ICSE Solutions for Chapter 4 Analytical Chemistry: Uses of Ammonium Hydroxide and Sodium Hydroxide Class 10 Selina Chemistry
Exercise 1 A
(a) Ferrous salts
(b) Ammonium salts
(c) Cupric salts
(d) Calcium salts
(e) Aluminium Salts
Solution 1: (a) Ferrous salts: Light green
(b) Ammonium salts: Colourless
(c) Cupric salts: Blue
(d) Calcium salts: Colourless
(e) Aluminium salts: Colourless
Question 2: Name:
(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 coloured 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 dissolves in alkalis to yield colourless solutions.
(j) a coloured cation not a representative element.
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
Question 3: Write balanced equations for Q.2 (g) and (i)
Solution 3: 2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2
(Sodium meta aluminate is colourless: NaAlO2)
PbO + 2NaOH → Na2PbO2 + H2O
(PbO: Lead oxide is Yellow in colour)
(PbO: Lead oxide is Yellow in colour)
(Na2PbO2: Sodium plumbate is colourless and soluble)
Question 4: What happens when ammonia solution is added first dropwise and then in excess to the following solution:
(i) CuSO4 (ii) ZnSO4 (iii) FeCI3
Solution 4:
Question 5: What do you observe when caustic soda solution is added to the following solution, first a little and then in excess:
(a) FeCl3
(b) ZnSO4
(c) Pb(NO3)2
(d) CuSO4
Write balanced equations for these reactions. I
Solution 5:
Question 6: Name the chloride of a metal which is soluble in excess of ammonium hydroxide. Write equation for the same.
Solution 6: Zinc chloride (ZnCl2) is soluble in excess of ammonium hydroxide.
ZnCl2 + 2NH4OH → Zn(OH)2↓ + 2NH4CI
With excess of NH4Oh ppt dissolves.
Zn(OH)2 + 2NH4CI + 2NH4OH (excess) → [Zn(NH3)4]Cl2 + 4H2O
([Zn(NH3)4]Cl2: Tetram mine zinc (II) Chloride is colourless)
([Zn(NH3)4]Cl2: Tetram mine zinc (II) Chloride is colourless)
Question 7: 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?
Solution 7: (a) ZnCl2
(b) Zn(OH)2
Question 8: Name:
(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
Solution 8: (a) PbO
(b) ZnO
(c) K2ZnO2
Question 9: What do you observe when freshly precipitated aluminium hydroxide reacts with caustic soda solution? Give balanced equation.
Solution 9: (a) (iii)
Aqueous solution of copper sulphate is blue.
(b) (iii)
FeSO4 + 2NaOH → Fe(OH)2 + Na2SO4
(Dirty green, (Colourless)
gelatinous ppt.)
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
Question 10: What do you understand by amphoteric oxide Give the balanced equations for the reaction with three different amphoteric oxides with a caustic alkali. Write you observation if any.
Solution 10: When freshly precipitated aluminum hydroxide reacts with caustic soda solution, whitesalt of sodium meta aluminate is obtained.
Al(OH)3 + NaOH → NaAlO2 + 2H2O
(NaAlO2: Sodium meta aluminate)
Zn + 2NaOH → Na2ZnO2 + H2
Sodium zincate (Colourless)
Zz Zn + HCl → ZnCl2 + H2
Question 10: What do you understand by amphoteric oxide Give the balanced equations for the reaction with three different amphoteric oxides with a caustic alkali. Write you observation if any.
Solution 10: When freshly precipitated aluminum hydroxide reacts with caustic soda solution, whitesalt of sodium meta aluminate is obtained.
Al(OH)3 + NaOH → NaAlO2 + 2H2O
(NaAlO2: Sodium meta aluminate)
Question 11: Distinguish by adding: (a) sodium hydroxide solution and (b) Ammonium hydroxide solution to
(i) Calcium salt solution and lead salt solution
(ii) Lead salt solution and ferrous salt solution
(iii) copper salt solution and ferrous salt solution
(iv) Fe (II) salt solution and Fe (III) Salt solution
(v) Ferrous nitrate and lead nitrate
Solution 11: (a) Distinguish by adding Sodium hydroxide solution:
(i) Ca(NO3)2 + 2NaOH → Ca(OH)2 + 2NaNO3
On adding excess of NaOH, ppt. of Ca (OH)2 is sparingly soluble.
Pb(NO3)2 + 2NaOH → Pb(OH)2 + 2NaNO3
On adding excess of NaOH, ppt of Pb(OH)2 is soluble.
Pb(NO3)2 + 2NaOH → Pb(OH)2 + 2NaNO3
On adding excess of NaOH, ppt of Pb(OH)2 is soluble.
(ii) Pb(NO3)2 + 2NaOH → Pb(OH)2 + 2NaNO3
On adding excess of NaOH, ppt of Pb(OH)2 is soluble.
ZnSO4 + 2NaOH → Zn(OH)2 + Na2SO4
With excess of NaOH, white gelatinous ppt. of Zn (OH)2 is soluble. So, these two cannot be distinguished by NaOH alone. However white ppt. of Pb (OH)2is readily soluble in acetic acid also.
ZnSO4 + 2NaOH → Zn(OH)2 + Na2SO4
With excess of NaOH, white gelatinous ppt. of Zn (OH)2 is soluble. So, these two cannot be distinguished by NaOH alone. However white ppt. of Pb (OH)2is readily soluble in acetic acid also.
(iii) CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4
With excess of NaOH, alkali pale blue ppt of Cu (OH)2 is insoluble.
FeSO4 + 2NaOH → Fe(OH)2 + Na2SO4
With excess of NaOH, dirty green ppt. of Fe(OH)2 is insoluble.
FeSO4 + 2NaOH → Fe(OH)2 + Na2SO4
With excess of NaOH, dirty green ppt. of Fe(OH)2 is insoluble.
(iv) FeSO4 + 2NaOH → Fe(OH)2 + NaSO4
With excess of NaOH, dirty green ppt of Fe (OH)2 is insoluble.
FeCl3 + 3NaOH → Fe(OH)3 + 3NaCl
With excess of NaOH, reddish brown ppt of Fe(OH)3 is insoluble.
(b) Distinguish by adding Ammonium hydroxide solution:
(i) 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 ionization of NH4OH is so low that it cannot precipitate the hydroxide of calcium.
Pb(NO3)2 + 2 NH4OH → Pb(OH)2 + 2NH4NO3
FeCl3 + 3NaOH → Fe(OH)3 + 3NaCl
With excess of NaOH, reddish brown ppt of Fe(OH)3 is insoluble.
(b) Distinguish by adding Ammonium hydroxide solution:
(i) 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 ionization of NH4OH is so low that it cannot precipitate the hydroxide of calcium.
Pb(NO3)2 + 2 NH4OH → Pb(OH)2 + 2NH4NO3
On adding excess of NH4OH, chalky white ppt. of Pb (OH)2 is insoluble.
(ii) Pb(NO3)2 + 2 NH4OH → Pb(OH)2 + 2NH4NO3
On adding excess of NH4OH, chalky white ppt. of Pb(OH)2 is insoluble.
ZnSO4 + 2NH4OH → Zn(OH)2 + (NH4)2SO4
On adding excess of NH4OH, chalky white ppt. of Pb(OH)2 is insoluble.
ZnSO4 + 2NH4OH → Zn(OH)2 + (NH4)2SO4
With excess of NH4OH, white gelatinous ppt. of Zn (OH)2 is soluble.
(iii) CuSO4 + 2NH4OH → Cu(OH)2 + (NH4)2SO4
With excess of NH4OH, pale blue ppt. of Cu (OH)2 is soluble.
FeSO4 + 2NH4OH → Fe(OH)2 + (NH4)2SO4
With excess of NH4OH, dirty green ppt. of Fe (OH)2 is insoluble.
With excess of NH4OH, pale blue ppt. of Cu (OH)2 is soluble.
FeSO4 + 2NH4OH → Fe(OH)2 + (NH4)2SO4
With excess of NH4OH, dirty green ppt. of Fe (OH)2 is insoluble.
(iv) FeSO4 + 2NH4OH → Fe(OH)2 + (NH4)2SO4
With excess of NH4OH, dirty green ppt. of Fe (OH)2 is insoluble.
FeCl3 + 3NH4OH → Fe(OH)3 + 3NH4Cl
With excess of NH4OH, reddish brown ppt of Fe (OH)3 is insoluble.
Question 12: 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?
Solution 12: 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 + 2NaOH → Ca(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.
With excess of NH4OH, dirty green ppt. of Fe (OH)2 is insoluble.
FeCl3 + 3NH4OH → Fe(OH)3 + 3NH4Cl
With excess of NH4OH, reddish brown ppt of Fe (OH)3 is insoluble.
Question 12: 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?
Solution 12: 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 + 2NaOH → Ca(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.
Intext Questions
(i) Analysis
(ii) Qualitative analysis
(iii) Reagent
(iv) Precipitation
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.
Question 2: Write the probable colour of the following salts:
(i) Iron (III) chloride
(ii) Potassium nitrate
(iii) Ferrous sulphate
(iv) Aluminium acetate
(v) Calcium carbonate
Solution 2: (i) Yellow
(ii) Colourless
(iii) PaleGreen
(iv) Colourless
(v) Colourless
Question 3: Name the probable cation present in each of the following solution: (i) Yellow coloured solution
(ii) blue coloured solution
(iii) Light blue coloured solution
(iv) Pink coloured solution
Solution 3: (i) Fe3+
(ii) Cu2+
(iii) Cu+2
(iv) Mn2+
Question 4: Name the metal hydroxides which are:
(i) Sparingly soluble
(ii) Insoluble
(iii) Soluble In caustic soda solution
Solution 4: (i) Ca(OH)2
(ii) Fe(OH)2 and Cu(OH)2
(iii) Zn(OH)2 and Pb(OH)2
Question 5: What do you observe when ammonium salt is heated with caustic soda solution? Write the balanced equation.
Solution 5: When ammonium salt is heated with caustic soda solution, ammonia gas is evolved. The balance equation is:
Question 6: How will you distinguish NH4OH solution from NaOH solution?
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 + 2NaOH → Ca(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.
Question 7: Name the metal hydroxides which are: (i) Insoluble (ii) Soluble. In ammonium hydroxide solution
Solution 7: (i) Fe(OH)2 and Pb(OH)2
(ii) Cu(OH)2 and Zn(OH)2