Practice, with the answer to each question folded up underneath it.
These are not marked, not counted, and not collected. Ever. They are how you find out whether you understood something before a test tells you that you did not.
How to use these pages
Answer the question first, on paper, all the way to a number with a unit. Then click the answer to unfold it.
Reading a worked answer feels like learning and mostly is not — recognising an answer is a completely different skill from producing one, and only one of them is any use in an exam.
Try it: click this line
That is what every answer on these pages looks like. Nothing is hidden from you — it is hidden from your eye, so that a page of questions stays a page of questions until you have had a go.
Every answer here is worked, not stated. The number at the end is the least interesting part; the reasoning above it is the part worth holding against your own.
Three rules that apply to every set
Carry the units through the working, not just onto the answer. If the units do not cancel to what you wanted, the arithmetic is wrong and the units have just told you so before you lost a mark for it. This is the cheapest error check in chemistry and almost nobody uses it.
Round once, at the end. Molar masses to two decimal places, every intermediate value kept at full precision in the calculator, and the final answer rounded to the number of significant figures the data allow. A number rounded twice is a number you can no longer defend. See Significant Figures and Units and Significant Figures in Practice.
Sanity-check before you move on. Is the answer roughly the size you expected? Is a mass positive, a yield near 100%, a temperature above absolute zero, a product mass in the same range as the reactant mass? A five-second check catches most of what a whole page of working can get wrong.
What each set is shaped like
Each set ramps. The first questions are routine and the last ones are not, and somewhere near the end of every set is a question asking you to say what is wrong with somebody else’s answer. Those are the ones worth doing slowly — finding the flaw in a plausible piece of reasoning is the skill the tests are actually built around, and it is also what you will be doing to your own lab data all year.
Stuck partway through a set? That is the set doing its job. Start with Getting Unstuck, and bring the specific question to Help Sessions rather than “I don’t get moles”.