Required practicals paper 2 Flashcards
Rate of reaction practical
- 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
what is the science word for cloudiness
turbidity
how can we tell a measurement is reproducible
it can be repeated by another person or using a different technique or equipment and still get the same resul
what is the problem with using a cross
different people have different eyesights, meaning some people can see the cross for longer than others, so they mat not get the same results
how to fix the disappearing cross problem
use the same size printed cross
Rate of reaction (GAS)
- 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
what is the result of these two experiments
the greater the concentration of a chemical in a reaction, the faster the reaction takes place
how can we make the practical more accurate
- instead of using a measuring cylinder to measure volume, use a gas syringe
- use cotton wool to stop acid splashing out
What is the aim of the paper chromatography experiment
to work out the colours in food colouring
Paper chromatography experiment method
- 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
why is it important that we keep the spots on the chromatography paper relatively small
to prevent the colours spreading into each other later
why must the pencil line with the spots of ink be above the surface of the water
because if not, the water will wash the ink off the line
why must the sides of the paper not touch the sides of the beaker walls
because if that happens, it will interfere with the way the water moved
why would we put a lid on top of the beaker in paper chromatography
to reduce evaporation of the solvent
control variables - paper chromatography
- position of beaker
