paper 2 RP

Question 1

rate of reaction - disappearing cross

Answer 1

-use a measuring cylinder to put 10cm(3) of sodium thiosulfate solution into a conical flask
-place the conical flask on a black cross
-add 10cm(3) of hydrochloric acid to the flask
-swirl the solution and start a stop watch
-look down from the top of the flask,the solution will turn cloudy
-we stop the stopwatch when we can no longer see the black cross
-we then carry out the experiment again using lower concentrations of sodium thiosulfate
-repeat the experiment and calculate a mean for each concentration

Question 2

what is the problem with the disappearing cross experiment

Answer 2

-different people have different eyesights
-some people may see the cross for longer
-the students used the same size cross to help minimise this issue

Question 3

rate of reaction- gas produced by reaction

Answer 3

-use a measuring cylinder to place 50cm(3) of hydrochloric acid into a conical flask
-attach the conical flask to a bung and a delivery tube
-place the delivery tube into a container filled with water
-place an upturned measuring cylinder also filled with water over the delivery tube
-add a 3cm strip of magnesium to the acid
-start a stopwatch
-the reaction produced hydrogen gas that is trapped in the cylinder
-every 10 seconds we measure the volume of gas in the measuring cylinder
-continue until no more hydrogen gas is produced
-repeat experiment using different concentrations of acid
-repeat a number of times and calculate a mean

Question 4

chromatography - how it can be used to finf unkown substances

Answer 4

-place a pencil line 2 cm from the bottom of chromatography paper
-place dots of unknown substances on pencil line
-pour water into a beaker with a depth of 1cm
-attach the paper to a glass rod with tape and lower it into the beaker, the bottom of the paper should dip into the water
-ensure pencil line is above water, the paper does not touch the beaker
-water will move up the paper carrying the substance
-measure distance moved by substance and solvent
-distance moved by substance/distance moved by solvent to find rf value
-search up the rf values in a data base

Question 5

testing for pure water

Answer 5

-take a sample of our water and test it in using universal indicator
-if its green PH7
-if its not green it contains dissolved acids or alkali therefore not pure
-we then get a balance and weigh the mass of an empty evaporating basin
-fill the evaporating basin with our water sample placing it on a tripod and gauze
-gently heat with bunsen burner until all the water is evaporated
-weigh the mass of the evaporating basin again
-if the water sample contained any dissolved substances at all the mass would have increased showing its not pure water

Question 6

how to purify water

Answer 6

-have a conical flask containing our water sample on a tripod and gauze
-the top on the conical flask has a delivery tube and is pointed into a test tube
-test tube is in a beaker containing ice and water
-gently heat the water using a bunsen burner, gently boiling the water
-the water will evaporate forming water vapour, travelling along the delivery tube
-when the water vapour enters the cold test tube it condenses back into liquid water
-this is distilled water, PH7 no dissolved solids