Chemistry exercise

Use it when students should produce chemical notation rather than recognise it: writing the formula of a product, completing an ion, or balancing an equation. You write the complete, correct notation and choose which positions to leave blank, so one question type covers anything from a single missing subscript to a full balancing exercise, and the answers are checked automatically.

1. In a worksheet, use the + between two items and choose Chemistry exercise. Click the pencil to open it and write the question.

2. Type the complete formula or equation into Formula or equation, for example Ca + Cl2 -> CaCl2, and press Enter.

3. If you want the equation written balanced, Balance the equation fills in the coefficients; when they add up, the button reads Balanced.

4. Under Choose what the student fills in, click the positions to leave blank: a coefficient, a subscript or an element symbol, or Whole substance under a formula to blank out all of it. All coefficients, All element symbols and All subscripts mark every position of that kind at once, and Clear removes all marks.

5. Click the tick when you are done.

If you mark nothing, students write the whole formula or equation themselves. A warning under the field tells you if the equation cannot be balanced or cannot be read, because then answers cannot be marked.

Each blank is a box students tap to fill in. A blank formula opens the formula builder: they pick elements from the periodic table, set the number after each element with the lower arrows or by typing, and click Done. Write it as text lets them type the formula instead. Coefficient and subscript boxes take whole numbers, and a coefficient of 1 can be left empty, as it is in chemistry. Then they submit.

If the presentation shows correct answers, each position is marked right or wrong after submitting, with a short note where it helps, such as Not balanced yet: Fe, O or that every coefficient is twice too large.

Answers are marked automatically, position by position:

• A formula is correct if it has the right elements in the right numbers. The order of elements, and of substances on each side, does not matter. A state symbol is checked only if you wrote one.

• Element symbols must match exactly, capital letters included, because Co and CO are different things.

• For coefficients, any set that balances the equation in lowest terms is correct. A balanced answer with every coefficient doubled is partly correct.

• An answer with some positions right is partly correct.

Open Results on the question to see what each student entered.

• Blank the one or two positions that carry the idea you are teaching, such as the subscript that follows from the ion charges, rather than everything at once.

• For balancing, write the equation without coefficients and use All coefficients. You do not need to balance it first: any correct balance is accepted.

• Building a formula asks more than choosing one, so it works well once students have met the ions in an explanation or a table.