SC25

Question 1

What are flame tests used for?

Answer 1

To identify the metal ions in a substance.

Question 2

What material is the wire loop used to conduct the experiment typically made out of?

Answer 2

nichrome alloy

Question 3

What colour is lithium in the flame test?

Answer 3

red

Question 4

What colour is sodium in the flame test?

Answer 4

yellow

Question 5

What colour is calcium in the flame test?

Answer 5

orange-red

Question 6

What colour is copper in the flame test?

Answer 6

blue-green

Question 7

What colour is potassium in the flame test?

Answer 7

lilac

Question 8

What may using scientific instruments improve?

Answer 8

• sensitivity (able to detect small amounts)
• accuracy (gives values closer to true values)
• speed
• qualitative

Question 9

What does a flame photometer do?

Answer 9

measure the light intensity given off by a flame produced by metal ions which determines the concentration of it in a solution.

Question 10

Do flame tests work with solids or solutions?

Answer 10

It works with both however it is easier to see colours from a solid.

Question 11

How do you retrieve data for a calibration curve from a flame photometer?

Answer 11

Using different standard solutions, each containing a known concentration of the same metal ion dissolved in distilled water, calibration curve data can be retrieved by using the flame photometer with each solution.

Question 12

In precipitation reactions, what colour is the precipitate of iron(II)?

Answer 12

green

Question 13

In precipitation reactions, what colour is the precipitate of iron(III)?

Answer 13

brown

Question 14

In precipitation reactions, what colour is the precipitate of copper?

Answer 14

blue

Question 15

In precipitation reactions, what colour is the precipitate of calcium?

Answer 15

white

Question 16

In precipitation reactions, what colour is the precipitate of aluminium?

Answer 16

white

Question 17

What are the three tests to detect ammonium ions?

Answer 17

• damp red litmus paper turns blue
• adding dilute sodium hydroxide to ammonia forms ammonia gas(NH4) which has a strong odour/choking smell
• a glass rod dipped in HCL held near the ammonia should form a white smoke of ammonium chloride.

Question 18

How can calcium and aluminium be identified if they have the same colour hydroxide precipitates?

Answer 18

adding sodium hydroxide to aluminium forms a colourless solution (aluminium hydroxide) whereas calcium hydroxide doesn’t form a colourless solution.

Question 19

What is the test for carbonates (CO3)?

Answer 19

Add HCl and look out for bubbling caused by CO2. The bubbling could be due to other gases like hydrogen so to confirm that its CO2, conduct limewater test to ensure it is milky white.

Question 20

What is the test for sulfates?

Answer 20

Add dilute HCl to the solution. Add barium chloride and a white precipitate of barium sulfate should form.

Question 21

What is the test for halide ions (not including fluoride ions)?

Answer 21

Add nitric acid to the solution then add silver nitrate. Different halides will form different coloured precipitates.

Question 22

Why is HCl added to the test for carbonates and the test for sulfates? (same reason why nitric acid is added to the halide test)

Answer 22

To acidify the solution and kill of any carbonates that may give off precipitates and deter the experiment.

Question 23

Why does the test for halide ions not include fluoride ions?

Answer 23

All halide ions besides fluoride are insoluble. Insolubility is needed for a precipitate to form.

Question 24

What is the precipitate colour of chloride?

Answer 24

white

Question 25

What is the precipitate colour of bromide?

Answer 25

cream

Question 26

What is the precipitate colour of iodide?

Answer 26

yellow

Question 27

What is the precipitate test for metal ions?

Answer 27

Adding dilute sodium hydroxide to the test solutions should form different coloured metal hydroxide precipitates.

Question 28

When using wooden splints for flame tests, what is done to it and why?

Answer 28

It is dipped in distilled water to ensure the splint doesn’t burn. Distilled water must be used and not tap water as tap water has different ions that can interfere with the test.