Goyal Brothers Class-10 Acid Base and Salts ICSE Chemistry Solutions Ch-3. Step by Step Solutions of Exercise and Objective Type Questions of Goyal Brothers Prakashan Chapter-3 Chemical Bonding Ionic and Covalent for ICSE Class 10 Chemistry.  Visit official Website CISCE  for detail information about ICSE Board Class-10 Chemistry .

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Exercise 1

### Goyal Brothers Class-10 Acid Base and Salts ICSE Chemistry Solutions Ch-3

Page-48

Question 1.
(a) What do you understand by the term acid?
(b) Show ionically why (i) phosphoric acid, (ii) sulphuric acid, (ii) acetic acid are called acids?
(a)Acid, any substance that in water solution tastes sour, changes the colour of certain indicators (e.g., reddens blue litmus paper), reacts with some metals (e.g., iron) to liberate hydrogen, reacts with bases to form salts, and promotes certain chemical reactions (acid catalysis)
(b)  The main concept of importance is that those substance which gives out hydronium ions or hydrogen ions upon dissociation with water are considered as acids

i) Phosphoric acid:

• When phosphoric acid is dissociated in the presence of water, the following reaction occurs:

• As it gives out hydronium ions, it is called as acids.

ii) Sulfuric acid:

• When sulfuric acid is dissociated in the presence of water, the following reaction occurs:

• As it gives out hydronium ions, it is called as acids.

iii) Acetic acid:

• When acetic acid is dissociated in the presence of water, the following reaction occurs:

• As it gives out hydrogen ions, it is called as acids.

Question 2.

(a) What do you understand by the term “basicity of an acid'”?
(b) Give two examples of (i) monobasic acids (ii) dibasic acids (ii) tribasic acids. Support your answer by ionic equations.
(a) Basicity of an acid is the number of hydrogen ions which can be produced by one molecule of acid. e.g. Acetic acid is monobasic in nature as it can lose one proton or hydrogen atom to form acetate ion
(b) two examples of

(i)Monobasic acid- Monobasic acids are acids that furnish only one hydrogen ion (H+) per molecule in water. Example: Hydrochloric acid, nitric acid, acetic acid.

(ii )Dibasic acid- Dibasic acids are acids that furnish two hydrogen ions (H+) per molecule in water. Example: Sulphuric acid, carbonic acid, oxalic acid.

(iii) Tribasic acid- Tribasic acids are acids that furnish three hydrogen ions (H+) per molecule in water. Example: Phosphoric acid, phosphorus acid.

Question 3. Explain why:
(a Sulphuric acid forms two series of salts?
(b) Phosphoric acid forms three series of salts?
(a) Explanation: The acids which on dissociation with water yields two hydrogen ions they are called dibasic acidsSulfuric acid belongs to dibasic acids as it gives two hydrogen ions on dissociation with water. Due to this reason on reaction with strong bases, sulfuric acid forms salts that are neutral
(b ) Phosphoric acid has three hydrogen which can replace with metal atom and form three types of salt. Explanation: Phosphoric acid has three hydrogen which can replace with metal atom and form three types of salt
Question 4.
(a) What are indicators?
(Page-49)
(b)State colour change, if to a very slightly alkaline solution of the following indicators, is added a few drops of
dilute sulphuric acid
(i) methyl orange, (ii) phenolphthalein (ii) litmus solution.

## (a) Those substances which give different colour indifferent medium and thus indicate the presence of acid or base in a solution are called indicators. Natural indicators : Turmeric, beetroot. Synthetic indicators : Phenolphthalein and Methyl orange

(b)

(i)Methyl orangeMethyl orange changes to red when added to an acid.

(ii) Phenolphthalein is pink in an alkaline solution but turns colourless in an acidic solution. .

(iii) The main use of litmus is to test whether a solution is acidic or basic. Blue litmus paper turns red under acidic conditions. So sulphuric acid turns blue litmus into red.

Question 5.  Write an equation when an acid reacts with:
(i) metallic oxide, (ii) metallic hydroxide, (iii) metallic carbonate, (iv) metallic hydrogen carbonate, (v) metallic sulphite, (vi) metallic sulphide, (vii) metallic hydrogen sulphide, (viii) metallic hydrogen sulphite, (ix) a metal higher in metal activity series than hydrogen.
refer to page-41 (full page)
Question 6. Dilute HCl and Sulfuric acid react with metals above hydrogen in the metal activity series to liberate hydrogen gas. However,
nitric acid liberates oxides of nitrogen. Explain, by giving two examples along with fully balanced equations.

Reaction of metals with dilute acids

Metals usually displace hydrogen from dilute acids.

Less reactive metal(Cu,Au,Ag) do not displace hydrogen from dilute acid.

2Na+2HCl——>2NaCl + hydrogen (react violently)

Mg(s) + + 2 HCl (aq) —–> MgCl(aq) + H2 (g)

Al(s) + 6 HCl (aq) —-> AlCl(aq) + 3 H2 (g)

Zn(s) + 2 HCl (aq) —-> ZnCl (aq) + H2 (g)

Fe (s) + 2 HCl (aq) —-> FeCl (aq) + H2 (g)

Silver and gold do not react with dilute acids.

The metals like Cu,Au,Ag are less reactive than hydrogen.They do not displace hydrogen from dilute acids.

Those metals which are above in the reactivity series displace hydrogen from dilute acids.

2Na (s) + H2SO (aq) ——> Na2SO(aq) + H2 (g)

Mg (s) + H2SO (aq) ——> MgSO(aq) + H2 (g)

2Al (s) + 3 H2SO (aq) ——> Al2(SO4)3 (aq) + H2 (g)

Zn(s) + H2SO (aq) ——>  ZnSO4 (aq) + H2 (g)

Cu (s) + H2SO (aq) ——>  no reaction

When a metal react with dilute nitric acid,then hydrogen gas is not evolved.Nitric acid is a strong oxidising agent.As soon as hydrogen gas is formed in reaction between metal and dilute nitric acid,the nitric acid oxidises this hydrogen to water.Nitric acid itself is reduced to nitrogen oxides such
as nitrogen monoxide,dinitrogen monoxide.
The arrangement of metals in decreasing order of their reactivities is called reactivity series or activity series of metals.

Question 7.
(a) What do you understand by the term “acidity of a base”?
(b) Give two examples of (i) monoacidic base (ii) diacidic base (iii) triacidic base.
(c) Which of the bases you have mentioned in (b) are alkalis and why?

(a)  Acidity of base. Number of replaceable Hydroxyl groups present in one molecule of base is known as acidity of a base.

(b) Give two examples of
(i) monoacidic base  – Number of replaceable OH groups present in one molecule of a base i.e for NaOH, the acidity is 1
(ii) diacid base–Diacidic base: Diacidic base furnish two hydroxyl ions (OH) per molecule in water. Example:Calcium hydroxide, copper (II) hydroxide.
(iii) triacid base.–Triacaidic base: Triacaidic base furnish three two hydroxyl ions (OH) per molecule in water. Example: Aluminium hydroxide, ferric hydroxide.
(c)  the bases  mentioned in (b) are alkalis  because the are soluble in water
Question 8.
(a) What do you understand by the pH value of a solution?
(b) What is the pH value of water?
(c) Will a given solution be acidic or alkaline if
(i) its pH value is less than 7
(ii) more than 7?
(a) In chemistrypH (/piːˈeɪtʃ/, denoting ‘potential of hydrogen’ or ‘power of hydrogen’) is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of H+ ions) are measured to have lower pH values than basic or alkaline solutions
(b)  the pH value of water is 7
(c)  solution be …………….. if
(i) its pH value is less than 7 then acidic
(ii) more than 7 then basic
Question 9. Concentration of H* (aq) ions in a solution is 10¯¹¹ moles/litre. Calculate its pH value. State the action of
(i) methyl orange,
(ii) phenolphthalein on this solution.
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