You may also like

problem icon

Epidemic Modelling

Use the computer to model an epidemic. Try out public health policies to control the spread of the epidemic, to minimise the number of sick days and deaths.

problem icon

Very Old Man

Is the age of this very old man statistically believable?

problem icon


bioNRICH is the area of the stemNRICH site devoted to the mathematics underlying the study of the biological sciences, designed to help develop the mathematics required to get the most from your study of biology at A-level and university.


Stage: 5 Challenge Level: Challenge Level:1


A spectophotometric assay is made by mixing a salt solution, acid buffer, bacterial cells and an enzyme catalyst. Using your skills of proportional reasoning, work out the volumes of given reagents required to create the standard assay. There are two different types of question: one in which you find the missing volumes and another in which you find the missing concentrations. Type your answers into the boxes and check them or generate new questions using the buttons.

If you can see this message Flash may not be working in your browser
Please see to enable it.

View in full screen mode


Mixing solutions of given concentrations from reagents in other concentrations is an essential scientific skill in the laboratory. In this question we convert between various ways of representing concentration and practise the crucial skill of dilutions. Recall that a concentration of, for example, $3.2$M means $3.2$ moles per litre and that the molecular weight is the weight in grammes of 1 moles of a compound.