A 32.5 g sample of K2SO4 is dissolved in a quantity of water and stirred well. A 40.00 mL sample of the solution is evaporated to dryness and leaves behind 5.00 g of solid K2SO4.what is the molarity. Calculate molar masses of solutes to .01 grams
mols K2SO4 in the 40 mL sample = g/molar mass = 5.00/molar mass K2SO4 = ?
Then M of the 40 mL sample is mols K2SO4/0.04 = ?
Septer 1 answer-
To calculate the molarity of a solution, we need to know the moles of solute and the volume of the solution in liters.
Step 1: Calculate the moles of K2SO4.
The molar mass of K2SO4 is the sum of the atomic masses of its constituent elements: K (potassium), S (sulfur), and O (oxygen).
Molar mass of K2SO4 = 2(K) + 1(S) + 4(O) = 2(39.10 g/mol) + 32.07 g/mol + 4(16.00 g/mol) = 174.26 g/mol
To convert grams of K2SO4 to moles, use the formula:
moles = mass (in grams) / molar mass (in g/mol)
moles = 5.00 g / 174.26 g/mol ≈ 0.0287 mol
Step 2: Calculate the volume of the solution in liters.
Given that a 40.00 mL (0.04000 L) sample of the solution was evaporated to dryness, we assume that the volume of the solution before evaporation was also 40.00 mL (0.04000 L).
Step 3: Calculate the molarity.
Molarity (M) = moles of solute / volume of solution (in liters)
Molarity = 0.0287 mol / 0.04000 L ≈ 0.717 M
Therefore, the molarity of the K2SO4 solution is approximately 0.717 M.
Note: We calculated the molar mass of K2SO4 earlier (174.26 g/mol) to the hundredth place because the given information asked us to calculate the molar masses of solutes to 0.01 grams.