Analytical Chemistry : Uses of Ammonium Hydroxide and Sodium Hydroxide Solutions

Intext - Question

1. What do you understand by the following:

(a) Analysis

Ans: The process of determining the chemical components of a sample is known as analysis.

(b) Qualitative analysis

Ans: It indicates the quality of the chemical substance. The purpose of qualitative analysis is to figure out what makes up an unknown sample or to determine the components or factors that make it up.

(c) Reagent

Ans: A reagent is a material or ingredient that is added to a system to either produce or test a chemical reaction.

(d) Precipitation

Ans: Precipitation in aqueous solution is the transformation of a dissolved component into an insoluble solid from a supersaturated solution.

2. Write the probable colour of the following salts:

(a) Iron (III) chloride

Ans: Yellow

(b) Potassium nitrate

Ans: Colourless

(C)  Ferrous sulphate

Ans: Pale green

(d) Aluminium acetate

Ans: Colourless

(e) Aluminium salts

Ans: Colourless

3. Name the probable cation based on the following observations:

(a) White precipitate insoluble in NH₄OH but soluble in NaOH.

Ans: Pb⁺²

(b) Blue coloured solution.

Ans: Cu⁺²

4. Name the metal hydroxides which are: 

(a) Insoluble (b) soluble in (i) caustic soda solution (ii) Ammonium hydroxide 

Ans: 

5. What do you observe when ammonium salt is heated with caustic soda solution? Write the word equation.

Ans: Ammonia gas is produced when ammonium salt is heated with caustic soda solution.

NH₄Cl + NaOH → NaCl + H₂O + NH₃  …..(on heating)

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

6. How will you distinguish NH4 OH solution from NaOH solution?

Ans: On adding sodium hydroxide (NaOH) to calcium nitrate {Ca(NO₃)₂, calcium hydroxide Ca(OH)₂ is formed as white ppt. which is sparingly soluble in excess of NaOH.

Ca(NO₃)₂ +2NaOH → Ca(OH)₂} + 2NaNO₃

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

7. Why the alkali is added drop by drop to the salt solution?

Ans: It's easy to miss a precipitate that redissolves in excess alkali, if an alkali is added too rapidly.

8. Write the balanced equations:

(a) Reaction of sodium hydroxide solution with iron (III) chloride solution.

Ans: 3NaOH + FeCl₃ → Fe(OH)₃ ↓+ 3NaCl

                                                Reddish 

                                              brown ppt

(b) Copper sulphate solution with ammonium hydroxide solution.

Ans: CuSO₄ + NH₄OH  → Cu(OH)₂  ↓ + (NH₄)₂SO₄

                                                    Pale blue

                                                    ppt

Exercise-4

1. Write the probable colour of the following salts:

(a) Ferrous salts

Ans: Green

(b) Ammonium Salts

Ans: Colourless

(c) Cupric salts

Ans: Blue

(d) Calcium salts

Ans: Colourless

2. Name:

(a) A metallic hydroxide soluble in excess of NH4OH

Ans: Copper hydroxide (Cu(OH)₂).

(b) A metallic oxide soluble in excess of caustic soda solution.

Ans: Zinc oxide (ZnO).

(c) A strong alkali.

Ans: Sodium hydroxide (NaOH).

(d) A weak alkali.

Ans: Ammonium hydroxide (NH₄OH).

(e) Two colourless metal ions.

Ans: Sodium ion (Na⁺) and Calcium ion (Ca⁺²).

(f) Two coloured metal ions.

Ans: Ferrous ion (Fe⁺²) and Manganese ion (Mn⁺²).

(g) A metal that evolves a gas which burns with a pop sound when boiled with alkali solutions.

Ans: Aluminium (Al).

(h) Two bases which are not alkalis but dissolve in strong alkalis.

Ans: Zinc hydroxide (Zn(OH)₂) and Aluminium hydroxide (Al(OH)₃).

(i) A coloured metallic oxide which dissolves in alkalis to yield colourless solutions.

Ans: Lead oxide (PbO).

(j) A colourless cation not a representative element.

Ans: Ammonium ion (NH⁺).

3. Write the balanced equation for Q.2 (g) and (i).

Ans: (g) 2Al + 2NaOH +2H₂O → 2NaAlO₂ + 3H₂

(i) PbO + 2NaOH → Na₂PbO₂ + H₂O

4. What happens when ammonia solution is added first dropwise and then in excess to the following solutions:

(i) CuSO₄

Ans: When ammonium solution is added first dropwise a pale blue colour ppt. Cu(OH)2 obtained. And when further excess of ammonia solution is added then a complex of Cu+ is formed which is deep blue colour and ppt. formed dissolves.

CuSO₄ + 2NH₄OH → Cu(OH)₂ + (NH₄)2SO₄

Cu(OH)₂ + (NH₄)₂SO₄ + 2NH₄OH → (Cu(NH₃)₄)SO₄ + 4H₂O

(ii) ZnSO4

Ans: When ammonia solution added dropwise it gives white gelatinous ppt. of  zinc hydroxide. Further addition of excess ammonia solution forms a [Zn(NH₃)₄]SO₄ complex which is colourless and dissolved completely.

ZnSO₄ + 2NH₄OH → Zn(OH)₄ + (NH₄)₂SO₄

Zn(OH)₂ + (NH₄)₄SO₄ + 2NH₄OH → (Zn(NH₃)₄)SO₄ + 4H₄O

(iii) FeCl₃. Write the balanced equations for  these reactions.

Ans: Iron tri chloride on treatment with ammonium hydroxide forms insoluble Fe(OH)₃ which have reddish brown. Excess of ammonia solution addition doesn’t dissolve ppt.

FeCl₃ + 3NaOH → Fe(OH)₃ + 3NH₄Cl

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 the balanced equations for these reactions.

Ans: (a) A reddish brown ppt. of ferric hydroxide is obtained which is insoluble in excess of caustic soda solution.

FeCl₃ + 3NaOH → Fe(OH)₃↓ + 3NaCl

(b) A gelatinous white ppt. of zinc hydroxide is obtained which is soluble in excess of caustic soda solution.

ZnSO₄ + 2NaOH → Zn(OH)₂ ↓+ Na₂SO₄

Zn(OH)₂ + 2NaOH → NaZnO₂ + 2H₂O

(c) A white ppt. of lead (II) hydroxide is obtained which is soluble in excess of caustic soda solution.

Pb(NO₃)₂ + 2NaOH → Pb(OH)₂↓ + 2NaNO₃

Pb(OH)₂ + 2NaOH → Na₂PbO₂ + 2H₂O

(d) A pie blue ppt. of copper (II) hydroxide is obtained which is insoluble in excess of caustic soda solution.

CuSO₄ + 2NaOH → Cu(OH)₂↓ + Na₂SO₄

6. Name the chloride of the metal which is soluble in excess of ammonium hydroxide. Write an equation for the same.

Ans: When zinc chloride reacts with ammonium hydroxide, it gets converted to ammonium chloride and zinc hydroxide which is insoluble and is in precipitated form, when excess ammonium hydroxide is poured it in, gets soluble in form of di-amine di-chloride-zinc(II).

ZnCl₂ + 2NH₄OH → Zn(OH)₂ + 2NH₄Cl

Zn (OH)₂ + 2NH₄Cl + 2NH₄OH → (Zn(NH₄)3)Cl₂ + 4H₂O

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?

Ans: Zinc metal.

ZnSO₄ + 2NH₄OH → Zn(OH)₂ ↓+ (NH₄)₂SO₄

(b) What is the formula of the white gelatinous precipitate obtained?

Ans: Zn(OH)₂

8. Name:

(a) A yellow monoxide that dissolves in hot and concentrated caustic alkali.

Ans: Lead oxide (PbO)

(b) A white, insoluble oxide that dissolves when fused with caustic soda or caustic potash.

Ans: Zinc oxide (ZnO)

(c) A compound containing zinc in the anion.

Ans: Potassium zincate (K₂ZnO₂)

9. Select the correct answers:

(a) Colour of an aqueous solution of copper sulphate is 

(i) Green

(ii) Brown

(iii) Blue

(iv) Yellow

Ans: Blue

(b) Colour of the precipitate formed on adding NaOH solution to iron (II) sulphate solution is

(i) White

(ii) Brown

(iii) Green

(iv) Pale blue

Ans: Green

(c)  A metal which produces hydrogen on reacting with alkali as well as with acid.

(i) Iron

(ii) Magnesium

(iii) Zinc

(iv) Copper

Ans: Zinc

(d) The salt solution which does not react with ammonium hydroxide is

(i) Calcium nitrate

(ii) Zinc nitrate

(iii) Lead nitrate

(iv) Copper nitrate

Ans: Calcium nitrate

10. What do you observe when freshly precipitated aluminium hydroxide reacts with caustic soda solution? Give balanced equation.

Ans: When freshly precipitated Al(OH)₃ (aluminium hydroxide) reacts with NaOH (caustic soda) solution, a white salt of sodium meta aluminate is obtained.

Al(OH)₃ + NaOH → NaAlO₂ + 2H₂O

11. You are provided with two reagent bottles marked A and B. One contains NH₄OH solution and the other contains NaOH solution. How will you identify them by a chemical test?

Ans: A white ppt is generated when caustic soda (NaOH) is added to the calcium nitrate solution. When NH₄OH is added to calcium nitrate, no ppt is produced.

12. Distinguish by adding: Sodium hydroxide solution or ammonium hydroxide solution to

(a) Calcium salt solution and lead salt solution.

Ans: When sodium hydroxide and ammonium hydroxide react with calcium salt, they produce Ca(OH)₂, a milky white precipitate, whereas when they react with lead salt solution, they produce Pb(OH)₂, a chalky white precipitate.

(b) Lead nitrate solution and zinc nitrate solution.

Ans: Lead nitrate creates a chalky white ppt. of lead hydroxide that does not dissolve in excess ammonium hydroxide and produces a colourless solution, whereas zinc nitrate produces a white ppt. of lead hydroxide that dissolves in excess ammonium hydroxide and produces a colourless solution.

(c) Copper salt solution and ferrous salt solution.

Ans: When sodium hydroxide and ammonium hydroxide react with copper salt, they produce a pale blue precipitate, however when they react with ferrous salt solution, they produce a muddy green precipitate.

(d) Fe (II) salt solution and Fe (III) salt solution.

Ans: When sodium hydroxide and ammonium hydroxide react with Fe(II) salt, a filthy green precipitate forms, however when they react with Fe(III) salt solution, a reddish brown insoluble precipitate forms.

(e) Ferrous nitrate and lead nitrate

Ans: Lead nitrate produces a chalky white ppt of lead hydroxide, whereas ferrous nitrate produces a dirty green ppt of ferrous hydroxide.

13. How will you distinguish lead nitrate and zinc nitrate solution?

Ans: Lead nitrate solution and zinc nitrate solution. Lead Nitrate and Zinc nitrate solution can be distinguished by adding NaCl in solution, Pb(NO₃)₂ will give a precipitate of PbCl₂ whereas Zn(NO₃)₂ will not.

14. What is observed when hot concentrated caustic soda solution is added to 

(a) Zinc and (b) Aluminium? Write balanced equations.

Ans: Zinc reacts with hot conc. caustic soda or hot conc. sodium hydroxide to produce zincate sodium and hydrogen. ii) Aluminum reacts with sodium hydroxide to produce sodium aluminate, hydrogen and sodium oxide.

Zn + 2NaOH → Na2ZnO₂ + H₂

2Al + 6 NaOH → 2NaAlO₂ + 3H₂ + 2Na₂O

15. (a) What do you understand by amphoteric oxide?

Ans: Metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. Many metals (such as zinc, tin, lead, aluminium, and beryllium) form amphoteric oxides or hydroxides.

(b) Give the balanced equations for the reaction with two different amphoteric oxides with caustic alkali.

Ans: ZnO + 2NaOH → Na₂ZnO₂ + H₂O

Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

(c)  Name the products formed.

Ans: Sodium zinc oxide, sodium aluminium oxide, and water.

16. Write the balanced equations for the following conversions

$\left( \text{a} \right)\text{ZnS}{{\text{O}}_{\text{4}}}\xrightarrow{\text{A}}\text{Zn}{{\left( \text{OH} \right)}_{\text{2}}}\xrightarrow{\text{B}}\text{N}{{\text{a}}_{\text{2}}}\text{S}{{\text{O}}_{\text{2}}}$

$\left( \text{b} \right)\text{CuS}{{\text{O}}_{\text{4}}}\xrightarrow{\text{A}}\text{Cu}{{\left( \text{OH} \right)}_{\text{2}}}\xrightarrow{\text{B}}\left[ \text{Cu}{{\left( \text{N}{{\text{H}}_{\text{3}}} \right)}_{\text{4}}}\text{IS}{{\text{O}}_{\text{4}}} \right]$

Ans: (a) ZnSO₄ + A (NaOH) → Zn(OH)₂ + Na₂SO₄

Zn(OH)₂ + B (NaOH) → Na₂ZnO₂ + 2H₂O

(b) CuSO₄ + A (NH₄OH) → Cu(OH)₂ + (NH₄)2SO₄

Cu(OH)₂ + (NH₄)2SO₄ + 2NH₄OH → (Cu(NH₃)₄)SO₄ + 4H₂O

Ammonium Hydroxide and Sodium Hydroxide Solutions for Class 10 Science

Introduction

Analytical chemistry uses instruments and styles to separate, descry and quantify matter. All three styles can be used independently or combined with another system. Separation isolates certain motes. Qualification styles are used to identify and describe analytes, while quantitative styles determine the attention of an analyte. 

Likewise, logical chemistry involves the use of classical, wet chemistry styles and necessary styles. Rush, birth, and distillation are classical qualitative styles used in separation. Other styles of identification include differences grounded on colour, melting point, boiling point, solubility, or radioactivity. Also, common quantitative logical styles use mass or volume changes to quantify the quantum. 

Generally, chromatography, electrophoresis, or field-inflow separation are the main necessary styles used for separation. Once the target analyte has been insulated, qualitative and quantitative styles can be used to determine attention. This is frequently achieved by either using the same instrument after separation or using indispensable spectroscopic styles for further characterization and analysis. Frequently the classical necessary styles use the same instrument to separate, describe and quantify samples. 

Still, spectroscopic instrumentation is frequently used in a reciprocal fashion because it has the advantage of secerning motes that might have the same elution time with chromatography, but different molecular characteristics. Also, chemometrics and multivariate statistics are used in confluence with these ways to further interpret the structure and describe top factors at low attention. This is especially important in pharmaceutical assistance.