Method. 1) Work out the concentration in grams per dm3. 1 litre = 1 dm3 = 1000 cm3. 10·6 g of sod ium carbonate in 200 cm3 is equivalent to 10·6 x (1000 ÷ 200) g of sod ium carbonate in 1000 cm = 53 g per dm3. 2) Convert grams per dm3 into mol / dm3.To convert mass into moles use moles = mass ÷ RFM. RFM of ammonium nitrate (NH4NO3) is (1 x 14) + (4 x 1) + (1 x 14) + (3 x 16) = 80. moles = 120 ÷ 80 = 1·5. So, 120 g of ammonium nitrate dissolved in 1 litre of water = 1·5 mol / dm3. Example 2.) Convert grams per dm3 into mol / dm3. To convert mass into moles use moles = mass ÷ RFM. RFM of sod ium carbonate (Na2CO3) is (2 x 23) + (1 x 12) + (3 x 16) = 106. moles = 53 ÷ 106 = 0·5. So, 10·6 g of sod ium carbonate in 200 cm3 of water = 0·5 mol / dm3.