[kelaklub]

The answer to the following question is choice E, but I am still interested in determining the right answer. I was able to calculate the number of moles of Ag as about 0.014 moles. That's as far as I can get. I don't know what the next step should be. Please advice.

[Albert]

 

In my opinion, D is the right answer.

[kelaklub]

It could very well be choice D, because this sample test had alot of typo's. Regardless, I have no real idea on how to approach this problem.

[Albert]

Ok, hoping not to have made a terrible mistake, here's how I solved it:

m_sample=5.0 g

AgNO₃ + Cl^- -> AgCl + NO₃^-

[Ag+]=0.201 mol/L     V=70.9 mL

Hence, n_Ag = n_Cl = 0.01425 mol

m_Cl = 0.5052 g

w/w% = (0.5052/5.0)*100 = 10.10 %

[kelaklub]

I was able to get the number of moles of silver, as you did. But based on what are you able to say that it is equivalent to the number of moles of chlorine

[Albert]

Well, it looks like a very common argentometric titration. The question gives you the reagents (silver nitrate and chloride) and a product (AgCl).

[kelaklub]

Can you base that on the oxidation number of silver being equal in magnitude to that Cl in AgCl?

[Albert]

Sorry but I can't understand what you want to know exactly.

The chemical equation I wrote describes the reaction taking place in an argentometric titration such as that used for determining the concentration of a sodium chloride sample.
If you want to investigate whether a reaction can occur, I think thermodynamics to be the answer.
However, I don't think you need it. The problems already shows you all the compounds involved: what other chemical equation could you predict, just reading the text of the problem?

[kelaklub]

I understand how to calculate the number of moles of silver. What I don't understand is how that is also equivalent to the number of moles of chlorine based on the way the reaction is written.

[Albert]

how that is also equivalent to the number of moles of chlorine based on the way the reaction is written.

The ratio silver/chloride is derived from the stoichometry of the reaction

AgNO₃ + Cl^- -> AgCl + NO₃^-

[kelaklub]

Oooh, one silver atom to one chlorine atom.

[Albert]

Yes: one mole of silver (nitrate) reacts with one mole of chloride.