Chemical Calculation: Molarity and Molality Calculation
How do we calculate the molarity and molality of a solution?
Given the following data: 50g of water dissolves 10g of NaCl with a density of 1.08 g/cm3.
Answer:
The correct option is b. 3.06 M and 3.4 m
Our solution consists of:
Solvent: NaCl (10g)
Solvent: water (50g)
First, we convert the mass of solute to moles:
10g * 1mol / 58.45g = 0.171 moles
Next, we convert the mass of solvent from grams to kilograms:
50g * 1kg / 1000g = 0.05kg
We calculate the molality of the solution:
m = moles / kg = 0.171 mol / 0.05 kg = 3.42 m
To calculate the molarity (M), we need the volume of the solution. We first add the mass of the solute and solvent to get the total mass of the solution:
50g + 10g = 60g of solution
Using the density formula (d = m / v), we can find the volume (v) of the solution:
60g / 1.08g/cm³ = 55.5 cm³
Converting the solution volume to milliliters (mL): 55.5 mL
Converting moles to millimoles and calculating the molarity:
0.171 mol * 1000 mmol / mol = 171 mmol
M = 171 mmol / 55.5 mL = 3.08 M