Identification of GasesYou have a sample of gas. You suspect it is carbon dioxide, but you are not sure. So you need to do a test. Below are some tests for common gases. Each is based on particular properties of the gas, including its appearance and some times its smell. Ammonia, NH3 Gas is lighter than air. Collect downward displacement of air. Properties Ammonia is a colourless alkaline gas with a pungent smell. Test Carefully smell gas, and hold damp indicator paper in it. Result Recognizable odour, and damp red litmus paper turns blue. Carbon dioxide,CO2 Gas is heavier than air. Collect the upward displacement of air or over water. Properties Carbon dioxide is colourless, weakly acidic gas. It reacts with lime water(a solution calcium hydroxide in water) to give a white precipitate of calcium carbonate). Turns damp blue litmus paper to red. CO2(g) + Ca(OH)2(aq) CaCO3(s) + H2O(l) Test Bubble the gas through lime water. Result Lime water turns cloudy or milky. Chlorine, Cl2 Gas is heavier than air. Collect the upward displacement of air.

Properties Chlorine is a green poisonous gas which bleaches dyes. Test Hold damp indicator paper in the gas, in a fume cupboard. Result Indicator paper turns white. (bleach) Hydrogen,H2 Gas is lighter than air. Collect downward displacement of air or over water. Properties Hydrogen is colourless.It combines violently with oxygen when ignite.tak care Test Collect the gas in a tube and hold a lighted splint to it. Result The gas burns with a squeaky pop.

Hydrogen chloride,HCl Gas is heavier than air. Collect the upward displacement of air.

Properties Hydrogen is a colourless, acidic gas with a choking smell. Turns damp blue litmus paper to red. It reacts with the alkali ammonia to form the salt ammonium chloride: HCl(g) + NH3(g) NH4Cl(s) Test Hold a rod dipped in concentrated ammonia solution in the gas,in a fume cupboard. Result A white ‘smoke’ of ammonium chloride form. Oxygen,O2 Gas is sparingly soluble in water. Density is equal to the air. over water method is used to collect. Properties Oxygen is colourless gas. Fuels burn much more readily in it than air. Test Collect the gas in a test tube and hold a glowing splint to it. Result The splint immediately bursts into flame. Sulphur dioxide,SO2 Gas is heavier than air. Collect the upward displacement of air. Properties Sulphur dioxide is a colourless gas. With a choking smell. Turns damp blue litmus paper to red. It reacts with acidified potassium dichromate solution, reducing the orange dichromate, Cr2O7

-2 to the green chromium ion Cr+3

3SO2 (g) + 2H+(aq) + Cr2O7-2(aq) 3SO4

-2 (aq) + H2O(l) + 2Cr+3(aq) acid orange solution green solution Test Hold a piece of filter paper soaked in acidified potassium dichromate solution in the gas, In a fume cupboard. Result The paper turns from orange to green. Hydrogen sulfide,H2S Hydrogen sulfide is a colourless gas. With a choking smell. Properties It reacts with acidified potassium chromate solution, reducing the yellow chromate, CrO4

-2 to the green chromium ion Cr+3

3H2S(g) + 2CrO4-2(aq) + 10H+(aq) S(s) + 2Cr+3(aq) + 8H2O(l)

Test Hold a piece of filter paper soaked in acidified potassium chromate solution in the gas, In a fume cupboard.

Result The paper turns from yellow to green

Test for Anions

Anion Test Test result Reactions that occur

Carbonate Add dilute Effervescence observed, CO3-2 + 2H+ CO2 + H2O

CO3-2 hydrochloric acid When gas evolved is

bubbled through limewater, Ca(OH)2 + CO2 CaCO3 + H2O a white precipitate is formed white The gas is carbon dioxide.

Chloride 1Add acidified 1White ppt formed, 1Ag+ + Cl- AgClCl- silver nitrate insoluble in dilute nitric acid whiteIn solution solution but soluble in dilute Ammonia. 2Add acidified 2A white ppt is formed. 2 Pb+2 + 2Cl- PbCl2 Lead(II)nitrate white solution

Bromide 1Add acidified 1Cream ppt formed, 1 Ag+ + Br- AgBr Br- silver nitrate Insoluble in dilute nitric acid creamIn solution solution but soluble in concentrated NH3not dilute NH3

2Add acidified 2Cream ppt formed. 2 Pb+2 + 2Br- PbBr2

Lead(II)nitrate cream solution

Iodide 1Add acidified 1Yellow precipitate is 1 Ag+ + I- AgII- AgNO3 formed, does not soluble yellow In solution in concentrated NH3.

2Add acidified 2Yellow ppt formed. 2 Pb+2 + 2I- PbI2

Pb(NO3)2 solution yellow

Nitrate Add aqueous Effervescence observed, NH3 + HCl NH4ClNO3

- NaOH then a pungent gas is producedIn solution aluminium powder, and it turns moist red litmus warm mixture. paper blue.

Gas also forms dense whitefumes with concentratedHCl.

Sulphate Acidify with dilute A white ppt is formed. Ba+2 + SO4-2 BaSO4

SO4-2 - nitric acid, then add white

In solution aqueous barium nitrate

Bicarbonate Add dilute Effervescence observed, HCO3- + H+ CO2 + H2O

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HCO3- hydrochloric acid when gas evolved is

bubbled through limewater, Ca(OH)2 + CO2 CaCO3 + H2O a white precipitate is formed white The gas is carbon dioxide.

1 A gas Y, is less dense than air, very soluble in water and is an alkali.Which method is used to collect a dry sample of the gas?

2 The diagram shows apparatus used to test the gases produced by burning coal.

Which substance is placed in tube R to show that sulphur dioxide is formed?A acidified potassium dichromate(VI)B aqueous potassium iodideC damp red litmus paperD limewater

3 An 80 cm3 sample of air is trapped in a syringe. The air is slowly passed over heated iron in a tube until there is no further decrease in volume.

When cooled to the original temperature, which volume of gas remains?A 80 cm3 B 64 cm3 C 20 cm3 D 16 cm3

4The equation for the reaction between aqueous lead(II) nitrate and aqueous potassium iodide is shown. Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)colourless colourless yellow colourlessWhich method could be used to separate the products?A chromatography B crystallization C distillation D filtration

5 Which of the following hazard warning signs should appear on a bottle of ethanol? A B C D

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6 Hydrogen chloride is very soluble in water, whereas chlorine is only slightly soluble in water. Both gases can be dried using concentrated sulphuric acid. Which diagram represents the correct method of obtaining dry chlorine from damp chlorine containing a small amount of hydrogen chloride?

A B

C D

7 An excess of hydrochloric acid is added to 0.10 mol of magnesium in the apparatus shown.

Why is it impossible to measure the total volume of hydrogen produced using this apparatus?

A Hydrogen is less dense than air.B Hydrogen is soluble in hydrochloric acid.C There is air in the tube.D The volume of hydrogen formed is greater than 100 cm3.

8A gas X is insoluble in water and less dense than air. An impure supply of X contains water vapour and a water-soluble impurity.

In which order should the pieces of apparatus shown be joined together to collect a pure, dry sample of X?A 1, 2, 3, 4 B 1, 2, 3, 5 C 1, 3, 2, 5 D 1, 3, 2,

9 Which method of preparation of a pure salt solution requires the use of a pipette and burette?

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A BaCl2(aq) + H2SO4(aq) BaSO4(s) + 2HCl (aq)B CuO(s) + 2HCl (aq) CuCl 2(aq) + H2O(l)C KOH(aq) + HCl (aq) KCl (aq) + H2O(l)D MgCO3(s) + H2SO4(aq) MgSO4(aq) + H2O(l) + CO2(g)

10 In an experiment 5 cm3 of 1.0 mol / dm3 sodium hydroxide are gradually added to10 cm3 of 1.0 mol / dm3 hydrochloric acid containing methyl orange.

Which change occurs in the mixture?A The concentration of the H+ ions increases. C More water molecules are formed.B A precipitate is formed. D The methyl orange changes colour.

11 A gas, X, is less dense than air and insoluble in water. Which method cannot be used to collect the gas?

12A student made some chlorine by the reaction between concentrated hydrochloric acid and potassium manganate(VII). Chlorine is more dense than air and soluble in water. Which of the following methods of collection is most suitable for chlorine?

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13 The diagram shows apparatus used to test the gases produced by burning coal.

Which substance is placed in tube R to show that carbon dioxide is formed?A aqueous potassium dichromate(VI) C aqueous potassium iodideB damp red litmus paper D limewater

14 This apparatus is used to show that a liquid hydrocarbon burns to produce water and carbon dioxide.

What are the most suitable substances to have at X and at Y?X Y

A anhydrous copper(II)sulphate lime waterB sodium hydroxide lime waterC sodium hydroxide universal indicator solutionD anhydrous copper(II)sulphate universal indicator solution

15 Aqueous hydrogen peroxide undergoes catalytic decomposition as shown in the equation below. 2H2O2(aq) 2H2O(l) + O2(g)The diagram shows part of the apparatus used to measure the rate of decomposition.

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Which piece of apparatus is connected at position X?A burette B gas syringe C measuring cylinder D pipette

16 The student was asked to produce a dry sample of a gas by passing it through a drying agent.Which apparatus should be used to dry the gas? A B C D

17 The diagram shows apparatus for measuring the volume of hydrogen given off when an excess of dilute hydrochloric acid is added to powdered metal. The volume of gas is measured at room temperature and pressure.

The experiment is carried out three times, using the same mass of powder each time but with different powders: pure magnesium pure zinc a mixture of magnesium and zincWhich powder gives the greatest volume of hydrogen and which the least volume?

greatest volume of hydrogen least volume of hydrogenA magnesium zincB magnesium the mixtureC zinc magnesiumD zinc the mixture

18Substance X melts at 53oC and boils at 100oC. It does not dissolve in water and it does not reactwith water. Which diagram shows the method most suitable for separating X from a mixture of X and water?

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21 The diagrams show mixtures of chemicals that react to produce gases.In which reaction will the litmus paper change colour?

A B C D

22 In an experiment, a student needs to measure out 36.50 cm3 of a solution.Which piece of apparatus would measure this volume most accurately?A beaker B burette C measuring cylinder D pipette

23 A student mixes 25 cm3 samples of dilute hydrochloric acid with different volumes of aqueous sodium hydroxide. Each time, the student measures the change in temperature to test if the reaction is exothermic.

Which piece of apparatus is not needed?

24 The apparatus shown can be used to prepare aqueous copper(II) sulphate.

What are substances X and Y?

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substance X substance YA copper iron(II)sulphateB copper(II)chloride sulphuric acidC copper(II)oxide sulphuric acidD sulphur copper(II)chloride

25 The reaction between solution P and solution Q is exothermic.A student is told to test this statement by mixing equal volumes of the two solutions andmeasuring the temperature change.Which two pieces of apparatus should the student use?A balance and clockB balance and thermometerC pipette and clockD pipette and thermometer

26 The word equation shows a chemical reaction.

What could substance Y be?

A copper(II) oxide B magnesium C sodium carbonate D sodium hydroxide27 Which piece of equipment can be used to show that a gas is hydrogen?

28 In an experiment to find the formula of magnesium oxide, magnesium metal is heated in a covered crucible.

Why is the crucible covered with a loose-fitting lid?A to prevent air escaping from the crucibleB to prevent magnesium carbonate formingC to prevent magnesium oxide escaping from the crucibleD to prevent water vapour entering the crucible

29 Which words in the table complete the following description of the preparation of copper(II) sulphate?An excess of copper(II) oxide was added to dilute sulphuric acid. The mixture was ——-1——to remove the excess of oxide. The solution was ——2—— to half its volume and then cooled, so that it ——-3—— .

1 2 3A distilled evaporated crystallised

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B distilled filtered evaporatedC filtered condensed crystallisedD filtered evaporated crystallised

30 The diagram shows a simple laboratory apparatus for the preparation and collection of a dry gas.

What is the gas?A carbon dioxide B chlorine C hydrogen D hydrogen chloride

31 Dry hydrogen gas is passed over a powdered solid and then through a cooled U-tube before the excess of hydrogen is burned in air.

A colourless liquid collects in the U-tube.What could the powdered solid be?A calcium oxide B copper(II) oxide C magnesium D zinc oxide

32 Lead(II) oxide is reduced in the apparatus shown.

How do the masses of parts X and Y of the apparatus change?X Y

A decreases decreasesB decreases increasesC increases decreases

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D increases increases

33 Anhydrous calcium chloride is used as a drying agent.An alkaline solution of pyrogallol absorbs oxygen and carbon dioxide.Clean air is passed through the apparatus shown.

Which gases are present in the air leaving the apparatus?argon nitrogen hydrogen

AB

C

D

34 Aqueous sodium hydroxide is added to two different solutions with the results shown.

Which cation is present in X and in Y?X Y

A ammonium iron(II)B copper(II) ammoniumC iron(II) copper(II)D iron(III) ammonium

35 Anhydrous calcium chloride is used as a drying agent. An alkaline solution of pyrogallol absorbs oxygen and carbon dioxide. Clean air is passed through the apparatus shown.

Which gases are present in the air leaving the apparatus?argon nitrogen hydrogen

ABCD

36 When hydrated copper(II) sulphate is heated in the apparatus shown, solid X and liquid Y are produced.

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Which changes are noticed when liquid Y is added to cold solid X?colour change heat change

A blue to white heat given outB blue to white heat taken inC white to blue heat given outD white to blue heat taken in

37 Which test method and gas are correctly linked?

test method gasA alighted splint oxygenB a glowing splint hydrogenC damp litmus paper chlorineD lime water ammonia

38 Which mixture can be separated by adding water, stirring and filtering?A barium chloride and sodium chlorideB copper and magnesiumC diamond and graphiteD silver chloride and sodium nitrate

39 Aqueous sodium hydroxide and aqueous ammonia each give a white precipitate when added toaqueous zinc sulphate.What happens when an excess of each of these reagents is added?

excess NaOH(aq) excess NH3(aq)A precipitate dissolves precipitate dissolvesB precipitate dissolves precipitate does not dissolveC precipitate does not dissolve precipitate dissolvesD precipitate does not dissolve precipitate does not dissolve

40 Aqueous sodium hydroxide is added to two different solutions with the results shown.

What are the cations present in X and Y?X Y

A copper(II) iron(II)B copper(II) iron(III)

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C iron(II) copper(II)D iron(III) copper(II)

41 In which experiment does the limewater not turn milky?

42 Aqueous lead(II) nitrate is added to a solution containing iodide ions. Lead(II) iodide is formed. Which type of reaction takes place?A neutralisation B oxidation C precipitation D reduction

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