CHEMISTRY COMMUNITY

Do molar masses contribute to your calculation of significant digits? For instance, if part of your calculation(i.e. grams of C) has 3 significant figures, and the molar mass has 2 significant figures, and I use both to come up with my answer, should my answer have 2 significant figures?

Things that are constant such as molar masses should not be taken into consideration for sig. fig.. We normally determine the number of sig.fig. by looking at the number given by the question that has the least number of sig. fig..

In addition to looking at the lowest number of significant figures, also keep in mind some common rules:

1. 300- 1 significant figure we do not count the zeroes after 3 for sig figures.
2. 0.50- 2 significant figures, we do count the zeroes that come after the decimal point.

When calculating, the constant values given should not be considered in terms of rounding for significant figures. The given values of a substance in the question with the least significant figures is what should be taken into consideration for rounding. The rest of the calculation should be done with as many decimals as possible to make it the most accurate.

I agree with the previous posters that constant values, like molar mass, should not count toward significant figures. Also, to add on to what Riya said, it's true that a whole number with zeroes like "300" only has one significant figure. However, if there is also a decimal point after this number, then there is more than one significant figure (e.g. 300.0 has four significant figures). I've noticed that the textbook reports values like this pretty frequently. I hope this makes sense!

No, do not use molar masses as part of figuring out how many significant figures should be used. Only use given usable values in the equation.