Nov 2017
Can anyone help me with this question?

What is the molarity of each ion present in aqueous solutions prepared by dissolving 15.0 g of the following compounds in water to make 655 mL of solution?

a.) scandium(iii) iodide
b.) sodium carbonate
c.) magnesium phosphate
d.) potassium oxide

I think my main issue is writing the reactions themselves, as well as the fact that I don't completely grasp the concept of ions in relation to calculating molarity.
for a)
ScI3 --> Sc^3+ + 3I^1-

Is that correct?
If so, my next steps would be to:
1. calculate MM of ScI3 = 425.66
2. Find molarity:
15g ScI3 = 0.035 mol

[ScI3] = 0.035 mol/0.655 L = 0.0534 mol/L

Using this, I know that:
- the molarity of Sc is 0.0534
- the molarity of I is 0.0534*3 = 0.1602

That's as far as i've gotten - I still feel like I might be doing something wrong.
Last edited:
Feb 2015
Every step of your calculation is completely correct.