rp 7 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 u want to test and put it into the blue flame of the Bunsen burner
• record the colour of the flame

Question 2

list precautions to take when using a bunsen burner

Answer 2

• dont leave unattended
• turn off gas or leave on orange safety flame when not in use
• tie back long hair
• keep flammable chemicals away from the flame

Question 3

why must the wire be cleaned before carrying out a flame test?

Answer 3

to remove any unwanted ions that might obscure the colour of the flame

Question 4

why can a flame test not be used when a compound contains a mixture of metal ions?

Answer 4

the flame colours of some ions may be hidden by the colours of other metal ions

Question 5

how can u test for carbonate ions?

Answer 5

• add a few drops of HCL to the sample in a test tube
• connect this test tube to a test tube of limewater
• if carbonate ions are present, carbon dioxide will be produced. Limewater will turn cloudy when CO2 is bubbled through.

Question 6

write the chemical equation for the reaction between HCL and Na2CO3

Answer 6

Na2CO3 + 2HCL -> CO2 + NaCl + H2O

Question 7

how can u test for sulphate ions?

Answer 7

• add HCL to remove any CO32- ions as these will obscure the results.
• add a couple of drops of barium chloride
• if sulfate ions are present a white precipitate of barium sulfate will form

Question 8

write the chemical equation for the reaction between BaCl2 and MgSO4

Answer 8

BaCl2 + MgSO4 -> BaSO4 + MgCl2

BaSO4 is a white precipitate

Question 9

how do u carry out a test for halide ions?

Answer 9

• add a couple of drops of nitric acid to react with any carbonate ions which might obscure the experiment
• add a couple of drops of silver nitrate
• observe the colour of the precipitate

Question 10

what colour precipitate is formed when silver nitrate as added to a chloride solution?

Answer 10

white precipitate of silver chloride

Question 11

what colour precipitate is formed when silver nitrate is added to a bromide solution?

Answer 11

cream precipitate of silver bromide

Question 12

what colour precipitation is formed when silver nitrate is added to an iodine solution

Answer 12

yellow precipitate of silver iodide

Question 12

what colour precipitation is formed when silver nitrate is added to an iodine solution

Answer 12

yellow precipitate of silver iodide

Question 13

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

Answer 13

white precipitate

Question 14

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

Answer 14

blue precipitate

Question 15

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

Answer 15

green precipitate

Question 16

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

Answer 16

brown precipitate

Question 17

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

Answer 17

white precipitate at first

Redissolves with excess NaOH to form a colourless solution

Question 18

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

Answer 18

white precipitate

Question 19

given 2 solutions, how can you identify which contains aluminium ions and which contains magnesium ions?

Answer 19

add excess sodium hydroxide

both will form white precipitates but the one containing aluminium ions will redissolve to form a colourless solution