8. Chemical analysis (purity, formulation, and chromatography)

Question 1

What is a pure substance?

Answer 1

A single element or compound, not mixed with any other substance

Question 2

What is a formulation?

Answer 2

A mixture of compounds in measured quantities that has been designed as a useful product

Question 3

Give examples of formulations?

Answer 3

• fuels
• cleaning agents
• skincare/cosmetic products
• medicines
• alloys

Question 4

Why are alloys a formulation?

Answer 4

they are a mixture of metals which are harder than pure metals, so have a particular purpose

Question 5

Describe the process of paper chromatography?

Answer 5

1. A start line is drawn in pencil near the bottom of the paper. The mixture is spotted on the line
2. A beaker is filled with a small amount of solvent, which cannot go above the start line when in the beaker
3. Paper is placed into the beaker
4. The solvent travels up the paper, separating the different components (dyes) in the ink
5. Before the solvent reaches the end of the paper, it is taken out and the solvent front is marked. The paper is dried

Question 6

What is the stationary phase in the chromotography experiment and why?

Answer 6

The paper, because it doesn’t move

Question 7

What is the mobile phase in the chromatography experiment and why?

Answer 7

The solvent, as it moves up the paper

Question 8

How is Rf calculated?

Answer 8

distance moved by the spot / distance moved by solvent

Question 9

What does a higher Rf value tell you about the solute?

Answer 9

The higher the Rf value, the more soluble the solute is in that solvent

Question 10

Describe the test for hydrogen?

Answer 10

1. Place a lit splint, in a test tube, in the presence of hydrogen
2. Squeaky pop indicates the presence of hydrogen

Question 11

Describe the test for oxygen?

Answer 11

1. Place a glowing splint, in a test tube, in the presence of oxygen
2. Relights in the presence of oxygen because the concentration of oxygen is higher in the test tube than in the air

Question 12

Describe the test for carbon dioxide?

Answer 12

1. Bubble carbon dioxide through limewater
2. Limewater turns milky or cloudy white in the presence of carbon dioxide
3. This turns cloudy due to the formation of calcium carbonate

Question 13

Describe the test for chlorine?

Answer 13

1. Place blue damp litmus paper in the presence of chlorine
2. This turns the litmus paper red if chlorine is present
3. This bleaches to white later on

Question 14

Why is the Rf value always less than 1?

Answer 14

because the distance travelled by the solute is always less than the distance travelled by solvent

Question 15

What does a Rf value of 0.85 tell you about the solute?

Answer 15

Because the solute travels up a greater distance of the paper, the solute has a higher affinity to the solvent than the paper

Question 16

Describe the flame test results

Answer 16

• Lithium compounds: crimson red flame
• Sodium compounds: yellow flame
• potassium compounds: lilac flame
• calcium compounds: brick red flame
• copper compounds: green flame

Question 17

What are instrumental methods?

Answer 17

they are accurate, sensitive and rapid methods which are useful when the amount of sample is very small

Question 18

What are cations and anions?

Answer 18

• cations - positive ions
• anions - negative ions

Question 19

What is the test for hydrogen?

Answer 19

squeaky pop test

Question 20

What is the test for oxygen?

Answer 20

relit splint test

Question 21

What is the test for carbon dioxide?

Answer 21

limewater test

Question 22

What is the test for chlorine?

Answer 22

litmus paper test