Calculate the mass fraction (%) of the following substances: a) Na2CO3; b) Ca (H2PO4) 2?
Calculate the mass fraction (%) of the following substances: a) Na2CO3; b) Ca (H2PO4) 2? How many grams of copper is in 5 mol: a) CuO; b) Cu (OH) 2?
The mass fraction of individual atoms of elements in the composition of a substance is as follows:
w% = Mr (element): Mr (total substance) * 100%.
Using this formula, we find the mass fraction of elements in the presented compounds:
a) Na2CO3:
w% (Na) = (2 * 23): Mr (Na2CO3) * 100% = 46: 106 * 100% = 43.4%
w% (C) = 12: 106 * 100% = 11.3%
Then oxygen accounts for 100% – (43.4% + 11.3%) = 100% – 54.7% = 45.3%
b) Ca (H2PO4) 2:
w% (Ca) = 40: 234 * 100% = 17.1%
w% (H) = (4 * 1): 234 * 100% = 1.7%
w% (P) = (2 * 31): 234 * 100% = 30.4%
w% (O) = (8 * 16): 234 * 100% = 54.7%
Now we find the mass of substances, based on the molar amount:
a) m (CuO) = n * M = 5 mol * 80 g / mol = 400 g.
b) m (Cu (OH) 2) = n * M = 5 mol * 98 g / mol = 490 g.