chemistry topic 3

Question 1

what is percentage by mass

Answer 1

used to calculate the percentage by mass of an element within a compound

% by mass= Ar*no. of atoms in compound/
Mr of the compound
*100

Question 2

What is Ar

Answer 2

relative atomic mass

Question 3

What is Mr

Answer 3

relative formula mass

Question 4

what is meant by the law of conservation of mass

Answer 4

the mass of reactants=mass of products in any chemical reaction
matter cannot be created or destroyed, only transferred from one form to another

Question 5

why does mass change when chemicals react

Answer 5

• hydrogen gas is being produced
• hydrogen gas will move out of the flask
• the decrease in mass on the balance will equal to the mass of the hydrogen gas

Question 6

what does aqueous mean

Answer 6

state symbol- (aq)
dissolved in water

Question 7

what is uncertainty

Answer 7

scientific uncertainty means there is a range of possible values within which the true value of measurement lies

Question 8

how can we estimate uncertainty

Answer 8

1. through repeated measurements
   OR
2. Through the resolution of instruments

Question 9

how do we estimate uncertainty through the resolution of instruments

Answer 9

the uncertainty can be estimated as half the smallest interval
(e.g. for a thermometer with resolution of 1 degree celcius, the uncertainty is 0.5 degrees celcius

Question 10

how do we estimate uncertainty through repeated measurements

Answer 10

1. calculate the mean
2. calculate the range
3. divide the range by 2
4. write the mean and the uncertainty (range/2) after the plus/minus symbol

Question 11

what is a saturated solution

Answer 11

a solution in which no more solute will dissolve

Question 12

what is dissolving

Answer 12

when the solute particles fill in the spaces between the solvent particles

Question 13

what is a pure substance

Answer 13

made of one type of atom or compound

Question 14

what is a solute

Answer 14

the substance that dissolves in a solvent

Question 15

what is insoluble

Answer 15

a substance that will not dissolve to form a solution

Question 16

what does the concentration of a solution tell you

Answer 16

how much solute is dissolved in a given volume of a solution

Question 17

what is volume

Answer 17

the amount of space that a substance or object takes up

Question 18

what is the scientific unit for volume

Answer 18

dm^3 (cubic decimetres)

1dm^3= 1L= 1000cm^3

Question 19

what is concentration

Answer 19

the mass of a solute in a certain volume of solvent
unit- g/dm^3

Question 20

how can you decrease concentration

Answer 20

by increasing the solvent (diluting it)

Question 21

how do you calculate concentration

Answer 21

mass (g)/ volume (dm^3)

Question 22

how do you calculate mass

Answer 22

concentration * volume

Question 23

how do you calculate volume

Answer 23

mass/ concentration

Question 24

what is the neutralisation reaction equation

Answer 24

acid+alkali= salt+water

Question 25

what pH range is alkaline

Answer 25

pH 8- pH 14

Question 26

what is melting

Answer 26

the change in state from solid to liquid

Question 27

products for reaction: acid+metal oxide=

Answer 27

salt+water

Question 28

products for reaction: acid+metal hydroxide

Answer 28

salt+water

Question 29

products for reaction: acid+ metal carbonate=

Answer 29

salt+ water+ carbon dioxide

Question 30

what is the form for hydrochloric acids

Answer 30

chlorides

Question 31

what is the form for sufluric acids

Answer 31

sulphates

Question 32

what is the form for nitric acid

Answer 32

nitrates

Question 33

what is a soluble base called

Answer 33

an alkali

Question 34

what are the hazards for hydrochloric acid

Answer 34

concentrated hydrochloric acid is corrosive and may cause chemical burns dilute hydrochloric acid is an irritant

Question 35

what are safety precautions when using hydrochloric acid

Answer 35

-use dilute acid -ensure beaker is away from edge of bench

Question 36

what are hazards when using bunsen burners

Answer 36

risks of burns or hair/clothing catching fire

Question 37

what are safety precautions when using bunsen burners

Answer 37

- do not touch apparatus until it cools - turn off when not in use - tie back hair - stand up

Question 38

what are hazards when using glassware

Answer 38

cut skin from broken glass

Question 39

what is neutralisation

Answer 39

the solid is added to the acid until no more reacts

Question 40

what is filtration

Answer 40

excess solid is filtered off to produce a solution of the salt

Question 41

what is evaporation

Answer 41

the solution is heated to evaporate the water to form a more concentrated solution

Question 42

how are soluble salts prepared

Answer 42

neutralisation, filtration, evaporation, crystallisation

Question 43

why do we heat the acid gently when preparing soluble salts

Answer 43

to speed up the reaction