Paper 33, Tue 24 May, Session 2 Paper 34, Thurs 2 June, Session 2 Lab practical's 2016 Paper 33, Tue 24 May, Session 2 Paper 34, Thurs 2 June, Session 2

General Advice RTQ3. Read the paper three times..... 1. The whole question before attempting to answer. Get an overview of what’s needed and see the inter-relationship between each part of the question. 2. Read carefully the part you now need to start answering* Sketch what you have to do

General Advice RTQ3 3. Once your answer is written, re-read the question.... Does the answer you’ve written actually answer the question stated?

Suggestion: Turn the instructions into pictures

FOLLOW THE INSTRUCTIONS… DO WHAT YOU ARE INSTRUCTED TO DO This is a test of your practical ability to carry out instructions, not a measure of your creativity or expanded chemical knowledge.

Indicators… “Is this the right colour Sir?”

Bromophenol blue

Phenolphthalein

It’s… 21.15 cm3

It’s… 41.15 cm3

Different backgrounds can help clarify where the meniscus is. It’s… 1.40 cm3

IF you use a funnel, DON’T FORGET TO REMOVE IT IF you use a funnel, DON’T FORGET TO REMOVE IT! Take Burette out of the stand for filling (I avoid using it, although there’s a greater risk of splashing)

Rinse down your titrant and analyte splashes Rinse down your titrant and analyte splashes. Titrations involve balancing the number of moles after which the volumes are read and if necessary, concentrations can be calculated.

It’s… 21.85 cm3

Top: 0.10 to 22.10 Bottom: 0.30 to 22.30

Mass generally to 2 dp.

Mass of EMPTY CONTAINER (handy for mistakes) TARE (if instructions don’t disallow) Take contain off balance Add compound Put container back on balance Remove excess material off the balance also

Be careful with titre values Can use rough reading. I really discourage it though! Rough Accurate titrations titration 1 2 3 Final burette reading / cm3  23.10  43.50   Initial burette reading / cm3  0.80  22.20 Vol of FB2 used / cm3  21.35  21.30 Used this for average titre

Be careful with titre values 1 dp accepted for rough, but ALWAYS BEST to always do 2 dp !! Can use rough reading. I really discourage it though! Rough Accurate titrations titration 1 2 3 Final burette reading / cm3  22.3  43.50  21.30  42.60 Initial burette reading / cm3  0.8  22.20  0.30 Vol of FB2 used / cm3  21.5 Used this for average titre   Indicate which you will use for average titre

Previous table = ‘suspicious’ Why….? Rough Accurate titrations titration 1 2 3 Final burette reading / cm3  22.3  43.50  21.30  42.60 Initial burette reading / cm3  0.8  22.20  0.30 Vol of FB2 used / cm3  21.5 Used this for average titre  

Previous table = ‘suspicious’ Why….? Rough Accurate titrations titration 1 2 3 Final burette reading / cm3  22.3  43.50  21.30  42.60 Initial burette reading / cm3  0.8  22.20  0.30 Vol of FB2 used / cm3  21.5 Used this for average titre   READ THE BURETTE ACCURATELY

YOU MUST SHOW YOUR CALCULATION for the average titre. Don’t just report a number. E.g. Average =21.30 Show it e.g. x+y+z / 3 if, say, you had 32.35, 32.45 32.40

STOPWATCH…. Round to the nearest second << The instructions for timing are supposed to say this.

Thermometers can be read half way between their graduation marks. E. g Thermometers can be read half way between their graduation marks. E.g. a 1oC thermometer can be read to the nearest 0.5 oC, Generating temperature data like 20.5, 18.5, 16.0, i.e. the decimal figure is either a 0 or a 5. Similar to reading half way between graduations on a burette (but that’s +/- 0.05 for a burette)

Be careful with significant figures… Keep “big calculator numbers in your calculator for use later on.” but report step-wise calculations to the correct number of s.f. IF you use the rounded up figures for later calculation, your error will rapidly increase. Your answer can NEVER be more accurate than the data it came from so of data = 3s.f. combined with data with 4 s.f. then answer should be to 3 s.f.

Graphs - rare for paper 3. Usually Paper 5!! “Draw a line of best fit” – sometimes can mean a “curve of best fit”. It did not say “draw a straight line of best fit!”

TRUST YOURSELF !!!!! Make sure you get the practical data FIRST…. Do the calculations only after you have gotten your ALL THE data.