[ubenla]

My professor in class never did a problem like this so i'm kind of lost... an explanation would be nice

Suppose 27.8 mL of 0.443 M MgCl2 is combined with 31.5 mL of 0.389 M AlCl3. assume no chemical reaction takes place. what is the total concentration of chloride ions in the mixture?
would i find the mass of each one add them and then use convert that to moles of chloride ions to find it?

[Borek]

Total number of moles in the final solution is a sum of moles of chlorides in each solution. Final volume is a sum of volumes. Once you know number of moles and volume calculating concentration is a breeze.

[curiouscat]

Final volume is a sum of volumes.

How good is that assumption? Maybe since no other data is offered, we're forced to. But might be bad pedagogy (whoever made that question) to teach volumes are additive.

[Borek]

How good is that assumption? Maybe since no other data is offered, we're forced to. But might be bad pedagogy (whoever made that question) to teach volumes are additive.

Yes, it is a bad pedagogy. It is a poor assumption and in other circumstances you would learn it is a pet peeve of mine. But there is no other information given and you are not going to find it in none of the common sources of physical and chemical data, as they never list densities for mixtures, just for single substances.

[curiouscat]

Yes, it is a bad pedagogy. It is a poor assumption and in other circumstances you would learn it is a pet peeve of mine. But there is no other information given and you are not going to find it in none of the common sources of physical and chemical data, as they never list densities for mixtures, just for single substances.

I was thinking of something based on partial molar volumes or excess quantities. Although don't know if that data would be any easier to dig up or model.