Can someone help me with these two questions?

Question

Thank you!

a.) Describe (give instructions) how you would prepare 7.00 L of 0.750 M K2CrO4 from a 2.25 M K2Cro4 stock solution

b.) A stock solution containing Ba2+ ions was prepared by dissolving 23.0 grams of pure barium metal in nitric acid and diluting to a final volume of 2.000 L. Calculate the concentrations of Ba2+ ions in the stock solution and the diluted solution if 125 mL of the stock solution was diluted to 500.0 mL

Again, thank you for your help!

Answer 1

you want to dilute it 2.25/.750 times, or 10/3 times. Which means, one part stock, 7/3 parts water.

What is one part? 7L/(10/3)=21/10=2.10liter

So, take 2.10 l of stock, add to 7/3 * 210 l water, stir and label. BTW, 7/3*2.10 l is 4.90 l

check: 4.90 + 2.1 l= 7liters

Answer 2

a.
The dilution formula is
L1 x M1 = L2 x M2
7 x 0.750 = L x 2.25
Solve for L of the 2.25M solution. Add that volume of a 2.25M solution to a flask and add enough water to make the final volume 7.00 L. This may be exactly what your prof wants and it COULD be a harder problem than that. WHY? Because you want to take exactly 2.333333333 L of the 2.25 M solution and add (7.000L-2.33333L) of water; BUT there are no EASY ways to measure out that exact volume to begin with nor to add exactly 4.6667 L H2O.

b.
mols Ba = grams/atomic mass = ?
M final solution = mols/2.000 L = ?
Then use the dilution formula for the M of the diluted solution.