Question

Washing soda is a hydrated compound whose formula can be written na2co3 i zh2o, where z is the number of moles of h2o per mole of na2co3. when a 2.123 g sample of washing soda was heated at 130°c, all of the water of hydration was lost, leaving 0.787 g of anhydrous sodium carbonate. calculate the value of z.

Answer 1

Weight of 1 mole of water = 18

2.123 = .787 + z*18

Answer :z = .074222

Answer 2

The value of z is 10,
`Na_2CO_3.10H_2O`.

Step-by-step explanation:

Mass of washing soda = 2.123 g

Mass of sodium carbonate = 0.787 g

Mass of water = 2.123 g-0.787 g =1.336 g

Wasing soda → Sodium carbonate + water

`Na_2CO_3.zH_2O\rightarrow Na_2CO_3+zH_2O`

Moles of sodium carbonate =

`(0.787 g)/(106 g/mol)=0.007424 mol`

Moles of water =
`(1.336 g)/(18 g/mol)=0.07422 mol`

According to reaction , 1 mol of sodium carbonate obtained with z moles of water.

`(1)/(z)=(0.007424 mol)/(0.07422 mol)`

z = 9.99 ≈ 10