Consider the HF solution with the concentration 5%(w/v). Calculate its concentration in the molarity. Use four significant figures in the answer.
5% w/v means 5 g HF/100 mL soln or 50 g HF/1000 mL soln.
50g HF = how many mols? mols = grams/molar mass, then
M = moles/L
To calculate the concentration of a solution in molarity, we need to convert the given weight/volume (w/v) percentage to molarity.
First, we need to find the number of moles of solute (HF) in 100 grams of the solution.
Step 1: Convert the percentage to grams per 100 mL
5% (w/v) means 5 grams of solute (HF) in 100 mL of solution. Therefore, we have 5 grams HF in 100 mL of solution.
Step 2: Convert the mL of solution to liters
100 mL is equivalent to 0.1 L.
Step 3: Calculate the molar mass of HF
The molar mass of HF is 1.0079 g/mol for hydrogen and 18.998 g/mol for fluorine.
Calculating the molar mass of HF:
(1.0079 g/mol H) + (18.998 g/mol F) = 20.0059 g/mol
Step 4: Calculate the number of moles
Number of moles = (mass of solute in grams) / (molar mass of solute)
Number of moles = 5 g / 20.0059 g/mol = 0.24998 mol
Finally, we need to convert moles to molarity.
Step 5: Convert mL to L
The solution's volume is 0.1 L.
Step 6: Calculate the molarity
Molarity (M) = (moles of solute) / (volume of solution in liters)
Molarity (M) = 0.24998 mol / 0.1 L = 2.4998 M
Since we need to use four significant figures in the answer, the final concentration of the HF solution in molarity is 2.500 M.