Using molality and molarity to describe a solution Calculate the percent concentration of 3.25ml of H2SO4 dissolve in 68.0ml water
To find the percent concentration of the solution, we need to know the amount of H2SO4 present in the solution. We can use either molality or molarity to calculate the amount.
Option 1: Using Molality
Molality is defined as the number of moles of solute dissolved per kilogram of solvent.
We need to convert the given volume of H2SO4 to mass using its density. The density of H2SO4 is 1.84 g/mL.
Mass of H2SO4 = Volume x Density
= 3.25 mL x 1.84 g/mL
= 5.99 g
Number of moles of H2SO4 = Mass / Molar mass
= 5.99 g / 98.08 g/mol
= 0.061 moles
Now, we need to find the amount of water in kilograms.
Mass of water = Volume x Density
= 68.0 mL x 1 g/mL
= 68.0 g
Mass of solvent = Mass of water / 1000
= 68.0 g / 1000
= 0.068 kg
Molality = Number of moles / Mass of solvent
= 0.061 moles / 0.068 kg
= 0.897 mol/kg
Now, we need to convert molality to percent concentration.
Percent concentration = Molality x Molar mass x 100
= 0.897 mol/kg x 98.08 g/mol x 100
= 87.9 %
Therefore, the percent concentration of the solution is 87.9%.
Option 2: Using Molarity
Molarity is defined as the number of moles of solute dissolved per liter of solution.
We need to convert the given volume of H2SO4 to liters.
Volume of H2SO4 = 3.25 mL / 1000
= 0.00325 L
Number of moles of H2SO4 = Concentration x Volume
where Concentration is the molarity of H2SO4.
We don't know the molarity of H2SO4, but we can find it using the given information.
Mass of H2SO4 = Volume x Density
= 3.25 mL x 1.84 g/mL
= 5.99 g
Number of moles of H2SO4 = Mass / Molar mass
= 5.99 g / 98.08 g/mol
= 0.061 moles
Molarity = Number of moles / Volume of solution
= 0.061 moles / (0.00325 L + 0.068 L)
= 0.859 M
Now, we need to convert molarity to percent concentration.
Percent concentration = Molarity x Molar mass x 1000
= 0.859 M x 98.08 g/mol x 1000
= 84.3 %
Therefore, the percent concentration of the solution is 84.3%.
Note: The two methods give slightly different results due to the different definitions of molality and molarity. Molality takes into account only the mass of solvent, while molarity takes into account the total volume of the solution.