RP3 - The effect of temperature on rate of reaction
Describe the method
- Measure out 10cm^3 of 1 mol/dm HCl with a measuring cylinder into a test tube and warm in a water bath using water from a kettle.
- Measure out 25cm^3 of Na2S2O3 using a measuring cylinder into a conical flask and warm in water bath, placing a visible cross underneath.
- Measure initial temperature using a thermometer and add 1cm^3 of the HCl to the thiosulfate solution, starting the timer immediately.
- Stop timer when the cross is no longer visible and record time taken. Ensure same person judges visibility of cross for every repeat.
- Record final temperature and dispose of the contents into a waste container.
- Obtain repeats for at least 4 different temperatures. Plot a graph of results with temperature against 1/t.
this is an initial rates method
RP3 - The effect of temperature on rate of reaction
sodium thiosulfate reacts with hydrochloric acid according to the equation…
Na2S2O3(aq) + 2HCl(aq) –> 2NaCl(aq) + S(s) + SO2(g) + H2O(l)
SO2(g) - choking gas
S(s) - precipitate
RP3 - The effect of temperature on rate of reaction
why are both the initial and final temperatures measured in this experiment?
to calculate an average temperature during the experiment since it starts to cool to room temperature
RP10 - Organic prep and purification
Describe the method
- Dissolve solid in minimum amount of hot solvent to form a saturated solution
- Filter when hot to remove insoluble impurities
- Let solution cool so crystalisation can occur
- Filter under reduced pressure
- Add cold solvent to dissolve any solubke impurities
- Leave to dry overnight
RP10 - Organic prep and purification
How is solvent chosen?
the solid must be soluble in hot solvent and readily dissolve, but needs to be insoluble in cold solvent
RP10 - Organic prep and purification
Why is a clean spatula used to compress the crystals during pressure filtration?
to allow air to pass through the sample and not only around it so it can be dried more effectively
RP10 - Organic prep and purification
Why is the sample washed with cold solvent?
to dissolve soluble impurities
this is because both the solid and the soluble impurities dissolve in hot solvent. however, only the impurities are soluble in cold solvent and solid is insoluble in cold solvent. when solution cools, the solid crystallises out and soluble impurities are left in the solution.
RP6 - Identifying organic compounds
How do you prepare Tollens’ reagent?
Add Icm^3 of 1 moldm^-3 of silver nitrate into a test tube. Add drops of 0.4 moldm^-3 of NaOH using a different dropping pipette into the test tube. This forms a brown precipitate. Add drops of ammonia solution and shake until the ppt redissolves. This forms Tollens’ reagent,
