[pajarita]

1.  How many mL of a solution HNO₃ 63.0% per mass and density is 1.389g/mL are needed to prepare 1500mL of a 0.300M solution?


2.  How would you prepare 250mL of HClO₄ 3.0M from a concentrated HClO₄ with density=1.60g/mL and 70.0% per mass of HClO₄?


3.  If you mix 20mL of KCl 0.20M, 30mL of K₂SO₄, 0.60M and 20mL of MgCl₂ 0.12M, calculate molarity of the following ions: K⁺, Cl^-, SO₄^2-

[pajarita]

I started #1 this way

1.5L(0.300mol/1L)= 0.45mol HNO₃

0.45mol HNO3(63.018gHNO₃/1 mol HNO₃)=28.36g HNO₃

.? then i do something with the mass percent, then i use density to find mL?

[Yggdrasil]

You've definitely got the correct idea.  63.0% mass means that in 100g of solution, you have 63.0g of HNO3.  So, if you have 63.0g of HNO3 per 100g of solution, can you figure out how many grams of solution contain 28.36g of HNO3?

[pajarita]

ah!

28.36g HNO₃ (100g solution/63g HNO₃)=45.02g solution

45.02g solution (1mL/1.389g)= 32.41mL


#2 is pretty much the same idea, and #3 someone already explained

thank you much