Everything Science Grade 10

19.1 CHAPTER 19. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE

Step 1:Write down the equation

n=Mm

Step 2:Find the moles

n=^127 g

63 , 5 g·mol−^1

= 2mol

There are 2 moles of copper in the sample.

Example 4: Calculating atoms from mass

QUESTION

Calculate the number of atoms there are in a sample of aluminium that with a

mass of 81 g.

SOLUTION

Step 1:Find the number of moles

n=Mm=^81 g

27 , 0 g·mol−^1

= 3mol

Step 2:Find the number of atoms

Number of atoms in 3 mol aluminium= 3× 6 , 022 × 1023

There are 1 , 8069 × 1024 aluminium atoms in a sample of 81 g.

338 Chemistry: Chemical change