calculate the number of atoms in aluminium weighing 28
Answers
Explanation:
Explanation:
The key to this problem is the correct interpretation of what atomic weight means.
Notice that aluminium is said to have an atomic mass of
26.982 u
. The unit used here is the unified atomic mass unit,
u
.
The unified atomic mass unit is defined as
1
12
th
of the mass of a neutral carbon-12 atom and is approximately equal to the mass of one nucleon, as in the mass of one proton or one neutron. Also, you should know that you have
1 u
x
=
x
1 g/mol
This means that the mass of one mole of aluminium atoms will be
26.982 g
.
As you know, one mole of any element contains exactly
6.022
⋅
10
23
atoms of that element.
This means that if you know how many moles of aluminium you have in
4.55 g
, you can use Avogadro's number to find the number of atoms.
4.55
g
⋅
1 mole Al
26.982
g
=
0.168631 moles Al
Therefore, you will have
0.168631
moles of Al
⋅
6.022
⋅
10
23
atoms of Al
1
mole Al
=
1.02
⋅
10
23
atoms of Al
The answer is rounded to three sig figs, the number of isg figs you gave for the mass of the sample.