1st Half Term

Question 1

What are all substances made of?

Answer 1

Atoms

Question 2

What is an atom?

Answer 2

An atom is the smallest part of an element that can exist.

Question 3

How are atoms of each element represented?

Answer 3

by a chemical symbol, eg O represents an atom of oxygen, Na represents an atom of sodium.

Question 4

Roughly how many elements are in the periodic table?

Answer 4

118

Question 5

List 3 traits of compounds

Answer 5

• have a fixed composition (ratio of elements present is same in the compound)
• chemical reactions are necessary to separate the elements
• chemically bonded atoms in a compound

Question 6

List 3 features of mixtures

Answer 6

• no fixed composition (substance proportion varies)
• the different elements or compounds in a mixture can be separated easily (physically)
• no chemical bonds between the atoms in a mixture

Question 7

When would you use filtration?

Answer 7

When you have an insoluble solid
E.g. sand in salt solution or water

Question 8

When would you use evaporation/crystallisation?

Answer 8

When you are separating a solvent and a soluble solid
E.g. water and salt

Question 9

When would you use distillation?

Answer 9

When. You want to collect the solvent and the solute . It can also be used for two liquids that have different boiling points
E.g.salt water and pure water

Question 10

When would you use fractional distillation?

Answer 10

• miscible liquids (liquids that mix together)
• more than two liquids (fractional distillation of oil)
• the substance with the lowest boiling point boils first

Question 11

When is chromatography used?

Answer 11

• to separate soluble dyes
• , more soluble dyes and those that are less attracted to the stationary phase will travel further up the paper

Question 12

How do you find the Rf value?

Answer 12

Rf = distance travelled by solute divided by distance travelled by solvent