Question 28

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dnpgr16513

Joined: 31 Dec 1969
Posts: 22

PostPosted: 25 Jun 2010 18:08

I understand the whole set up for the problem, but why do we divide the values by 1000 ml? I just multiplied the concentration and volume used( in liters) together to obtain the number of moles. And then I added the moles and divided by the total volume.

Also, why do we multiply K+ by 2? Why don't we divide?

thanks.

[jellywing_2058]

Knowing the concentrations are given in mol/L, when you see the volumes are given in ml, you need to remember to convert your units; this is why you needed to divide by 1000 ml.

You could have also done it this way:
50 ml = 0.05 l
Therefore,
(0.5 mol/l)(0.05 l) = 0.025 moles K+ ** The units cancel out leaving moles

For the K2CO3, you need to multiply the amount of moles by two, because you get 2 moles of K+ for every dissociated mole of K2CO3-->> 2 mole K+ : 1 mole K2CO3.