Oxalic acid, #H_2C_2O_4#, occurs as the potassium or calcium salt in many plants, including rhubarb and spinach. An aqueous solution of oxalic acid is 0.585 molal #H_2C_2O_4#. The density of the solution is 1.022 g/mL. What is the molar concentration?
1 Answer
Explanation:
The first thing that you need to do here is to pick a sample of this solution and use its molality to determine how many moles of solute it contains.
To make the calculations easier, let's pick a sample that contains exactly
Next, use the molar mass of oxalic acid to calculate how many grams of solute are present in this sample.
#0.585 color(red)(cancel(color(black)("moles H"_2"C"_2"O"_4))) * "90.03 g"/(1color(red)(cancel(color(black)("mole H"_2"C"_2"O"_4)))) = "52.68 g"#
This means that the total mass of the sample, which includes the mass of the solute and the mass of the solvent, which is equal to
#10^3 quad "g" + "52.68 g" = "1052.68 g"#
Now, in order to find the molarity of the solution, you need to find the number of moles of solute present in exactly
Use the density of the solution to find the total volume of the sample
#1052.68 color(red)(cancel(color(black)("g"))) * "1 mL"/(1.022color(red)(cancel(color(black)("g")))) = "1030.0 mL"#
Since you know that this sample contains
#10^3 color(red)(cancel(color(black)("mL solution"))) * ("0.585 moles H"_2"C"_2"O"_4)/(1030.0color(red)(cancel(color(black)("mL solution")))) = "0.568 moles H"_2"C"_2"O"_4#
This means that the solution has a molarity of
#color(darkgreen)(ul(color(black)("molarity" = "0.568 mol L"^(-1))))#
The answer is rounded to three sig figs, the number of sig figs you have for the molality of the solution.
