Topic 10 - Analysis

Question 1

what are flame tests used for?

Answer 1

You can carry out a flame test to test for metal ions within compounds.

Question 2

how are flame tests carried out

Answer 2

• clean a nichrome wire loop by dipping in hydrochloric acid and rinsing with distilled water
• dip the loop into the sample you want to test
• put it in the clear blue part of the flame
• record colour of flame

Question 3

potassium flame test colour

Answer 3

lilac

Question 4

cooper flame test colour

Answer 4

green

Question 5

sodium flame test colour

Answer 5

yellow

Question 6

lithium flame test colour

Answer 6

crimson - red

Question 7

calcium flame test colour

Answer 7

orange - red

Question 8

Precipitation reaction

Answer 8

• the metal hydroxide formed is insoluble and precipitates out of solution when formed
• add Sodium Hydroxide to solution of metal ions and note down the colour of precipitate

Question 9

calcium precipitate

Answer 9

white

Question 10

copper precipitate

Answer 10

blue

Question 11

iron ( Fe2+) precipitate

Answer 11

green

Question 12

iron ( Fe3+ ) precipitate

Answer 12

brown

Question 13

aluminium precipitate

Answer 13

white , redissolves in excess NaOH to become colourless

Question 14

Ammonium ions test (NH4+)

Answer 14

• hold a piece of damp, red litmus paper over ammonia gas
• if the gas is ammonia, it will turn blue

Question 15

testing for Carbonate ions

Answer 15

• if you add acid to a carbonate it should react to produce carbon dioxide gas as one of its products
• bubble the gas produced through limewater
• if the limewater turns cloudy it is a carbonate

Question 16

testing for Halide ions

Answer 16

• add dilute nitric acid to get rid of any carbonate impurities
• add silver nitrate solution
• it should form a precipitate in solution

Question 17

chloride precipitate

Answer 17

white

Question 18

bromide precipitate

Answer 18

cream

Question 19

iodide precipitate

Answer 19

yellow

Question 20

testing for sulfate ions

Answer 20

• add dilute hydrochloric acid to get rid of any carbonate impurities
• add barium chloride to it.
• it should produce a white precipitate of barium sulfate

Question 21

what is Flame photometry?

Answer 21

An instrumental method that allows you to identify metal ions by viewing the light the ions emit through a spectroscope

Question 22

About the spectroscope

Answer 22

each ion produces a unique line spectrum on the spectroscope, and if there are two or more ions, it shows the line spectrums for all the ions

Question 23

why is flame photometry more useful than flame tests?

Answer 23

it can be used to identify more than 1 ion in a mixture, whereas flame tests only work for substances that contain a single metal ion

Question 24

advantages of using machines

Answer 24

• very sensitive
• very fast
• can be automated
• very accurate
• no room for human error