principles of chemistry

Question 1

isotopes

Answer 1

-isotopes are different atomic forms of the same element, which have the same number of protons but different numbers of neutrons

Question 2

how to separate rock salt

Answer 2

-grind up the rock salt with a pestle and mortar
-dissolve it in a breaker and stir
-filter through filter paper in a funnel
-evaporate in an evaporating dish

Question 3

what is chromatography used for

Answer 3

-method used by chemists to separate out mixtures

Question 4

how to carry out paper chromatography

Answer 4

-draw a line near the bottom of a sheet of filter paper)pencil as they are insoluble
-add spots of different inks to the line at regular intervals
-loosely roll the sheet up and put it in a beaker of solvent(water)
-make sure the level of solvent is below the baseline(so ink doesn’t dissolve into the solvent
-place a lid on top of the container to stop solvent evaporating
-the solvent will seep up the paper, carrying the inks with it
-each different dye in the inks will move up the paper at a different rate and form a spot in a different place
-when the solvent has nearly reached the top of the paper take the paper out of the beaker and leave it to dry
-end results is a pattern of spots called a chromatogram

Question 5

how to calculate the Rf value for each chemical

Answer 5

Rf = distance travelled by solute/distance travelled by solvent

Question 6

distillation

Answer 6

-solution is heated
-the part of the solution that has the lowest boiling point evaporates
-the vapour is then cooled, condenses(turns back into a liquid and is collected)
-rest of the solution is left behind in the flask

Question 7

neutralisation

Answer 7

-add excess solid to the acid
-stir the mixture to make sure reaction is complete
-filter the mixtures to remove excess
-transfer the solution into an evaporating dish
-heat up the filtrate until saturated
-check saturation point using a glass rod
-if crystals form then saturation point has been reached
-allow to cool and crystalise
-filter to remove crystals
-dry crystals in a warm oven

Question 8

titration

Answer 8

-using a pipette, add alkali(usually 25 cm3) to a conical flask, along with two or three drops of indicator
-fill a burette with the acid
-using burette add the acid to the alkali a bit at a time, giving the conical flask a regular swirl
-the indicator changes colour when all the alkali has been neutralised
-record the volume of acid used to neutralise the alkali

Question 9

precipitation

Answer 9

-mix the solutions
-stir the mixture
-filter off the precipitate
-wash with distilled water
-dry the solid in warm oven

Question 10

metal + acid

Answer 10

salt +hydrogen

Question 11

carbonate + acid

Answer 11

salt + carbon dioxide + water

Question 12

alkali + acid

Answer 12

salt +water

Question 13

base + acid

Answer 13

salt + water

Question 14

are common salts of sodium potassium and ammonium soluble

Answer 14

-soluble

Question 15

nitrates solube?

Answer 15

yes

Question 16

common chlorides soluble

Answer 16

yes except silver and lead

Question 17

common sulfates soluble

Answer 17

yes except lead, barium and calcium

Question 18

common carbonates soluble

Answer 18

no except sodium potassium and ammonium

Question 19

common hydroxides soluble

Answer 19

no except sodium potassium and calcium

Question 20

test for chlorine

Answer 20

-chlorine bleaches damp blue litmus paper, turning it white
-might turn red first as chlorine solution is acidic

Question 21

test for oxygen

Answer 21

oxygen relights a glowing splint

Question 22

test for carbon dioxide

Answer 22

CO2 turns limewater cloudy-bubble the gas through a test tube of limewater

Question 23

test for hydrogen

Answer 23

-hydrogen makes a squeaky pop with a lighted splint

Question 24

test for ammonia

Answer 24

-ammonia turns damp red litmus paper blue

Question 25

reactivity series

Answer 25

potassium sodium lithium calcium magnesium aluminium zinc iron copper silver gold

Question 26

how to prevent rusting

Answer 26

Barrier methods -painting/coating with plastic to keep -out the water and oxygen Sacrificial methods -zinc is often used as a sacrificial metal -zinc is more reactive than iron, further up in the reactivity series -zinc will be oxidised instead of iron -a coating of zinc can be sprayed onto the object-known as galvanising -big blocks of zinc can be bolted to the iron, used on ships' hulls or on underground iron pipes

Question 27

equation for rust

Answer 27

iron + oxygen + water ->hydrated iron III oxide (rust)

Question 28

how can you measure how catalysts affect rate

Answer 28

-decomposition of hydrogen peroxide -add hydrogen peroxide to a beaker attached to a gas syringe with a bung -add manganese oxide powder to the hydrogen peroxide -measure the volume of gas produced at regular time intervals and record the results -repeat the experiment using copper oxide(same amount of catalyst) -plot a graph

Question 29

catalyst

Answer 29

Catalyst: A substance that speeds up a chemical reaction while remaining chemically unchanged at the end of the reaction. A catalyst is not used up in a reaction. A catalyst speeds up a reaction by providing an alternative pathway with lower activation energy.