Question

When calculating molar mass , can you round it or it has to be specific ?

Answer 1

For many (but not all) problems, you can simply round the atomic weights and the molar mass to the nearest 0.1 g/mole. HOWEVER, make sure that you use at least as many significant figures in your molar mass as the measurement with the fewest significant figures. In other words, never let your molar mass be the measured value that determines how many signficant figures to use in your answer!