Separating Substances

Question 1

What does a particle diagram look like for a solid?

Answer 1

Question 2

What does a particle diagram look like for a liquid?

Answer 2

Question 3

What does a particle diagram look like for a gas?

Answer 3

Question 4

What is diffusion?

Answer 4

Diffusion is the random, mixing and moving of particles and liquids and gases. (from high concentration of particles to low concentration bracket)

Question 5

What happens in the experiment where ammonia and hydrochloric acid are an opposite end of a diffusion tube?

Answer 5

• This experiment shows how particles diffuse in vapour at different speeds.
• concentrated hcl soaked cotton wool at one end of the tube, concentrated ammonia soaked cotton wool at the other end.
• After a couple of minutes, a white ring of ammonium chloride ( a solid) will form where the two gases meet.
• This will be closer to the source of the hydrogen chloride than to the source of the ammonia because hydrogen chloride diffuses more slowly than ammonia. This is because ammonia molecules are smaller.

Question 6

What is the word equation for the experiment where ammonia and hydrochloric acid are an opposite end of a diffusion tube?

Answer 6

ammonia + hydrogen chloride → ammonia chloride

Question 7

What is the symbol equation for the experiment where ammonia and hydrochloric acid are an opposite end of a diffusion tube?

Answer 7

NH₃ + HCl → NH₄Cl

Question 8

What is a solvent?

Answer 8

Something that a substance dissolves into

Question 9

What is a solute?

Answer 9

A substance that will dissolve in a solvent

Question 10

What is a solution?

Answer 10

Solute dissolved in a solvent

Question 11

What is a saturated solution?

Answer 11

A solution in which no more solute will dissolve

Question 12

What does soluble mean?

Answer 12

Can dissolve

Question 13

What does insoluble mean?

Answer 13

Cannot dissolve

Question 14

What is excess?

Answer 14

undissolved solute after saturation point

Question 15

How does solubility change with temperature? and why?

Answer 15

In general, solids become more soluble as the temperature increases.
The addition of more heat facilitates the dissolving reaction by providing energy to break bonds in the solid.

(ASK TEACHER)

Question 16

Explain the term saturation point

Answer 16

The saturation point is at the point when no more solute will dissolve

Question 17

How do you interpret graphs of solubility curves?

Answer 17

Each solute has a different solubility at different temperatures and the change in solubility with temperature depends on the solute.

solubility of all three solutes increases as temperature increases

Question 18

What is a pure substance?

Answer 18

Pure substance contains one element or compound, and has a fixed, melting or boiling point.

Question 19

What is an impure substance?

Answer 19

An impure substance contains more than one element or compound and melts and boils over range of temperatures.

Question 20

What is an element?

Answer 20

A substance that contains only one type of atom

Question 21

What is a compound?

Answer 21

Two or more elements that are chemically bonded.

Question 22

What is a mixture?

Answer 22

Two or more substances mixed, but not chemically joined

Question 23

What is a molecule?

Answer 23

Two or more atoms bonded together, they can be the same or different, for example, O₂ - same, CO₂ - different.

Question 24

What is crystallisation?

Answer 24

• When you have a soluble solid dissolved in a liquid.
• Crystallisation happens when heat a solution until it becomes a saturated solution (don’t evaporate all the water)
• Crystals will form at this point.
• As the solution cools, the solubility of the solute decreases so more crystals form.
• You can separate them from the remaining solution by filtration, and dry them in a warm oven or by patting them dry with filter paper.

Question 25

How do you work out the purity percentage?

Answer 25

Purity percentage = (mass of pure substance/ mass of original sample) * 100

Question 26

What is simple distillation?

Answer 26

Separates the solvent from a solution by evaporation then condensation. It relies on the solvent having a much lower boiling point than the solute.

Question 27

What is fractional distillation?

Answer 27

Fractional distillation is used when used to separate two or more liquids of different boiling points

Question 28

What is chromatography?

Answer 28

Chromatography is a separation method used to separate a mixture of soluble (in the solvent chosen to dissolve them) substances. These are usually colours.

Question 29

What are the key points of chromatography?

Answer 29

* Draw baseline in pencil (pen would dissolve + affect the results) * solvent added must be below the baseline (otherwise spots will dissolve in solvent plus run down) * the more soluble a substance is the faster the spot travels. * If a substance is insoluble – use a different solvent. * measure to the middle of the spots.

Question 30

How do you work out the Rf value?

Answer 30

Rf = Distance travelled by substance/ distance travelled by solvent Rf values vary from 0 to 1, and have no units.

Question 31

When is filtration used?

Answer 31

When you want to separate an insoluble solid from a liquid

Question 32

When is crystallisation used?

Answer 32

to separate a soluble substance from a solvent

Question 33

When is distillation used?

Answer 33

When you need to separate a solvent (with a much lower boiling point than the solute) and the solute.

Question 34

When is fractional distillation used?

Answer 34

When you need to separate 2 or more liquids of different boiling points.

Question 35

When is chromatography used?

Answer 35

When you want to separate a mixture of soluble substances