Calculate the relative molecular mass of Na₂CO₃.10H₂O [H=1, C=12; Na=23; O=16]

Explanation

Na₂CO₃.10H₂O is called washing soda or hydrated sodium trioxocarbonate(IV). The “.10H₂O” means 10 molecules of water are attached to each unit of Na₂CO₃. This is called a hydrated salt, and we must include the water when calculating the total molecular mass.

First, calculate the mass of Na₂CO₃:

Na₂ = 2 × 23 = 46
C = 1 × 12 = 12
O₃ = 3 × 16 = 48
Total for Na₂CO₃ = 46 + 12 + 48 = 106

Next, calculate the mass of 10H₂O:

One H₂O = (2 × 1) + (1 × 16) = 2 + 16 = 18
10H₂O = 10 × 18 = 180

Finally, add both parts together:

Na₂CO₃.10H₂O = 106 + 180 = 286

The relative molecular mass of Na₂CO₃.10H₂O is 286.