[Update] Please refer to the latest post https://www.simplechemconcepts.com/tips-for-o-level-pure-chemistry-paper-3-practical-exam-2018/
Today’s blogpost we will discuss on some of the important tips for Chemistry Practicals & SPA (School-based Science Practical Assessment) ..In fact, i won’t even call it tips but some crucial things that you would need to take note in Chemistry Practicals.
I received an email enquiry last few days from a local student that is seeking for some “tips for chemistry practicals” for her Pure Chemistry Practical Exams on 9th October and decided to siphon out an hour to share some important points. “Zhiying” – i hope you are in time to read this email before your Chemistry Practical Exams.
Before going to a Chemistry Practical or SPA exams, you must first be very sure of the type of questions (and thus the hands-on practicals) that you will be tested. You should have some experiences by now, based on those Chemistry Practicals sessions you went through with your school teachers. Check your Practical Worksheets to revise..
In a Snap-Shot, you will be tested on:
(a) quantitative experiments involving the use of a pipette, burette and an indicator such as methyl orange or screened methyl orange; if titrations other than acid/alkali are set, full instructions and other necessary information will be given;
(b) speeds of reaction;
(c) measurements of temperature based on thermometers with 1oC graduations;
(d) problems of an investigatory nature, possibly including suitable organic compounds;
(e) simple paper chromatography;
(g) tests for oxidising and reducing agents as specified in the syllabus;
(h) identification of ions and gases as specified in the syllabus
The question paper will contain notes on qualitative analysis for the use in the examination.
Candidates may also be required to perform simple calculations.
See below for important TIPS on Chemistry Practicals – I have split them into the 2 major tests: Qualitative Analysis & Volumetric Titrations
Common Mistakes: Wrong Observations in Qualitative Analysis (Identification of Ions & Gases)
(a) Some students think there must always be a visible change in every test. In fact, sometimes the examiners want to test you on your “confidence” – nothing happens in some tests and you should record “No Change” or “No Reaction”. It is incorrect to write down changes when you actually see nothing. One Word – Have confidence in yourself!
(b) It is incorrect to state that you observe a “colourless gass” in any experiment. The most you can see is “bubbles of colourless gas”. If not, state some other tests on how you can verify that a certain colourless gas (such as O2, H2 and CO2) is produced.
(c) If you are asked to heat up an unknown substance with sodium hydroxide (NaOH) and Aluminium, don’t assume that ammonia gas (NH3) is the gas given off. It could be hydrogen or other gas. Obtain your answer from your observations and not from memorizing the theory.
(d) Observations on Effervescence are commonly missed out from students. Remember to focus your attention to see if there is an BUBBLES!
(e) When describing solutions, do NOT use the word “clear” when you mean colourless. In chemistry, Clear just means that you can see through it, and the opposite of Cloudy. Use Colourless!
(f) When observing colour changes, make sure that you observe all the colour changes, not just the first and last colours.
Common Mistakes: Volumetric Titrations
(a) In volumetric titrations, students are required to repeat the experimental steps until they get at least two consistent results and tick them.
(b) You must average the consistent results that you have ticked, and not all the titration results (cos some maybe off specs/accuracy due to human error)
There are alot more things that you need to pay special attention to in a Chemistry Practical Exam.
Until next time (next year i will have the Master Your Chemistry Practicals Guidebook ready- tentative name). Stay tuned if you are taking your major Chemistry Practical Exam next year or so…
Wishing all the best in your Chemistry Practicals Exams,
Master Trainer & Author