Practical 1- Paper 1 And 3- Amount Of Substance Flashcards
How to make up a standard solution- 6 marks
Stage 1: transfers known mass of solid
A. Weigh the sample bottle containing the solid on a balance
B. Transfer to beaker and reweigh the sample bottle
C. Record the difference in mass
Stage 2:
A. Add distilled/deionised water
B. Stir with a glass rod
C.until all has dissolved
Stage 3:
A. Transfer to volumetric flask using a funnel
B.with washings
C. Make up to 250cm3
D. Shake/invert to mix
3 keys points for titration
- normally assessed as a calculation
- concordant results are +/- 0.1 cm3
Calculation for percentage error
Error of equipment/ amount measured. X100
How do you reduce percentage error
Use a larger titre volume
(Increase the concentration in the conical flask and decrease the concentration in the burette)
Why is it important to remove any air bubbles from the burette tap and what will it do to the titre
The volume of the air bubbles would be counted in the burette reading
Titre value will increase
Why is it important to remove the funnel used to fill up the burette before starting a titration
Solution drops could fall from the funnel into the burette and affect the burette reading
Why is it good practice to swirl the concical flask and rinse the walls of the concical flask with distilled water during a titration
Ensures all reagents mix and no reagent is left unreacted on the sides of the flask
Why does adding water to the concical flask not affect titre value
It doesn’t change the moles
Why is a conical flask preferred to a beaker for the titration
Less chance of spilling liquid whilst swirling
What should the burette be washed with before doing a titration
Whatever solution it is going to be filled with
Why not wash the walls with distilled water
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 it is going to contain
What should the Pipette used to fill up the conical flask be washed with
Whatever solution it is going to contain
Why is it bad practice to wash the pipette with water before using it to fill up the conical flask
Water would take up the space in the pipette and decrease the number of moles transferred to the conical flask, which would reduce the number of moles transferred to the conical flask, which would reduce the volume needed for the burette for complete reaction
