chemistry問題

1) Molar mass of ammonium carbonate = 2 × (14 + 4 × 1) + 12 + 3 × 16 = 96 g/mol
∴ 9.6g of (NH4)2CO3 contains 0.1 moles of substance.
a) According to the formula, one mole of (NH4)2CO3 contains 2 mole of ammonium ions and hence the number of ammonium ions here will be:
0.1 × 2 × 6.02 × 1023 = 1.204 × 1023.
b) According to the formula, one mole of (NH4)2CO3 contains 1 mole of carbonate ions and hence the number of moles of carbonate ions here will be:
0.1 × 1= 0.1.
c) As from (a), there are 0.2 moles of ammonium ions and since one ammonium ion contains four hydrogen atoms, the number of moles of hydrogen atoms will be 0.8 moles.
d) Further from (c), number = 0.8 × 6.02 × 1023 = 4.816 × 1023.
2a) Molar mass of water = 2 × 1 + 16 = 18 g/mol. It is not easy to measure one mole of water since it is rather difficult to count the number of water molecules to be as exactly as 6.02 × 1023.
b) Mass of one water molecule = 18/(6.02 × 1023) = 2.99 × 10-23 g.
c) If 1018 is selected to be number of particles in one mole of substances, then molar mass of water will be 2.99 × 10-23 × 1018 = 2.99 × 10-5 g/mol and in this case, measurement of one mole of water is even more difficult than before since it is rather difficult to find out the measuring device having a precision scale as 10-5 g.
3a) Number of moles = 3.01 × 1024/6.02 × 1023 = 5
b) Molar mass of Na2SO4 = 2 × 23 + 32 + 4 × 16 = 142 g/mol
So in 2.84 g, there are 0.02 moles of compound.
Moreover, in one mole of Na2SO4, there are 2 moles of sodium ions and 1 mole of sulphate ions, summing up to a total of 3 moles.
Therefore the number of moles of ions in 2.84 g of Na2SO4 = 0.02 × 3 = 0.06