[Geddoe]

ZnCl2 reacts with AgNO3 in aqueous solutions to produce a precipitate of AgCl that can be filtered and
weighed. The balanced equation for the reaction is:
ZnCl2 (aq) + 2 AgNO3 (aq) -> 2 AgCl (s) + Zn(NO3)2 (aq)
Suppose you have a mixture that contains ZnCl2, plus other compounds that do not react with AgNO3. If 0.4490
g of the mixture yields 0.6390 g of AgCl, what is the percentage of ZnCl2 in the mixture?


To be honest I'm really not sure how I should look at a question like this. I did this so far:


0.6390 g of AgCl * (35.45g Cl / 1 mole Cl) = 22.65255g Cl

I'm not sure if that is a useful step or not or what the next one shall be that I take. Any guidance is appreciated.

[DrCMS]

To be honest I'm really not sure how I should look at a question like this. I did this so far:


0.6390 g of AgCl * (35.45g Cl / 1 mole Cl) = 22.65255g Cl

I'm not sure if that is a useful step or not or what the next one shall be that I take. Any guidance is appreciated.

No its not a useful step and I have no idea what you are doing here at all.

Think about it again you have a known weight of unknown composition.

ZnCl2 (aq) + 2 AgNO3 (aq) -> 2 AgCl (s) + Zn(NO3)2 (aq)

From this equation you know that for every mole of ZnCl₂ in the sample you'll get 2 moles of AgCl solid.

You are told the sample gives 0.6390g of AgCl.

How many moles of AgCl is that.
How many moles of ZnCl₂ does that mean were in the sample?
What is the weight of the ZnCl₂ calculated from the no. of moles?
That weight of ZnCl₂ divided by the sample weight give the %ZnCl₂ in the sample.

[Geddoe]

0.6390g of AgCl.

How many moles of AgCl is that.

0.6390g AgCl * (1 mole AgCl / 143.35) = 0.004457621 mol

How many moles of ZnCl2 does that mean were in the sample?

0.004457621 mol AgCl * (1 mole ZnCl2 / 2 mole AgCl) = 0.002228811 mole ZnCl2

What is the weight of the ZnCl2 calculated from the no. of moles?

0.002228811 * (100.84  / 1 Mole ZnCl2) = 0.224753301g ZnCl2


Sample weight calculation:

0.224753301g / 0.4490g =0.500564145

would I multiply this value by 100% ?

Is this the correct method?

[DrCMS]

Yes and Yes