Everything Science Grade 10

CHAPTER 19. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE 19.1

(1.) 007j (2.) 007k

An equation to calculate moles and mass ESAFZ

We can calculate molar mass as follows: molar mass (M)=mole (mol)mass (g)
This can be rearranged to give the number of moles:

n=Mm

The following diagram may help to remember the relationship between these three vari-
ables. You need to imagine that the horizontal line is like a division sign and that the
vertical line is like a multiplication sign. So, for example, if you want to calculate M, then
the remaining two letters in the triangle are m and n and m is above n with a division sign
between them. Your calculation will then be M=mn

Tip

Remember that when

you use the equation

n = mM, the mass

is always in grams (g)

and molar mass is in

grams per mol (g·

mol−^1 ). Always write

the units next to any

number you use in a

formula or sum.

m

n M

Example 3: Calculating moles from mass

QUESTION

Calculate the number of moles of copper there are in a sample that with a mass of

127 g.

SOLUTION

Chemistry: Chemical change 337