Unit 19- testing ions and gases

Question 1

Test for carbon dioxide

Answer 1

Bubble the gas through limewater. Lime water turns cloudy or milky

Question 2

Test for ammonia gas. Chemical symbol for ammonia

Answer 2

Hold damp red litmus paper, the indicator turns blue. NH3

Question 3

Test for chlorine, explain why you can’t do the test in an open area.

Answer 3

Hold damp indicator in the gas, in a fume cupboard. Indicator paper turns white. Chlorine is a toxic gas.

Question 4

Test for hydrogen

Answer 4

Collect the gas in a test tube and hold a lighted splint to it. The gas burns with a squeaky pop.

Question 5

Test for oxygen

Answer 5

Collect the gas in a test tube and hold a glowing splint to it. The splint immediately bursts into flame.

Question 6

Test for Sulfur dioxide

Answer 6

Soak a piece of filter paper in acidified aqueous potassium manganate(VII). Place it in the gas. The colour on the paper changes from purple to colourless.

Question 7

Test for water, give two possible methods.

Answer 7

1) using anhydrous copper(ii) sulfate powder. If water is present, there will be a colour change from white to blue.
2) using anhydrous cobalt (ii) chloride, if water is present, there will be a colour change from blue to pink

Question 8

Describe steps for flame test

Answer 8

Clean a platinum wire by dipping into concentrated HCl acid, and hold it in a hot bursen flame. Moisten the clean wire by dipping into the acid again. Then dip into the salt, so that some sticks to it. Hold it in the burden flame, and observe the colour.

Question 9

Colour of the flame for Lithium-ion, Li +

Answer 9

red

Question 10

Colour of the flame for Sodium-ion, Na +

Answer 10

orange-yellow

Question 11

Colour of the flame for potassium ion, K +

Answer 11

lilac

Question 12

Colour of the flame for Copper ion, Cu 2+

Answer 12

blue-green

Question 13

Test for ammonium ion. NH4 + and its positive result.

Answer 13

Add dilute aqueous sodium hydroxide. Heat gently. Ammonia gas is given off.( it turns litmus blue)

Question 14

Test for copper(ii) ion. Cu 2+ and its positive result.

Answer 14

Add dilute aqueous sodium hydroxide.pale blue precipitate, adding more no effect.
Add aqueous ammonia. pale blue precipitate, adding more gives a deeper blue solution.

Question 15

Test for iron(ii) ion. Fe 2+ and its positive result.

Answer 15

Add dilute aqueous sodium hydroxide or aqueous ammonia. pale green precipitate.

Question 16

Test for iron(iii) ion. Fe 3+ and its positive result.

Answer 16

Add dilute aqueous sodium hydroxide or aqueous ammonia. Red-brown precipitate.

Question 17

Test for aluminium ion. Al 3+ and its positive result.

Answer 17

Add dilute aqueous sodium hydroxide. white precipitate, adding more gives colourless solution.
Add aqueous ammonia. White precipitate, adding more no effect.

Question 18

Test for zinc ion. Zn 2+ and its positive result.

Answer 18

Add dilute aqueous sodium hydroxide. white precipitate, adding more colourless solution
Add aqueous ammonia. White precipitate, adding more colourless solution.

Question 19

Test for calcium ion. Ca 2+ and its positive result.

Answer 19

Add dilute aqueous sodium hydroxide. white precipitate, adding more no effect.
Add aqueous ammonia. No precipitate.

Question 20

Test for chromium ion. Cr 3+ and its positive result.

Answer 20

Add dilute aqueous sodium hydroxide. grey-green precipitate, adding more give green solution.
Add aqueous ammonia. grey-green precipitate, adding more no effect

Question 21

Test for halide ions

Answer 21

To a small amount of the solution, add an equal volume of dilute nitric acid. Then add aqueous silver nitrate. Silver halides are insoluble. If there are halide ions, a precipitate will form.

Question 22

For halide test, if the precipitate is white, which ion does it contain?

Answer 22

Cl -

Question 23

For halide test, if the precipitate is cream, which ion does it contain?

Answer 23

Br -

Question 24

For halide test, if the precipitate is yellow, which ion does it contain?

Answer 24

I -

Question 25

Test for sulfate ions SO4 2-

Answer 25

To a small amount of solution add an equal volume of dilute HCl acid. Then add barium nitrate solution. Barium sulfate is insoluble, if there are sulfate ions,white precipitate will form.

Question 26

Test for Sulfite ions SO3 2-

Answer 26

To a small amount of solution add an equal volume of dilute HCl acid. Heat the mixture, sulfur dioxide is given off. Test for SO2

Question 27

Test for nitrate ions NO3 -

Answer 27

To a small amount of solution or solid add little dilute aqueous sodium hydroxide, and then small pieces of aluminium foil. Heat gently, ammonia gas is given off. Test for ammonia gas

Question 28

Test for carbonate ions CO3 2-

Answer 28

To a small amount of the solid, add a little dilute HCl acid. CO2 is given off. Test for CO2