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ICSE 2010 Important Papers of Chemistry By Mr. M.P.Keshari

ICSE Guess > ICSE Papers > Important Questions > Class X > 2010 > Chemistry > Chemistry By Mr. M.P.Keshari

Analytical Chemistry (Use of NaOH and NH4OH)

Q.9. Write observations and balanced equations for the following reactions.

  1. Sodium hydroxide is added drop wise till in excess to a solution of Zinc sulphate.
  2. Ammonium hydroxide is added first in a small quantity and then in excess to a solution of copper sulphate.
  3. Excess of Ammonium hydroxide is added to a substance obtained by adding hydrochloric acid in silver nitrate solution.

Ans.:

  1. When sodium hydroxide solution is added drop by drop to zinc sulphate solution a white precipitate is formed which is soluble in excess of sodium hydroxide.
    ZnSO4 + 2NaOH → Zn(OH)2 + Na2SO4
    Zn(OH)2 + 2NaOH → Na2ZnO2 + 2H2O.
  2. When NH4OH solution is added drop by drop to copper sulphate solution a pale blue / bluish white precipitate is formed which is soluble in excess of NH4OH and deep blue / inky blue solution is formed.
    CuSO4 + 2NH4OH → Cu(OH)2 + (NH4)2SO4
    Cu(OH)2 + 4NH4OH → Cu(NH3)4(OH)2 + 4H2O.
  3. When hydrochloric acid is added to silver nitrate solution a white precipitate is obtained which is soluble in excess of Ammonium hydroxide solution.
    AgNO3 + HCl → AgCl + HNO3
    AgCl + 2NH4OH → [Ag(NH3)2]Cl + 2H2O.

Q.10. Sodium hydroxide solution is added first in a small quantity, then in excess to the aqueous salt solution of copper (II) sulphate, zinc nitrate, lead nitrate, calcium chloride and iron (III) sulphate. Copy the following table and write the colour of the precipitate in (i) to (v) and the nature of the precipitate (soluble or insoluble) in (vi) to (x).

Aqueous salt solution. Colour of precipitate when NaOH is added in a small quantity. Nature of precipitate (soluble or insoluble) when NaOH is added in excess.
Copper (II) sulphate (i) (vi)
Zinc nitrate (ii) (vii)
Lead nitrate (iii) (viii)
Calcium chloride (iv) (ix)
Iron (II) sulphate (v) (x)

Ans.:

Aqueous salt solution. Colour of precipitate when NaOH is added in a small quantity. Nature of precipitate (soluble or insoluble) when NaOH is added in excess.
Copper (II) sulphate (i) Light Blue (vi) Insoluble
Zinc nitrate (ii) White (vii) Soluble
Lead nitrate (iii) White (viii) Soluble
Calcium chloride (iv) White (ix) Insoluble
Iron (II) sulphate (v) Dirty green (x) Insoluble


Paper By Mr. M.P. Keshari
Email Id - mpkeshari@yahoo.com
Phone No. - 09434150289

 

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