Topic 6 - Solutions And Mixtures

Question 1

Define solute

Answer 1

A substance dissolved in a solvent to form a solution

Question 2

Define solvent

Answer 2

The substance in which absolute is dissolved to form a solution

Question 3

Define solution

Answer 3

The mixture formed through the dissolving of a solute into a solvent that does not separate out.

Question 4

Define suspension

Answer 4

A mixture in which small particles of a substance are dispersed

Question 5

Define soluble

Answer 5

A substance that can dissolve

Question 6

Define insoluble

Answer 6

A substance which cannot dissolve

Question 7

Define saturated

Answer 7

A solution into which no more solute can be dissolved

Question 8

What are the solubility rules

Answer 8

SOLUBLE:
all compounds containing Li, Na, K, NH4, and NO3
all compounds containing Cl, except AgCl and PbCl2
all compounds containing SO4, except Ag2SO4, PbSO4, CaSO4 and BaSO4
INSOLUBLE:
all compounds containing O2, OH or CO3, except Li, Na, K, NH4 and NO3

Question 9

Describe filtration

Answer 9

Purpose: Separates an insoluble solid
Diagram: A funnel containing filter paper is placed in a conical flask. Label filtrate and residue
Explanation: the solid particles are too large to pass through the filter paper, they become the residue

Question 10

Describe simple distillation

Answer 10

Purpose: separates a solvent from its solution
Diagram: a spherical beaker with a Bunsen burner underneath contains the solution along with some anti-bumping granules. It has a bung at the top with a thermometer sticking out. There is a condenser coming out of the side (label where the water goes in and out) which feeds into a conical flask contains this distillate.
Explanation: the solvent has a much lower boiling point than the solute. When the solution is heated, the solvent evaporated, leaving the solute behind. It is then cooled and condensed, and collected in the conical flask as the distillate.

Question 11

Describe fractional distillation

Answer 11

Purpose: to separate miscible liquid
Diagram: same as simple distillation, however there is a Column above the spherical beaker that has downhill glass shards (this is the fractionating column)
Explanation: the fractionating column is needed because miscible liquids have similar BPs. The column cools the gas and condensed the liquid with the higher BP, before it escapes into the condenser. The glass shards lose water quickly and have a high SA for condensing

Question 12

Describe the separating funnel

Answer 12

Purpose: separates immiscible liquids
Diagram: label the less dense liquid, the more dense liquid, the boundary between liquids and the Tao
Explanation: the Tao can be closed when the boundary reaches it

Question 13

Describe chromatography

Answer 13

Purpose: separates multiple solutes from a solution
Diagram: rolled up chromatogram in a lidded beaker containing the solvent with a pencil base line.
Explanation: different dyes move up the paper at different rate (some stick to the paper and some dissolve more quickly). The further the dye travels, the more soluble it is.

Question 14

How do you calculate Rf value?

Answer 14

Distance travelled by the dot/ distance travelled by the solvent

If two dots have the Rf value, they are the same substance.

Standard reference materials are sometimes used for comparison- they have controlled concentration and purities.

Question 15

Describe the process of dissolving

Answer 15

When you add a solid (the solute) to a liquid (the solvent), the bonds holding the solute molecules together sometimes break and the molecules then mix with the solvent molecules, forming a solution

Question 16

Define solubility

Answer 16

A measure of how much solute will dissolve in a solvent

The ability of a substance to dissolve in a solvent

Question 17

What is solubility measured in?

Answer 17

Grams of solute/100g of solvent

Question 18

Describe the relationship between solubility and temperature

Answer 18

The solubility of most solid substances increases as the temperature increases

Question 19

What is a solubility curve?

Answer 19

A graph of the solubility of a substance against the temperature

Question 20

Investigating how temperature affects solubility

Answer 20

1) make a saturated solution by adding an excess of ammonium chloride to 10cm3 of water in a boiling tube. You will know when the ammonium chloride is in excess because it will start to sink to the bottom of the tube
2) stir the solution, and place the boiling tube in a water bath at 25°C
3) after 5 minutes, check that all of the excess solid has sunk to the bottom of the tube, and use a thermometer to check that the solution has reacher 25°C
4) weigh an empty evaporating basin. Pour some of the solution into the basin, ensuring not to pour in any of the undissolved solid
5) re-weigh the basin and its contents, then gently heat it using a Bunsen burner to remove all of the water (if heated too strongly, the ammonium chloride could boil and escape, causing the mass of the solid in the basin to decrease- your solubility value will be lower than it should be)
6) once all the water has evaporated, you’re left with pure ammonium chloride. Reweigh the evaporations basin and it’s contents
7) repeat steps 1-6 twice more, but with the water bath at different temperatures
8) use the different masses to work out the solubility at each temperature
9) plot a solubility curve

Question 21

How to calculate solubility from the masses of the solid and water

Answer 21

mass of solid (g)
Solubility = ————————
mass of water removed (g)

X100

Question 22

Describe crystallisation

Answer 22

1) pour the solution into an evaporating dish and gently heat it. Some of the water will evaporate and the solution will become more concentrated.
2) Once the point of crystallisation has been reached (you see crystals start to form), remove the dish from the heat and leave it to cool
3) the salt should start to form crystals as it becomes insoluble in the cold- a highly concentrated solution
4) finger the crystals out of the solution and leave the in a drying oven