A student dissolved 6.00 g of Co(NO3)2 in enough water to make 100. mL of stock solution. He took 4.00 mL of the stock solution and then diluted it with water to give 275. mL of a final solution. How many grams of NO3 - ion are there in the final solution?

Answer 1

How many grams of NO3^- are in the 100 mL. That's
6.00 x (2 x molar mass NO3^-/molar mass Co(NO3)2 = ? which I will call G.
Now, how many grams will be in the 4.00 mL? That's G x (4.00 mL/100 mL) = ? grams which is in the 275 mL.