SELINA Solutions for Class 10 Chemistry Chapter 4 - Analytical Chemistry
Chapter 4 - Analytical Chemistry Exercise Intext 1
What do you understand by the following:
(ii) Qualitative analysis,
(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.
Write the probable colour of the following salts:
(i) Iron (III) chloride,
(ii) Potassium nitrate,
(iii) Ferrous sulphate,
(iv) Aluminum acetate,
Name the probable cations present in the following observations:
a. White precipitate insoluble in NH4OH but soluble in NaOH
b. Blue-coloured solution
Name the metal hydroxides which are :
- Caustic soda solution
- Ammonium hydroxide solution.
Name of solution
Soluble metal hydroxides
Insoluble metal hydroxides
Caustic soda solution
Ammonium hydroxide solution
What do you observe when an ammonium salt is heated with caustic soda solution? Write the word equation.
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:
(NH4)2SO4 + 2NaOH Na2SO4 + 2H2O + 2NH3↑
How will you distinguish NH4OH solution from NaOH solution?
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.
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.
Why is an alkali added drop by drop to the salt solution?
If an alkali is added too quickly, then it is easy to miss a precipitate which redissolves in excess alkali.
Write balanced equations:
(a) Reaction of sodium hydroxide solution with iron (III) chloride solution.
(b) Copper sulphate solution with ammonium hydroxide solution.
Chapter 4 - Analytical Chemistry Exercise Ex. 4
Write the probable colour of the following salts?
(a) Ferrous salts
(b) Ammonium salts
(c) Cupric salts
(d) Calcium salts
(e) Aluminium salts
(a) Ferrous salts: Light green
(b) Ammoniumsalts: Colourless
(c) Cupric salts: Blue
(d) Calcium salts: Colourless
(e) Aluminium salts: Colourless
(a) a metallic hydroxide soluble in excess of NH4OH.
(b) a metallic oxide soluble in excess of caustic soda solution.
(c) a strong alkali.
(d) a weak alkali.
(e) Two colourless metal ions.
(f) Two coloured metal ions.
(g) a metal that evolves a gas which burns with a pop sound when boiled with alkali solutions.
(h) Two bases which are not alkalis but dissolve in strong alkalis.
(i) a coloured metallic oxide which dissolves in alkalis to yield colourless solutions.
(j) a colourless cation not a representative element.
(e) Na+, Ca2+
(f) Fe2+, Mn2+
(h) Zn(OH)2 and Al(OH)3
(j) Ammonium ion
Write balanced equations for Q.2 (g) and (i).
What happens when ammonia solution is added first dropwise and then inexcess to the following solutions:
Write balanced equations for these reactions.
What do you observe when caustic soda solution is added to the following solution: first a little and then in excess.
(a) FeCl3 ,
(c) Pb(NO3)2 ,
Write balanced equations for these reactions.
Name the chloride of a metal which is soluble in excess of ammonium hydroxide. Write equation for the same.
Zinc chloride (ZnCl2) is soluble in excess of ammonium hydroxide.
On adding dilute ammonia solution to a colourless solution of a salt, a white gelatinous precipitate appears. This precipitate however dissolves on addition of excess of ammonia solution. Identify (choose from Na, Al, Zn, Pb, Fe)
(a) Which metal salt solution was used?
(b) What is the formula of the white gelatinous precipitate obtained?
(a) A yellow monoxide that dissolves in hot and concentrated caustic alkali.
(b) A white, insoluble oxide that dissolves when fused with caustic soda or caustic potash.
(c) A compound containing zinc in the anion.
Select the correct answers:
(a) Colour of an aqueous solution of copper sulphate is
(b) Colour of the precipitate formed on adding NaOH solution to iron (II) sulphate solution is
(iv) Pale blue
(c) A metal which produces hydrogen on reacting with alkali as well as with acid.
(d) The salt solution which does not react with ammonium hydroxide is
(a) Calcium nitrate
(b) Zinc nitrate
(c) Lead nitrate
(d) Copper nitrate
Aqueous solution of copper sulphate is blue.
FeSO4 + 2NaOH → Fe(OH)2 + Na2SO4
(Dirty green, (Colourless)
Zn + 2NaOH → Na2ZnO2 + H2
Zz Zn + HCl → ZnCl2 + H2
(d) Option (a)
The salt solution which does not react with ammonium hydroxide is calcium nitrate.
What do you observe when freshly precipitated aluminum hydroxide reacts with caustic soda solution?Give balanced equation.
When freshly precipitated aluminum hydroxide reacts with caustic soda solution, whitesalt of sodium meta aluminate is obtained.
You are provided with two reagent bottles marked A and B. One of which contains NH4OH solution and the other contains NaOH solution. How will you identify them by a chemical test?
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.
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.
Distinguish by adding: sodium hydroxide solution and ammonium hydroxide solution to
(a) Calcium salt solution and lead salt solution
(b) Lead nitrate solution and zinc nitrate solution
(c) Copper salt solution and ferrous salt solution
(d)Fe(II) salt solution and Fe(III) salt solution
(e) Ferrous nitrate and lead nitrate
(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.
How will you distinguish lead carbonate and zinc carbonate in solution?
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.
What is observed when hot concentrated caustic soda solution is added to
Write balanced equations.
a. Zn + 2NaOH → Na2ZnO2 + H2
b. 2Al + 2NaOH + 2H2O → 2Na2AlO2 + 3H2
a. What do you understand by amphoteric oxide?
b. Give the balanced equations for the reaction with two different amphoteric oxides with a caustic alkali.
c. Name the products formed.
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
Write balanced equations for the following conversions:
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