Solved: Calculate Ion Concentration (27.6 g)

[temaire]

[SOLVED] Ion concentration

Homework Statement

http://img225.imageshack.us/img225/9918/chemch0.jpg​

Homework Equations

C = n/v

The Attempt at a Solution

My work is shown up above. Sorry if my work looks a little messy. My answer is 27.6 grams.

 

[temaire]

I just want someone to tell me if I'am right, and correct me if I'am not.

 

[eli64]

good effort

your error is in your dissociation equation

MgBr2 --> Mg+2(aq) + 2Br-(aq)

the bromide ion is twice the concentration of the MgBr2 so the moles of MgBr2 is half what you calculated (.15/2).

your mass of MgBr2 is half of your answer

 

[temaire]

But isn't Br supposed to have a subscript of 2?

 

[eli64]

MgBr2 is a compound that dissociates into its ions in water.

the Br- ions don't stay together in water so you get 2 Br- ions

Br2 by itself is only written when you are referring to bromine as an diatomic element, not as ions in solution

 

[temaire]

Thanks a lot for the help.