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1. 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) Ammonium salts - COLOURLESS
(c) Cupric salts - BLUE
(d) Calcium salts - COLOURLESS
(e) Aluminium salts - COLOURLESS
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 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 dissolves in strong alkalis
(i) a coloured metallic oxide which dissolve in alkalis to yield colourless solutions
(j) a chocolate brown oxide which becomes colourless on addition of hot Caustic Potash solution
(a) Lead hydroxide [ Pb(OH)2 ]
(b) Zinc oxide [ ZnO ]
(c) Potassium hydroxide [KOH ]
(d) Ammonium hydroxide [ NH4OH ]
(e) (1) Potassium ion [ K+ ] (2) Sodium ion [ Na+ ]
(f) (1) Cupric (Blue) [ Cu2+ ] (2) Ferric (yellow) [ Fe3+ ]
(g) Metal is Zinc [Zn ]
(h) Two bases are ZnO and PbO
(i) Lead monoxide [ PbO ] yellow
(j) Lead dioxide [ PbO2 ]
3. Write balanced equations of metal in Zinc and Lead monoxide?
Zn + 2 KOH → K2ZnO2 + H2
[Hot. and conc] [pot.Zincate]
PbO + 2 KOH → K2PbO3 + H2O
Yellow [Hot.] [Pot.Plumbate colourless solution]
4. What happens when ammonia solution is added
(a) dropwise and then
(b) in excess to the following solutions:
(i) CuSO4 (ii) ZnSO4 (iii) FeCl3 (iv) Al2(SO4)3
(c) Write balanced reactions.
(i) CuSO4
(a) When added dropwise Cu(OH)2 blue ppt.
CuSO4 + 2 NH4OH → Cu(OH)2 ↓ + [NH4]2 SO4
Blue Pale blue ppt Ammonium sulphate(Colourless in solution)
(ii) ZnSO4
(a) When added dropwise Zn(OH)2 ↓ [white, gelatine ppt.]
ZnSO4 + 2 NH4OH → Zn(OH)2 ↓ + (NH4)2 So4
(colourless solution (white gelatinous ppt.) (colourless in solution)
(b) When added in excess ppt. dissolves
Zn(OH)2 + 4 NH4OH → [Zn(NH3)4] (OH)2 + 4 H2O
Excess Tetra ammine zinc (II) hydroxide (colourless solution))
(iii) FeCl3 ppt. insolution in excess of NH4OH
FeCl3 + 3 NH4OH → Fe(OH)3 ↓ + 3 NH4Cl
(yellow solution) (Reddish brown ppt.) (colourless solution)
(Ferric hydroxide)
(iv) Al2(SO4)3
Al2(SO4)3 + 6 NH4OH → 2 Al[OH]3 ↓ + 3(NH4)2 SO4
Aluminium Sulphate Aluminium hydroxide
(colourless sol.) (white gelatinous)
5. What do you see 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 (e) Al2(SO4)3
(a) FeCl3 Reddish brown ppt. of Fe[OH]3
Formed does not dissolve in excess of NaOH
FeCl3 + 3 NaOH → Fe(OH)3 ↓ + 3 NaCl
(yellow solution) Caustic soda (Reddish brown) Colourless
(colourless)
(b) ZnSO4 White gelatinous ppt. of Zn(OH)2 formed is soluble in excess NaOH.
ZnSO4 + 2 NaOH → Zn(OH)2 ↓ + Na2SO4
(colourless) (colourless) (white gelatinous) colourless
In excess Na2ZnO2 dissolves in NaOH
Zn(OH)2 + 2 NaOH (excess) → Na2ZnO2 + 2 H2O
soluble
(colourless)
(c) Pb(NO3)2 White ppt. of Pb(OH)2 is formed which dissolves in excess of NaOH.
Pb[NO3]2 + 2 NaOH → Pb[OH]2 ↓ + 2 NaNO3
(colourless) (colourless) (white) (colourless)
Pb(OH)2 dissolves in excess of (NaOH)
Pb(OH)2 + 2 NaOH → Na2PbO2 + 2 H2O
(excess) Sodium plumbite
(colourless soluble)
(d) CuSO4 Pale blue ppt. of Cu(OH)2 formed is insoluble in excess.
CuSO4 + 2 NaOH → Cu(OH)2 ↓ + Na2SO4
(blue) (colourless) (pale blue)
(e) Al2[SO4]3 (white, gelatinous) ppt. of Al(OH)3 formed dissolves in excess of NaOH.
Al2(SO4)3 + 6 NaOH → 2 Al[OH]3 ↓ + 3 Na2SO4
(colourless) caustic soda (white, gelatinous) (colourless)
In excess
Al(OH)3 + NaOH → NaAlO2 + 2 H2O
(colourless soluble)
6. write balanced equations for:
(a) FeCl3 Reddish brown ppt. of Fe[OH]3
Formed does not dissolve in excess of NaOH
FeCl3 + 3 NaOH → Fe(OH)3 ↓ + 3 NaCl
(yellow solution) Caustic soda (Reddish brown) Colourless
(colourless)
(b) ZnSO4 White gelatinous ppt. of Zn(OH)2 formed is soluble in excess NaOH.
ZnSO4 + 2 NaOH → Zn(OH)2 ↓ + Na2SO4
(colourless) (colourless) (white gelatinous) colourless
In excess Na2ZnO2 dissolves in NaOH
Zn(OH)2 + 2 NaOH (excess) → Na2ZnO2 + 2 H2O
soluble
(colourless)
(c) Pb(NO3)2 White ppt. of Pb(OH)2 is formed which dissolves in excess of NaOH.
Pb[NO3]2 + 2 NaOH → Pb[OH]2 ↓ + 2 NaNO3
(colourless) (colourless) (white) (colourless)
Pb(OH)2 dissolves in excess of (NaOH)
Pb(OH)2 + 2 NaOH → Na2PbO2 + 2 H2O
(excess) Sodium plumbite
(colourless soluble)
(d) CuSO4 Pale blue ppt. of Cu(OH)2 formed is insoluble in excess.
CuSO4 + 2 NaOH → Cu(OH)2 ↓ + Na2SO4
(blue) (colourless) (pale blue)
(e) Al2[SO4]3 (white, gelatinous) ppt. of Al(OH)3 formed dissolves in excess of NaOH.
Al2(SO4)3 + 6 NaOH → 2 Al[OH]3 ↓ + 3 Na2SO4
(colourless) caustic soda (white, gelatinous) (colourless)
In excess
Al(OH)3 + NaOH → NaAlO2 + 2 H2O
(colourless soluble)
7. Name a chloride of a metal which is soluble in excess of ammonium hydroxide. What is the product formed ?
It is silver chloride [AgCl] dissolves in excess of Nh4OH.
Product formed is [Ag(NH3)2]Cl [ Soluble colourless Diamine Argentous( l ) chloride ]
8. 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)Zn
(b) Zn(OH)2 white gelatinous ppt.
9. 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.
(d) a hydroxide which is soluble in excess of ammonium hydroxide.
(a) PbO [Lead monoxide]
(b) Al2O3 [Aluminium oxide]
(c) Na2ZnO2 [Sodium zincate]
(d) Zn(OH)2 [Zinc hydroxide]
10. What do you observe when freshly precipitated aluminium hyroxide reacts with caustic soda solution ? Give equation?
Al(OH)3 + NaOH → NaAlO2 + 2 H2O
(Sodium Aluminate)
11. What do you understand by amphoteric oxide ? Give the balanced equations for the reaction with three different amphoteric oxides with a caustic alkali. Write your observation if any.
Amphoteric oxides, " metallic oxides which react with both acids and alkalis to form salt and water" are called amphoteric oxides.
(i) ZnO + 2 NaOH → Na2ZnO2 + water
Zinc oxide (conc.) Sodium zincate
(ii) PbO + 2 NaOH → Na2PbO2 + H2O
(yellow) (Hot) Sodium plumbite
(colourless)
(iii) PbO2 + 2 KOH → K2PbO3 + H2O
Chocolate brown (Hot) pot.plumbate
(colourless)
12. Distinguish by adding:
(a) Sodium hydroxide solution and
(b) Ammonium hydroxide solution:
(i) Calcium salts and lead salts
(ii) Lead salts and zinc salts
(iii) Copper salts and ferrous salts
(iv) Fe(II) salts nd Fe(III) salts
| Salt | NaOH | Ammonium Hydroxide |
| i) Calcium | white ppt. sparingly soluble | No ppt |
| Lead | white ppt. soluble in excess | white ppt. insoluble in excess |
| ii) Zinc | white gelatinous soluble in ppt. excess | white gelatinous ppt. |
| iii)Copper | pale blue ppt. |
pale blue ppt. Deep blue in excess |
|
Ferrous F(II) |
Dirty green gelatinous ppt. | Dirty green ppt. insoluble in excess |
| (iv) Fe(III) | Reddish brown ppt. insoluble in excess | Reddish brown ppt. |
