CBSE Class 10 Science Acids Bases And Salts Worksheet Set D

Multiple Choice Questions

Question. An aqueous solution ‘A’ turns phenol-phthalein solution pink. On addition of an aqueous solution ‘B’ to ‘A’ and ‘B’.
(a) A is strongly basic and B is a weak base.
(b) A is strongly acidic and B is a weak acid.
(c) A has pH greater than 7 and B has pH less than 7.
(d) A has pH less than 7 and B has pH greater than 7.
Answer: C

Question. When you add a few drops of acetic acid to a test-tube containing sodium bicarbonate powder, which one of the following is your observation ?
(a) No reaction takes place.
(b) A colourless gas with pungent smell is released with brisk effervescence.
(c) A brown coloured gas is released with brisk effervescence.
(d) Formation of bubbles of a colourless and odourless gas.
Answer: D

Question. A student requires hard water for an experiment in his laboratory which is not available in the neighbouring area. In the laboratory there are some salts, which when dissolved in distilled water can convert it into hard water. Select from the following groups of salts, a group, each salt of which when dissolved in distilled water will make it hard.
(a) Sodium chloride, potassium chloride
(b) Sodium sulphate, potassium sulphate
(c) Sodium sulphate, calcium sulphate
(d) Calcium sulphate, calcium chloride
Answer: D

Question. You have four test tubes, A, B, C and D containing sodium carbonate, sodium chloride, lime water and blue litmus solutions respectively. Out of these the material of which test tube/test tubes would be suitable for the correct test of acetic/ethanoic acid ?
(a) Only A
(b) A and B
(c) B and C
(d) A and D
Answer: D

Question. For demonstrating the preparation of soap in the laboratory which of the following combination of an oil and a base would be most suitable ?
(a) Mustard oil and calcium hydroxide
(b) Castor oil and calcium hydroxide
(c) Turpentine oil and sodium hydroxide
(d) Mustard oil and sodium hydroxide.
Answer: D

Question. A student took four test tubes P, Q, R and S and filled about 8 ml. of distilled water in each. After that he dissolved an equal amount of \( \text{Na}_2\text{SO}_4 \) in P, \( \text{K}_2\text{SO}_4 \) in Q, \( \text{CaSO}_4 \) in R and \( \text{MgSO}_4 \) in S. On adding an equal amount of soap solution and shaking each test tube well, a good amount of lather will be obtained in the test tubes :
(a) P and Q
(b) P and R
(c) P, Q and S
(d) Q, R and S
Answer: A

Question. If you take some distilled water in a test-tube, add an equal amount of acetic acid to it, shake the test-tube well and leave it undisturbed on the test-tube stand, then after about 5 minutes, what would you observe ?
(a) There is a layer of water over the layer of acetic acid.
(b) A precipitate is settling at the bottom of the test tube.
(c) Bubbles of colourless gas are coming out of the test-tube.
(d) There is a clear, colourless transparent solution in the test-tube.
Answer: D

Question. Which of the following is used for dissolution of gold ?
(a) Hydrochloric acid
(b) Sulphuric acid
(c) Nitric acid
(d) Aqua regia
Answer: D

Question. Which of the following is not a mineral acid ?
(a) Hydrochloric acid
(b) Citric acid
(c) Sulphuric acid
(d) Nitric acid
Answer: B

Question. Which among the following is not a base ?
(a) \( \text{NaOH} \)
(b) \( \text{KOH} \)
(c) \( \text{NH}_4\text{OH} \)
(d) \( \text{C}_2\text{H}_5\text{OH} \)
Answer: D

Question. Which of the following gives the correct increasing order of acidic strength ?
(a) Water < Acetic acid < Hydrochloric acid
(b) Water < Hydrochloric acid < Acetic acid
(c) Acetic acid < Water < Hydrochloric acid
(d) Hydrochloric acid < Water < Acetic acid
Answer: A

Question. Sodium hydrogen carbonate when added to acetic acid evolves a gas. Which of the following statements are true about the gas evolved ?
(i) It turns lime water milky.
(ii) It extinguishes a burning splinter.
(iii)It dissolves in a solution of sodium hydroxide.
(iv)It has a pungent odour.
(a) (i) and (ii)
(b) (i), (ii) and (iii)
(c) (ii), (iii) and (iv)
(d) (i) and (iv)
Answer: B

Question. If a few drops of a concentrated acid accidentally spills over the hand of a student, what should be done ?
(a) Wash the hand with saline solution.
(b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate.
(c) After washing with plenty of water apply solution of sodium hydroxide on the hand.
(d) Neutralise the acid with a strong alkali.
Answer: B

Question. One of the constituents of baking powder is sodium hydrogen carbonate, the other constituent is :
(a) Hydrochloric acid
(b) Tartaric acid
(c) Acetic acid
(d) Sulphuric acid
Answer: B

Question. Which of the following phenomena occur, when a small amount of acid is added to water ?
(i) Ionisation,
(ii) Neutralisation,
(iii)Dilution,
(iv)Salt formation.
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer: B

Question. Which one of the following can be used as an acid–base indicator by a visually impaired student?
(a) Litmus
(b) Turmeric
(c) Vanilla essence
(d) Petunia leaves
Answer: C

Question. Which of the following substance will not give carbon dioxide on treatment with dilute acid ?
(a) Marble
(b) Limestone
(c) Baking soda
(d) Lime
Answer: D

Question. Match the following
Column I
(a) Bleaching powder
(b) Baking soda
(c) Washing soda
(d) Sodium chloride

Column II
(i) Preparation of glass
(ii) Production of \( \text{H}_2 \) and \( \text{Cl}_2 \)
(iii) Decolourisation
(iv) Antacid
Answer: (a) (iii), (b) (iv), (c) (i), (d) (ii).

Fill in the blanks

Question. (a) The pH of the gastric juices released during digestion is .................. .
(b) When acid reacts with a metal, .................. gas is evolved.
(c) On heating gypsum, it loses water molecules and form .................. .
Answer: (a) Less than 7, (b) \( \text{H}_2 \) (hydrogen), (c) \( \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} \) (Plaster of paris).

Very Short Answers Type Questions

Question. A teacher provided acetic acid, water, lemon juice, aqueous solution of sodium hydrogen carbonate and sodium hydroxide to students in the school laboratory to determine the pH values of these substances using pH papers. One of the students reported the pH values of the given substances as 3, 12, 4, 8 and 14 respectively. Which one of these values is not correct ? Write its correct value stating the reason.
Answer: The value of pH for water is not correct. The correct value of pH of water is 7 because it has almost equal concentration of \( \text{H}^+ \) and \( \text{OH}^- \) due to which it is neutral.

Question. What is observed when a pinch of sodium hydrogen carbonate is added to 2 ml of acetic acid taken in a test tube ? Write chemical equation for the reaction involved in this case.
Answer: \( \text{CO}_2 \) gas is evolved with brisk effervescence when sodium hydrogen carbonate is added to acetic acid.
\( \text{NaHCO}_3 + \text{CH}_3\text{COOH} \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2 \)

Question. Blue litmus solution is added to two test tubes A and B containing dilute HCl and NaOH solution respectively. In which test tube a colour change will be observed ? State the colour change and give its reason.
Answer: Test tube A will show colour change because acids turn blue litmus to red. So the final colour of test tube would be red.

Question. What is observed when 2 ml of dilute hydrochloric acid is added to 1 g of sodium carbonate taken in a clean and dry test tube ? Write chemical equation for the reaction involved.
Answer: A brisk effervescence would be observed if HCl is added to \( \text{Na}_2\text{CO}_3 \) due to the evolution of \( \text{CO}_2 \) gas.
\( \text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 \)

Question. A gas is liberated immediately with a brisk effervescence, when you add acetic acid to sodium hydrogen carbonate powder in a test tube. Name the gas and describe the test that confirms the identity of the gas.
Answer: Gas evolved is \( \text{CO}_2 \). It is tested by passing \( \text{CO}_2 \) in lime water which turns milky due to formation of insoluble \( \text{CaCO}_3 \).
\( \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3\downarrow + \text{H}_2\text{O} \)

Question. Name one animal and one plant whose stings contain formic acid (or methanoic acid).
Answer: Animal that contains formic acid—ant. Plant that contains formic acid—nettle plant.

Question. If someone is suffering from the problem of acidity after overeating, which of the following would you suggest as remedy ? Lemon juice, Vinegar, Baking soda solution. Give reason for your choice.
Answer: Baking soda solution. The solution being basic in nature, it neutralises excess acid in the stomach.

Question. How is the neutralisation of a carbonate with an acid different from the neutralisation of an oxide or a hydroxide ?
Answer: Neutralisation of a carbonate with an acid produces carbon dioxide gas but not with an oxide or hydroxide.

Question. Why do acids not show acidic behaviour in the absence of water ?
Answer: Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only. It is the hydrogen ions that are responsible for the acidic behaviour.

Question. On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue-green.
(a) Predict the new compound formed which imparts a blue-green colour to solution.
(b) Write a balanced chemical equation of the reaction which takes place.
(c) On the basis of the above reaction, what can you say about the nature of copper oxide ?
Answer: (a) The new compound formed is Copper (II) chloride, \( \text{CuCl}_2 \).
(b) \( \text{CuO}(s) + 2\text{HCl}(aq) \rightarrow \text{CuCl}_2(aq) + \text{H}_2\text{O}(l) \)
(c) Copper oxide is basic in nature.

Question. A substance X which is used as an antacid reacts with dilute hydrochloric acid to produce a gas Y which is used in one type of fire-extinguisher. Name the substance X and gas Y. Write a balanced equation for the chemical reaction which takes place.
Answer: Substance X is sodium hydrogen carbonate; gas Y is carbon dioxide.
\( \text{NaHCO}_3 + \text{HCl} \rightarrow \text{NaCl} + \text{CO}_2 + \text{H}_2\text{O} \)

Question. (a) Why is it wrong to treat a bee sting with vinegar ?
(b) Why is it wrong to treat a wasp sting with baking soda solution ?
Answer: (a) Bee injects acid into the skin. Vinegar is acetic acid so it can’t be used to treat bee sting.
(b) Since baking soda is basic in nature so it can’t be used to treat wasp sting because wasp injects alkaline liquid into the skin.

Question. What happens when phenolphthalein is added to an acidic solution ?
Answer: There is no change in colour as it remains colourless.

Question. In the laboratory of a school, the sample of hard water is not available “to study the comparative cleaning capacity of a sample of soap in soft and hard water”. Which salt from the laboratory can be added to tap water to make it hard ? In the experiment how is cleaning capacity of soap compared ?
Answer: (a) Sulphate, chloride or hydrogen carbonate of calcium or magnesium can be added to tap water to make it hard.
(b) By adding equal amount of soap to water taken in two test tubes, shaking vigorously and comparing the length of lather or foam formed in each test tube. The cleaning capacity of soap is compared.

Short Answers Type Questions

Question. Complete and balance the following chemical equations :
(i) \( \text{NaOH}(aq) + \text{Zn}(s) \rightarrow \)
(ii) \( \text{CaCO}_3(s) + \text{H}_2\text{O}(l) + \text{CO}_2(g) \rightarrow \)
(iii) \( \text{HCl}(aq) + \text{H}_2\text{O}(l) \rightarrow \)
Answer: (i) \( 2\text{NaOH} + \text{Zn} \xrightarrow{550^{\circ}\text{C}} \text{Na}_2\text{ZnO}_2 + \text{H}_2 \)
(ii) \( \text{CaCO}_3(s) + \text{CO}_2 (g) + \text{H}_2\text{O} (l) \rightarrow \text{Ca(HCO}_3)_2(aq) \)
(iii) \( \text{HCl} + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+ + \text{Cl}^- \)

Question. On heating blue coloured powder of copper (II) nitrate in a boiling tube, black copper oxide, \( \text{O}_2 \) and a brown gas X is formed.
(a) Identify the type of reaction and the gas X.
(b) Write balanced chemical equation of the reaction.
(c) Write the pH range of aqueous solution of the gas X.
Answer: (a) Decomposition reaction : The gas X is nitrogen dioxide (\( \text{NO}_2 \))
(b) \( 2\text{Cu(NO}_3)_2 \cdot 3\text{H}_2\text{O} \xrightarrow{\Delta} 2\text{CuO} + 4\text{NO}_2\uparrow + \text{O}_2\uparrow + 6\text{H}_2\text{O} \)
(c) Oxides of non-metals are acidic. Therefore, aqueous solution of this gas would be acidic. The pH would be less than 7 or 6.9.

Question. (a) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
(b) Dry hydrogen chloride gas does not change the colour of dry litmus paper why ?
Answer: (a) The process of mixing the concentrated acid with water is highly exothermic. So, when a concentrated acid is added to water then heat is easily absorbed by the large amount of water. Thus it is recommended to add acid to water and not water to the acid.
(b) Dry hydrogen chloride does not contain any hydrogen ions in it, so it does not show acidic behaviour and thus does not change the colour of dry litmus paper.

Question. How is sodium hydroxide manufactured in industries? Name the process. In this process a gas X is formed as by-product. This gas reacts with lime water to give a compound Y, which is used as a bleaching agent in the chemical industry. Identify X and Y and write the chemical equation of the reaction involved.
Answer: Sodium hydroxide is manufactured by the electrolysis of concentrated aqueous solution of sodium chloride.
\( 2\text{NaCl}(aq.) + 2\text{H}_2\text{O}(l) \xrightarrow{\text{Electricity}} 2\text{NaOH}(aq.) + \text{Cl}_2(g) + \text{H}_2(g) \)
The process of manufacture of sodium hydroxide by electrolysis process is called chlor-alkali process.
Gas X is chlorine gas and compound Y is calcium oxychloride (Bleaching powder)
\( \text{Cl}_2(g) + \text{Ca(OH)}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O} \)

Question. What would a student report nearly after 30 minutes of placing duly cleaned strips of aluminium, copper, iron and zinc in freshly prepared iron sulphate solution taken in four beakers ?
Answer: Aluminium displaces the iron from iron sulphate and the colour of two solution changes from green to colourless.
No change takes place when copper strip is dipped in iron sulphate solution.
No change will be observed when iron strips are dipped in iron sulphate solution.
The colour of the solution changes from green to colourless when zinc is added to iron sulphate solution.

Question. An ore on treatment with dil. HCl gives the smell of rotten egg. Name the type of this ore. How can the metal be obtained from its concentrated ore?
Answer: Smell of rotten eggs is usually produced by Sulphide. It must be a sulphide ore. Let us suppose that the ore is Zinc Blende (\( \text{ZnS} \)).
Concentration of ore: First of all, the ore is concentrated by the method of froth floatation.
Conversion into metal oxide: Then it is roasted converted into its metal oxide via roasting in supply of excess air.
Ex: \( \text{ZnS} + \text{O}_2 \xrightarrow{\text{Roasting}} \text{ZnO} + \text{SO}_2 \uparrow \)
Conversion into metal: It is then converted into its metal form by using a reducing agent like carbon, aluminium etc.
Ex: \( \text{ZnO} + \text{C} \xrightarrow{\text{Reduction}} \text{Zn} + \text{CO} \)
It is further refined to get it in its pure form.

Question. Identify the acid and the base from which sodium chloride is obtained. Which type of salt is it ? When is it called rock salt ? How is rock salt formed ?
Answer: \( \text{NaCl} \) is made by reacting an acid and a base. The base is \( \text{NaOH} \) (sodium hydroxide). So,
\( \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} \)
It is a neutralisation reaction. It is known as rock salt in crystalline form. It is the result of the evaporation of ancient oceans millions of years ago. Sometimes pressure from deep inside the Earth forces up large masses of rocks to form salt like domes.

Question. Identify the acid and base which form sodium hydrogen carbonate. Write chemical equation in support of your answer. State whether this compound is acidic, basic or neutral. Also write its pH value.
Answer: The acid and base that forms sodium hydrogen carbonate are as follows :
Acid – \( \text{H}_2\text{CO}_3 \)
Base – \( \text{NaOH} \)
The chemical equation for its formation will be :
\( \text{NaOH} + \text{H}_2\text{CO}_3 \rightarrow \text{NaHCO}_3 + \text{H}_2\text{O} \)
The compound will be basic and its pH value will be around 8 or in the range between 7 and 10.

Question. 2 ml of sodium hydroxide solution is added to a few pieces of granulated zinc metal taken in a test tube. When the contents are warmed a gas evolves which is bubbled through a soap solution before testing. Write the equation of the chemical reaction involved and the test to detect the gas. Name the gas which will be evolved when the same metal reacts with dilute solution of a strong acid ?
Answer: \( \text{NaOH}(aq) + \text{Zn}(s) \xrightarrow{\Delta} \text{Na}_2\text{ZnO}_2 + \text{H}_2(g) \)
Thus, in this reaction, hydrogen gas is evolved. As the gas is passed through soap solution, bubbles filled with hydrogen gas come out. Bring a candle near the bubbles evolved, the bubble bursts & the gas inside it starts burning with a pop sound & extinguishes the candle. This tests the presence of \( \text{H}_2 \) gas in them. Even if the zinc metal reacts with a solution of strong acid, hydrogen gas is produced.
\( \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \)

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. List its two uses.
Answer: The salt commonly used to make tasty and crispy pakoras is baking soda i.e., sodium hydrogen carbonate (\( \text{NaHCO}_3 \)).
Chemical equation for its formation :
\( \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 + \text{NH}_3 \rightarrow \text{NH}_4\text{Cl} + \text{NaHCO}_3 \)
Uses of Baking Soda :
(a) It is used in fire extinguisher.
(b) It is also used as ingredient of antacid.

Question. Complete the following chemical equations :
(a) \( \text{CH}_3\text{COOH} + \text{Na}_2\text{CO}_3 \rightarrow \)
(b) \( \text{CH}_4 + \text{O}_2 \rightarrow \)
(c) \( 2\text{C}_2\text{H}_5\text{OH} + \text{Na} \rightarrow \)
Answer: (a) \( 2\text{CH}_3\text{COOH} + \text{Na}_2\text{CO}_3 \rightarrow 2\text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2\uparrow \)
(b) \( \text{CH}_4 + 2\text{O}_2 \xrightarrow{\Delta} \text{CO}_2\uparrow + 2\text{H}_2\text{O} \)
(c) \( 2\text{C}_2\text{H}_5\text{OH} + 2\text{Na} \rightarrow 2\text{C}_2\text{H}_5\text{ONa} + \text{H}_2\uparrow \)

Question. What happens when an acid reacts with a base ? Explain by taking the example of hydrochloric acid and sodium hydroxide. Give equation of the chemical reaction which takes place. What is the special name of such a reaction ?
Answer: When an acid reacts with a base, then a salt and water are formed. When hydrochloric acid reacts with sodium hydroxide solution, then a neutralisation reaction takes place to form sodium chloride and water.
\( \text{NaOH}(aq) + \text{HCl}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l) \)
Such a reaction is termed as neutralisation reaction.

Question. What happens when chlorine is passed over slaked lime at 313 K ? Write chemical equation of the reaction involved and state two uses of the product obtained.
Answer: Bleaching powder is formed.
\( \text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O} \)
(a) It is used as bleaching agent in paper and textile industries.
(b) It is used as disinfectant in purification of drinking water.

Question. How following metals react with acids : magnesium, zinc, iron and copper?
Answer: (a) Magnesium react vigorously with acids.
(b) Zinc reacts less vigorously with acids than magnesium.
(c) Iron react slowly.
(d) Copper does not react at all.

Question. 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 ?
Answer: Hydrogen gas is usually liberated when an acid reacts with a metal. Take few pieces of zinc granules and add 5 ml of dilute \( \text{H}_2\text{SO}_4 \). Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.
\( \text{Zn} + 2\text{H}_2\text{SO}_4 \rightarrow \text{Zn(SO}_4)_2 + 2\text{H}_2 \)
We can test the evolved hydrogen gas by burning it with a pop sound when a candle is brought near the soap bubbles.

Question. (a) What is produced if an acid is added to a base ?
(b) Why does dry HCl gas not change the colour of dry litmus paper ?
(c) What colour does phenolphthalein indicator turn when added to an alkali (such as sodium hydroxide) ?
Answer: (a) Salt and water.
(b) Dry HCl gas does not change the colour of dry litmus paper because it has no hydrogen ions (\( \text{H}^+ \) ions) in it which can impart acidic properties to it.
(c) Pink.

Question. Why should curd and sour substances not be kept in brass and copper vessels ?
Answer: Curd and other sour substances not be kept in brass and copper vessels as they contain acids. When these substances are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products. As a result, food gets spoiled.

Question. You have been provided with three test-tubes. One of these test-tubes contains distilled water and the other two contain an acidic and a basic solution respectively. If you are given only blue litmus paper, how will you identify the contents of each test-tube ?
Answer: Acidic solution will turn blue litmus red. This red litmus will turn blue in basic solution. Distilled water will have no effect on any type of litmus paper.

Question. A group of students measured the pH of some substances they found in their homes. Their results are given in the following table :
(a) What would the students have used to measure the pH ?
(b) Which solution is the most acidic ?
(c) Which solution is the most alkaline ?
(d) Which solutions are neutral ?
(e) Which solution can be used to treat wasp stings ?
(f) Which solution can be used to treat bee stings ?
Answer: (a) Universal indicator paper is used to measure the pH.
(b) Lemon juice with pH = 2.5 is the most acidic.
(c) Household ammonia with pH = 12 is the most alkaline.
(d) Salt solution and sugar solution with pH = 7 are neutral.
(e) Vinegar (acid) can be used to treat wasp stings since it injects an alkaline liquid into the skin.
(f) Baking soda can be used to treat bee stings since, it injects methanoic acid into the skin.

Question. 1 g of solid sodium chloride is taken in a clean and dry test tube and 2 ml of conc. sulphuric acid is added to it. If the gas evolved is tested first with dry and then with wet blue litmus paper, in which case will the litmus paper change colour ? Give reason for your answer. What inference can be drawn about the nature of the evolved gas ? Support your answer with chemical equation for the reaction.
Answer: Wet blue litmus paper will change the colour because hydrogen ions are produced by HCl in the presence of water. It has acidic nature and the reaction involved is :
\( \text{HCl} + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+ + \text{Cl}^- \)

Question. (a) For the preparation of cakes, baking powder is used. If at home your mother uses baking soda instead of baking powder, how will it affect the taste of the cake and why ?
(b) How is baking soda be converted into baking powder ?
(c) What makes the cake soft and spongy ?
Answer: (a) The cake will have a bitter taste because of the formation of \( \text{Na}_2\text{CO}_3 \) or sodium carbonate while baking or heating the cake.
(b) By adding tartaric acid baking soda can be converted into baking powder.
(c) The \( \text{CO}_2 \) gas liberated makes the cake soft and spongy.

Question. (a) If you are asked to report your observations about the following two properties of acetic acid, what would you report ?
(i) Odour
(ii) Effect on litmus
(b) If you take a pinch of sodium hydrogen carbonate powder in a test-tube and add drop-by-drop acetic acid to it, what would you observe immediately ? List any two main observations.
Answer: (a) (i) Smells like vinegar. (ii) Turns blue litmus red.
(b) (i) Brisk effervescence will be observed. (ii) Evolution of colourless gas.

Long Answers Type Questions

Question. In the following schematic diagram for the preparation of hydrogen gas as shown in figure what would happen if following changes are made ?
(a) In place of zinc granules, same amount of zinc dust is taken in the test tube.
(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken.
(c) In place of zinc, copper turnings are taken.
(d) Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.
Answer: (a) If in place of zinc granules, same amount of zinc dust is taken, hydrogen gas will evolve with greater speed.
(b) If instead of dilute sulphuric acid, dilute hydrochloric acid is taken, almost same amount of gas is evolved.
(c) Hydrogen gas is not evolved.
(d) If sodium hydroxide is taken, sodium zincate is formed and hydrogen gas will be evolved.
\( \text{Zn} + 2\text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2 \)

Question. For making cake, baking powder is taken. If at home your mother uses baking soda instead of baking powder in cake.
(a) How will it affect the taste of the cake and why ?
(b) How can baking soda be converted into baking powder ?
(c) What is the role of tartaric acid added to baking soda ?
Answer: (a) Baking soda is sodium hydrogen carbonate. On heating, it is converted into sodium carbonate which is bitter to taste. Thus, if baking soda is used the taste of cake changes.
\( \text{NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2 \)
(b) Baking powder is a mixture of baking soda, cream of tartar (a dry acid), and sometimes corn starch.

Therefore, baking soda can be converted into baking powder by the addition of appropriate amount of tartaric acid to it.

(c) Tartaric acid is added to neutralise the sodium carbonate formed on heating by the decomposition of \( \text{NaHCO}_3 \). If it is not added, the cake would taste bitter due to the presence of sodium carbonate in it. Also, \( \text{CO}_2 \) produced during the reaction causes cake to rise making them soft and spongy.