Properties of hydrogen chloride gas

Physical properties

  1. It is a colourless gas with an irritating, choking smell.
  2. It forms misty fumes in damp air as it forms tiny droplets of hydrochloric acid.
  3. It turns moist blue litmus paper red.
  4. It is also soluble in methyl benzene (toluene)
  5. Hydrogen chloride gas is denser than air.
  6. It is very soluble in water. When it dissolves in air, it forms hydrochloric acid.
    The high solubility of hydrogen chloride gas in water can be demonstrated by the fountain experiment as that of ammonia.

Chemical properties

  1. Deduction of the composition of hydrogen chloride
    a) Action of dry hydrogen chloride gas on heated iron
    When dry hydrogen gas is passed over heated iron, the gaseous product that is collected over water burns with a pop sound indicating that the gas is hydrogen.
image 340
image 341

b) Reaction with potassium permanganate (KMnO4)
When hydrogen chloride gas is slowly passed over potassium permanganate, a greenish yellow gas is formed. The greenish yellow gas is chlorine.

image 342

From the above two reactions, conclusions can be made that the components of hydrogen chloride are chlorine and hydrogen.

  1. Reaction with ammonia
    Hydrogen chloride reacts with ammonia forming white fumes of ammonium chloride.
image 343

Preparation of a solution of hydrogen chloride in water (hydrochloric acid)

The solution of the gas in water forms hydrochloric acid. When the gas is bubbled through water until no more of the gas can dissolve, then the product is concentrated hydrochloric acid and contains 36% by mass of hydrogen chloride.
When dissolving, the apparatus should be arranged as below. The method is only suitable if the gas is very soluble.

image 344

The rim of the funnel must just be at the surface of water in the beaker this avoids water being sucked into the preparation apparatus; a delivery tube cannot also be used because it would suck up water in to the preparation apparatus.
Properties of hydrochloric acid
It has all the properties typical of an acid like

  • Sour taste
  • Turns blue litmus paper red
  • It is fully ionized in aqueous solution indicating that it is a strong acid
image 345
image 346

These properties are due to the fact that hydrogen chloride although a covalent compound ionizes completely when dissolved in water and therefore show typical acidic characteristics.

Uses of hydrochloric acid

  • It is used in the removal of rust from iron (descaling) before it is galvanized.
  • It is used in cleaning metals before they are electroplated.
  • It is used in the manufacture of plastics like polyvinylchloride
  • Used in the preparation of soluble chlorides
    Preparation of solution of hydrogen chloride in methyl benzene
    The preparation is done the same way as above. Hydrogen chloride dissolves but does not ionize in organic solvents like methyl benzene and exists as a covalent compound. Therefore, the solution does not conduct electricity; has no effect on litmus paper; does not react with metals above copper and does not react with carbonates or hydrogen carbonates but reacts with ammonia to form white precipitates of ammonium chloride since the salt is insoluble in organic solvents.

Test for chlorides
Solid chlorides

When concentrated sulphuric acid is added to any chloride, hydrogen chloride gas is evolved.
The gas forms fumes in moist air; turns moist blue litmus paper red; and forms thick white fumes of ammonium chloride with ammonia; and forms white precipitates of silver chloride with acidified silver nitrate solution.

Chloride in solution
To a solution of chloride, add a little nitric acid and then silver nitrate solution. White precipitates of silver chloride are seen.

image 347

When a little ammonia solution is added to the above solution, the white precipitates dissolve. The precipitates are insoluble in nitric acid. The only two insoluble chlorides are lead(II) chloride and silver chloride.

Sample questions on Chlorine and its compound

  1. Describe and explain the laboratory preparation and manufacture of chlorine. Using equations, describe the reactions of chlorine with: metals, non metals, water, dilute acids and hydrocarbons. How would you show experimentally that hydrogen chloride is very soluble in water? Outline the uses of chlorine.
  2. With the aid of a labeled drawing, explain how hydrogen chloride and hydrochloric acid are prepared in the laboratory. Describe experiments to deduce the composition of hydrogen chloride. Describe the reactions of hydrogen chloride with ammonia. Explain the behaviour of hydrogen chloride in (i) water and (ii) methyl benzene.
  3. Describe one experiment in each case to show (a) how hydrochloric acid acts as a reducing agent (b) how hydrogen chloride can be identified. Give the uses of hydrochloric acid.

Sulphur is in period 3 and group VI of the periodic table. It has atomic number number 16 and electronic configuration 2.8.6.

It occurs in both Free State and combined state. In the free state it occurs in underground deposits and it is widely distributed in volcanic regions. In combined states it occurs as sulphates, sulphides (mainly hydrogen sulphide) and sulphite. It also occurs in crude oil.

Extraction of sulpur
Sulphur is found deep below the ground (160-200) metres, this makes mining it impossible. It is extracted by a method invented by a man called Frasch and the method is Frasch process. Sulphur is extracted from the underground deposits by this method basing on its low melting point.

The Frasch process

image 348


  • Drill the Frasch pump consisting of three concentric pipes down the sulphur deposit.
  • Super heated water (steam) at about 170˚C is then forced down the outer most tube to melt the sulphur.
  • A jet of hot compressed air is then pumped down through the inner most tube. This hot compressed air pumps the molten sulphur out through the middle tube to the surface where the sulphur is cooled and solidified. The sulphur obtained is about 99.5% pure and can be used directly. It is usually sold in two forms either as ―flowers of sulphur‖ a powder or ―roll sulphur‖, cylindrical sticks.
    Sulphur from natural gas and petroleum
    Natural gas obtained during the distillation of petroleum contains hydrogen sulphide. The hydrogen sulphide can be removed by dissolving it in a suitable solvent. The gas is removed from the solvent and one third (1/3) of the hydrogen sulphide obtained is burnt in oxygen to form sulphurdioxide.
image 349

Physical properties of sulphur

  1. It is a yellow solid at room temperature
  2. It is a typical non metal
  3. It is insoluble in water but soluble in some organic solvents e.g. methyl benzene and carbon disulphide
    Allotropes of sulphur
    Sulphur has two major crystalline forms .i.e. allotropes namely
  4. Rhombic sulphur (alpha sulphur, α-sulphur)
    Rhombic is an octahedral crystal; its bright yellow in color; its melting point is 114˚C; it has a density of 2.8g/cm3 and it is stable at a temperature below 96˚C.
image 350
  1. Monoclinic sulphur (Beta sulphur,β-sulphur)
    It is a needle shaped crystal (prismatic); it is very pale yellow in color (almost transparent); it has a melting point of 119˚C; it has a density of 1.98 g/cm3; it is stable above 96˚C, below 96˚C it reverts to rhombic sulphur.
image 351

Transition temperature is a temperature at which rhombic sulphur changes to monoclinic sulphur and vice versa. At a temperature below 96˚C, rhombic sulphur exists and as the temperature goes above 96˚C, the rhombic sulphur changes to monoclinic form. The transition temperature is there fore 96˚C.

To show that both rhombic and monoclinic sulphur are allotropes of sulphur
When the same mass of either rhombic or monoclinic sulphur is burnt in oxygen, the same mass of sulphur dioxide is obtained in each case and nothing else.
Other forms of sulphur

Amorphous sulphur
This is a non crystalline form of sulphur which is insoluble in carbon disulphide(CS2). It is formed as an almost insoluble powder if a saturated solution of hydrogen sulphide is oxidized by leaving it to stand in open air for some times i.e.

image 352

Plastic sulphur
If sulphur at its boiling point is poured into cold water, a dark-sticky (elastic) solid called plastic sulphur is formed. Plastic sulphur is elastic because it contains zig-zag (entangled) chains of S8 molecules.
N.B Plastic sulphur is unstable and slowly hardens to form yellow rhombic sulphur. Plastic sulphur is not a separate allotrope of sulphur since it is not crystalline in nature.

Action of heat on sulphur
Sulpur under goes a series of changes when it is heated. Both rhombic and monoclinic sulphur consist of S8 molecules with different arrangements. It is this differences in arrangement of sulphur atoms that is responsible for the different observations made when sulphur is heated.

  1. If yellow powdered sulphur is heated in the absence of air just above the melting point (about 115˚C), it melts into a clear amber (pale yellow) mobile liquid. This liquid is mobile because the sulphur-8 (S8) molecule rings can flow over one another with ease.
  2. On further heating (to about 160˚C), the yellow liquid becomes darker and very viscous. This is because the S8 rings are broken and form long chains of sulphur 8 (S8) atoms. The liquid is viscous because the long chains entangle with one another and thus do not flow readily over each other. Above 160˚C the darker viscous sulphur liquid becomes mobile and reddish brown in color.
  3. Near its boiling point (444˚C), the liquid now becomes lighter in color, thin and more mobile (less viscous). This is because the long entangled chains break down forming chains of S1 and S2 atoms which can flow more readily.
  4. The sulphur eventually boils at 444˚C and forms a light brown sulphur vapor.
    Other properties of sulphur
  5. It is a reactive element and it combines directly with other elements (metals and non metals)
    a) If a piece of burning sulphur is lowered into a gas jar of oxygen, it continues to burn even more brightly with a blue flame forming whites fumes with a choking smell. The white fumes with a choking smell are a mixture of white sulphur trioxide and colorless sulphur dioxide gases.
image 353

b) If mixture of iron dust (iron fillings) and powdered sulphur is heated in a hard glass test tube, the two elements combine vigorously and a spontaneous red glow

image 354

Uses of sulphur

  1. It is used in the making of matches, gun powder and fire works.
  2. Used in the vulcanization (hardening) of rubber
  3. Used in the manufacture of sulphuric acid in the contact process.
  4. Used as a fungicide and in medicine, ointments and drugs used for the treatment of skin diseases. e.g. Sulphonamide.
  5. Used in the production of calcium hydrogen sulphite,Ca(HSO3)2 that acts as a bleaching agent in the wood pulp in manufacture of paper.
  6. Sulphur is used in the manufacture of various compounds like carbon disulphide (CS2) and sodium thiosulphide Na2S2O3 used in photography.
  7. Fruit trees are sprayed with sulphur products like carbon disulphide (CS2) to kill insects and fungi which cause diseases.
    Laboratory preparation

It can be prepared in a laboratory by the action of dilute hydrochloric acid or dilute sulphuric acid on iron(II) suphide. The preparation must be done in a fume cupboard as hydrogen sulphide gas is very poisonous.
Set up of apparatus

image 355

As the acid reaches the iron (II)sulphide, effervescence begins and the hydrogen sulphide is collected over warm water since in is soluble in cold water. If it is required dry, the gas is passed over anhydrous calcium chloride and then collected by downward delivery method.

image 356

Physical properties
i) It has a strong repulsive characteristic of a rotten egg smell
ii) It is a colorless gas
iii) It is very poisonous but not as dangerous as carbon monoxide
iv) It is slightly denser than air that is why it is collected by downward delivery
v) It can be liquefied under high pressure
vi) It dissolves in cold water forming a fairly weak acidic solution

image 357

Test for hydrogen sulphide

a) Hydrogen sulphide can easily be detected by its strong repulsive smell of rotten eggs.
b) When hydrogen sulphide is passed through a solution of Lead(II)nitrate or Lead(II)ethanoate, a black precipitate of lead(II)sulphide is observed.

image 358

c) When hydrogen sulphide is bubbled through a solution of iron(III)chloride, the solution changes from pale yellow to pale green. This is because hydrogen sulphide reduces iron(III)chloride (the pale yellow solution) to iron(II)chloride (a pale green solution). The hydrogen sulphide itself is oxidized to sulphur which appears as a yellow deposit. Hydrogen chloride gas is also formed which dissolves to form hydrochloric acid.

image 359

d) When hydrogen sulphide is bubbled through a solution of acidified potassium manganate(VII), the solution changes color from purple to colorless and a yellow deposit of sulphur is also formed. This is because, hydrogen sulphide reduces manganate(VII) ions (purple in color) to manganese(II) ions(colorless) and the hydrogen sulphide itself is oxidized to sulphur.

image 360

e) When hydrogen sulphide is bubbled through a solution of acidified potassium dichromate(VI) the solution changes from orange to green as a result of reduction of the the dichromate(VI) ions to chromium(III) ions.

image 361

f) Hydrogen sulphide reduces concentrated sulphuric acid according to the following reaction

image 362

g) When hydrogen sulphide is bubbled through concentrated nitric acid, brown fumes of nitrogen dioxide together with a pale yellow precipitate of sulphur are observed.

image 363

Hydrogen sulphide gas precipitates insoluble sulphides e.g. it precipitates black copper(II)sulphide from blue copper(II)sulphate solution.

image 364

There are two principle oxides of sulphur namely sulphur dioxide and sulphur trioxide.

Laboratory preparation

Sulphur dioxide in the laboratory can be prepared in two ways
a) Action of concentrated sulphuric acid on copper metal
b) By action of dilute sulphuric acid or hydrochloric acid on any sulphite salt e.g sodium sulphite(Na2SO3).

Preparation by the action of concentrated H2SO4 on copper metal

image 365

Place copper metal in the flask and arrange the apparatus as shown above.
Gently heat the mixture until when it is hot. Effervescence occurs as sulphur dioxide is evolved.

image 366

The gas is passed through a wash bottle containing concentrated sulphuric acid to dry the gas and it is the collected by downward delivery since it is denser than air. The gas is not collected over water as it is very soluble in water.

Laboratory preparation of sulphur dioxide from sodium sulphite and dilute sulphuric or hydrochloric acid
The procedure and the arrangement of apparatus remains as shown above but no heating is required for the reaction. However, if the reaction slows down, the flask may be heated gently.

image 367
image 368

Physical properties of sulphur dioxide

  1. It is a poisonous gas
  2. It is a colorless gas with a characteristic pungent smell
  3. It is denser than air
  4. It can easily be liquefied under pressure
  5. It is an acidic gas i.e. it turns moist blue litmus paper red
  6. It is very soluble in water forming sulphurous acid
    Chemical properties of sulphurdioxide
  7. Reaction with alkalis
    Sulphur dioxide is neutralized by alkalis
    i) When the alkali is in excess sulphites are formed.
image 369

NB This is a characteristic test for sulphurdioxide
b) Sulphur dioxide also reduces acidified potassium Manganate(VII) to manganese (II) sulphate. The color changes from purple to colorless and the sulphur dioxide is itself oxidized to sulphuric acid.

image 370

This is also used as a test for sulphur dioxide.
c) When sulphur dioxide is bubbled through a solution of iron(III)suphate, the color changes from yellow to pale green. This is because the sulphur dioxide reduces iron (III) sulphate to iron (II) sulphate and the sulphur dioxide is oxidized to sulphuric acid.

image 371

d) Sulphur dioxide reduces concentrated nitric acid to form brown fumes of nitrogen dioxide and itself is oxidized to sulphuric acid.

image 372

e) Colored solutions of halogen are made colorless when sulphur dioxide is bubbled through them. This is because sulphur dioxide reduces the halogens to hydrogen halides. For example
When sulphur dioxide is bubbled through chlorine water (yellowish green liquid), a mixture of hydrochloric acid and sulphuric acid are obtained which appear colorless.

image 373

Bromine water (a reddish brown liquid) is turned colorless as bromine is reduced to hydrobromic acid by sulphur dioxide.

image 374
  1. As an oxidizing agent
    Sulphur dioxide acts as an oxidizing agent when it reacts with reducing agents more powerful than itself. Consider the reactions below
    a) When sulphurdioxide is bubbled through a solution of hydrogen sulphide, a yellow precipitate is observed. This is because sulphur dioxide oxidizes hydrogen sulphide to yellow sulphur and sulphur dioxide is itself reduced to sulphur.
image 375

b) When a piece of magnesium ribbon is lowered into a gas jar of sulphur dioxide, it continuous to burn with a bright flame to form white solids (magnesium oxide) and a yellow solid(sulphur). This is because sulphur dioxide oxidizes magnesium to magnesium oxide and itself is reduced to sulphur.

image 376
  1. As a bleaching agent
    Sulphur dioxide bleaches wet flowers like roses and hibiscus and any other wet material by reduction. It does this by removing oxygen from the colored material.
image 377

The original color of the bleached material may be restored after prolong exposure to air due to aerial oxidation. This explains why old news papers appear yellow after some times.

  1. Reaction with oxygen

Under normal conditions, sulphur dioxide does not react with oxygen. However when a mixture of dry and pure sulphur dioxide and oxygen is passed over heated platinum catalyst (or vanadium(V)oxide), sulphur trioxide gas is formed.

image 378
  1. As an acid anhydride
    Sulphur dioxide is an acid anhydride, reacting with water to form sulphurous acid.
image 379

Sulphurous acid is a dibasic acid and reacts with sodium hydroxide solution to form two salts of sodium, the acid salt;sodium hydrogen sulphite (NaHSO3)and the normal salt;sodium sulphite (Na2SO3)

image 380

Uses of sulphur dioxide

  1. It is used in the manufacture of sulphuric acid by contact process.
  2. It is a poisonous gas and it is used in fumigation to kill germs in clothes and houses.
  3. It is used for preservation of food staff and fruits during transportation and storage, as it prevents fermentation.
  4. It is used as a bleaching agent e.g it is used to make calcium hydrogen sulphite (Ca(HSO3)2) that makes wood pulp white in paper manufacture, used to bleach silk, straw e.t.c.
image 381

Test for sulphite

To a solution of substance containing sulphite, add 3 drops of barium nitrate solution followed by excess nitric acid. (or add barium chloride solution followed by excess hydrochloric acid)
White precipitates immediately appear which dissolve with effervescence on adding dilute nitric acid.

image 382
image 383

Laboratory preparation
It can be prepared in the laboratory by passing a dry mixture of oxygen and sulphur dioxide over a heated platinum catalyst or (Platinized asbestos) at a temperature of 450-500˚C.

Set up of apparatus

image 384
image 385

The sulphur trioxide is seen as dense white fumes and may be solidified in a freezing mixture of ice and a little sodium chloride. The sulphur trioxide container is protected from atmospheric moisture by calcium chloride tube.

Properties of sulphur trioxide

  1. It has very high affinity for water and combines with it violently forming sulphuric acid.
image 386

This reaction is highly exothermic i.e. it gives out a lot of heat and it is because of this that sulphur trioxide is kept in air tight containers.

  1. Sulphur trioxide combines with concentrated sulphuric acid to form fuming sulphuric acid called oleum.
image 387

Large scale (Industrial) manufactureof sulphuric acid by contact process

In the manufacture of sulphuric acid by contact process, sulphur dioxide and oxygen are the starting materials.
The sulphur dioxide is oxidized to sulphur trioxide which is then absorbed by concentrated sulphuric acid forming oleum (fuming sulphuric acid) to which water is added to form the sulphuric acid.
This process can be divided into the following essential stages;

a) Preparation of sulpur dioxide
Sulpur dioxide can be obtained from the following source;
i) Burning sulpur in air. This is cheap and produces sulphur dioxide in large quantities

image 388
image 389

Other sources of sulphur dioxide include; burning of hydrogen sulphide from crude oil in air; flue gas desulphurization in power stations e.t.c.
Oxygen is obtained from fractional distillation of liquid air.

b) Purification of the gases
The sulphur dioxide and the oxygen are purified and dried (i.e. cleared off any dust particles and other impurities which can poison the catalyst especially if it is platinum.

c) Preparation of sulphur trioxide
The purified gases are passed over a finely divided vanadium (V) oxide,(V2O5) catalyst at a temperature of 450-500 C and a pressure of 2-3 atmospheres, sulphur trioxide is formed. Vanadium (V) oxide is commonly used because it is cheaper and not easily poisoned by impurities.

image 391

The catalyst Vanadium (V) oxide is so effective that 95% conversion of sulphur dioxide to sulphur trioxide is achieved at 450-500 C and 2 atmospheres. The reaction is exothermic and there fore produces heat enough to maintain the temperature of the catalyst

d) Conversion of sulphur trioxide to sulphuric acid
Sulphur trioxide,SO3 must not be allowed to come in contact with water as the reaction is intensely exothermic that it vaporizes the sulphuric acid formed (i.e. produces a lot of mist consisting of dry droplets of H2SO4 ).
To prevent this happening, the sulphur trioxide, SO3 is absorbed in concentrated sulphuric acid, H2SO4 to form an oily liquid called an Oleum

image 392

In the above process, the following conditions favor high yield of sulphur trioxide:

  • Presence of a catalyst. The catalyst must be finely divided to increase the surface area for the reaction.
  • Low temperature(450-500 C) as the reaction is exothermic (releases heat),
  • Slightly high pressure above the atmospheric pressure as the reaction is accompanied by a decrease in volume.
  • High concentration of oxygen or sulphur dioxide.

Properties of sulphuric acid
a) Physical properties

  1. Concentrated Sulphuric acid is a dense, colorless and oily liquid.
  2. Concentrated sulphuric acid has very high affinity for water and a lot of heat is produced when the acid is diluted.
  3. Concentrated sulphuric acid is hygroscopic. I.e. gradually absorbs moisture from the air and therefore when left exposed to air, in a beaker, the total volume gradually increases due to absorption of water. This is why it is used as a drying agent for many of the gases.
    b) Chemical properties
  4. Sulphuric acid as an acid
    It is the dilute sulphuric acid that reacts as a typical acid.
    i. Dilute sulphuric acid ionizes to form hydrogen ions
image 393
image 394
image 395

NB With calcium carbonate and lead (II) carbonate, there is little effervescence and the reaction stops soon because the sulphates formed are insoluble and form a coating around the carbonate preventing any further attack by sulphuric acid on the carbonate.

  1. As an oxidizing agent
    Hot concentrated sulphuric acid is a powerful oxidizing agent and in all reactions, it is itself reduced to sulphur dioxide. Metals are oxidized to sulphates and non metals to their oxides. Example include:
    a) Hot concentrated sulphuric acid oxidizes copper to copper (II) sulphate and the sulphuric acid itself is reduced to sulphur dioxide.
image 396
  1. As a dehydrating agent
    Concentrated sulphuric acid is a very strong dehydrating agent i.e. it removes the elements of water from many compounds. Examples
    a) When concentrated sulphuric acid is added to blue copper (II) sulphate crystals, the copper(II)sulphate crystals gradually become white as their water of crystallization is lost.
image 397

b) When cold concentrated sulphuric acid is added to sugar crystals in an evaporating dish, the sugar crystals turn progressively from white, to yellow then to brown and finally to black. A spongy black mass of charcoal rises almost filling up the dish , water vapor is given off and the dish becomes very hot as the reaction is exothermic (generates energy).

image 398

In this reaction ,the concentrated acid removes the elements of water from sugar leaving a black mass of carbon.
A similar action is the explanation of a very marked corrosive action of the acid on flesh and cloth made of cotton. Cotton is largely cellulose whose simplest formula is (C6H10O5)n.
c) Concentrated sulphuric acid dehydrates oxalic acid on heating to form a mixture of carbon monoxide, carbon dioxide and water.

image 399

d) Excess concentrated sulphuric acid dehydrates ethanol at a temperature of 170 C forming ethene.

image 400

When concentrated sulphuric acid removes elements of water from a compound with the formation of a new compound, it is described as a dehydrating agent.

  • As a drying agent
    When concentrated sulphuric acid removes water from a mixture, it acts as a drying agent.
    Concentrated sulphuric acid reacts exothermically with water. When a solution is made, it is essential to pour the acid into water, stirring to disperse the heat evolved. It is dangerous to add water to concentrated sulphuric acid as small pockets of water are likely to boil.
    Gases are dried by bubbling them through concentrated sulphuric acid. For basic gases like ammonia, another drying agent is used.

Uses of sulphuric acid

  • Used in the manufacture of fertilizers like ammonium sulphate.
  • Making of paints and pigments
  • Manufacture of detergents and soap
  • Production of other chemicals such as metallic sulphates, hydrochloric acid, hydrofluoric acid and plastics.
  • Extraction of metals and metal manufacturing including pickling to clean metallic surfaces.
  • Extraction of alkenes in petroleum refinery.
  • With nitric acid, it is used to make dyes and explosives.
  • Sulphates

These salts are derived from sulphuric acid.
All sulphates are soluble in water except barium sulphate, lead(II)sulphate and calcium sulphate is slightly soluble in water.
Action of heat on sulphates
Most of the sulphates are resistant to heat, but if they are hydrated, they lose their water of crystallization and become powdery upon slight heating. E.g.

image 401

However, iron (II) sulphate, copper (II) sulphate, ammonium sulphate and sulphates of other metals lower than copper in the reactivity series are decomposed upon strong heating. For example
i. When a green hydrated solid of iron (II) sulphate is heated gently, it loses its water of crystallization which condenses on the cooler part of the test tube forming dirty yellow anhydrous solids of iron (II) sulphate.

image 402

On further heating, the anhydrous dirty yellow solids decompose giving off sulphur dioxide (which turn orange potassium dichromate green) in addition to white fumes of sulphur trioxide and leave a brown solid of iron (III) oxide.

image 403
image 405

Chemical test for sulphates
To the solution of the suspected sulphate in water, add barium chloride and dilute hydrochloric acid (barium nitrate solution and dilute nitric acid can also be used.) a white precipitate which is insoluble in excess acid indicates the presence of a sulphate.

image 406

Sulphur and its compounds

  1. Describe fully the changes which take place when powdered sulphur is gradually heated to its boiling point in the absence of oxygen. Mention briefly the proof that rhombic and monoclinic sulphur are allotropes.
  2. Describe the large scale extraction of sulphur. Describe the preparation and collection of gas jars of hydrogen sulphide starting from powdered sulphur. Describe an experiment to show the action of this gas as (a) a combustible substance (b) a reducing agent (c) an acid forming salt.
  3. What is the effect of heat on ferrous sulphate crystals? Make a drawing to show how you can convert sulphur dioxide to sulphur trioxide. What is the action of sulphur dioxide on (a) nitric acid (b) hydrogen sulphide (c) chlorine.
  4. Explain how sulphuric acid is manufactured on a large scale. Outline four large scale uses of the acid. Describe one experiment in each case to show how sulphuric acid acts as (a) an oxidizing agent (b) a dehydrating agent (c) a bleaching agent
  5. Give atleast five chemical properties of concentrated sulphuric acid. Why is this acid said to be dibasic? How can sulphates and sulphites be identified in the laboratory.
  6. Describe the preparation and collection of hydrogen sulphide. Give four chemical properties of the gas. What changes occur when the gas is bubbled through solutions of (a) copper sulphate (b) lead nitrate (c) chlorine. Write equations for the reactions.
  7. Make a labeled drawing of apparatus you would use to prepare sulphur dioxide. How does this gas react with (a) chlorine water (b) hydrogen sulphide (c) sodium hydroxide solution? How can sulphur dioxide be converted to sulphuric acid?
  8. Starting with roll sulphur, how can rhombic sulphur crystals, monoclinic sulphur crystals and plastic sulphur are obtained.