- sulfur dioxide will never be tested (for gas test) → it is toxic gas
- chlorine possibility as it is smelly
- for PPT → just state colour of PPT formed, or what PPT is formed. Colour of solution is not necessary
- Special cases when solid is deposited at the bottom → you can say “solution above turns from xxx to xxx” and a xxx solid is deposited at the bottom
- Hydrogen peroxide → most likely gas is always oxygen
- when you have colourised solution → you want to answer with regards to change that happened to that coloured solution. (e.g. purple solution is decolourised.)
Potassium Manganate
- Very obvious as it is a strong purple
- First marking point is stating whether it is decolourised or not
- Do not use the word precipitate when brown/black solid is formed as it is not formed immediately
Precipitate Recordings
- Do not use this word when the precipitate is not formed immediately
Gas Recordings
- identify the gasses formed.
- No metal used → very low chance that hydrogen is formed. always test for oxygen first
Others
- When question asks you to repeat or add drop by drop → don’t waste time writing down every single drop and its effects. Write down with regards to time taken for colour change. E.g. time taken for xxx to happen becomes shorter/longer
Accuracies
- electronic balance - 2 d.p.
- stopwatch: whole number
Table
- unless given column for computed data, only record measured data in the table
if graph has anomolous point as the last point, then dont draw line until that value.
Titration
- final reading must be above the initial reading. else it will be marked wrong in the table.
Others
- don’t write increases at decreasing rate or vice versa. just write increases or decreases
QA
Gas Tests
-
if metal, prep hydrogen gas (most likely)
-
if metal compound, prep carbon dioxide test. (most likely)
-
if there is any oxidising agent added, prep for oxygen gas test
-
if there is any reducing agent added, prep for hydrogen gas test
Usage of Instruments
How to use a syringe?
- before placing syringe in the liquid, ensure the plunger is pushed out all the way
- this ensures that there is no solution in syringe before we obtain solution of interest, as well as no air bubbles
- place syringe in liquid, ensuring that the tip of the syringe is fully submerged in the liquid
- draw up liquid by pulling plunger of the syringe to the desired marking, and go slightly higher
- push out the remaining liquid with the syringe markings placed in line with our eye to reduce parallax error, and stop when the reading is the reading we want (e.g. 5 cm3)
- OR place syringe markings perpendicular to the line of sight of our eye to prevent parallax (preferred)
Limiting Reagents
**How should i confirm whether reagent is limiting or not, purely based off observations?”
- all the solid has dissolved. i.e. there is no solid left. all solid has reacted