Question

A sample of Manganese (II) chloride has a mass of 19.8 grams before heating, and 12.6 grams after heating until all the water is driven out. Based on this information, how many water molecules were attached to each molecule of Manganese (II) chloride

Answer 1

no. of water molecules associated to each molecule of
`MnCl_2` = 4

Step-by-step explanation:

Mass of
`MnCl_2` before heating = 19.8 g

Mass of
`MnCl_2` after heating = 12.6 g

Difference in mass of
`MnCl_2` before and after heating

= 19.8 - 12.6 = 7.2 g

Difference in mass corresponds to mass of water driven out.

Molar mass of water = 18 g/mol

No. of moles of water =
`(7.2)/(18) = 0.4\ mol`

Mass of
`MnCl_2` obtained after heating is mass of anhydrous
`MnCl_2`.

Mass of anhydrous
`MnCl_2` = 12.6 g

Molar mass of
`MnCl_2` = 125.9 g/mol

No. of mol of anhydrous
`MnCl_2` =
`(125.9)/(125.9) = 0.1\ mol`

so,

0.1 mol of
`MnCl_2` have 0.4 mol of water

1 mol of
`MnCl_2` will have =
`(0.4)/(0.1) =4\ mol`

Hence, no. of water molecules associated to each molecule of
`MnCl_2` = 4