A student weighs out a 13.7 g sample of Cr(NO3)3, transfers it to a 300 mL volumetric flask, adds enough water to dissolve it and then adds water to the 300 mL tic mark.
What is the molarity of chromium(III) nitrate in the resulting solution?
To find the molarity of the chromium(III) nitrate solution, we need to first calculate the number of moles of chromium(III) nitrate in the solution and then divide by the volume of the solution in liters.
Step 1: Calculate the number of moles of Cr(NO3)3
To do this, we'll need the molar mass of Cr(NO3)3. Chromium (Cr) has an atomic mass of 51.9961 g/mol, nitrogen (N) has an atomic mass of 14.0067 g/mol, and oxygen (O) has an atomic mass of 15.9994 g/mol.
Molar mass of Cr(NO3)3 = (51.9961 g/mol) + (3 x (14.0067 g/mol + 3 x 15.9994 g/mol))
Step 2: Calculate the moles of Cr(NO3)3
Given that the student weighs out a 13.7 g sample of Cr(NO3)3, we can use the molar mass calculated in step 1 to find the number of moles.
moles of Cr(NO3)3 = (mass of Cr(NO3)3) / (molar mass of Cr(NO3)3)
Step 3: Calculate the volume of the solution in liters
The student transfers the Cr(NO3)3 into a 300 mL volumetric flask and then adds water to the 300 mL tic mark. So the volume of the solution is 300 mL or 0.3 L.
Step 4: Calculate the molarity
Finally, we can calculate the molarity by dividing the moles of Cr(NO3)3 by the volume of the solution in liters.
Molarity (M) = (moles of Cr(NO3)3) / (volume of solution in liters)
Let's plug in the values and calculate:
Molar mass of Cr(NO3)3 = (51.9961 g/mol) + (3 x (14.0067 g/mol + 3 x 15.9994 g/mol))
Molar mass of Cr(NO3)3 = 51.9961 g/mol + 3 x (14.0067 g/mol) + 3 x (15.9994 g/mol) = 51.9961 + 42.0201 + 47.9982 = 142.0144 g/mol
moles of Cr(NO3)3 = (13.7 g) / (142.0144 g/mol)
moles of Cr(NO3)3 = 0.0964 mol
Molarity (M) = (0.0964 mol) / (0.3 L)
Molarity (M) = 0.3213 M
Therefore, the molarity of chromium(III) nitrate in the resulting solution is approximately 0.3213 M.
moles Cr(NO3)3 = grams/molar mass
M = moles/L soln.