5.5 500 g of Al₂(SO₄)₃ is dissolved in 2 dm³ water. 5.5.1 Define the term concentration. (2) 5.5.2 Calculate the concentration of the solution. (4)
Answer (1)
5.5.1 The term 'concentration' refers to the amount of a substance (solute) that is present in a certain volume of solution. It is usually expressed in terms of moles per liter (mol/L) or grams per liter (g/L). In essence, concentration tells us how much solute is dissolved in a given quantity of solvent.
5.5.2 To calculate the concentration of the solution:
Determine the molar mass of Al 2 ( SO 4 ) 3 :
Aluminum (Al): 2 × 27 g/mol = 54 g/mol
Sulfur (S): 3 × 32 g/mol = 96 g/mol
Oxygen (O): 12 × 16 g/mol = 192 g/mol
Adding these together gives the molar mass of Al 2 ( SO 4 ) 3 : 54 + 96 + 192 = 342 g/mol
Calculate the number of moles of Al 2 ( SO 4 ) 3 dissolved :
Given mass = 500 g
Moles = molar mass mass = 342 500 ≈ 1.46 moles
Calculate the concentration of the solution :
The solution's volume is given as 2 dm³, which is equivalent to 2 L.
Concentration (C) = volume of solution in liters moles of solute = 2 1.46 ≈ 0.73 mol/L
Therefore, the concentration of the Al 2 ( SO 4 ) 3 solution is approximately 0.73 mol/L.
