Can anyone help me with this chemistry problem?

[Artimacia]

Describe how you would prepare each of the following aqueous solutions, starting with solid KBr:

0.95L of 1.4×10−2 M KBr (find mass of KBr and Volume of Water)

125g of 0.180 molality of KBr (find mass of KBr and mass Water)

1.65 L of a solution that is 14.0 % KBr by mass (the density of the solution is 1.10 g/mL) (Find mass of KBr and Volume of water)

a 0.140 M solution of KBr that contains just enough KBr to precipitate 17.0 g of AgBr from a solution containing 0.480 mol of AgNO3 (Find mass of KBr and Volume of water)


If you can help me figure out how to solve even just one, that would help a lot. I didn't know where else to post this, and figured no one would answer in the pre-MD thread.

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[jp134711]

For the first 2, use dimensional analysis and the definitions of molarity (mol solute/L solvent) and molality (mol solute/kg solvent) to solve for the # of moles of KBr needed. Then find the molecular weight and solve for the mass in grams. For the third, find the mass of the solution using density=mass*volume. Then you find out how much of that is due to KBr.

The last one is a little tricky, so others might need to check my work on this.
The reaction you're concerned with is
KBr+AgNO3----->AgBr+KNO3

Solubility rules should tell you that AgBr is insoluble. Also you expect 17 g or 0.091 mol of it to precipitate. In the initial reaction, you can assume that KBr is the limiting reactant, so since it is in 1:1 ratio with AgBr, you should initially start off with 0.091 mol KBr. Finding the rest is easy from here. I think the 0.480 mol AgNO3 is extra info and isn't needed.

These are basic chemistry questions, so you should get comfortable doing these, esp if you plan on taking MCAT. G/L.

 

[DrMattOglesby]

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