Question

MOLES AND MASS

Name
Determine the number of moles in each of the quantities below.
1.25 g of Naci
2. 125 g of H,504
3. 100. g of KMnO,
4.'74 g of KCI
5. 35 g of CuSO,•54,0

Answer 1

1) 0.428 mol

Here the compound that we have is
`NaCl`.

We know that:

- Molar mass of sodium (
`Na`):
`22.990 g/mol`

- Molar mass of chlorine (
`Cl`):
`35.453 g/mol`

Since the ratio between
`Na,Cl` in the compound is 1:1, the molar mass of the
`NaCl` is:

`M_(NaCl)=M_(Na)+M_(Cl)=22.990+35.354=58.344 g/mol`

Here the mass of the compound is

`m=25 g`

Therefore, the number of moles is:

`n=(m)/(M)=(25)/(58.344)=0.428 mol`

2) 1.27 mol

The compound in this problem is

`H_2 SO_4`

The molar mass of each element is:

`M_H=1.0079 g/mol` (hydrogen)

`M_S=32.065 g/mol` (solphur)

`M_O=15.994 g/mol` (oxygen)

In this compound, we have 2 atoms of hydrogen, 1 atom of solphur and 4 atoms of oxygen, therefore the total molar mass is:

`M_(H_2SO_4)=2M_H+M_S+4M_O=2(1.0079)+(32.065)+4(15.994)=98.057 g/mol`

Here the mass of the compound is

`m=125 g`

So the number of moles is

`n=(m)/(M)=(125)/(98.057)=1.27 mol`

3) 0.633 mol

The compound in this problem is

`KMnO_4`

The molar mass of each element is:

`M_K=39.0983 g/mol` (potassium)

`M_(Mn)=54.9380 g/mol` (manganese)

`M_O=15.994 g/mol` (oxygen)

Here we have 1 atom of potassium, 1 atom of manganese and 4 atoms of oxygen, so the total molar mass of the compound is

`M=M_K+M_(Mn)+4M_O=(39.0983)+(54.9380)+4(15.994)=158.012 g/mol`

Here the mass of the compound is

`m=100 g`

So the number of moles is

`n=(m)/(M)=(100)/(158.012)=0.633 mol`

4) 0.993 mol

The compound in this problem is

`KCl`

The molar mass of each element is:

`M_K=39.0983 g/mol` (potassium)

`M_(Cl)` =
`35.453 g/mol` (chlorine)

So, the total molar mass of the compound is:

`M_(KCl)=M_K+M_(Cl)=39.0983+35.453=74.551 g/mol`

The mass of the compound here is

`m=74 g`

Therefore, the number of moles is

`n=(m)/(M)=(74)/(74.551)=0.993 mol`

5) 0.140 mol

The compound in this problem is

`CuSO_4\cdot 5H_2O`

The molar mass of each element is:

`M_(Cu)=63.546 g/mol` (copper)

`M_S=32.065 g/mol` (solphur)

`M_O=15.994 g/mol` (oxygen)

`M_H=1.0079 g/mol` (hydrogen)

Here we have 1 atom of copper, 1 of solphure, (4+5=9) of oxygen, and (5*2=10) atoms of hydrogen, so the total molar mass is

`M=M_(Cu)+M_S+9M_O+10M_H=\\=63.546+32.065+9(15.994)+10(1.0079)=249.636 g/mol`

Here the mass of the compound is

`m=35 g`

So, the number of moles is

`n=(m)/(M)=(35)/(249.636)=0.140 mol`