[infinity]

1. A 5.00 gram sample of a dry mixture of potassium hydroxide (KOH), potassium carbonate (K[/sub]2[/sub]CO₃) and potassium chloride (KCL) is mixed with .100 L of 2.00 M HCl.  Potassium carbonate and potassium hydroxide react with HCl but potassium chloride is inert to HCL.

a. What is the total number of moles of HCl mixed with the solid mixture?
I thought that this answer is 2.00 moles but I doubt that is the answer.

b. The potassium carbonate from the sample reacts with HCl to form carbon dioxide and two other compounds.  Write a balanced net ionic equation for this reaction.
Ok so the potassium carbonate + the HCl forms carbon dioxide.  I think that the other two compounds are kind of a mix, but I'm not sure how to write it.

c. 249 mL of CO₂ from the reaction in (b) was collected over water at 22.0 degrees Celsius and at an atmospheric pressure of 762.5 torr.  The vapor pressure of H₂O is 22.5 torr at 22.0 degrees Celsius.
    i. How many moles were collected?
My answer came out to be 24.9 ish?
    ii. How many moles of HCl were used in the reaction?
I got 48.9 due to my weird stoichiometry?
    iii. What is the mass percent of potassium carbonate in the sample?
46%, which I'm not sure of.

d. Write a balanced net ionic equation for the reaction of the potassium hydroxide component with HCl.
The answer is HCl(aq) + KOH (aq) ----> KCl (aq) + H2O (l),  I think? 

e. After a complete reaction of the HCl with the potassium carbonate and potassium hydroxide, the Excess HCl was titrated to the phenolphthalein endpoint with 90.0 ml of 1.50 M NaOH.  Determine:
     i. how many moles of HCl were in excess.
Ok I'm so stuck on this problem.  I tried to find the grams of HCl that were in the reaction, but can't.
     ii. How many moles of HCl reacted with the potassium hydroxide in (d)
I don't even know the grams of the potassium hydroxide in (d)
     iii. What is the mass percent of potassium hydroxide in the sample?
The answer is a majority of the mixture?
     iv. What is the mass percent of potassium chloride in the sample?
I'm so lost now.  I don't know how I can answer this.

[rabolisk]

All right, it seems like you are pretty lost on what to do. I am going to go line by line and ask you to justify your answers or propose a way of solving the problem and drop some hints. How did you arrive at the answer you did? What line of reasoning did you use, what data if any, what formula if any?

1a. The answer given is wrong, but how did you arrive at this? What formula/reasoning did you use? Pretty straightforward question once you understand how to solve it.

b. K₂CO₃ + HCl  CO₂ + _____ + _____
There is one tricky part of this problem having to do with the carbon dioxide that you pretty much have to memorize in order to solve. But imagine I asked you to predict the reaction between a generic salt (e.g. CuCO₃) and HCl. How would you solve this? Alternatively suppose that this salt is also a base (e.g. NaOH). What would you do? You should be able to reason your way to one of the compounds. Also, I am confused by what you mean when you say that "the other two compounds are kind of a mix"

c. i. How did you get 24.9? What formula(s) did you use?
ii. What was the balanced reaction you used for this?
iii. How did you arrive at your answer?

d. You're almost correct, but the question is asking for net ionic equation.

e. i. How familiar are you with titrations? What is the definition of endpoint?
ii. This requires answers from other parts of the question. You can get the total moles of HCl used from (a), the amount used to react with carbonate from (c), and the excess (remaining) amount from (e). Suppose you knew all those answers, explain how you would find the amount of HCl that was used to react with the hydroxide.
iii. Once you know the answer to ii, then you can use stoichiometry to find the moles of KOH that was initially present. From there, you need to get to mass percentage of KOH in the sample.
iv. Looks awfully familiar to iii.

I can give you the answers and I can tell you step by step how to do it, but that is not how learning works. Besides, if you are taking AP chem and you are serious about taking the exam in May, you need to understand the chemical principles behind these questions, and how to solve them. The math is not hard; full understanding of chemistry is.