Practical Work Exe-9C Chemistry Class-9 ICSE Selina Publishers

Practical Work Exe-9C Chemistry Class-9 ICSE Selina Publishers Solutions Chapter-9. Step By Step ICSE Selina Concise Solutions of Chapter-9 Practical Work with All Exercise including MCQs, Very Short Answer Type, Short Answer Type, Long Answer Type, Numerical and Structured/Application Questions Solved . Visit official Website CISCE for detail information about ICSE Board Class-9.

Practical Work Exe-9C Chemistry Class-9 ICSE Concise Selina Publishers

Board	ICSE
Publications	Selina Publication
Subject	Chemistry
Class	9th
Chapter-9	Practical Work
Book Name	Concise
Topics	Solution of Exercise – 9C (Flame Test)
Academic Session	2023-2024

C. Exercise – 9C

Practical Work Class-9 Chemistry Concise Solutions

Page-161

Question 1.

Carbon dioxide and sulphur dioxide gas can be distinguished by using :

(a) moist blue litmus paper

(b) lime water

(d) none of the above

Answer:

acidified potassium dichromate paper

Reason — There is no effect of CO₂ gas on potassium dichromate whereas SO₂ turns acidified potassium dichromate from orange to clear green.
K₂Cr₂O₇ + H₂SO₄ + 3SO₂ ⟶ K₂SO₄ + Cr₂(SO₄)₃ + H₂O

Question 2.

Match the gases in column I to the identification of the gases mentioned in column II

Column I	Column II
(a) Hydrogen sulphide	A. Turns acidified potassium dichromate solution green
(b) Nitric oxide	B. Turns lime water milky
(c) Carbon dioxide	C. Turns reddish brown when it reacts with oxygen
(d) Sulphur dioxide	D. Turns moist lead acetate paper silvery black

Answer:

Column I	Column II
(a) Hydrogen sulphide	D. Turns moist lead acetate paper silvery black
(b) Nitric oxide	C. Turns reddish brown when it reacts with oxygen
(c) Carbon dioxide	B. Turns lime water milky
(d) Sulphur dioxide	A. Turns acidified potassium dichromate solution green

Question 3.

Match column A with column B

Column A	Colum B
(a) Blue salt changes to white and then black	(i) Ammonium dichromate
(b) Orange coloured compound changes to green	(ii) Iodine
(c) Red compound changes to brown and then yellow	(iii) Zinc Nitrate
(d) White to yellow when hot and white when cold	(iv) Copper Sulphate
(e) Violet solid changes to violet vapours	(v) Red Lead

Answer:

Column A	Colum B
(a) Blue salt changes to white and then black	(iv) Copper Sulphate
(b) Orange coloured compound changes to green	(i) Ammonium dichromate
(c) Red compound changes to brown and then yellow	(v) Red Lead
(d) White to yellow when hot and white when cold	(iii) Zinc Nitrate
(e) Violet solid changes to violet vapours	(ii) Iodine

Question 4.

Identify the following substances:

(a) An alkaline gas A which gives dense white fumes with hydrogen chloride.

(b) Gas B that has an offensive smell as of rotten eggs.

(d) A brown gas D with irritating smell.

Answer:

(a) A : Ammonia

(b) B : Hydrogen sulphide

(d) D : Nitrogen dioxide

Question 5.

Name the gases which :

(a) extinguishes burning wooden splinter.

(b) turns moist red litmus blue.

(d) affect the acidified K₂Cr₂O₇ paper and also turns lime water dirty milky.

Answer:

(a) NH₃, HCl, SO₂, H₂S, CO₂, NO₂, Cl₂.

(b) Ammonia [NH₃]

(d) Sulphur dioxide [SO₂]

Question 6.

What do you observe when dilute sulphuric acid is added to the following:

(a) Sodium Sulphide

(b) Sodium Carbonate

Answer:

(a) When dil. sulphuric acid is added to sodium sulphide and heated, hydrogen sulphide gas is evolved which has the smell of rotten eggs and turns lead acetate paper black.

Na₂S + H₂SO₄ ⟶ Na₂SO₄ + H₂S

(b) When dilute sulphuric acid is added to sodium carbonate a colourless gas [CO₂] is evolved with brisk effervescence that turns lime water milky and has no effect on acidified potassium dichromate paper.

Na₂CO₃ + H₂SO₄ ⟶ Na₂SO₄ + H₂O + CO₂ (g)

Zn + H₂SO₄ (dil) ⟶ ZnSO₄ + H₂ (g)

Question 7.

(a) How is the flame test performed?

(b) How will you distinguish between:

(i) sodium chloride, potassium chloride and calcium chloride?

(ii) soft water and hard water ?

(iii) temporary hard water and permanent hard water ?

Answer:

(a) The procedure to detect the colour imparted by flame test is as follows:

A thin platinum wire is first thoroughly cleaned by dipping it in conc. hydrochloric acid. It is then heated in the non-luminous flame of the burner. The process is repeated. When the wire imparts no colour to the flame, it is ready for use.

Now, wire is first dipped in conc. hydrochloric acid and then in the salt to be tested. It is then introduced into the non-luminous part of the flame and the colour imparted to the flame is observed.

(b)

(i) We can distinguish between the three salts [sodium chloride, potassium chloride and calcium chloride] with the help of flame test as described below:

Method:

Thin platinum wire is thoroughly cleaned and then heated in a non-luminous flame of a burner.
When the wire imparts no colour it is dipped in conc. HCl and then into the substance to be identified.

Observation:

The golden yellow flame confirms the presence of sodium [Na¹⁺] ion.
Lilac colour of flame confirms the presence of Potassium [K¹⁺]

(ii) Differentiating hard water from soft water:

Two unknown samples ‘X’ and ‘Y’ containing hard water and soft water are taken separately in a trough or beaker.
Ordinary soap is rubbed by the hands inside each sample.

Observation:

One sample of water ‘X’ lathers with soap
The sample of water ‘Y’ does not lather with soap.

Result:

The sample ‘X’ which lathers with soap is soft water.
The sample ‘Y’ which does not lather with soap is hard water.

(iii) Distinguish between temporary hard water and permanent hard water:

Two unknown samples ‘A’ and ‘B’ containing temporary and permanent hard water are taken separately in a trough or beaker.
Ordinary soap is rubbed by the hands inside each filtered sample.

Observation:

One sample of water ‘A’ lathers with soap.
The sample of water ‘B’ does not lather with soap.

Result:

The boiled and filtered sample ‘A’ which lathers is temporary hard water whose hardness is removed by boiling.
Sample ‘B’ is permanent hard water whose hardness cannot be removed by boiling.

Question 8.

(a) What do you understand by :

(i) temporary hardness

(ii) soft water

(iii) permanent hardness

(b) How are temporary and permanent hardness removed ?

Answer:

(a) (i) Temporary hardness — Hardness of water due to the presence of calcium and magnesium bicarbonates — Ca(HCO₃)₂, Mg(HCO₃)₂ — that can be removed by boiling and filtration is called temporary hardness.

(ii) Soft water — Water that does not contain dissolved calcium and magnesium salts is called soft water. This water forms lather with ordinary soap.

(iii) Permanent hardness — Hardness of water due to the presence of calcium and magnesium chlorides and sulphates — CaCl₂, MgCl₂, CaSO₄, MgSO₄ — that cannot be removed by boiling is called permanent hardness.

(b) Temporary hardness can be removed by boiling followed by filtration and permanent hardness can be removed by addition of washing soda or caustic soda.

Question 9.

(a) What are soaps and detergents?

(b) Why do they differ in their actions ?

Answer:

(a) Soap — It is the sodium or potassium salt of an organic fatty acid. It reacts with hard water forming scum, which is why ordinary soap is wasted.

CaSO₄ + 2NaSt (soap) ⟶ CaSt₂ (scum) + Na₂SO₄

Detergents — They are the sodium salts of alkyl sulphonic acids. Detergents contain a sulphonic acid group (-SO₃H) instead of a carboxylic group (-COOH).

(b) Soaps reacts with hard water forming scum, which is why ordinary soap is wasted.

Detergents can lather even with hard water. Due to the solubility of their calcium and magnesium salts in water, they do not form scum.

(c) Soap or detergent molecules form clusters called micelles when dissolved in water. The molecules arrange themselves with their tails inward and their heads outward. During the cleansing process, the hydrocarbon tail of the detergent attaches to oil and dirt. When water is stirred, the oil and dirt separate into smaller fragments. This allows other tails to attach to the fragmented oil and dirt. The detergent molecules surround these small oil and dirt globules. The negatively charged heads in the water prevent the globules from recombining into larger aggregates. As a result, when clothes are rinsed with water, the oil and dirt are effectively removed.

(Practical Work Exe-9C Chemistry Class-9)

Question 10.

Compare the effect of soap and detergent on hard water.

Answer:

Soaps react with hard water forming scum which is why ordinary soap is wasted whereas detergents can lather even with hard water. Due to the solubility of their calcium and magnesium salts in water, they do not form scum.

Question 11.

Copy and complete the following table that refers to the action of heat on some carbonates:

Carbonate	Colour of residue on cooling
Zinc carbonate
Lead carbonate
Copper carbonate

Answer:

Carbonate	Colour of residue on cooling
Zinc carbonate	Yellow when hot, white when cold
Lead carbonate	Yellow
Copper carbonate	Black

Question 12.

Complete the following table and write your observations.

	Hydrogen sulphide	Ammonia	Sulphur dioxide	Hydrogen chloride
Shake the gas with red litmus solution
Shake the gas with blue litmus solution
Apply a burning splint to the gas

Answer:

	Hydrogen sulphide	Ammonia	Sulphur dioxide	Hydrogen chloride
Shake the gas with red litmus solution	No change	Red litmus becomes blue	No change	No change
Shake the gas with blue litmus solution	Blue litmus becomes red	No change	Blue litmus becomes red	Blue litmus becomes red
Apply a burning splint to the gas	Burning splint is extinguished	Burning splint is extinguished	Burning splint is extinguished	Burning splint is extinguished