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Class 10 SELINA Solutions Chemistry Chapter 4 - Analytical Chemistry

Analytical Chemistry Exercise Intext 1

Solution 1

(i) Analysis: The determination of chemical components in a given sample is called analysis.

(ii) Qualitative analysis: The analysis which involves the identification of the unknown substances in a given sample is called qualitative analysis.

(iii) Reagent:A reagent is a substance that reacts with another substance.

(iv) Precipitation: It is the process of formation of an insoluble solid when solutions are mixed. The solid thus formed is called precipitate.

Solution 2

(i) Yellow

(ii) Colourless

(iii) PaleGreen

(iv) Colourless

Solution 3

 a. Pb2+

 b. Cu2+

Solution 4

Name of solution

Soluble metal hydroxides

Insoluble metal hydroxides

Caustic soda solution

 

Zn(OH)2 Pb(OH)2

Fe(OH)3

Ammonium hydroxide solution

Zn(OH)2

Cu(OH)2

Fe(OH)3

Fe(OH)2

Solution 5

When ammonium salt is heated with caustic soda solution, ammonia gas is evolved.

The word equation is:

Ammonium chloride + Sodium hydroxide  Sodium chloride + water + ammonia


Ammonium sulphate + Sodium hydroxide    Sodium sulphate + water + ammonia

 

  

The balance equation is:

NH4Cl+NaOHNaCl+H2O+NH3

(NH4)2SO4 + 2NaOH Na2SO4 + 2H2O + 2NH3

Solution 6

NH4OH and NaOH can be distinguished by using calcium salts.

For example on adding NaOH to Ca(NO3)2, Ca(OH)2 is obtained as white precipitate which is sparingly soluble in excess of NaOH.

Ca(NO3)2+2NaOHCa(OH)2+2NaNO3

On addition of NH4OH to calcium salts, no precipitation of Ca(OH)2 occurs even with the addition of excess of NH4OH.This is because the concentration of OH- ions from the ionization of NH4OH is so low that it cannot precipitate the hydroxide of calcium.

Solution 7

If an alkali is added too quickly, then it is easy to miss a precipitate which redissolves in excess alkali.

Solution 8

(a)

(b)

Analytical Chemistry Exercise Ex. 4

Solution 1

(a) Ferrous salts: Light green

(b) Ammoniumsalts: Colourless

(c) Cupric salts: Blue

(d) Calcium salts: Colourless

(e) Aluminium salts: Colourless

Solution 2

(a) Cu(OH)2

(b) ZnO

(c) NaOH

(d) NH4OH

(e) Na+, Ca2+

(f) Fe2+, Mn2+

(g) Aluminium

(h) Zn(OH)2 and Al(OH)3

(i) PbO

(j) Ammonium ion

Solution 3

Solution 4

(i)

(ii)

(iii)

Solution 5

Solution 6

Zinc chloride (ZnCl2) is soluble in excess of ammonium hydroxide.

Solution 7

(a) ZnCl2

(b) Zn(OH)2

Solution 8

(a) PbO

(b) ZnO

(c) K2ZnO2

Solution 9

(a) (iii)

Aqueous solution of copper sulphate is blue.

(b) (iii)

 FeSO4 + 2NaOH  Fe(OH)2 + Na2SO4

  (Dirty green, (Colourless)

  gelatinous ppt.)

(c) (iii)

 Zn + 2NaOH  Na2ZnO2 + H2

 Sodium zincate

   (Colourless)

Zz Zn + HCl → ZnCl2 + H2 

(d) Option (a)

The salt solution which does not react with ammonium hydroxide is calcium nitrate.

Solution 10

When freshly precipitated aluminum hydroxide reacts with caustic soda solution, whitesalt of sodium meta aluminate is obtained.

Solution 11

Reagent bottles A and B can identified by using calcium salts such as Ca(NO3)2.

On adding NaOH to Ca (NO3)2, Ca (OH) 2 is precipitated as white precipitate which is sparingly soluble in excess of NaOH.

Ca(NO3)2+2NaOHCa(OH)2+2NaNO3

Whereas, on addition of NH4OH to calcium salts, no precipitation of Ca(OH)2 occurs even with addition of excess of NH4OH because the concentration of OH-ions from the ionization of NH4OH is so low that it cannot precipitate the hydroxide of calcium.

So the reagent bottle which gives white precipitate is NaOH and the other is NH4OH.

Solution 12

(a) Sodium hydroxide on reaction with calcium salt gives a milky white precipitate, while that of with lead it gives chalky white precipitate.

(b) Sodium hydroxide and ammonium hydroxide on reaction with lead salt gives brown coloured precipitate, while that of with zinc it forms white gelatin like precipitate.

(c) Sodium hydroxide and ammonium hydroxide on reaction with Copper salt gives pale blue coloured precipitate, while that of with ferrous salt solution it forms dirty green coloured precipitate.

(d)Sodium hydroxide and ammonium hydroxide on reaction with Fe(II) salt gives dirty green coloured precipitate, while that of with Fe(III) salt solution it forms reddish brown insoluble precipitate.

(e) Ammonium hydroxide on reaction with lead nitrate gives a chalky white insoluble precipitate, while that of with ferrous nitrate will not give any precipitation.

Solution 13

Lead carbonate is dissolved in dilute nitric acid and then ammonium hydroxide is added to it. A white precipitate is formed which is insoluble in excess.

Zinc carbonate is dissolved in dilute nitric acid and then ammonium hydroxide is added to it. A white precipitate is formed which is soluble in excess.

Solution 14

a. Zn + 2NaOH Na2ZnO2 + H2

b. 2Al + 2NaOH + 2H2O 2Na2AlO2 + 3H2

Solution 15

a. Amphoteric oxides are compounds which react with both acids and alkalis to form salt and water.

b. ZnO + 2NaOH Na2ZnO2 + H2O

 Al2O3 + 2NaOH 2NaAlO2 + H2O

c. Sodium zincate

Aluminium zincate

Solution 16

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