YEAR 9 – Topic 2 – Elements, Mixtures and Compounds

Question 1

How do you determine whether a substance is pure using boiling or melting points?

Answer 1

A pure substance has a fixed melting and boiling point.

Question 2

How do you determine whether a substance is a mixture with melting or boiling points?

Answer 2

A mixture may melt or boil over a range of temperatures.

Question 3

What is simple distillation?

Answer 3

Simple distillation is a method of separating a solvent from a solution. Eg water from a salt water solution. It works because the solvent may have a lower boiling point than the solute.

Question 4

What is fractional distillation?

Answer 4

Fractional distillation is the method of separating a liquid from a mixture of two or more liquids. It works because different liquids have different boiling points.

Question 5

What is crystallisation?

Answer 5

The process to obtain crystals from a saturated solution.

Question 6

How can chromatography be used to separate a mixture?

Answer 6

It can separate mixtures of substances into their components.

Question 7

How does a chromatogram provide information about the composition of a mixture?

Answer 7

Chromatography separates out a mixture of soluble solids. You can tell what a substance is made up of. You can then compare it to other substances and see whether they have a similar composition.

Question 7

What is the RF value?

Answer 7

Rf= Retention Factor
RF= distance travelled by component/distance travelled by solvent
IT IS ALWAYS SMALLER THAN 1!!!

Question 7

How do you calculate the RF value?

Answer 7

Rf value = distance travelled by component/ distance travelled by solvent

Question 7

How does the RF value help you determine the components of a mixture?

Answer 7

Certain components of a mixture in a certain solvent will travel a certain distance. The Rf value shows this.

Question 8

What is a molecule?

Answer 8

2 or more atoms chemically bonded together.

Question 9

What is an element?

Answer 9

A substance that only contains one type of atom.

Question 10

What is a compound?

Answer 10

A substance made up of 2 or more different elements chemically bonded together.

Question 11

What is a mixture?

Answer 11

2 or more substances together which are not chemically bonded.

Question 12

What is a pure substance?

Answer 12

May be an element or a compound. Contains only 1 substance and one type of particle.

Question 13

How do you know if you calculated the Rf value wrong?

Answer 13

The Rf value should be below 1, if it isn’t then it is wrong and try again.

Question 14

What mixture is separated in decanting?

Answer 14

A mixture of immiscible liquids and insoluble solids from liquids. Eg. Oil and water.

Question 15

What mixture is separated in filtration?

Answer 15

Insoluble solids and liquids. Eg. Sand and water.

Question 16

What mixture is separated in evaporation?

Answer 16

Solute from a solvent. Eg. Salt from a salt solution.

Question 17

What mixture is separated in distillation?

Answer 17

Solvent from a solution. Eg. Alcohol from a sugar solution. Or water from a salt solution.

Question 18

What mixture is separated in fractional distillation?

Answer 18

A mixture of miscible liquids. Eg petrol and diesel from crude oil.

Question 19

What mixture is separated in a separating funnel?

Answer 19

Mixture of immiscible liquids. Eg. Oil and water.

Question 20

What mixture is separated in chromatography?

Answer 20

Mixture of soluble solids. Eg. Mixture of food dye.

Question 21

What does immiscible mean?

Answer 21

Two or more substances that do NOT mix up.

Question 22

What does miscible mean?

Answer 22

Two or more substances that DO mix up.

Question 23

What is the solvent?

Answer 23

It is a liquid that dissolves a solute to form a solution.

Question 24

What is a solute?

Answer 24

A solute is the substance that dissolved into the solvent to form a solution.

Question 25

Why can samples have a different Rf value in different solvents (chromatography)?

Answer 25

Because substances have different levels of solubility in different solvents. The more soluble a sample is in a solvent, the higher up the chromatography it will get.

Question 26

What NOT to do in chromatography?

Answer 26

• draw the baseline in pen because it will dissolve and run up the paper ruining your results
• make the solvent over the baseline because it will wash off the solutes and the will dissolve into the solvent.