1. The molar mass of a compound is the sum of the atomic masses of all the atoms present in one molecule of the compound. To calculate the relative molecular mass (also called the molecular weight or molar mass) of a compound, we add up the atomic masses of all the atoms in the compound.
1a) H₂SO₄
The atomic masses of H, S, and O are 1.008, 32.06, and 16.00, respectively.
Relative molecular mass of H₂SO₄ = (2 x atomic mass of H) + atomic mass of S + (4 x atomic mass of O)
= (2 x 1.008) + 32.06 + (4 x 16.00)
= 98.08
1b) Ca(NO₃)₂
The atomic masses of Ca, N, and O are 40.08, 14.01, and 16.00, respectively.
Relative molecular mass of Ca(NO₃)₂ = atomic mass of Ca + (2 x atomic mass of N) + (6 x atomic mass of O)
= 40.08 + (2 x 14.01) + (6 x 16.00)
= 164.09
1c) CuSO₄.7H₂O
The atomic masses of Cu, S, O, and H are 63.55, 32.06, 16.00, and 1.008, respectively.
Relative molecular mass of CuSO₄.7H₂O = atomic mass of Cu + atomic mass of S + (4 x atomic mass of O) + (14 x atomic mass of H)
= 63.55 + 32.06 + (4 x 16.00) + (14 x 1.008)
= 249.69
2. An oxide of nitrogen contains only one nitrogen atom per molecule and has a relative molecular mass = 30. Determine its molecular formula.
The relative molecular mass of the oxide of nitrogen (NOx) is 30.
The atomic mass of N is 14.01, and the atomic mass of O is 16.00.
We can set up the equation: 14.01 + 16.00x = 30
Solving for x, we get x = 1.
Therefore, the molecular formula of the oxide of nitrogen is NO.
3. An oxide of nitrogen contains only one oxygen atom per molecule and has a relative molecular mass = 44. Determine its molecular formula.
The relative molecular mass of the oxide of nitrogen (NOx) is 44.
The atomic mass of N is 14.01, and the atomic mass of O is 16.00.
We can set up the equation: 14.01x + 16.00 = 44
Solving for x, we get x = 2.
Therefore, the molecular formula of the oxide of nitrogen is N₂O.
4. An oxide of sulfur contains only one sulfur atom per molecule and has a relative molecular mass = 80. Determine its molecular formula.
The relative molecular mass of the oxide of sulfur (SOx) is 80.
5. The atomic mass of S is 32.06, and the atomic mass of O is 16.00.
We can set up the equation: 32.06 + 16.00x = 80
Solving for x, we get x = 3.
Therefore, the molecular formula of the oxide of sulfur is SO₃.
6. The molar mass of the oxide of silicon (SiOx) is 60 g/mol.
The atomic mass of Si is 28.09, and the atomic mass of O is 16.00.
We can set up the equation: 28.09 + 16.00x = 60
Solving for x, we get x = 2.
Therefore, the molecular formula of the oxide of silicon is SiO₂.
1. The molar mass of Ar is 39.95 g/mol. Therefore, the number of moles of Ar in 8 g is:
moles = mass / molar mass = 8 g / 39.95 g/mol = 0.200 moles
2. The molar mass of H₂SO₄ is 98.08 g/mol (2 + 32 + 32 + 4x16). Therefore, the number of moles of H₂SO₄ in 1.25 kg is:
moles = mass / molar mass = 1250 g / 98.08 g/mol = 12.73 moles
3. The molar mass of Ca(OH)₂ is 74.09 g/mol (40.08 + 2x1.01 + 2x16.00). Therefore, the mass of 0.04 moles of Ca(OH)₂ is:
mass = moles x molar mass = 0.04 moles x 74.09 g/mol = 2.96 g
4. The molar mass of CuSO₄·5H₂O is 249.68 g/mol (63.55 + 32.07 + 4x16.00 + 5x18.02). Therefore, the mass of 0.001 moles of CuSO₄·5H₂O is:
mass = moles x molar mass = 0.001 moles x 249.68 g/mol = 0.250 g
5. The mass of the hydrocarbon is given as 6 g, and the number of moles is 0.2 moles. Therefore, the molar mass of the hydrocarbon is:
molar mass = mass / moles = 6 g / 0.2 moles = 30 g/mol
6. The mass of the oxide of nitrogen is given as 115 g, and the number of moles is 2.5 moles. Therefore, the molar mass of the oxide of nitrogen is:
molar mass = mass / moles = 115 g / 2.5 moles = 46 g/mol.
1.a) In 1 molecule of HCl, there is 1 hydrogen atom. Therefore, in 0.5 moles of HCl, there are:
0.5 moles HCl x 1 mole H per 1 mole HCl = 0.5 moles H
b) In 1 molecule of H₂O, there are 2 hydrogen atoms. Therefore, in 0.5 moles of H₂O, there are:
0.5 moles H₂O x 2 moles H per 1 mole H₂O = 1 mole H
c) In 1 molecule of Na₂CO₃, there are 3 oxygen atoms. Therefore, in 0.2 moles of Na₂CO₃, there are:
0.2 moles Na₂CO₃ x 3 moles O per 1 mole Na₂CO₃ = 0.6 moles O
d) In 1 molecule of MgCl₂, there are 2 chloride ions. Therefore, in 1.2 moles of MgCl₂, there are:
1.2 moles MgCl₂ x 2 moles Cl⁻ per 1 mole MgCl₂ = 2.4 moles Cl⁻