Question

A 0.3120 g sample of a compound made up of aluminum and chlorine is dissolved in 150 mL H2O. When excess AgNO3 is added, 1.006 g of AgCl is precipitated. What is the number of moles Cl in the aluminum chloride sample?What is the number moles of aluminum in the sample.

I thought this was a simple question of how many molecules there are, so I put 3 for the first question and 2 for the second. Apparently that was wrong so I put 2 and 1, which is still wrong. Help?

Answer 1

mols AgCl = 1.006/molar mass AgCl = 0.0072.
It isn't clear in the problem if Al and Cl are combined as AlCl3 or if they are there as a mixture. In my ignorance I would go with 0.0072 mols Cl in the AlCl3 and 1/3 of that for mols Al.

Answer 2

Thanks, but that wasn't the right answer?

Answer 3

Well, i made a typo. That's 0.00702 and not 0.0072. I usually check my post immediately after I respond but I didn't on this one. Also I notice the 0.3120 and 1.006 are to four significant figures so the 0.00702 number is revised to 0.007019 mols. Mols Al in the sample HAS to be 1/3 of 0.007019. I'm still of the opinion that mols Cl = 0.007019 and mols Al = 1/3 x 0.007019.