[pimcub2011]

Hard water contains Ca^2 +, Mg^2 +, and Fe^2 +, which interfere with the action of soap and leave an insoluble coating on the insides of containers and pipes when heated. Water softeners replace these ions with Na^+.

If 1400 L of hard water contains 0.024  M Ca^2+ and 0.0010  M Mg^2 +, how many moles of Na^+ are needed to replace these ions?


How do I approach this? I don't even know where to start.
Someone told me that the charges affect the answer, but I don't know how.

[Arkcon]

How do I approach this? I don't even know where to start.
Someone told me that the charges affect the answer, but I don't know how.

I'm not exactly sure that's true.  Let's try this, let's pretend it's not.  Then can you being to solve this problem?  You're given a volume in L, a concentration in M, and your answer has to be in moles.  So can you convert from one to the other, you do realize, at some point in the problem, you will have to, right?

[pimcub2011]

Yeah, I can convert from concentration to moles if I'm given the volume and the concentration but what am I converting to what?

[Arkcon]

but what am I converting to what?

That answer "what into what" is actually in the question, isn't it?

[pimcub2011]

I mean in the problem, I found the moles and the mass of Mg and Cl but what do I do with them?

[Borek]

If you remove one Ca²⁺ from the solution, how many Na⁺ do you have to introduce to keep the solution electrically neutral?

[pimcub2011]

2?

[pimcub2011]

Do I find the moles of Ca and Mg, then convert them to grams, then add them together, then divide it by the molecular weight of Na?

33.6 and 1.4 moles=1344 and 33.6 g=1377.6 g total=59.9 moles of Na?

[Borek]

No, you find total charge of magnesium/calcium/iron present in the solution and you replace it with sodium.

Yo were right - 2. How many Na⁺ per Fe²⁺? Mg²⁺?