chemistry - identifying ions

Question 1

how do you carry out a flame test to identify metal ions?

Answer 1

• clean a platinum wire loop by dipping it in HCl and then holding it in the blue flame until it burns without any colour
• dip the loop into the sample you want to test and place into the blue flame of a bunsen burner
• record the colour change

Question 2

what is each result of a flame test?

Answer 2

lithium - crimson red
sodium - yellow
potassium - lilac
calcium - orange/red
copper (2+) - green

Question 3

what is the acronyms to remember the flame tests?

Answer 3

ions: Lively Snakes Paint Colourful Chickens
colours: Crazy Yellow Lions Offer/Real Greatness

Question 4

how to test for carbonate ions?

Answer 4

• add a few drops of HCl to the sample in a test tube
• connect this test tube to a test tube of limewater (calcium hydroxide)
• if carbonate ions are present, the limewater will turn cloudy, as carbon dioxide is produced

Question 5

how to test for sulphate ions?

Answer 5

• add HCl to remove any other ions as this will impact the results
• add barium chloride
• if sulphate ions are present, a white precipitate is formed

Question 6

how to carry out a test for halide ions?

Answer 6

• add a couple drops of nitric acid to react any carbonate ions that are present
• add a few drops of silver nitrate
• observe the colour of the precipitate

Question 7

what is the colour of each precipitate when silver nitrate is added to a bromide solutions?

Answer 7

chloride ions - white
bromide ions - cream
iodide ions - yellow

Question 8

what colour precipitate forms when sodium hydroxide reacts with calcium ions?

Answer 8

white precipitate

Question 9

what colour precipitate forms when sodium hydroxide reacts with copper (II) ions?

Answer 9

blue precipitate

Question 10

what colour precipitate forms when sodium hydroxide reacts with iron (II) ions?

Answer 10

green precipitate

Question 11

what colour precipitate forms when sodium hydroxide reacts with iron (III) ions?

Answer 11

brown precipitate

Question 12

what colour precipitate forms when sodium hydroxide reacts with aluminium ions?

Answer 12

• white precipitate at first
• redissolves with excess NaOH to form a colourless solution

Question 13

what colour precipitate forms when sodium hydroxide reacts with magnesium ions?

Answer 13

white precipitate

Question 14

given two solutions, how can you identify which contains aluminium ions and which contains magnesium ions?

Answer 14

• add excess sodium hydroxide
• both will form white precipitates but the one containing aluminium ions will redissolve to form a colourless solution