C2-ELEMENTS,COMPOUNDS AND MIXTURES

Question 1

what is relative atomic mass

Answer 1

the mean mass of an atom of an element compared of 1/12 the mass of a carbon 12 atom

Question 2

how can masses of atoms be described

Answer 2

relative atomic mass

Question 3

mass rules of atoms in terms of carbon relative atomic mass(12.0)

Answer 3

-less mass than a carbon 12 atom if its A is below 12
-more mass than a carbon 12 if its A is about 12

Question 4

what is relative formula mass

Answer 4

mean mass of a unit of substance compared to 1/12 the mass of a carbon 12 atom

Question 4

periodic table shows:

Answer 4

the relative atomic masses of the elements.The bottom number in each box is the A,for that elements atoms

Question 5

what does a chemical formula tell you

Answer 5

-how many atoms of each element that there are in a substance.

for eg- H20 is 2 hydrogens and 1 oxygen

Question 6

how do you calculate relative formula mass

Answer 6

-write down the A’s of each substance
-times by how many of each substance there is in the chemical formula given
-multiply these values

Question 7

what is an empirical formula

Answer 7

shows the simplest whole-number ratio of the atoms of each element in a compound.

Question 8

how to calculate empirical formula

Answer 8

-find highest common factor
-divide the chemical formula by the highest common factor
-write down the empirical formula

Question 9

What does a balanced chemical equation show

Answer 9

the formulae and number of units for all the substances in a reaction.

Question 10

what does pure mean

Answer 10

describes natural substances that have not been processed or changed

Question 11

what is a mixture

Answer 11

A mixture contains two or more substances not chemically combined together

Question 12

what is a compound

Answer 12

A pure substance made from more than one type of element chemically bonded together

Question 13

how are mixtures useful

Answer 13

as you can deliberately choose different substances to mix and in result produce desired properties

Question 14

What is an alloy

Answer 14

a mixture of a metal with one or more other elements.

for e.g.-most jewellery are made from copper and gold mixed together ad pure gold is very soft

Question 15

What is the melting point

Answer 15

The temperature at which a substance changes from a solid to a liquid

Question 16

What is the melting point of a pure substance like

Answer 16

A single temperature

for e.g. 17 degrees Celsius

Question 17

What is the melting point of an impure substance like

Answer 17

-less than that of the pure substance
-often melts over a range of temperatures.Not just one

for e.g. 12-16 degrees Celsius

Question 18

how can you determine purity using melting point

Answer 18

the greater the difference between the measured melting point for a substance and its accepted melting point,the lower its purity is likely to be

Question 19

how do you determine melting point

Answer 19

-by heating it
-you can measure it at which it melts or measure the temperature at regular time intervals and plot a graph

Question 20

what should you make sure to do when measuring melting point

Answer 20

-heat the substance slowly
-stir the substance as it melts

Question 20

why must you heat slowly and stir substance

Answer 20

-allows temperature of whole sample to increase

-mixing ensures that the entire sample is at the same temperature

-improves the accuracy of a measurement of the melting point of a sample

Question 21

what is a solution

Answer 21

one substance dissolves into another

Question 21

solvent and solute

Answer 21

-solute is the substance that dissolves

-solvent is the substance it dissolves in

Question 22

what happens when a particle dissolves

Answer 22

the substances separate and become completely mixed with the particles of the solvent

Question 23

soluble and insoluble

Answer 23

-if a substance can dissolve in a particular solvent, it is soluble in that solvent.

-if it can’t-it is insoluble in that solvent.

-substances can be soluble in one solvent but insoluble in another solvent.

For example,nail varnish dissolves in nail-varnish remover but not in water.

Question 24

FILTRATION

Answer 24

-separates an insoluble substance in the solid state from substances in the liquid state

-filter paper has tiny holes-when u filter a mixture of sand and water , the water molecules are small enough to pass through,sand cannot

-sand (residue) stays in the filter paper while the water (filtrate passes through)

Question 25

Crystallisation

Answer 25

slowly heating a solvent and forming regularly shaped crystals

-heat until becomes saturated solution(when no more solute can be dissolved at that temperature)

-crystals will start to form,so let it cool and as solution cools the solubility of solute decreases, so more crystals form.

-you can separate from the remaining solution using filtration

-dry in a warm oven or by patting with filter paper

Question 26

what does a water bath do

Answer 26

heats solutions slowly-enables regular crystals to form on crystallisation.

Question 27

Simple distillation

Answer 27

-separates a solvent from a solution by relying on the solvent to have a much lower boiling point that the solute

-when heated,solvent escapes in gas state after evaporating.

-then cooled and condensed back into liquid state by a condenser(piece of apparatus kept cold using a flow of cold water)

Question 28

how is simple distillation useful

Answer 28

if you want to purify a substance

also can provide purified water for chemisits

Question 28

Fractional distillation

Answer 28

-separating mixtures of liquids
-heat up mixture
-when boiling point is reached, will rise and condense into pure liquid
-if others by chance evaporate,will be caught by glass rods in fractional column and it it cooler than their boiling point,so will condense into a liquid and go back into the mixture.

Question 29

what is each substance separated by fractional distillation called

Answer 29

fractions-they are just a part of the original mixture

Question 30

how does the fractioning column improve the separation of the mixture

Answer 30

it has a large surface area on which the vapours can continually condense.

Question 31

what happens to the column during frac distillation

Answer 31

the column becomes hottest at the bottom and coolest at the top

Question 31

chromotography- the two chemical phases

Answer 31

stationary(does not move)
mobile(does move)

Question 31

What is a phase

Answer 31

a substance in the soliq,liquid or gas state

Question 32

in paper chromotography

Answer 32

-the stationary phase is absorbent paper
-the mobile phase is is a solvent in a liquid state

Question 33

how is thin-layer chromotography worked