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CHLORINE AND ITS COMPOUNDS

1. INTRODUCTION:

Atomic mass: 35.5

Atomic number: 17

Colour: Yellowish-green gas

Electronic configuration: 2:8:7

Group: vii Reason: has 7 electrons in the outermost shell;

Period: 3 Reason: electrons fill 3 shells;/orbitals;/energy levels;

Isotopes: Chlorine-35 and Chlorine-37

Group seven elements are called halogens (salt formers)

2. LABORATORY PREPARATION OF CHLORINE GAS:

Chlorine is generally prepared by the removal of hydrogen from hydrochloric acid i.e.

oxidation of hydrochloric acid. This can be done by a substance containing oxygen (an

oxidizing agent)

Method 1;

Raw materials/reagents

Manganese(IV) oxide [ MnO4 ]

Concentrated hydrochloric acid

Conditions for the reaction

Heating is required

The hydrochloric acid must be concentrated

Method 2:

a) Raw materials/reagents

Potassium manganate(VII) / Potassium permanganate [ KMnO4 ]

Concentrated hydrochloric acid

b) Conditions for the reaction

No heating is required

The hydrochloric acid must be concentrated

Question [uneb 2019]

Describe how a dry sample of chlorine can be prepared in the laboratory. [Diagram

not required]

Concentrated hydrochloric acid; in a funnel is added to solid manganese(IV)

oxide; in a round-bottomed flask; fitted with a delivery tube;

The mixture is heated gently;

Bubbles of a yellowish-green gas is given off according to;-

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MnO2(S) + 4HCl(aq) MnCl2(aq) + 2H2O(l) + Cl2(aq)

The gas is passed through the first wash bottle containing water; to remove

traces of hydrogen chloride gas;/acid sprays;

The gas is then passed through the second wash bottle containing concentrated

sulphuric acid; to dry the gas; because they do not react;

Chlorine gas is then collected by downward delivery; because it is denser than

air.

Set-up of apparatus;

NB: The same set-up and description can be used to prepare chlorine gas

using potassium permanganate; only that no heating is required.

Equation:

2KMnO4(s) + 16HCl(aq) 2KCl(aq) + 2MnCl2(aq) + 8H2O(aq) + 5Cl2(aq)

3. TEST FOR CHLORINE GAS;

Chlorine is confirmed using moist blue litmus paper

Observation: the moist blue litmus paper turns red and finally white (bleached)

4. PROPERTIES OF CHLORINE

a) Physical properties;

It is a yellowish-green gas;

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Has an irritating or pungent smell;

It is denser than air;

It is slightly soluble in water

Turns moist blue litmus paper red and finally whitish [bleached]

Does not burn or support combustion;

b) Chemical properties:

(i) Reaction with phosphorous;

Phosphorous burns in chlorine to give white fumes of phosphorous(III)

chloride and phosphorous(V) chloride.

P4(s) + 6Cl2(g) 4PCl3(g)

P4(s) + 10Cl2(g) 4PCl5(g)

(ii) Reaction with turpentine [C10H16]

Turpentine combines violently with chlorine forming white fumes of

hydrogen chloride gas; and a black solid; which is carbon.

C10H16(s) + Cl2(g) 10C(s) + 16HCl2(g)

(iii) Reaction with Iron

When dry chlorine is passed over heated iron wire, a black solid;/sublimate is

formed;

Fe(s) + Cl2(g) FeCl3(s)

(iv) Reaction with Iron(II) chloride

When chlorine is bubbled through a green solution of iron(II) chloride, the

green solution turns to a yellow solution.

Reason: chlorine oxidizes iron(II) ions to iron(III) ions

2Fe2+(aq) + Cl2(aq) 2Fe3+

(aq) + 2Cl-(aq)

(v) Bleaching action of chlorine

When moist red and blue flowers;/litmus papers are added to a gas jar

containing chlorine, the colour is removed and turned whitish. i.e bleached.

Explanation:

Chlorine reacts with the moisture;/water forming hypochlorous acid; the

hypochlorous acid formed then gives a way its oxygen atom; to the dye (red

or blue colour) and the colour is removed;

Cl2(g) + H2O(I) HOCl(aq) + HCl(aq)

HOCl(aq) + [dye] [dye + O] + HCl(aq)

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(vi) Effect of sunlight on chlorine water

When chlorine water is exposed to sunlight, the yellowish green solution

turns to a colourless solution; and a colourless gas that relights a glowing

splint is formed;

HOCl(aq) HCl(aq) + O2(g)

(vii) Reaction with dilute sodium hydroxide solution

Chlorine reacts with cold dilute sodium hydroxide solution to form a pale-

yellow solution.

Cl2(g) + NaOH(aq) NaOCl(aq) + NaCl(aq) + H2O(l)

5. Uses of Chlorine:

Used as a disinfectant during water treatment;

Used to bleach cotton and wood pulp in the textile and paper industry

respectively;

Used in the manufacture of plastics e.g. polyvinyl chloride[P.V.C]

Used in the manufacture of organic chemicals e.g. tetra chloromethane (CCl4)

Used in the manufacture of insecticides;

Used in the manufacture of weed killers;

HYDROGEN CHLORIDE GAS:

Laboratory preparation of hydrogen chloride gas; Raw materials: Solid sodium chloride; Concentrated sulphuric acid;

Conditions for the reaction: The sulphuric acid must be concentrated; No heating is required;/room temperature;

Question [UNEB 2015 PAPER 2 QN 12]: Briefly describe how a dry sample of hydrogen chloride can be prepared in the laboratory. [Diagram is not required] (5½mks) Concentrated sulphuric acid in a thistle;/dropping;/tap funnel; is added to

solid sodium chloride in a round bottomed flask; fitted with a delivery tube;

Bubbles of a colourless gas; is given off according to the equation; NaCl(s) + H2SO4(l) HCl(g) + NaHSO4(aq)

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The gas is passed through a wash bottle containing concentrated sulphuric acid; to dry the gas;

The gas is then collected by downward delivery; because it is denser than air;

Set-up of apparatus

TEST FOR HYDROGEN CHLORIDE GAS; Reagent: Concentrated ammonia solution Description: A glass rod dipped in concentrated ammonia solution is brought close to the top of a test tube containing hydrogen chloride gas; Observation: Dense white fumes are formed [ammonium chloride is formed] Properties of hydrogen chloride a) Physical properties:

It is a colourless gas; Its denser than air; Has an irritating smell; Turns moist blue litmus red, i.e. its acidic

b) Chemical properties:

Reaction with ammonia: When a gas jar of hydrogen chloride is inverted over that of ammonia; dense white fumes are formed; HCl(g) + NH3(g) NH4Cl(s)

Reaction with Iron: When hydrogen chloride gas is passed over heated Iron wire, a green precipitate of iron(II) chloride is formed. 2HCl(g) + Fe(s) FeCl2(s) + H2(g)

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Uses of hydrogen chloride: Used in the manufacture of fertilizers; dyes; etc Used in the separation of cotton from wool; Manufacture of polyvinyl chloride;

HYDROCHLORIC ACID:

Hydrochloric acid is a solution of hydrogen chloride in water. It is prepared by dissolving hydrogen chloride gas in water. Question: Briefly describe how hydrochloric acid can be prepared in the laboratory. Solution; Concentrated sulphuric acid; in a funnel; is added to solid sodium chloride; in a flat

bottomed flask; fitted with a delivery tube; Effervescence;/bubbles of a colourless gas is formed;/produced; The gas is then absorbed in water; using a filter funnel; inverted over a beaker of water;

Chemical properties of Hydrochloric Acid 1. Action of hydrochloric acid as an acid.

This is when the acid is dilute. It reacts with metals, carbonates and bases. a) It reacts with metals forming a salt and hydrogen gas;

Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

b) It reacts with carbonates forming a salt, water and carbon dioxide gas; 2H+(aq) + CO3

2-(aq) H2O(l) + CO2(g)

c) It reacts with bases forming a salt and water only.

NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

2. Action of hydrochloric acid as a reducing agent. a) Concentrated hydrochloric acid reacts with solid manganese(IV) oxide

forming a salt, water and a yellowish-green gas; (Chlorine gas) b) Concentrated hydrochloric acid reacts with solid potassium permanganate

forming two salts, water and a yellowish-green gas; [See Equations on lab preparation of chlorine gas]

Uses of Hydrochloric acid:

Used in the manufacture of chlorine gas;

Used for pickling;

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NB; Pickling refers to the cleaning of metal surfaces in order to make them ready for galvanization

Used in the preparation of soluble chlorides; eg calcium chloride. CHLORIDES: Chlorides are salts of Hydrochloric acid. Examples of chlorides include; Sodium chloride Potassium chloride Ammonium chloride Lead(II) chloride Silver chloride Aluminium chloride Manganese chloride; etc;

Properties of Chlorides:

1. Solubility of Chlorides: All Chlorides are soluble in Water; Except; lead(II) chloride and Silver Chloride. NB: Lead(II) chloride is insoluble in cold water BUT soluble in Hot water.

2. Action of Heat on Chlorides: a) Potassium chloride; Sodium chloride; and Calcium chloride are not affected by

heat. b) Ammonium chloride and anhydrous aluminium chloride sublime on heating. c) Hydrated chlorides decompose to give hydrogen chloride gas;

CuCl2. 2H2O(s) CuO(s) + 2HCl(g) + H2O(l)

3. Action of Concentrated Sulphuric acid on Chlorides: Any Chloride will evolve hydrogen chloride on treatment with concentrated sulphuric acid. NaCl(s) + H2SO4(l) HCl(g) + NaHSO4(s)

TEST FOR CHLORIDES:

QUESTION :

Briefly describe a test that can be used in the laboratory to confirm the presence of Chloride ion (Equation required).

o To the solution of the suspected chloride in a test tube, add 2-3 drops of silver nitrate solution; followed by dilute nitric acid drop wise until in excess.

o Observation: A white precipitate is formed; which is insoluble in excess acid.

o Equation: Ag2+(aq) + Cl

-(aq) AgCl(s)

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OR; To the solution to be tested for the presence of chloride ion; add Lead(II) nitrate

solution and warm; Observation:

A white precipitate which dissolves on warming and reappears on cooling; Equation:

Pb2+(aq) + 2Cl-(aq) PbCl2(s)

Summary

1. Reagent: Silver nitrate solution and dilute nitric acid;/or; Lead(II) nitrate solution and warm;

2. Observations: A white precipitate; insoluble in excess/ or soluble on warming and reappears on cooling

NB: 1. The purpose of warming is to differentiate between lead(II) chloride and lead(II)

sulphate. The later does not dissolve on warming. 2. Soluble chlorides are prepared by the action of dilute hydrochloric acid on a metal; an

oxide or a carbonate. 3. Insoluble Chlorides are prepared by Double Decomposition method/ Precipitation.

Here 2 soluble salts are reacted together to form an insoluble salt.

O’ LEVEL CHEMISTRY CHLORINE AND ITS COMPOUNDS Topical test

1.(a)Describe how a pure dry sample of chlorine can be prepared in the laboratory starting from potassium manganate(VII). (NO diagram is required, but your description must include conditions and equation for the reaction). (b) State what would be observed and write equation(s) for the reaction(s) that would occur if Chlorine was bubbled into an aqueous sodium hydroxide (02 marks) Burning magnesium was lowered into a jar of dry chlorine. (03 marks) Chlorine was passed through a solution of potassium iodide. (2 ½ marks) (c) State one use of chlorine. ( ½ mark) P2/section B/2012 2.(a)Hydrogen chloride can be prepared from sodium chloride according to the following ionic equation. Cl-(s) + H

+ (aq) → H Cl (g) Calculate the mass of sodium chloride that would be required to produce 3.60 dm3 of hydrogen chloride measured at room temperature. [H = 1, Na = 23, Cl = 35.5; One mole of a gas at room temperature occupies 24.0 dm3.] (2½ marks) (b) State what would be observed and in each case write an equation for the reaction that would take place when:

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(i) an aqueous solution of hydrogen chloride is added to a solution containing lead (II) ions.(02 marks) (ii) excess dry hydrogen chloride is passes over strongly heated iron heated wire. (2½ marks) (c) Briefly explain the following observations and in each case illustrate your answer with equation(s). (i) Anhydrous iron (II) chloride cannot be prepared by direct synthesis using chlorine and iron.(2½mks) (ii) An aqueous solution of hydrogen chloride gives a white precipitate with silver nitrate whereas a solution of hydrogen chloride in tetra chloromethane shows no observable change when treated with silver nitrate solution. (04 marks) (d) Write an ionic equation for the reaction between an aqueous solution of iron(II) chloride and excess ammonia solution. (1½ marks) P2/SECTİON B/2009 3.( i) Name one substance that when reacted with dilute hydrochloric acid can produce sulphur dioxide. (01 mark) (ii) State the condition for the reaction. (½ mark) (iii) Write an ionic equation for the reaction leading to the formation of sulphur dioxide. (1½ marks) ( b ) A gas jar containing hydrogen sulphide was inverted over a gas jar containing moist sulphur dioxide.

(i) State what was observed. (½ mark ) (ii) Write an equation for the reaction that took place. (1½ marks )

P1/section A/ 2008 4. (a) When dilute hydrochloric acid was added to iron II sulphide , a gas was evolved. Write an equation for the reaction that took place. (b) State; (i) How the gas was identified. (ii) Why the gas is normally prepared in a fume cupboard or outside the laboratory. (c) The gas was reacted with sulphur dioxide. (i) State what was observed. (ii) Give a reason for your answer in © (i). P1/section A/ 2006 5. (a) Name one compound that when reacted with dilute hydrochloric acid can produce carbon dioxide (b) Excess carbon dioxide was passed through ice cold sodium hydroxide solution. (i) State what was observed (ii) Write equations for the reaction that took place. P1/section A/ 2006 6. (a) Name two crystalline allotropes of carbon. (b) State two differences between the allotropes you have named in (a). (c) Give one use of each of the allotropes. P1/section A/ 2005 7. (a) (i) Name two substances which can react to produce hydrogen chloride. (ii) Write an equation for the reaction leading to the formation of hydrogen chloride.

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(b) Hydrogen chloride reacts with lead (II) nitrate to form lead (II) chloride according to the following equation. Pb(NO3)2(aq) + 2HCl(g) 2HNO3(aq) + PbCl2(s). Calculate the volume of hydrogen chloride measured at s.t.p. that would be required to form 5.53 g of lead (II) chloride. [PbCl2=227; 1 mole of a gas at s.t.p. occupies 22.4 dm

3] P1/section A/ 2005 8. State what would be observed and write an ionic equation for the reaction that would take place when aqueous ammonium chloride was: (a) heated with sodium hydroxide solution. (i) Observation. (ii) Equation. (b) added to silver nitrate solution. (i) Observation. (ii) Equation. P1/section A/2004 9. (a) Write equation to show how hydrogen chloride can be prepared from sodium chloride. (b) Draw a labelled diagram to show how aqueous hydrogen chloride can be prepared in the laboratory. (c) State what would be observed and write equation for the reaction that would take place when aqueous hydrogen chloride is reacted with: (i) Solid calcium carbonate. (ii) Silver nitrate solution. (iii) Magnesium. (d) State why aqueous hydrogen chloride does not react with copper. P1/section B/ 2003 10. (a) Chlorine can be prepared from concentrated hydrochloric acid. (i) Name a substance that can react with hydrochloric acid to produce chlorine. (ii) Write equation for the reaction. (b) Chlorine gas was passed through cold dilute sodium hydroxide solution. (i) State what was observed. (ii) Write equation for the reaction that took place. P2/section A/2002 11. (a) (i) Name one substance that is reacted with hydrochloric acid to produce Sulphur dioxide in the laboratory. (ii) State the conditions for the reaction. (iii) Name a substance that can be used to dry the sulphur dioxide. (iv) Write equation for the reaction leading to the formation of sulphur dioxide. (b) State what would be observed and explain what would happen if sulphur dioxide is passed through a solution containing (i) Acidified potassium dichromate. (ii) a dye. (c) Briefly describe how sulphur dioxide can be converted to sulphuric acid. Your answer should include equations and conditions for the reaction(s). P2/section B/2002

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12. (a) (i) Describe with the aid of a well-labelled diagram how a dry sample of chlorine can be prepared in the laboratory. (ii) Write an equation for the reaction that took place. (iii) State any three uses of chlorine. (b) State with the aid of equations, what would be observed if chlorine was added to (i) Iron (II) chloride solution, (ii) Potassium iodine solution. (c) Burning sodium was plunged into a jar of chlorine. P2/section B/ 1999 13. (a) Describe how a dry sample of hydrogen chloride can be prepared from a named chloride. (No diagram is required). Your answer should include the following: - Conditions for the reaction. - Name of the drying agent. - Method of collection. - Equation for the reaction. (b) Name the substance that is formed when hydrogen chloride is passed through water. (c) (i) Name one reagent that can be used to test for the presence of chloride ions in solution. (ii) State what would be observed if the reagent was added to chloride solution. (d) Write an ionic equation to show the reaction between aqueous hydrogen chloride and calcium hydrogen carbonate solution. (e) 25.0 cm3 of a 0.2 M lead (II) nitrate solution was shaken with excess aqueous hydrogen chloride. Lead (II) ions react with chloride ions according to the following equation: Pb2+(aq) + 2 Cl

-(aq) PbCl2(s).

Calculate the mass of lead (II) chloride formed. P2/section B/ 1998 14. During the preparation of chlorine in the laboratory, the gas may be passed through water and concentrated sulphuric acid before collection. (a) State the use of (i) Water. (ii) concentrated sulphuric acid. (b) Chlorine is a bleaching agent when in the presence of water. (i) Write an equation for the reaction between chlorine and water. (ii) Using equations explain the bleaching action of chlorine. (c) (i) State what would be observed if chlorine was bubbled through a solution of iron (II) sulphate solution. (ii) Write an ionic equation for the reaction between chlorine and iron (II) ions. P2/section A/1997 15. (a) Draw a labelled diagram of the apparatus you would use to prepare chlorine in the laboratory, using potassium permanganate. (b) State what is observed when (i) a piece of yellow phosphorus is lowered in a jar of chlorine. (ii) Burning turpentine (C10H16) is lowered in a jar of chlorine. Chlorine is bubbled in a solution of potassium bromide.

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P2/section B/1997 THE END