Amount of substance
1. Calculate the number of nitric oxide molecules in a container that contains 4.5 mol of this gas.
Solution:
We start from the equation for calculating the amount of substance:
N(NO) = n(NO).NA = 4.5 mol × 6.022 × 1023 = 2.7 × 1024
The container contains 2.7 × 1024 NO molecules.
2. What amount of substance corresponds to 1.806 × 1027 carbon atoms?
Solution:
We use the relation for the amount of substance.
The amount of carbon substance containing 1.806 × 1027 atoms is 3 kmol.
3. How many molecules are in a container containing 2.5 mol of carbon dioxide?
Solution:
We use a similar procedure as in example 2.
1.5 × 1024 molecules.
4. Calculate the amount of substance:
- a) 2.58 × 1027 atoms of aluminum
- b) 5.55 × 1019 sodium cations
- c) 8.68 × 1022 chloride anions
- d) 1.75 × 1025 molecules of white phosphorus (P4)
Solution:
We use the same procedure as in example 2.
- a) 4.28 kmol
- b) 9.22 × 10-2 mmol
- c) 0.144 mol
- d) 29.1 mol
5. The charge of an electron is 1.6 × 10-19 C. What is the charge of 1 mol of electrons (Faraday’s constant)?
Solution:
According to Avogadro’s constant, 1 mol contains 6.022 × 1023 particles. Each particle, in our case the electron, carries a charge of 1.6 × 10-19 C. One mole of electrons therefore carries a charge of 1.6 × 10-19 × 6.022 × 1023, which equals 96352 C.
6. How many silver atoms are contained in 1 cm3 of this metal, which has a density of ρ = 10.5 × 103 kg·m-3?
Solution:
From density and volume we calculate the mass of silver:
The molar mass of Ag is 107.868 g/mol, so for the amount of silver substance:
and for the number of particles:
1 cm3 of silver contains 5.86 × 1022 atoms.
7. What amount of substance of H2O is in one liter of water?
Solution:
The density of water is 1 g/cm3, so 1 liter of water weighs 1 kg, i.e. 1000 g. The molar mass of water is 18 g/mol, so the amount of substance is:
One liter of water contains 55.5 mol of H2O molecules.
8. What amount of sodium is in 10 g of NaCl? How many chlorine atoms correspond to this amount of sodium in the compound?
Solution:
The procedure is similar to example 6.
0.17 mol Na; 1.03 × 1023 Cl atoms
9. What amount of substance corresponds to 1 g of H2SO4 and 200 g of CH4?
Solution:
The procedure is similar to example 6.
0.01 mol; 12.47 mol
10. What amount of aluminum is in a cube with an edge of 10 cm? (use data from chemical tables)
Solution:
Procedure as in example 6.
100.07 mol