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Question 1

What does purity mean in chemistry?

Answer 1

A pure substance contains only one compound or element throughout and is not mixed with anything else.

In everyday terms, purity may refer to natural states like pure milk or beeswax, but in chemistry, it is more specific.

Question 2

How can you determine the purity of a substance using its boiling or melting point?

Answer 2

A chemically pure substance will melt or boil at a specific temperature. Impurities lower the melting point and widen the melting range, while they increase the boiling point and may cause a boiling range.

The closer the measured melting or boiling point is to the known value, the purer the sample.

Question 3

What are formulations?

Answer 3

Formulations are mixtures designed for a particular use, made by following a specific recipe with carefully measured components.

Examples include paints, cleaning products, fuels, and medicines.

Question 4

What are the components of paint as a formulation?

Answer 4

Paint is made up of:
* Pigment
* Solvent
* Binder
* Additives

Each part serves a specific purpose, such as giving color or altering viscosity.

Question 5

What is chromatography?

Answer 5

Chromatography is a method used to separate different components in a mixture.

It involves a mobile phase and a stationary phase.

Question 6

What role does the solvent play in paper chromatography?

Answer 6

The solvent moves up the paper, carrying the substances with it, allowing for the separation of components based on solubility.

The more soluble a chemical is in the solvent, the further it will travel.

Question 7

True or False: Impurities in a sample can make the melting point more consistent.

Answer 7

False

Impurities typically widen the range of melting points.

Question 8

Fill in the blank: In everyday life, formulations can be found in _______.

Answer 8

cleaning products, fuels, medicines, cosmetics, fertilisers, metal alloys, food and drink.

These formulations are tailored for specific applications.

Question 9

What happens to the spots in chromatography if you repeat the experiment?

Answer 9

The spots should remain consistent in position and size, indicating reproducibility of the results.

Variability in results may indicate issues with the sample or technique.

Question 10

Why is knowing if a product is pure important?

Answer 10

It is crucial for the production of medicines and food to ensure safety and effectiveness.

Chemists utilize various methods to verify the purity of substances.

Question 11

What is chromatography?

Answer 11

A method used to separate the substances in a mixture

Chromatography can also be used to identify the substances.

Question 12

What are the two phases of chromatography?

Answer 12

• Mobile phase
• Stationary phase

In paper chromatography, the mobile phase is a solvent, and the stationary phase is the paper.

Question 13

What is the mobile phase in paper chromatography?

Answer 13

A solvent (e.g. water or ethanol)

The mobile phase allows molecules to move.

Question 14

What is the stationary phase in paper chromatography?

Answer 14

The paper

The stationary phase does not allow molecules to move.

Question 15

What does the solvent do in paper chromatography?

Answer 15

Moves up the paper and carries substances in the mixture with it

This movement allows for the separation of different chemicals.

Question 16

What is ‘distribution’ in chromatography?

Answer 16

The amount of time a chemical spends dissolved in the solvent or stuck on the paper

This affects how far the chemical moves up the paper.

Question 17

What happens to more soluble chemicals during chromatography?

Answer 17

They spend more time dissolved in the solvent and move further up the paper

This results in a higher position on the chromatogram.

Question 18

What is a chromatogram?

Answer 18

A visual representation showing the results of chromatography experiments

It displays different spots for different chemicals.

Question 19

What is the solvent front in chromatography?

Answer 19

The furthest point reached by the solvent during a chromatography experiment

It indicates how far the solvent has traveled.

Question 20

What does it mean if a chromatogram shows only one spot?

Answer 20

There is only one chemical in the substance, indicating it is pure

This should be consistent across different solvents.

Question 21

What does it indicate if a substance shows multiple spots on a chromatogram?

Answer 21

The substance contains at least that many different chemicals

For example, three spots indicate at least three chemicals.

Question 22

What happens if you repeat chromatography with a different solvent?

Answer 22

You will get a different chromatogram

The spots may travel different distances compared to the solvent front.

Question 23

Fill in the blank: The more soluble a chemical is, the more time it spends _______.

Answer 23

dissolved in the solvent

Question 24

True or False: You can see the chemicals moving between the two phases in chromatography.

Answer 24

False

The movement occurs but is not visible.

Question 25

What is the Rf value in chromatography?

Answer 25

The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent. ## Footnote Rf stands for 'retention factor' and is a key measurement in chromatography.

Question 26

How does the distance a substance moves through the stationary phase relate to its Rf value?

Answer 26

The further a substance moves through the stationary phase, the larger the Rf value.

Question 27

What is the formula to calculate the Rf value?

Answer 27

Rf = distance moved by substance (B) / distance moved by solvent (A)

Question 28

Calculate the Rf value if the distance moved by the substance is 29 mm and the distance moved by the solvent is 41 mm.

Answer 28

Rf = 29 mm / 41 mm = 0.70731... = 0.7 ## Footnote Give the answer to the smallest number of significant figures in the calculation.

Question 29

What happens to the Rf value of a chemical if the solvent is changed?

Answer 29

The Rf value of a chemical will change if you change the solvent.

Question 30

How can chromatography be used to identify substances in mixtures?

Answer 30

By running a pure sample of a substance next to the mixture and comparing Rf values.

Question 31

What indicates that a substance is likely present in a mixture when using chromatography?

Answer 31

If the Rf value of the reference compound matches one of the spots in the mixture.

Question 32

If two substances have the same Rf value in one solvent, what should you do to confirm their identity?

Answer 32

Repeat the experiment with a different solvent.

Question 33

What is the range of Rf values in chromatography?

Answer 33

Rf values will always be between 0 and 1.

Question 34

If a spot on a chromatogram moved 6.3 cm from the baseline and the solvent front moved 8.4 cm, what is the Rf value?

Answer 34

Rf = 6.3 cm / 8.4 cm ## Footnote Calculate this Rf value to determine the retention factor of the substance.

Question 35

True or False: An Rf value can be greater than 1.

Answer 35

False

Question 36

What is the Rf value in chromatography?

Answer 36

The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent. ## Footnote Rf stands for 'retention factor' and is a key measurement in chromatography.

Question 37

How does the distance a substance moves through the stationary phase relate to its Rf value?

Answer 37

The further a substance moves through the stationary phase, the larger the Rf value.

Question 38

What is the formula to calculate the Rf value?

Answer 38

Rf = distance moved by substance (B) / distance moved by solvent (A)

Question 39

Calculate the Rf value if the distance moved by the substance is 29 mm and the distance moved by the solvent is 41 mm.

Answer 39

Rf = 29 mm / 41 mm = 0.70731... = 0.7 ## Footnote Give the answer to the smallest number of significant figures in the calculation.

Question 40

What happens to the Rf value of a chemical if the solvent is changed?

Answer 40

The Rf value of a chemical will change if you change the solvent.

Question 41

How can chromatography be used to identify substances in mixtures?

Answer 41

By running a pure sample of a substance next to the mixture and comparing Rf values.

Question 42

What indicates that a substance is likely present in a mixture when using chromatography?

Answer 42

If the Rf value of the reference compound matches one of the spots in the mixture.

Question 43

If two substances have the same Rf value in one solvent, what should you do to confirm their identity?

Answer 43

Repeat the experiment with a different solvent.

Question 44

What is the range of Rf values in chromatography?

Answer 44

Rf values will always be between 0 and 1.

Question 45

If a spot on a chromatogram moved 6.3 cm from the baseline and the solvent front moved 8.4 cm, what is the Rf value?

Answer 45

Rf = 6.3 cm / 8.4 cm ## Footnote Calculate this Rf value to determine the retention factor of the substance.

Question 46

True or False: An Rf value can be greater than 1.

Answer 46

False

Question 47

What gas bleaches damp litmus paper, turning it white?

Answer 47

Chlorine ## Footnote Chlorine is a common gas tested in practical experiments.

Question 48

What happens when a glowing splint is placed in a test tube containing oxygen?

Answer 48

The glowing splint relights ## Footnote This is a classic test for oxygen.

Question 49

How can you test for carbon dioxide?

Answer 49

By bubbling it through calcium hydroxide solution ## Footnote Calcium hydroxide solution is also called limewater.

Question 50

What is the result when carbon dioxide is bubbled through limewater?

Answer 50

The solution turns cloudy ## Footnote This indicates the presence of carbon dioxide.

Question 51

What sound is produced when a lit splint is placed in hydrogen gas?

Answer 51

A 'squeaky pop' ## Footnote This is a distinctive test for hydrogen.

Question 52

Fill in the blank: The solution of calcium hydroxide is also called _______.

Answer 52

limewater ## Footnote Limewater is commonly used in gas tests.

Question 53

True or False: Chlorine gas can be tested using litmus paper.

Answer 53

True ## Footnote Chlorine gas bleaches damp litmus paper.

Question 54

What is the purpose of bubbling gas through limewater in the context of gas tests?

Answer 54

To check for the presence of carbon dioxide ## Footnote This reaction produces a cloudy solution if CO2 is present.

Question 55

What is the chemical formula for hydrogen gas?

Answer 55

H2 ## Footnote Hydrogen gas is tested by its characteristic sound when ignited.

Question 56

What is the result of a successful test for oxygen?

Answer 56

Glowing splint relights ## Footnote This is a reliable indicator of oxygen's presence.

Question 57

What practical experiment is described for testing gases?

Answer 57

Tests for 4 common gases ## Footnote The gases include chlorine, oxygen, carbon dioxide, and hydrogen.