phenolphthalein has imparted pink colour to it. Sol `B` is an acid it has made solution A colourless by neutralizing by its basic effect.

Question : A student heated a few crystals of copper sulphate in a dry boiling tube.
a) What will be the color of the copper sulphate after heating?
(b) Will you notice water droplets in the boiling tube?
c) Where have these come from?
Answer : (a) White (b) Yes (c) Copper sulphate crystals which seem to be dry contain water of crystallization.

Question : A substance `X` used in the kitchen for making tasty crispy pakoras.and is also an ingredient of antacid. Name the substance `X`.
(i) How does `X` help to make cakes and bread soft and spongy.
(ii) Is the pH value of solution of `X` is lesser than or greater than 7.0?
Answer : ( i) When CO2 gas escapes as bubbles it leaves behind pores which make the cake or bread soft and spongy.
(ii) It is a salt of strong base so the pH of the solution will be more than 7.0

Question : After drinking access of cold drink, a person suffered from acidity. Explain?
Answer : Cold drink contains carbon dioxide dissolved in them under pressure. Some amount of the gas escapes when a bottle of cold drink is opened while a portion of it remain dissolved. Carbon dioxidemdissolved in water forms a weak acid, carbonic acid. Consumption of excess of cold drink accumulation of carbonic acid in the stomach which is responsible for the development of acidity.

Question : Although acetic acid is highly soluble in water but still it is a weak acid. Explain why?
Answer : The strength of an acid depends upon the extent of ionization. Acetic acid is highly soluble in water but it dissociates partially in the aqueous solution to produce a small amount of H+ ions and , therefore, considered as a weak acid.

Please refer to link below for CBSE Class 10 Chemistry Hots-Acids Bases and Salts.

Acids Bases And Salts