Flame Tests

Question 1

Flame tests are used to test for…

Answer 1

cations - metal ions

Question 2

Steps for a flame test:

Answer 2

1. take a nichrome wire loop
2. clean it by dipping it into hydrochloric acic, then rinsing it in distilled water before running it through the bunsen burner.
3. dip the wire loop into the compound you want to test for
4. hold the wire in the blue part of a bunsen burner
5. see what colour the flame burns

Question 3

a limitation of flame tests

Answer 3

A limitation of the flame test is that if you have 2 or more different metals in your sample, then the colours of the flames will mix together, and you probably won’t be able to tell which metals you have.

Question 4

colours flame test

Answer 4

sodium - yellow
lithium - crimson
potassium - lilac
copper - green
calcium - orange-red

Question 5

Alternative to flame tests:

Answer 5

Another test we can do for metal ions is react them with a solution of sodium hydroxide (NaOH), and see what colour the solution turns.

This is possible because some metal ions form coloured precipitates when they react with hydroxide ions, and these coloured precipitates then determine the colour of the solution.

Question 6

copper and hydroxide ions

Answer 6

blue

Question 7

calcium and hydroxide ions

Answer 7

white

Question 8

iron II and hydroxide ions

Answer 8

green

Question 9

magnesium and hydroxide ions

Answer 9

white

Question 10

aluminium and hydroxide ions

Answer 10

initially white, but if the solution is in excess, it might turn colourless

Question 11

iron III and hydroxide ions

Answer 11

brown

Question 12

comparing metals with flame tests can be difficult…

Answer 12

since they might have similar colours/ a sample may have multiple different metals

Question 13

Instead of a flame test we can use a….

Answer 13

spectroscope in a test called flame emission spectroscopy

Question 14

every metal ion produces…

Answer 14

a different pattern of wavelengths

Question 15

the main advantage of flame emission spectroscopy is…

Answer 15

if there are multiple metal ions in a sample, the spectrum will show the lines for all of them.

Question 16

if scientists have a sample of an unknown metal then they can compare that to the spectrum of known metals and figure out what ions they are composed of.

Answer 16

through this they can also find the concentration of ions

Question 17

Pros and cons of flame tests (manual method) and flame emission spectroscopy (instrumental method)

Answer 17

instrumental:

very accurate/ fast/ sensitive

manual:

basic and cheap