Solubility, Elements, Compounds, Mixtures

Question 1

What is a solvent?

Answer 1

The liquid which a solute is dissolved into

Question 2

What is a solute?

Answer 2

The soluble solid being dissolved in the solvent

Question 3

What is a solution?

Answer 3

A solute dissolved in a solvent

Question 4

What is a saturated solution?

Answer 4

A solution where no more solute can be dissolved, leaving sediment

Question 5

What is an element?

Answer 5

One type of atom

Question 6

What is a compound?

Answer 6

Two or more atoms, chemically bound together

Question 7

What is a mixture?

Answer 7

Two or more substances mixed together, but not chemically bonded

Question 8

What is the solubility equation?

Answer 8

Solubility = mass of solute (g) ➗ mass of solvent removed ✖️100

Question 9

What is the difference between pure substances and mixtures?

Answer 9

pure substances have a fixed melting or boiling point, mixtures melt or boil over a range of temperatures.

Question 10

How would you investigate solubility at different temperatures?

Answer 10

1. Add 20ml water to a boiling tube and measure the temp. of the water. Let the water cool to the temp. you want to work at.
2. Add the solute until saturated then filter this
3. Record the mass of the evaporating basin
4. Put into this the filtrate, then evaporate this.
5. Record the mass of the evaporating basin and solute.
6. From this work out the solubility and compare to the solubility at different temperatures

Question 11

What are the 5 ways to separate mixtures?

Answer 11

Crystallisation, Simple Distillation, Fractional Distillation, Paper Chromatography and Filtration

Question 12

What is Simple Distillation used for?

Answer 12

To separate a liquid or solid from a solution, if we want to keep the liquid

Question 13

How do you do Simple Distillation?

Answer 13

1. Heat the solution. The part of the solution with the lowest boiling point evaporates
2. This vapour is condensed in the condenser and then collected in a beaker
3. The rest of the solution is left behind in the flask

Question 14

What is Fractional Distillation used for?

Answer 14

To separate a mixture of liquids

Question 15

How do you do Fractional Distillation?

Answer 15

1. Put the mixture into a flask and put ontop a fractionating column
2. Heat this and, because different liquids have different boiling points, they will evaporate at different temperatures.
3. The liquid with the lowest boiling point will evaporate first. When the temp. on the thermometer reads the boiling point of this liquid, it will reach the top of the column
4. Liquids with higher boiling points may also start to evaporate, but will condense and drip back into the flask
5. When the liquid has been condensed and collected, turn up the heat to collect the next liquid

Question 16

What is Crystallisation used for?

Answer 16

To separate a soluble solid from a solution

Question 17

How do you do Crystallisation?

Answer 17

1. Put the solution into a evaporating basin and heat
2. The liquid will evaporate. When you start to see crystals forming, remove the dish from the heat and leave it to cool.
3. The solid should start to become insoluble in the cold, highly saturated solution

Question 18

What is Filtration used for?

Answer 18

To separate an insoluble solid from a liquid

Question 19

How do you do filtration?

Answer 19

1. Put folded filter paper on top of a filter funnel and put in the mixture
2. The mixture will drip through into the beaker, leaving behind the solid

Question 20

What is paper chromatography used for?

Answer 20

To separate dyes in inks

Question 21

What is the stationary phase is paper chromatography?

Answer 21

The chromatography paper

Question 22

What is the mobile phase in paper chromatography?

Answer 22

The inks travelling up the paper

Question 23

Why is the baseline drawn in pencil in paper chromatography?

Answer 23

Pencil marks are insoluble and won’t dissolve in the solvent

Question 24

What is the solvent front?

Answer 24

The line on the paper where the solvent stops

Question 25

What is a chromatogram?

Answer 25

A record of the results of chromatography

Question 26

How to do paper chromatography

Answer 26

1. Draw a pencil line at the bottom of a sheet of filter paper
2. Draw spots of different inks on this baseline at regular intervals
3. Place the paper into a beaker of solvent standing up, so that the solvent surface is just beneath the baseline.
4. The solvent will seep up the paper, carrying the inks with it
5. Each different dye will move up the paper at a different rate and form a spot in a different place.
6. The solvent will rise to the top of the paper.

Question 27

What does the Rf value show?

Answer 27

The solubility of a particular pigment

Question 28

What is the equation for the Rf value?

Answer 28

Rf value = distance travelled by a component ➗ distance travelled by solvent front

Question 29

What does ‘Rf value’ stand for?

Answer 29

Retardation Factor

Question 30

What is the observation of lithium reacting in water?

Answer 30

• floats

- fizzes steadily and becomes smaller, until it eventually disappears.

Question 31

What is the observation of sodium reacting in water?

Answer 31

• melts to form a ball that moves around on the surface.
• fizzes rapidly
• the hydrogen produced may burn with an orange flame before the sodium disappears.

Question 32

What is the observation of potassium reacting with water?

Answer 32

• melts and floats
• It moves around very quickly on the surface of the water.
• The hydrogen ignites instantly. The metal is also set on fire, with sparks and a lilac flame. There is sometimes a small explosion at the end of the reaction.

Question 33

What is the equation for when an alkali metal reacts with water?

Answer 33

Metal + water -> metal hydroxide + hydrogen

Question 34

What pH are alkali metal hydroxides?

Answer 34

Over 7 (alkaline)

Question 35

what is solubility?

Answer 35

the mass of a solid required to saturate 100 g of water at a given temperature. Solubility is measured in grams of a solute per 100 g of water.