Qualitative Analysis

Question 1

What is the method used to conduct a flame test?

Answer 1

• clean a metal loop with concentrated acid
• check the loop is clean by passing it through a blue flame until no colour is present as repeat till clean so the colour is purer
• place the clean loop in the sample and pass it through the flame to record a colour

Question 2

Why do flame test work and why are they unique?

Answer 2

Each test must be unique as its results depend on the ion present, without this you couldn’t distinguish between them

Question 3

When colour flame does sodium go?

Answer 3

Yellow

Question 4

What colour flame does lithium go?

Answer 4

Red

Question 5

What colour flame does potassium go?

Answer 5

Lilac

Question 6

What colour flame does calcium go?

Answer 6

Orange-red

Question 7

What colour flame does copper go?

Answer 7

Blue/ green

Question 8

Why can the use of machines be both better and worse for this process?

Answer 8

• faster and multiple repeats making them more reliable
• more sensitive for smaller samples
• more accurate as they offer quantitive data
• machines are expensive and require further expenses for training to work them
• time and money for calibration/maintenance

Question 9

How do you carry our a precipitate test?

Answer 9

• they involve reacting sodium hydroxide with a cation solution
• different metal ions produce different coloured hydroxide precipitates and can have varying effects if this is added in excess or just a few drops

Question 10

What does aluminium form in a precipitate reaction?

Answer 10

• white precipitate

- if added in excess dissolves to form a colourless solution

Question 11

What does calcium form in a precipitate reaction?

Answer 11

• white precipitate

- no change

Question 12

What does copper form in a precipitate reaction?

Answer 12

• blue precipitate

- no change

Question 13

What does iron (11) form in a precipitate reaction?

Answer 13

• dirty green precipitate

- no change

Question 14

What does iron(111) form in a precipitate reaction?

Answer 14

• red/brown precipitate

- no change

Question 15

What is the chemical test for ammonium ions?

Answer 15

• add dilute sodium hydroxide solution
• ammonia gas NH3 is produced when the mixture containing ammonium ions is warmed
• this forms a sharp smell (can be toxic) and changes the colour of damp red litmus paper blue

Question 16

How do you test for a carbonate?

Answer 16

• add acid to the compound and if carbonate ions are present they will turn limewater from clear and colourless to milky
• it should also fizz as the two will react to produce carbon dioxide gas

Question 17

How do you test for sulphate ions?

Answer 17

• add some hydrochloric acid to the substance to remove contaminants
• add barium nitrate solution and if present a white precipitate will form

Question 18

How do you test for halide ions?

Answer 18

• add nitric acid to a substance to remove contaminants
• then add silver nitrate solution to test
• if chloride is present a grey/white precipitate will form, bromide will form a cream precipitate, iodide will give a yellow precipitate

Question 19

What is flame photometry?

Answer 19

An instrumental method that allows you to identify ions in a dilute solution as each ions produces a unique line spectra

• the intensity of the measured wavelength indicates the concentration of that ion in the solution using a calibration curve
• they can be used to identify ions in mixtures making them more useful than flame tests that only work on a single metal ion