PRACTICAL GUIDE Flashcards
6 marker standard solutiom
Weigh sample bottle conatining solid on a balance
Transfer sample to beaker and reqeigh sample bottle
Record difference in mass
Add distilled water
Stir
Until solid dissolved
Transfer to volumetric flask using funnel
With washing
Make upto 250cm3
Mix
Percentage error
(Eror in experiment x 100)/ amount measured
Why is it important to remove any air bubbles from the burette tap
Volume of air bubble would be counted in the burette reading
If bubble was not rmoved from the burette tap , how would this effect the titre
Increase it
Why is it important to remove funnel used to fill up the burette before starting a funnel
Solution drops could fall from the funnel intothe burette and affect the burette reading
Why is it good practice to swirl the clonical flask and rinse the walls of the clonical flask with distillated water during titration
Encures all reactants mix and no reagents is left untreated on sides of flask
Why does adding water to the conical flask not affect the titre?
It doesn’t change the number of moles in the conical flask
Why is a conical flask is preferred to a beaker for a titration?
There is less chance of splashing liquid while swirling
What should the burette be washed with before a titration?
Whatever solution it is going to be filled with
Why is it bad practice to wash the burette with water before a titration?
Water would decrease the concentration of the solution in the burette, which would increase the titre
- What should the pipette used to fill up the conical flask be washed with?
Whatever solution is going to be put in the conical flask
10.Why is it bad practice to wash the pipette with water before using it to fill up the
conical flask?
Water would take up space in pipette and decrease the number of moles
transferred to the conical flask, which would reduce the volume needed from the
burette (titre) for complete reaction
6 marker measurement of an enthalpy change
Record the temperature for a suitable time (3 minutes) before adding reactants together
• To establish an accurate initial temperature
• Mix reactants then record temperature every minute until a trend is seen
• Plot a graph of temperature against time
• Extrapolate the cooling curve back to the point of addition
• To establish a theoretical temperature change accounting for heat loss
The initial rate of the reaction between sodium thiosulfate and hydrochloric acid
can be monitored by measuring the time taken for a fixed amount of sulfur
to be produced.
Na2S2O3(aq) + 2 HCl(aq) → 2 NaCl(aq) + SO2 (g) + S(s) + H2O(l)
Describe an experiment to investigate the effect of temperature on the
initial rate of this reaction.
Include
• a brief outline of your method
• how you will measure the time taken for a fixed amount of sulfur to
be formed
• how you will present your results in graphical form
• a sketch of the graph that you would expect.
Stage 1 Method
(1a) Idea of using disappearing cross or colorimetry
(1b) Puts acid into container on cross or in
colorimeter
(1c) Add second reactant and start timing
Stage 2 Measurements
(2a) Repeat at different temperatures
(2b) Record time, t, for cross to disappear / defined reading on colorimeter
(2c) ensure other variables (cross, volumes, concentrations) kept constant
Stage 3 Use of Results
(3a) 1/t is a measure of rate
(3b) plot of rate against T
(3c) sketch of plot as shown
Initial Rates
A(aq) + B(aq) + C(aq) → D(aq) + E(aq)
In aqueous solution, A, B, C and D are all colourless but E is dark blue.
A reagent (X) is available that reacts rapidly with E. This means that, if a small amount of X is included in the initial reaction mixture, it will react with any E produced until all of the X has been used up.
Explain, giving brief experimental details, how you could use a series of experiments to determine the order of this reaction with respect to A. In each experiment you should obtain a measure of the initial rate of reaction.
Stage 1 Preparation
1a Measure (suitable/known volumes of) A, B and C
1b Use of colorimeter
1c into separate container(s)
Stage 2 Procedure
2a Start clock/timer at the point of mixing
2b Take series of colorimeter readings at regular time intervals
2c Use of same concentration of B and C / same total volume / (same
volume/amount of X)
2d Same temperature
2e Repeat with different concentrations of A
Stage 3 Use of Results
3a Plot absorbance vs time and measure/calculate gradient at time=0
3b plot of gradient against volumes/concentrations of A
3c description of interpreting order from shape of 1/time vs volume or concentration graph