Question

Describe how you would prepare \(465 \mathrm{~mL}\) of \(0.3550 \mathrm{M}\) potassium dichromate solution starting with (a) solid potassium dichromate. (b) \(0.750 \mathrm{M}\) potassium dichromate solution.

Short answer

Answer: (a) To prepare the solution using solid potassium dichromate, 48.55 g of K₂Cr₂O₇ is required. (b) To prepare the solution using a 0.750 M potassium dichromate solution, 219.2 mL of the concentrated solution is required.

Step-by-step solution

Calculate the moles of potassium dichromate required

We'll use the formula M = n/V to find the number of moles of K₂Cr₂O₇ needed. Rearranging the formula to find n, we get n = M * V. In this case, M = 0.3550 M, and the volume V = 465 mL = 0.465 L. Now we calculate n = M * V: n = (0.3550 \mathrm{M}) \times (0.465 \mathrm{L}) n = 0.1651 \mathrm{mol}

Convert moles to grams

We will now convert 0.1651 mol of K₂Cr₂O₇ into grams using the molar mass of K₂Cr₂O₇, which is 294.18 g/mol: mass = (0.1651 \mathrm{mol}) \times (294.18 \mathrm{g/mol}) mass = 48.55 \mathrm{g}

Prepare the solution

Measure 48.55 g of solid potassium dichromate and dissolve it in a volumetric flask by adding water. Continue adding water up to the 465 mL mark to reach the desired volume. Mix well to ensure the solute is completely dissolved. (b) Preparing the solution using a 0.750 M potassium dichromate solution

Calculate the volume of 0.750 M solution required

Start by using the dilution formula M1V1 = M2V2, where M1 is the initial concentration (0.750 M), V1 is the initial volume, M2 is the final concentration (0.3550 M), and V2 is the final volume (0.465 L). Rearrange the formula to find V1: V1 = (M2 * V2) / M1 V1 = (0.3550 \mathrm{M} \times 0.465 \mathrm{L}) / (0.750 \mathrm{M}) V1 = 0.2192 \mathrm{L} = 219.2 \mathrm{mL}

Prepare the solution

Measure 219.2 mL of the 0.750 M potassium dichromate solution with an appropriate volumetric pipette. Add the measured solution to a 465 mL volumetric flask. Fill the volumetric flask with water until the 465 mL mark is reached. Mix well to ensure homogeneity. The final concentration of the solution will be 0.3550 M potassium dichromate.