Question

What is the minimum amount of water needed to dissolve 3mol potassium dichromate? (please show work)

Answer 1

Potassium dichromate = K₂Cr₂O₇

Molar mass of K₂Cr₂O₇ = 294.18 g/mol

So,

1 mole of K₂Cr₂O₇ = 294.18 g
3 mole of K₂Cr₂O₇ = 3 x 294.18 g = 882.54 g

Solubility of K₂Cr₂O₇ (from literature) are
4.9 g/100 mL (0 ^oC)
13 g/100 mL (20 ^oC)
102 g/100 mL (100 ^oC)

You have not given any specified temperature. I am taking the temperature as 20 ^oC (close to room temperature).

Now, at 20 ^oC:

13 g of K₂Cr₂O₇ dissolves in = 100 mL
1 g of K₂Cr₂O₇ dissolves in = (100/13) mL
882.54 g of K₂Cr₂O₇ dissolves in = 882.54 x (100/13) mL
= 6788.77 mL
= 6.79 L