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

Answer:

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

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 =

$\frac{0.787 g}{106 g/mol}=0.007424 mol$

Moles of water = $\frac{1.336 g}{18 g/mol}=0.07422 mol$

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

$\frac{1}{z}=\frac{0.007424 mol}{0.07422 mol}$

z = 9.99 ≈ 10