{"id":27131,"date":"2022-06-05T06:00:05","date_gmt":"2022-06-05T00:30:05","guid":{"rendered":"https:\/\/mcq-questions.com\/?p=27131"},"modified":"2022-05-23T15:43:25","modified_gmt":"2022-05-23T10:13:25","slug":"ncert-solutions-for-class-10-science-chapter-2","status":"publish","type":"post","link":"https:\/\/mcq-questions.com\/ncert-solutions-for-class-10-science-chapter-2\/","title":{"rendered":"NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts"},"content":{"rendered":"

These NCERT Solutions for Class 10 Science<\/a> Chapter 2 Acids, Bases and Salts Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.<\/p>\n

Acids, Bases and Salts NCERT Solutions for Class 10 Science Chapter 2<\/h2>\n

Class 10 Science Chapter 2 Acids, Bases and Salts InText Questions and Answers<\/h3>\n

In-text Questions (Page 18)<\/span><\/p>\n

Question 1.
\nYou 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?
\nAnswer:
\nWe dip the red litmus paper in any one of the three test tubes. If there is no change in the colour of the litmus paper, it means this test tube contains water or acidic solution.<\/p>\n

If the colour of the red litmus paper turns blue, it means this test tube contains basic solution.<\/p>\n

Now, again we dip this litmus paper in any one of the remaining two test tubes. If we do not observe any change in the colour of the litmus paper it is surely water and if a colour change is noticed, then it will be an acidic solution.<\/p>\n

In-text Questions (Page 22)<\/span><\/p>\n

Question 1.
\nWhy should curd and sour substances not be kept in brass and copper vessels?
\nAnswer:
\nBrass is an alloy of copper and zinc, Brass and copper vessels reacts with atmospheric oxygen and to form metal oxides. The nature of metal oxides is basic. Curd and sour substances contains acids, e.g., curd contains lactic acid and orange contains citric acid. If we keep curd and sour substances in brass and copper vessels the layer of oxides present on the surface of brass and copper reacts with the acids present in curd and sour substances to form salt and water and taste of sour substances chages from sour to bitter. So curd and sour substance are not be kept in brass and copper vessels.<\/p>\n

Question 2.
\nWhich 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?
\nAnswer:
\nHydrogen has is usually liberated when an acid reacts with a metal.
\ne.g.
\n\"NCERT
\nThis gas buns with a pop sound when a burning candle is placed near the evolved gas.<\/p>\n

Question 3.
\nA Metal 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.
\nAnswer:
\nMetal compound ‘A’ is CaCO3<\/sub>
\n\"NCERT<\/p>\n

\"NCERT<\/p>\n

In-text Questions (Page 25)<\/span><\/p>\n

Question 1.
\nWhy do HCl, HNO3<\/sub>, etc show acidic character in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
\nAnswer:
\nA substance is said to be an acid, when it produces H+<\/sup> ions in its aqueous solution and turns blue litmus paper into red. HCl, HNO3<\/sub>, etc. ionise in their aqueous solutions and produce H+<\/sup> ions. They turn the colour of blue litmus paper into red. When electric current is passed through the aqueous solutions of acids, the H+<\/sup> ions reach the cathode and form hydrogen. But in their aqueous solutions alcohol and glucose do not produce H+<\/sup> ions and they do turn blue litmus into red. So they do not show acidic character in their aqueous solution.<\/p>\n

Question 2.
\nWhy does an aqueous solution of an add conduct electricity?
\nAnswer:
\nAcids are ionised in their aqueous solution and produce H+<\/sup> (aq) ions. These ions are responsible for the flow of electricity in the aqueous solutions of acids. H+<\/sup> ions migrates towards cathode and gain electron to produce hydrogen gas. So when electricity is passed through the aqueous solution of an acid, hydrogen gas is liberated at cathode.<\/p>\n

So an aqueous solution of an acid conducts electricity because it contains H+<\/sup> (aq) ions or hydronium ions.<\/p>\n

Question 3.
\nWhy does dry HCl gas not change the colour of the dry litmus paper?
\nAnswer:
\nThe separation of H+<\/sup> ion from HCl molecules cannot occur in the absence of water. In fact H+<\/sup> ion is an atom that has lost an eletron, it is simply isolated proton and is smallest positive ion. It is attracted very strongly towards electrons of anything. So the separation of H+<\/sup> ion from HCl molecules cannot occur and the reaction.
\nH – Cl(g) H+<\/sup> \u2192 + Cl–<\/sup><\/p>\n

cannot occur in the absence of water, because highly concentrated positive charge of TP would join back with the Cl–<\/sup> ion to get back electron and reform covalent \u2018H – Cl\u2018 molecules. It means dry HCl does not contain H+<\/sup> ions so it does not change the colour of the dry litmus paper.<\/p>\n

Question 4.
\nWhile diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
\nAnswer:
\nThe process of dissolving an add or a base in water is a highly exothermic process. Be careful while mixing concentrated sulphuric acid with water During dilution of an acid, the acid must always be added slowly to water with constant stirring. It water is added to a concentrated acid the heat generated may cause the mixture lo splash out from the container and cause bums. The glass container may also break due to heal release during dilution. So it is recommended that the acid should be added to water and not water to the acid.<\/p>\n

Question 5.
\nHow is the concentration of hydronium ions (H3<\/sub>O)+<\/sup> affected when a solution of an acid is diluted?
\nAnswer:
\nAn aqueous solution of an acid contains the specific number of H3<\/sub>O+<\/sup> ions per unit volume. These H3<\/sub>O+<\/sup> ions are responsible for the acidic character of an acid. When water is added in an acid it results in decrease in inconcentration of H3<\/sub>O+<\/sup> ions per unit volume of the acid because the specified volume of an acid contains the definite no. of H3<\/sub>O+<\/sup> ions, when its volume increases by addition of water, the no. of H3<\/sub>O+<\/sup> ions decreases per unit volume of the acid. So we can say that on dilution the concentration of H3<\/sub>O+<\/sup> ions decreases per unit volume of the acid.<\/p>\n

Question 6.
\nHow is the concentration of hydroxide ions (OH–<\/sup>) affected when excess base is dissolved in a solution of sodium hydroxide?
\nAnswer:
\nA solution of sodium hydroxide contain Na+<\/sup> and OH–<\/sup> ions. When a base is dissolved in a solution of sodium hydroxide, it results in increase of concentration of OH–<\/sup> ions per unit volume because added base is ionised and produce a large no. of hydroxide ions (OH–<\/sup>) in the solution of sodium hydroxide.<\/p>\n

\"NCERT<\/p>\n

In-text Questions (Page 28)<\/span><\/p>\n

Question 1.
\nYou have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
\nAnswer:
\nThe hydrogen ion concentration of a solution is calculated by the formula :
\n[H+<\/sup>] = 10-pH<\/sup>
\n\u2234 The conc. of H+<\/sup> ions in solution ‘A’ = 10-6<\/sup>
\nand the conc, of H+<\/sup> ions in solution ‘B’ = 10-8<\/sup>
\nSo solution ‘A’ has more hydrogen ion concentration than ‘B’.
\nSolution A’ is acidic and solution ‘B’ is basic.<\/p>\n

Question 2.
\nWhat effect does the concentration of H+<\/sup>(aq) ions have on the nature of the solution?
\nAnswer:
\nOn the basis of concentration of H+<\/sup> (aq) ions in a solution we can justify the nature of the solution i.e., whether it is acidic, basic or neutral. A solution which has the concentration of H+<\/sup> (aq) ion equal to 10-7<\/sup> mole\/litre will be neutral and if the concentration is slightly less than 10-7<\/sup> then it will be basic and if the cone, of H+<\/sup> (aq) ions in a solution is slightly higher than 10-7<\/sup> then it will be acidic.<\/p>\n

Question 3.
\nDo basic solutions also have H+<\/sup>(aq) ions? If yes, then why are these basic?
\nAnswer:
\nYes, basic solutions also have H+<\/sup> (aq) ions and similarly acidic solutions have OH–<\/sup> (aq). because acids or bases shows acidic or basic character in water. Distilled water also has 10-7<\/sup> mol\/L, H+<\/sup> and 10-7<\/sup> mole\/L, OH–<\/sup> ions at 298K.<\/p>\n

If an aqueous solution has an equal concentration of hydrogen ions and hydroxide ions in it, it is said to be neutral. Now, if an aqueous solution has more of hydrogen ions and less of hydroxide ions, it will be acidic solution. On the other hand, if an aqueous solution has more of hydroxide ions and less of hydrogen ions it will be basic in nature.<\/p>\n

Question 4.
\nUnder what soil condition do you think a fanner would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
\nAnswer:
\nIf the soil has acidic nature, then famer would treat the soil of his fields with quick lime or slaked lime or chalk to maintain its pH near about neutral.<\/p>\n

In-text Questions (Page 33)<\/span><\/p>\n

Question 1.
\nWhat is the common name of the compound CaOCl2<\/sub>?
\nAnswer:
\nBleaching powder.<\/p>\n

Question 2.
\nName the substance which cm treatment with chlorine yields bleaching powder,
\nAnswer:
\nDry slaked lime : Ca(OH)2<\/sub>
\nChlorine : Cl2<\/sub><\/p>\n

Question 3.
\nName the sodium compound which is used for softening hard water.
\nAnswer:
\nWashing soda : Sodium carbonate (Na2<\/sub>CO3<\/sub>)<\/p>\n

\"NCERT<\/p>\n

Question 4.
\nWhat will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
\nAnswer:
\nOn heating sodium hydrocarbonate, it produces sodium carbonate, carbondioxide and water.
\n\"NCERT<\/p>\n

Question 5.
\nWrite an equation to show the reaction between Plaster of Paris and water,
\nAnswer:
\n\"NCERT<\/p>\n

Class 10 Science Chapter 2 Acids, Bases and Salts Textbook Questions and Answers<\/h3>\n

Page No. 34<\/span><\/p>\n

Question 1.
\nA solution turns red litmus blue, its pH is likely to be:
\n(a) 1
\n(b) 4
\n(c) 5
\n(d) 10
\nAnswer:
\n(d) 10<\/p>\n

Question 2.
\nA solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains.
\n(a) NaCl
\n(b) HCl
\n(c) LiCl
\n(d) KCl
\nAnswer:
\n(b) HCl<\/p>\n

Question 3.
\n10 mL of a solution of NaOH is found to be completely neutralised 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 neutralise it will be:
\n(a) 4 mL
\n(b) 8 mL
\n(c) 12 mL
\n(d) 16 mL
\nAnswer:
\n(d) 16 mL<\/p>\n

Question 4.
\nWhich one of the following types of medicines is used for treating indigestion ?
\n(a) Antibiotic
\n(b) Analgesic
\n(c) Antarid
\n(d) Antiseptic
\nAnswer:
\n(c) Antacid.<\/p>\n

Question 5.
\nWrite word equations and then balanced equations for the reactions taking place when:
\n(a) dilute sulphuric add reacts with zinc granules.
\n(b) dilute hydrochloric acid reacts with magnesium ribbon.
\n(c) dilute sulphuric acid reacts with aluminium powder.
\n(d) dilute hydrochloric acid reacts with iron fillings.
\nAnswer:
\n(a) Dilute sulphuric acid reacts with zinc granules to form zinc sulphate and hydrogen.
\nSulphuric acid + Zinc \u2192 Zinc Sulphate + Hydrogen
\nH2<\/sub>SO4<\/sub> + Zn \u2192 ZnSO4<\/sub> + H2<\/sub><\/p>\n

Step I.<\/p>\n\n\n\n\n\n\n\n
Element<\/td>\nNo. of atoms in Reactants<\/td>\nNo. of atoms in Products<\/td>\n<\/tr>\n
H<\/td>\n2<\/td>\n2<\/td>\n<\/tr>\n
S<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
O<\/td>\n4<\/td>\n4<\/td>\n<\/tr>\n
Zn<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The above equation is a balanced equation because it contains the equal no. of atoms of different elements in reactants to the no. of atoms of different elements in products.<\/p>\n

(b) Hydrochloric add + Magnesium \u2192 Magnesium chloride + Hydrogen
\nHCl + Mg \u2192 MgCl2<\/sub> + H2<\/sub>
\nStep I.<\/p>\n\n\n\n\n\n\n
Element<\/td>\nNo. of atoms in Reactants<\/td>\nNo. of atoms in Products<\/td>\n<\/tr>\n
H<\/td>\n1<\/td>\n2<\/td>\n<\/tr>\n
Cl<\/td>\n1<\/td>\n2<\/td>\n<\/tr>\n
Mg<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Step II. Balance hydrogen and chlorine by multiplying ‘HCl’ with \u20182′ we get
\n2 HCl + Mg \u2192 MgCl2<\/sub> = H2<\/sub><\/p>\n

(c) Sulphuric acid + Aluminium \u2192 Aluminium sulphate + Hydrogen
\nH2<\/sub>SO4<\/sub> + Al \u2192 Al2<\/sub>(SO4<\/sub>)3<\/sub> + H2<\/sub>
\nStep I.<\/p>\n\n\n\n\n\n\n\n
Element<\/td>\nNo. of atoms in Reactants<\/td>\nNo. of atoms in Products<\/td>\n<\/tr>\n
H<\/td>\n2<\/td>\n2<\/td>\n<\/tr>\n
S<\/td>\n1<\/td>\n3<\/td>\n<\/tr>\n
O<\/td>\n4<\/td>\n12<\/td>\n<\/tr>\n
Al<\/td>\n1<\/td>\n2<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Step II. Balance oxygen by multiplying ‘H2<\/sub>SO4<\/sub>‘ with ‘3’ we get:
\n3H2<\/sub>SO4<\/sub> + Al \u2192 Al2<\/sub>(SO4<\/sub>)3<\/sub> + H2<\/sub>
\nStep III. Balance aluminium by multiplying ‘Al’ in reactants side with ‘2’ we get;
\n3H2<\/sub>SO4<\/sub> + 2Al \u2192 Al2<\/sub>(SO4<\/sub>)3<\/sub> + H2<\/sub>
\nStep IV. Balance hydrogen by multiplying ‘H2<\/sub>‘ in product side with ‘3’ we get:
\n3H2<\/sub>SO4<\/sub> + 2Al \u2192 Al2<\/sub>(SO4<\/sub>)3<\/sub> + 3H2<\/sub>
\nThis is a balance equation.<\/p>\n

(d) Hydrochloric acid + Iron \u2192 Iron (III) chloride + Hydrogen
\nHCl + Fe \u2192 FeCl3<\/sub> + H2<\/sub>
\nStep I.<\/p>\n\n\n\n\n\n\n
Element<\/td>\nNo. of atoms in Reactants<\/td>\nNo. of atoms in Products<\/td>\n<\/tr>\n
H<\/td>\n1<\/td>\n2<\/td>\n<\/tr>\n
Cl<\/td>\n1<\/td>\n3<\/td>\n<\/tr>\n
Fe<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Step II. Balance chlorine by multiplying ‘FeCl3<\/sub>‘ with ‘2’ and ‘HCl’ with ‘6’ we get:
\n6HCl + Fe \u2192 2FeCl3<\/sub> + H2
\nStep III. Balance hydrogen and iron by multiplying ‘Fe’ with ‘2’ and ‘H2<\/sub>‘ with ‘3’ we get:
\n6HCl + 2Fe \u2192 2FeCl3<\/sub> + 3H2<\/sub>
\nThis is a balance equation.<\/p>\n

\"NCERT<\/p>\n

Question 6.
\nCompounds such as alcohols and glucose also contain hydrogen but are not categorised as adds. Describe an activity to prove it.
\nAnswer:
\nA substance is said to be an acid when it can produce H+<\/sup> ions in its aqueous solution and turns blue litmus paper to red.<\/p>\n

HCl, HNO3<\/sub> etc. are ionized in their aqueous solution and furnished H+<\/sup> ions. When electricity is passed through aqueous solutions of acids, hydrogen liberates at cathode.<\/p>\n

Compounds such as alcohols and glucose contain hydrogen but they do not ionise in their aqueous solution and not produce H+<\/sup> ions, and they do not turn blue litmus to red so they are not categorised as acids.<\/p>\n

Activity: Take four test tubes namely, A, B, C and D. Add ethyl alcohol (alcohol) aq. solution of glucose ; hydrochloric acid and nitric acid, 2 mL of each in test tube A, B, C and D respectively. Now add 1-2 drops of blue litmus solution in each test tube. We observe that the colour of test tube ‘A’ and ‘B’ remain unchanged however the colour of test tube and ‘C’ and ‘D’ turns red. If proves that alcohol and glucose are not categorised as acid.<\/p>\n

Question 7.
\nWhy does distilled water not conduct electricity, whereas rainwater does ?
\nAnswer:
\nDistilled water does not contain ions (H+<\/sup> or OH–<\/sup>) or it contains a very poor concentration of H+<\/sup> or OH–<\/sup> ions \u2248 1 \u00d7 10-7<\/sup> moles per litre. So it does not conduct electricity, whereas rainwater has some acidic character due to the presence of acids such as H2<\/sub>SO4<\/sub>, HNO3<\/sub> etc. So rainwater has a sufficient amount or concentration of H+<\/sup> ions, so it conducts electricity.<\/p>\n

Question 8.
\nWhy do acids not show acidic behaviour in the absence of water ?
\nAnswer:
\nA substance is said to be an acid when it can furnish H+<\/sup> ions in its aqueous solution. The separation of H+<\/sup> ions from the molecules of an acid cannot occur in the absence of water. The molecule of water are polar in nature, so the negative pole of ‘H2<\/sub>O’ molecule pull the H+<\/sup> ions from acids towards itself and separate them from acids e.g,
\nHCl + H2<\/sub>O \u2192 H3<\/sub>O+<\/sup> + Cl–<\/sup>. Hydrogen ions cannot exist alone, but they exist after combining with water molecules. Thus hydrogen ions must always be shown as H+<\/sup> (aq) of hydronium ion (H3<\/sub>O+<\/sup>).<\/p>\n

In absence of water ‘H+<\/sup>‘ are does not furnish by an acid so it does not show acidic behaviour.<\/p>\n

Question 9.
\nFive solutions A, B, C, D and E when tested with universal indicater showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is:
\n(a) neutral ?
\n(b) strongly alkaline ?
\n(c) strongly acidic
\n(d) weakly acidic ?
\n(e) weakly alkaline ?
\nArrange the pH in increasing order of hydrogen ion concentration.
\nAnswer:
\n(a) Solution ‘D’ is neutral because it has pH 7.
\n(b) Solution ‘C’ is strongly alkaline because it has pH 11.
\n(c) Solution ‘B’ is strongly acidic because it has pH 1.
\n(d) Solution ‘A’ is weakly acidic because it has pH 4.
\n(e) Solution ‘E’ is weakly alkalin because it has pH 9.<\/p>\n

Hydrogen ion concentration is inversely proportional to the pH of the solution. It means, higher the ‘pH’ lower will be the hydrogen ion concentration.<\/p>\n

The ‘pH’ of the given solution can be arranged m increasing order of hydrogen-ion concentration as follows :
\npH : 11 > 9 > 7 > 4 > 1
\nHydrogen ion concentration : C < E < D < A < B<\/p>\n

Question 10.
\nEqual lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A which acetic acid (CH3<\/sub>COOH) is added to test tube B. In which test tube will the fizzing occurs more vigorously and why ?
\nAnswer:
\nFizzing occurs more vigourosly in test tube A’ because hydrochlonic acid is a strong acid while acetic acid is a weak acid.<\/p>\n

Magnesium metal reacts with acids and produce repective salt and hydrogen gas.
\n\"NCERT<\/p>\n

Question 11.
\nFresh milk has a pH of 6. How do you think the pH will change as it turns into curd ? Explain your answer.
\nAnswer:
\nThe fresh milk has a pH of 6. Milk has slightly sweet taste But when it turns into curd its taste has changed from lightly sweet taste to intense sour taste. It means its pH has changed. The intense sour taste of curd is the presence of the strong acidic character. So when milk changes into curd its pH decreases because acidic character increases.<\/p>\n

\"NCERT<\/p>\n

Question 12.
\nA milkman adds a very small amount of baking soda to fresh milk.
\n(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline ?
\n(b) Why does this milk take a long time a set as curd ?
\nAnswer:
\n(a) Milk contains lactose and pH of milk is approximately 6. The micro-organism which converts milk into curd work effectively in slightly acidic medium. Baking soda has slightly alkaline nature. So milkman adds small quantity of baking soda to protect it from curding because in alkaline medium micro-organism do not function properly and thus milk is prevented from rancidity or curding. So milkman makes milk alkaline.<\/p>\n

(b) The process of converting milk into curd takes place in slightly acidic medium, Micro-organism converts lactose of milk into lactic acid. But in alkaline medium curding takes place very slowly, so this milk takes long to set as curd.<\/p>\n

Question 13.
\nPlaster of Paris should be stored in moisture-proof container. Explain why ?
\nAnswer:
\nPlaster of Paris (CaSO4<\/sub>. \\(\\frac {1}{2}\\)H2<\/sub>O) has a very remarkable Property of setting into a hard mass on wetting with water or moisture. The setting of Plaster of Paris is due to its hydration to form crystals of gypsum which set to form a hard, solid mass as follows :
\n\"NCERT
\nSo, to protect the hydration of Plaster of Paris it is stored in moisture proof container.<\/p>\n

Question 14.
\nWhat is a neutralisation reaction ? Given two examples.
\nAnswer:
\nNeutralisation reaction : A reaction in which an acid reacts with a base and to form a salt and water is called neutralisation reaction.
\nExamples:
\n(i)
\n\"NCERT
\n(ii)
\n\"NCERT<\/p>\n

Question 15.
\nGiven two important uses of washing soda and baking soda.
\nAnswer:
\nUses of washing soda :<\/p>\n