Tests for ions

Question 1

What is the flame test colour for lithium?

Answer 1

Red

Question 2

What is the flame test colour for sodium?

Answer 2

Yellow

Question 3

What is the flame test colour for potassium?

Answer 3

Lilac

Question 4

What is the flame test colour for calcium?

Answer 4

Orange/red

Question 5

What is the flame test colour for copper?

Answer 5

Blue/green

Question 6

What should you do between each flame test?

Answer 6

Clean the flame test loop in acid

Question 7

What colour hydroxide precipitate does copper make?

Answer 7

Blue

Question 8

What colour hydroxide precipitate does iron make?

Answer 8

Green when it is Fe2+ and brown when it is Fe3+

Question 9

What is the test for sulfate ions?

Answer 9

Add dilute Hcl to a test tube and then add barium chloride, if sulfate ions are present then a white precipitate will be formed (barium sulfate)

Question 10

What is the test for carbonate ions?

Answer 10

Add acid to a test tube that might contain carbonate ions, if carbonate ions are present then bubbles of carbon dioxide will appear. We can test to see if this is carbon dioxide by adding lime water, it will turn milky if carbon dioxide is present

Question 11

What is the test for halide ions?

Answer 11

Add nitric acid to a test tube and then add silver nitrate solution, if chloride ions are present then a white precipitate will appear, if bromide ions are present then a cream precipitate will appear, if iodide ions are present then a yellow precipitate will appear

Question 12

What is the test for ammonium ions?

Answer 12

Add sodium hydroxide solution to a test tube, if ammonium ions are present then ammonium gas is produced. You can test for ammonia gas using damp red litmus paper as it will turn blue if ammonia gas is present. You could also test for it by adding hydrochloric acid, white smoke will be formed if ammonia gas is present

Question 13

What is the ionic equation for the reaction between ammonium ions and sodium hydroxide solution?

Answer 13

NH4+ (aq) + OH- (aq) → H2O (l) + NH3 (g)

Question 14

What are instrumental methods of analysis?

Answer 14

Methods of analysis for substances that use machines

Question 15

What are the advantages of instrumental methods?

Answer 15

• They’re sensitive, they can detect very small amounts of a substance
• They’re accurate, they measure amounts of different substances very accurately
• The tests are very quick, they carry out the analysis very quickly and the machines can run all the time

Question 16

Give some examples of instrumental methods

Answer 16

• Mass spectrometry, this measures relative atomic mass and identifies compounds
• Infared spectroscopy, detects covelant bonds and identifies compounds
• Gas chromotography, measures amounts of each component in mixtures

Question 17

What is flame photometry?

Answer 17

An instrumental method of analysis based on flame tests:

• The sample is vapourised in a hot flame
• A spectrum of the light emitted by metal ions is produced
• The brightness of a particular wavelength is measured

Question 18

What can flame photometry be used to do?

Answer 18

• Identify the metal ions present in the sample by comparing the spectrum with a reference spectrum from a known substance
• Determine the concentration of ions in a solution using a calibration curve