Concentrated hydrochloric acid is 38% HCl by weight and has a density of 1.19 g/mL. A solution is prepared by measuring 70 mL of the concentrated HCl, adding it to water, and diluting to 0.500 L. Calculate the approximate molarity of this solution from the volume, percent composition, and density.
First determine the molarity of the concentrated HCl.
That's
1.19 g/mL x 1000 mL x (38/100) x (1 mol/36.5 g) = ?M HCl
Then use the dilution formula of
mL1 x M1 = mL2 x M2
1.734mol/l=M
To calculate the approximate molarity of the solution, we need to understand the relationship between molarity, percent composition, volume, and density.
1. First, we need to determine the number of moles of HCl in the 70 mL concentrated hydrochloric acid.
To do this, we need to calculate the mass of HCl in this volume.
Mass of HCl = volume × density = (70 mL) × (1.19 g/mL) = 83.3 g
The percent composition of the acid is given as 38%, which means that 38 g of the 83.3 g is HCl.
2. Now, we need to convert the mass of HCl to moles.
Molar mass of HCl = 1 g/mol (hydrogen) + 35.5 g/mol (chlorine) = 36.5 g/mol
Number of moles = Mass / Molar mass = 38 g / 36.5 g/mol ≈ 1.04 mol
3. We have the number of moles of HCl in 70 mL of concentrated HCl. We need to dilute this to a final volume of 0.500 L.
We can assume that the number of moles of HCl remains the same after dilution.
4. Finally, we can calculate the molarity of the solution.
Molarity = Number of moles / Volume in liters = 1.04 mol / 0.500 L = 2.08 M
Therefore, the approximate molarity of the solution is approximately 2.08 M.