Atoms, Elements and Compounds Ch2

Question 1

Use melting and boiling points to assess purity of a substance

Answer 1

Pure substances have definite sharp melting and boiling points. Impurities in substances cause the melting points to fall and the boiling points to rise, and impure substances melt and boil over a range of temperatures.

Question 2

Soluble-

Answer 2

a property of a substance to dissolve in a solvent

Question 3

Insoluble-

Answer 3

when a substance cannot dissolve in a solvent

Question 4

Aqueous solution-

Answer 4

A solution where the solvent is water

Question 5

Dissolve-

Answer 5

when a solute passes into a solution

Question 6

Impure-

Answer 6

when something (ie. substance) contains substances other that itself

Question 7

Insoluble-

Answer 7

when a substance does not dissolve in a solvent

Question 8

Mixture-

Answer 8

a mixture contains a number of different substances not chemically bonded together

Question 9

Pure-

Answer 9

to consist of only one element/compound

Question 10

Saturated-

Answer 10

when no more solute can be dissolved into the solution

Question 11

Solute-

Answer 11

the substance dissolved to make the solution

Question 12

Soluble-

Answer 12

when a substance dissolves in a solvent

Question 13

Solubility-

Answer 13

a measurement of how much of a substance will dissolve in a given volume of a liquid

Question 14

Solution-

Answer 14

a homogeneous mixture composed of two or more substances made when a solute is dissolved into a solvent

Question 15

Solvent-

Answer 15

the substance that dissolves to make a solution

Question 16

Volatile-

Answer 16

a substance that vaporizes readily

Question 17

Suggest apparatus that is suitable for

measuring time, temperature and mass

Answer 17

Time - stopwatch
Temperature - thermometer / temperature probe
Mass - digital mass balance

Question 18

Suggest suitable apparatus for measuring volume

Answer 18

Measuring cylinder
Burette
Pipette with pipette filler

Question 19

What is paper chromatography used for?

Answer 19

Separating and identifying a mixture of substances

Question 20

How does separation occur in paper chromatography?

Answer 20

There is a stationary phase (chromatography
paper) and a mobile phase (solvent).
Substances have different solubilities in the mobile
phase so will travel at different rates causing
separation. More soluble substances travel further.

Question 21

Describe how you could use paper chromatography to separate a mixture of food colourings

Answer 21

• Draw a pencil line 2 cm from the bottom of chromatography paper.
• Place one dot of 3 known food colourings and one dot of the unknown
  mixture along the line. Label each dot.
• Place the chromatography paper in a beaker containing 1 cm of water.
• Wait for the water to travel up most of the paper and then remove the
  paper from the beaker and mark the height reached by the solvent. Dry
  the paper.
• Observe the chromatogram and record results.