Q: Question 10Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?

Fizzing will be more vigorous in test tube A due to the higher concentration of H+(aq) ions in hydrochloric acid (HCl) as compared to acetic acid (CH3COOH). Hydrochloric acid (HCl) is the stronger acid and its reactions with magnesium ribbon will result in faster rate of release of hydrogen gas.

Question 1

Question 1A solution turns red litmus blue, its pH is likely to be14510

Accepted Answer

10Reason — As the solution turns red litmus blue, hence it is basic in nature. Therefore, its pH should be greater than 7, hence, 10.

Question 2

Question 2A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution containsNaClHClLiClKCl

Accepted Answer

HClReason — Egg shells are made up of calcium carbonate and when calcium carbonate reacts with HCl it liberates CO2 gas which turns lime water milky.CaCO3 + 2HCl ⟶ CaCl2 + H2O + CO2 ↑

Question 3

Question 310 mL of a solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralize it will be4 mL8 mL12 mL16 mL

Accepted Answer

16 mLReason — When 10 mL of a solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl, then is we take 20 mL of the same solution of NaOH i.e, double the initial solution of NaOH so double amount of HCl will be required i.e. 16 mL.

Question 4

Question 4Which one of the following types of medicines is used for treating indigestion?AntibioticAnalgesicAntacidAntiseptic

Accepted Answer

AntacidReason — Antacids are alkaline in nature. So it neutralizes the acid produced in the stomach. Hence, antacids are advised for acidity.

Question 5

Question 5Write word equations and then balanced equations for the reaction taking place when -(a) dilute sulphuric acid reacts with zinc granules.(b) dilute hydrochloric acid reacts with magnesium ribbon.(c) dilute sulphuric acid reacts with aluminium powder.(d) dilute hydrochloric acid reacts with iron filings.

Accepted Answer

(a) Zinc + Sulphuric acid (dilute) ⟶ Zinc sulphate + Hydrogen gasZn (s) + H2SO4 (dil.) ⟶ ZnSO4 (aq) + H2 (g)(b) Magnesium + Hydrochloric acid (dilute) ⟶ Magnesium chloride + Hydrogen gasMg (s) + 2HCl (dil.) ⟶ MgCl2 (aq) + H2 (g)(c) Aluminium + Sulphuric acid (dilute) ⟶ Aluminium sulphate + Hydrogen gas2Al + 3H2SO4 (dil.) ⟶ Al2(SO4)3 (aq) + 3H2 (g)(d) Iron + Hydrochloric acid (dilute) ⟶ Iron chloride + HydrogenFe (s) + 2HCl (dil.) ⟶ FeCl2 (aq) + H2 (g)

Question 6

Question 6Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an Activity to prove it.

Accepted Answer

Materials required — Bulb, switch, beaker, nails, battery, connecting wires, glucose, alcohol, hydrochloric acid, sulphuric acidProcedure —Fix two nails on a cork and place the cork in a 100 ml beaker.Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch, as shown in the figure above.Now pour glucose and alcohol solutions one by one and switch on the current.Repeat the activity using hydrochloric acid and sulphuric acid.Observation —The bulb does not glow when glucose and alcohol are used.Bulb glows when hydrochloric acid and sulphuric acid are used.Result — Glowing of the bulb indicates that there is a flow of electric current through the solution. The electric current is carried through the acidic solution by ions.This activity proves that hydrogen containing compounds alcohols and glucose do not ionise to give H+(aq) ions, hence, they are not categorized as acids.

Question 7

Question 7Why does distilled water not conduct electricity, whereas rain water does?

Accepted Answer

Distilled water consists entirely of molecules. Due to the lack of ions, it does not conduct electricity. Rain water on the other hand contains small traces of acids formed due to the dissolutions of atmospheric gases like carbon dioxide, sulphur dioxide, etc. Hence, due to the presence of ions, rain water can conduct electricity.

Question 8

Question 8Why do acids not show acidic behaviour in the absence of water?

Accepted Answer

Acids show acidic behaviour by generating hydrogen ions [H+(aq)] in aqueous solutions. In the absence of water, acids do not produce hydrogen ions [H+(aq)] and, therefore, do not display their acidic characteristics.

Question 9

Question 9Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is(a) neutral?(b) strongly alkaline?(c) strongly acidic?(d) weakly acidic?(e) weakly alkaline?Arrange the pH in increasing order of hydrogen-ion concentration

Accepted Answer

(a) D(b) C(c) B(d) A(e) EIncreasing order of hydrogen-ion concentration — C < E < D < A < B

Question 10

Question 10Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?

Accepted Answer

Fizzing will be more vigorous in test tube A due to the higher concentration of H+(aq) ions in hydrochloric acid (HCl) as compared to acetic acid (CH3COOH). Hydrochloric acid (HCl) is the stronger acid and its reactions with magnesium ribbon will result in faster rate of release of hydrogen gas.

Question 11

Question 11Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

Accepted Answer

As milk changes to curd due to action of bacteria, the lactose in milk is converted to lactic acid which makes it more acidic. Hence, pH will decrease from its initial value of 6 to a lower pH value.

Question 12

Question 12A 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 long time to set as curd?

Accepted Answer

(a) To prevent the milk from turning sour and spoiling due to lactic acid formation, the milkman shifts its pH from 6 to slightly alkaline by adding baking soda.(b) For this milk to set as curd, the lactic acid formed during curdling process needs to first neutralise the baking soda added. Hence, it takes longer time to set as curd.

Question 13

Question 13Plaster of Paris should be stored in a moisture-proof container. Explain why?

Accepted Answer

Plaster of Paris absorbs moisture and gets converted into a hard solid substance known as gypsum. To prevent this change, Plaster of Paris should be stored in a moisture-proof container.

Question 14

Question 14What is a neutralisation reaction? Give two examples.

Accepted Answer

The reaction between an acid and a base to give a salt and water as the only products is referred to as neutralisation reaction.Examples :Reaction of ammonium hydroxide and HCl:NH4OH + HCl ⟶ NH4Cl + H2OReaction of sodium hydroxide and H2SO4:2NaOH + H2SO4 ⟶ Na2SO4 + 2H2O

Question 15

Question 15Give two important uses of washing soda and baking soda.

Accepted Answer

Uses of washing soda —It is used in glass, soap and paper industries.It is used for removing permanent hardness of water.Uses of baking soda —It is used for making baking powder.It is an ingredient in antacids.

Question 16

Question 1You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Accepted Answer

We take three pieces of red litmus paper. The solution which turns red litmus paper to blue is basic solution. Distilled water (neutral) and acidic solution will not effect red litmus paper.Now we divide the so formed blue litmus paper into two pieces. The test tube containing distilled water does not change the colour of the blue litmus paper.The test tube containing acidic solution changes the colour of the blue litmus paper to red. Hence, we can identify the three solutions.

Question 17

Question 1Why should curd and sour substances not be kept in brass and copper vessels?

Accepted Answer

Curd and sour substances are acidic in nature, they react with metals present in brass and copper vessels and results in formation of soluble salts and hydrogen gas. These salts are poisonous in nature and make the food unfit for consumption.

Question 18

Question 2Which 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?

Accepted Answer

Hydrogen gas is released when an acid reacts with a metal along with formation of salt.Metal + Acid ⟶ Salt + Hydrogen gas ↑For example : When sodium hydroxide is reacted with Zn, salt of sodium zincate is formed along with hydrogen gas.2NaOH(aq) + Zn(s) ⟶ Na2ZnO2(s) + H2(g)In order to test the presence of hydrogen gas, a burning candle is bought near hydrogen gas, the gas burns with a pop sound.

Question 19

Question 3Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride?

Accepted Answer

Metal carbonates react with dil HCl to produce metals chloride and carbon dioxide gas. As the products formed in the above reaction are carbon dioxide and calcium chloride, hence the reaction is as follows :CaCO3 + 2HCl [dil.] ⟶ CaCl2 + CO2 ↑ + H2OTherefore, the metal A is calcium carbonate [CaCO3].

Question 20

Question 1Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

Accepted Answer

HCl and HNO3 show acidic character because they ionise in aqueous solution to form hydronium ions (H3O+).Ionisation of HCl in water:HCl ⟶ H+ + Cl-H+ + H2O ⟶ H3O+Ionisation of HNO3 in water:HNO3 ⟶ H+ + NO3-H+ + H2O ⟶ H3O+C2H5OH (Ethanol) and C6H12O6 (Glucose) are covalent compounds. They do not ionise in water to form hydronium ions [H3O+]. Hence, they don't show acidic character.

Acids, Bases and Salts

Exercises

Intext Questions 1

Intext Questions 2

Intext Questions 3

Intext Questions 4

Intext Questions 5