Paper 2 - Chemical Analysis

Question 1

How can we test for purities?

Answer 1

A chemically pure substance will =
Melt at a specific temperature
Boil at a specific temperature

Question 2

How can we test for impurities?

Answer 2

An impurity will:
Have a lower melting point and increase melting range
Increase boiling point and increase boiling range

Question 3

What is a formulation?

Answer 3

A formulation is a useful mixture with a precise purpose

Question 4

What are examples of formulations?

Answer 4

Examples of formulations include :

Metal alloys, cleaning products, medicines, food

Question 5

What is the stationary phase in chromatography?

Answer 5

In chromatography, the stationary phase is when the molecules can’t move

Question 6

What is the mobile phase in chromatography?

Answer 6

The mobile phase in chromatography is when the molecules can move ( the solvent)

Question 7

What is chromatography?

Answer 7

Chromatography is used to separate substances in a mixture

Question 8

What is the process of chromatography?

Answer 8

Chromatography:

1) . The substances dissolve in mobile phase
2) . Mobile phase moves through stationery phase
3) . Substances that are more soluble in mobile phase or less attracted to stationary phase move futher

Question 9

How can we test for hydrogen?

Answer 9

We can test for hydrogen when a lighted splint burns quickly with a pop (“squeaky pop test”)

Question 10

How can we test for oxygen?

Answer 10

We can test for oxygen by relighting a glowing splint

Question 11

How can we test for chlorine?

Answer 11

We can test for chlorine with litmus paper, where the litmus paper will turn white in chlorine gas

Question 12

How can we test for carbon dioxide?

Answer 12

We can test for carbon dioxide when limewater turns cloudy in presence of CO2 gas

Question 13

How can we test for carbonates?

Answer 13

Test for carbonates:

1) . Add a couple of drops of dilute acid
2) . Connect the test tube to a tube of lime water
3) . Carbonatic ions react to form CO2 which turns lime water cloudy

Question 14

How can we test for halides? (BRINCLHOF elements)

Answer 14

We can test for halides by adding dilute nitric acid followed by silver nitrate solution to mystery solution

Question 15

In the halide test, what will chloride show as?

Answer 15

Chloride has a white precipitate during the halide test

Question 16

In the halide test, what will bromide show as?

Answer 16

Bromide will have a cream precipitate in the halide test

Question 17

In the halide test, what will iodide show as?

Answer 17

Iodide will have a yellow precipitate in the halide test

Question 18

What are the advantages of instrumental analysis? (flame emission spectroscopy)

Answer 18

The advantages of instrumental analysis are that it is sensitive (meaning it can detect tiny amounts), it’s fast and it’s accurate

Question 19

What is flame emission spectroscopy?

Answer 19

Flame emission spectroscopy identifies ions in a solution (Each ion has a unique spectrum) and determines the concentration of ions

Question 20

What colour will the lithium, sodium, potassium, calcium and copper flames appear as in flame tests for metal cations? (each)

Answer 20

Lithium = Red flame
Sodium = Yellow flame
Potassium = Purple flame
Calcium = Orange flame 
Copper = Green flame

Question 21

What is the symbol for a reversible reaction?

Answer 21

The symbol for a reversible reaction is ⇌ (two arrows pointing away from each other)

Question 22

Complete the sentence: Equilibrium is reached when the forward and reverse reactions happen at exactly the same ____

Answer 22

rate

Question 23

How do you find the rf value in chromatography?

Answer 23

You can find the rf value in chromatography by dividing the distance of the substance by the distance of the solvent

Question 24

Plan out a chromatography experiment to investigate the colours in an ink

Answer 24

Chromatography experiment:

1) . put dots of known colours and ink on pencil line on chromatography paper
2) . place edge of the paper in water (the line is above the water )
3) . leave for the solvent to rise up through the paper
4) . when the solvent is near the top of the paper, remove and leave to dry
5) . compare positions of dots for known colours with that ink

Question 25

Explain how paper chromatography separates the dyes in food colours (do not give details of how to do the experiment)

Answer 25

Paper chromatography separates dyes in food colouring as dyes move at different rates and different dyes have different solubilities

Question 26

How can you tell there is more than one dye in an ink during a chromatography experiment?

Answer 26

You can tell there is more than one dye in an ink during a chromatography experiment as there will be more than one spot produced in a vertical column

Question 27

How can you use chromatography to identify unknown dyes in food colouring?

Answer 27

You can use chromatography to identify unknown dyes in food colouring as you can compare the rf values and you can identify that the ones which move the same distance are the known dyes