Question #68fe6

The problem wants you to use the number of moles, `n`, present in a sample of a given compound and the molar mass, `M`, of said compound to determine the mass of the sample, `m`.

The idea here is that a compound's molar mass can be used as a conversion factor between number of moles and mass expressed in grams.

That is the case because the molar mass essentially tells you the mass of one mole of a given compound. In your case, the compound is said to have a molar mass of

`M = "44 g/mol"`

This tells you that every mole of said compound has a mass of `"44 g"`.

Since you know that the sample contains `0.0021` moles, you can say that its mass will be equal to

`0.0021 color(red)(cancel(color(black)("moles"))) * overbrace("44 g"/(1color(red)(cancel(color(black)("mole")))))^(color(purple)("= molar mass")) = color(green)(|bar(ul(color(white)(a/a)color(black)("0.092 g")color(white)(a/a)|))) ->` rounded to two sig figs.

This can also be calculated by using the equation

`color(blue)(|bar(ul(color(white)(a/a)m = n * M_Mcolor(white)(a/a)|)))`

Since the mass of the sample is equal to the number of moles it contains multiplied by the molar mass of the compound, you will once again have

`m = 0.0021 color(red)(cancel(color(black)("moles"))) * "44 g"/color(red)(cancel(color(black)("mol"))) = color(green)(|bar(ul(color(white)(a/a)color(black)("0.092 g")color(white)(a/a)|)))`

The answer must be rounded to two sig figs because that's how many sig figs you have for the number of moles present in the sample.