Ncert intext question of class 10 of chapter 2

Q1. You have been provided with three test tubes one of them contains distilled water and other two contain an acid solution and a basic solution ,respectively .if you are given only red litmus paper how will you identify the contains of each test tube?

ANSWER--> (I) first dip the red litmus paper in each of the three test tubes the tube in which it turns blue will indicate the basic solution .

(II) Now, dip this blue litmus paper formed in (I) in the remaining two test tubes the tube in which again changes back to read indicate the acidic solution .

(III) the remaining tube in which neither red litmus turn blue litmus turns red contain the distilled water .


Q1- why should curd and sour substance not be kept in copper vassels ?

ANSWER-----> curd and sour substances are acidic in nature the acid present in curd and sour substances react with metals surface of brass and copper vassals to produce toxic compounds which are not fit for human consumption in short we can say that 'it cause toxicity of food' .

Q2- which gas is usually liberated when an acid reacts with a metal illustrate with an example how will you test for presence of this gas

ANSWER---> when a metal react with an acid usually hydrogen gas liberated .

Reason -- metals lose electrons easily and thus can reduce hydrogen ions of an acid to hydrogen
When zinc reacts with dilute sulphuric acid it produces Hydrogen gas

Test: the hydrogen gas evolved can be tested by passing the gas through soap solution and then bringing a burning candle near a gas filled bubble

Result: the soap bubbles bursts and  the hydrogen gas burns with a pop sound

Q3-- 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 .

ANSWER ---> we know that (I) Co2 extinguishes fire and (II) carbonates and bicarbonates when react with dilute acids produce Co2

It implies that compound a must be calcium carbonate (CaCO3)

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Q1- why do HCI, HnO3 etc. Show acidic characters In while solution of compounds like alcohol and glucose do not show acidic character?

ANSWER----> the acid like hydrochloric acid and nitric acid ionise completely in   aqueous solution while solution of compound like alcohol and glucose do not show  acidic character on the other hand  the compound like glucose (c6h12o6) and ethanol (c2h5oh)do not ionise in the aqueous solution to give hydrogen ions hence they do not show acidic character .

Q2-why does an aqueous solution of an acid conduct electricity ?

ANSWER ---> when an acid is added to water then it is called as an aqueous solution of an acid in an aqueous solution , acid ionises completely to form cation(positive ion) and anion(negative ion) these ions carry the charge towards opposite electrodes as anions move towards anode and cation move towards cathodes due to this fact acid conducts elelctricity in aqueous medium

Q3-why does dry HCI gas not change the colour of the dry litmus paper ?

ANSWER---> HCI ionises in aqueous medium therefore dry HCI does not ionise to form hydrogen ions (H+) hence it dies not change colour of the dry litmus paper
Does not show acidic behavior

Q4- while diluting an acid why is it recommended that the acid should be added to water and no water to the acid ?

ANSWER----> dilution of concentrated acid with water is a highly exothermic process the concentrated acid must be always added slowly to water with constant stirring if water is added to the concentrated acid then the heat generated so large that it may cause the mixture to splash out and cause burns .

Q5- how is the concentration of the hydrogen ions affected when a solution of an acid is diluted

ANSWER----> the concentration of hydronium ions per unit volume decreases when a solution of an acid is diluted

Q6- How will the concentration of hydroxide ion affected when excess base is dissolved in a solution of sodium hydroxide ?

ANSWER---> the concentration of hydroxide ions per unit volume increases when excess base is  dissolved in a solution of sodium hydroxide .


Q1- you have two solution 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

ANSWER-----> (i) The solution A has more hydrogen ion concentration .

(ii)  the solution A having more hydrogen ion is acidic .
(iii) the solution B is basic

Q2- what effect does the concentration of H+ ions have on the nature of the solution ?

ANSWER---> the concentration of H+ ions is directly proportional to the acidic nature of the solution
More is the concentration of H+ ions in a solution more acidic will be the solution .

Q3-- do basic solution also have H+ ions ? If yes then why are these basic ?

ANSWER---> yes basic solution also have H+(AQ) ions  in addition to OH- (aq) ions but they are basic in nature because the concentration of OH- (aq)ions in these solution is much greater than H+ ions
Water is a neutral compound because it contains equal number of both H+(AQ) and OH-(aq) ions

Q4- under what soil condition do you think a farmer would treat the soil of his fields with quick lime or slaked lime or chalk ?

ANSWER----> since quick lime (Cao) slaked lime [Ca(Oh)2] and chalk (CaCO3) are basic in nature this suggest that soil might bee to much acidic by adding these alkaline substances the PH of soil can be maintained very close to7 which is very essential for the healthy growth plants

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Q1- what is common name of compound( caOCI2)

ANSWER----> CaOCI2 is commonly known as bleaching powder

Q2- name the substance which on treatment with chlorine yields bleaching powder

ANSWER-----> Dry slaked lime [Ca(Oh)2]

Q3- name the sodium compound which are used for softening of hard water

ANSWER-------> washing soda ( sodium carbonate)

Q4- what will happened when solution of sodium hydrocarbonate is heated ? Give the equation of the reaction involved

ANSWER------>   sodium hydrogen carbonate decomposes on heating forming sodium carbonate carbon dioxide and water


Q5- write an equation to show reaction between plaster of Paris and water ?

ANSWER------> plaster of Paris  is a white powder which changes into a hard solid mass ( called gypsum )

When it is mixed with water .

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