Required practicals paper 2

• Use a measuring cylinder to put 10cm3 of sodium thiosulfate into a conical flask • Place the conical flask onto a printed black cross • Add 10cm3 of hydrochloric acid into the conical flask • Swirl the solution and start a stopwatch • Look down though the top of the flask and after a certain time, the solution will turn cloudy • Stop the stopwatch after you cant see the cross • Carry out the experiment again using lower concentration of sodium thiosulfate solution • Repeat the whole experiment and calculate the mean for each concentration of sodium thiosulfate solution

turbidity

it can be repeated by another person or using a different technique or equipment and still get the same resul

different people have different eyesights, meaning some people can see the cross for longer than others, so they mat not get the same results

use the same size printed cross

• Use a measuring cylinder to place 50cm3 of hydrochloric acid into a conical flask • Attach the conical flask to a bung and 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 hydrochloric acid and start a stopwatch • the reaction produces hydrogen gas which is trapped in the measuring cylinder • every 10 seconds, we measure the volume of hydrogen gas in the measuring cylinder • Continue until no more hydrogen is given off • Repeat the experiment with different concentrations of hydrochloric acid

the greater the concentration of a chemical in a reaction, the faster the reaction takes place

• instead of using a measuring cylinder to measure volume, use a gas syringe • use cotton wool to stop acid splashing out

to work out the colours in food colouring

• Use a ruler to draw a horizontal pencil line on the chromatography paper • Mark 5 pencil spots at equal spaces across the line, leaving at least 1cm clear at each side • Use a capillary tube to put a small spot of each of the known food colours and the unknown colour onto the pencil spots • Pour water into a beaker to a depth of 1cm and attach the paper to a glass rod using tape, and lower the paper into the beaker • The water will move up the paper and the colours will be carried up • Remove the paper when the water has travelled around 3/4 up • Use a pencil to mark the point that the water has reached • Hang the paper up to dry

to prevent the colours spreading into each other later

because if not, the water will wash the ink off the line

because if that happens, it will interfere with the way the water moved

to reduce evaporation of the solvent

• position of beaker

• Check the pH of the water by placing a small drop of the water on a piece of universal indicator paper • if pH is not 7, water contains dissolved acid or alkali and is therefore not pure - if the pH is 7, it doesnt mean the water is pure, we still need to test for dissolved solids • Use a balance to weigh an empty evaporating basin and record the mass • Fill the evaporating basin with our water sample and place this on a tripod and gauze • use a bunsen burner to gently heat the water until it has all evaporated • allow the evaporating basin to cool and weigh it again - if the water sample contained any dissolved solids, the mass of the empty evaporating basin wouldve increased

because the water has evaporated, but the dissolved solids would have formed crystals on the surface of the evaporating basin

• conical mask containing water sample • conical flask is on a tripod and gauze • the top of the conical flask has a delivery tube and is pointed into the test tube • the test tube is sitting in a beaker containing ice and water • gently heat the water using. a bunsen burner • The water will evaporate and form water vapour/ steam • the water vapour then travels along the collecting tube • when the water vapour enters the cold test tube, it condenses into liquid water - this is distilled water, which contains no dissolved solids and has a pH of 7 (it is pure)