Elements, Compounds and Mixtures

Question 1

What is an Element

Answer 1

These are substances that have atoms with the same atomic number (proton number)

Cannot be broken down into anything simpler using chemical means.

Question 2

What is a compound

Answer 2

These are substance that are made when two or more elements chemically combine in fixed proportions.

They cannot be separated using physical means.

Question 3

What is a mixture

Answer 3

This is created with the combination of two or more elements or compounds that are not chemically joined together

Can easily be separated by physical means.

Question 4

What is a pure substance

Answer 4

These contain only one substance and have no other substances mixed together.

They have a fixed meting and boiling point because they consist of only one substance, so all molecules have the same melting and boiling point.

Question 5

Mixture Vs Pure substances

Answer 5

1. Pure substances have a fixed melting and boiling point. Mixtures may melt and boil over a range of temperatures.
2. Mixtures contain a variety of elements or compounds that are not chemically joined together, and pure substances consist of only one type of substance.

Question 6

What affect do impurities have on the melting and boiling point of a substance.

Answer 6

They lower the melting point and increases the boiling point of a substance.

Question 7

How can the purity of a substance be tested

Answer 7

By checking if they melt or boil at the exact melting point or boiling point.

Question 8

What is the use of simple distillation

Answer 8

It is used to separate a soluble solid from a solution

Question 9

How does simple distillation work

Answer 9

The solution is put into a container and is heated.

The water vapour then rises and enters a condenser. This has a continuous flow of water through it, meaning that the water vapour will condense and turn back into liquid.

The solute will be left behind.

Question 10

What is the use of fractional distillation

Answer 10

It is used to separate 2 or more liquids that are miscible with each other.
Ex: Ethanol and Water.

Question 11

How does fractional distillation work

Answer 11

The solution is heated at the temperature of the substance with the lowest boiling point.

The substance then evaporates and goes through a condenser where it gets condensed and turns back into a liquid.

Question 12

What is the use of filtration

Answer 12

This is used to separate undissolved solid from a solution of a solid and a liquid.

During filtration, it leaves behind a residue and produces a filtrate.

Question 13

How does filtration work

Answer 13

Filter paper is inserted into a funnel, which leads to a beaker

The solution is then poured into the funnel containing the filter paper

The filter paper will only allow small liquid particles to pass through and the insoluble solid will be left behind as a residue because they are too large to pass through.

Question 14

What is the use of crystallisation

Answer 14

Used to separate dissolved solid from a solution.

Question 15

What is the use of paper chromatography

Answer 15

This is used to separate substances with different chromatography levels.

A pure substance will only show one spot on the chromatography paper because pure substances only contain one substance.

Question 16

Why is the actual mass of a substance obtained in a chemical reaction less than the theoritical maximum mass

Answer 16

1. Because the solution was not left for long enough
2. Because all of the reactant did not react
3. Some of the product may have gotten lost during transfer between pieces of the apparatus
4. The products are impure