CC1/2

Question 1

What are the particles like in solid, liquid and gas states?

Answer 1

solid: regular, close together
liquid: random, close together
gas: random, far apart

Question 2

What changes

Question 3

what changes happen to particles during the different changes of state?

Answer 3

The number of particles does not change during a change of state, only their spacing and arrangement. As a result, the total mass has not changed. It does not matter if a substance melts, freezes, boils, evaporates, condenses or sublimates, the mass does not change.

Question 4

how do you decide what state a substance will be in at a given temperature?

Answer 4

You can predict the state of a substance if you know it’s temperature, and it’s melting & boiling points. if the temperature is:
- below the melting point, the substance is solid
- between the meting point & boiling point, the substance is liquid
- above the boiling point, the substance is gas

Question 5

What is a state change?

Answer 5

State changes are physical changes. They can be reversed, and the chemical properties of the substance do not change. This is because the particles themselves do not change - only their arrangement movement and amount of stored energy.

Question 6

How are particles attracted to one another?

Answer 6

Particles are attracted to one another by weak forces of attraction.

Question 7

what is the difference between a pure substance and a mixture?

Answer 7

a pure substance has the same fixed composition in all its parts and so we can’t separate it into other substances using physical methods (such as filtering or picking bits out)

a mixture contains elements and/or compounds that are not chemically joined together. You can use physical processes to separate mixtures into different substances.

Question 8

what happens to a solid’s particles when it melts?

Answer 8

when a solid melts, it’s particles fain enough energy to overcome the weak forces of attraction between them. they move further away from one another and the solid becomes a liquid.

Question 9

how do melting points allow you to spit the differences between pure substances and mixtures?

Answer 9

All of a pure substance will melt at the same temperature until all the substance has changed state. Mixtures, however, do not have fixed, sharp melting points,

Question 10

What is a melting point?

Answer 10

the temperature at which a solid’s particles overcome the weak forces of attraction between them

Question 11

What are the characteristics of the composition (make-up) of a pure substance?

Answer 11

• cannot be changed
• is the same in all parts of a piece of the substance

Question 12

How can crystallisation be used to separate mixtures?

Answer 12

a solution is a mixture made of solutes in a liquid called the solvent. Solutes can be separated from a solution by evaporating the solvent to leave the solutes behind.

Question 13

how can filtration be used to separate mixtures?

Answer 13

filters can be used to separate some mixtures. They let smaller pieces of liquids through but trap bigger pieces or insoluble pieces.

Question 14

what are the hazards and risks when separating mixtures by filtration and crystallisation?

Answer 14

bits of unsolvable substance cannot fit through the holes so leave a residue in the filter paper. Care must be taken so not the overhear the solution once it is saturated as hot crystals may spit out. further heating may also cause the crystals to change chemically.

Question 15

How can chromatography be used to separate mixtures?

Answer 15

paper chronograph is a simpler technique that works because some compounds dissolve better in a solvent than others.

Question 16

What are the differences between mixtures and pure substances on a chromatogram?

Answer 16

a pure substance produces one spot on the chromatogram. an impure substance, or mixture, produces two or more spots.

Question 17

how do you calculate an r(f) value?

Answer 17

r(f) = distance moved by the spot / distance moved by the solvent [R(f) means normal sized r little tiny f]

Question 18

what is distillation?

Answer 18

When mineral water evaporates, only the water turns to a gas (vapour). The solid minerals, which have much higher boiling points, are left behind. The water vapour (steam) is pure.
If the vapour is then condensed, it anti-bumping turns back to liquid water again the liquid water will now be pure. This combination of evaporation followed by condensation is called distillation. The apparatus used is called a still.

Question 19

what is fractional distillation?

Answer 19

the original mixture will be split into several parts, or fractions. The first fraction to be collected contains the liquid with the lowest boiling point. The fractions could be pure liquids, or may still be mixtures.
Hot vapour rises up the column, heati
it up. This crea
a temperatur gradient.
Fractional distillation can be used:
• to separate the different products in crude oil
• to make alcoholic drinks such as whisky and vodka
• to separate out the gases in the air, after the air has been cooled and turned into a liquid at -200 °C.

Question 20

what is chemical analysis?

Answer 20

chemical analysis involves using chemical reactions or sensitive machines to identify and measure substances in a sample

Question 21

why just water used in chemical analysis be pure?

Answer 21

The water used for chemical analysis should not contain any dissolved salts, otherwise incorrect results will be obtained. Tap water contains small amounts of dissolved salts which may react to form unexpected cloudy precipitates. These may hide the correct result of the analysis. Also, the machines used for analysis may detect the salts, again leading to an incorrect conclusion.