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### Topic: Chemistry Stoicheometry Review Help  (Read 5765 times)

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#### Bunsen Burner

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##### Chemistry Stoicheometry Review Help
« on: September 08, 2007, 01:45:17 PM »
Pure Calcium is added to water
CaO+2H20-----> Ca(OH)2 + H2 gas

1.)Assume the CA piece is pure (not part oxidized) and weighs 4.5645 g. Assuming the reaction goes to completion, how many grams of Ca(OH)2 should you have made?

2.)Phenolphthalein turns pink in solutions that are 1.0 x 10 to the -5 M in hydroxide ions. The only source of hydroxide ions is Ca(OH)2. Lets assume that the amount of water left behind in the beaker to test for complete transfer is about 3 drops or 0.15 mL

how many moles of Ca(OH)2 would be in the three drops. How many grams of Ca(OH)2?

Ive been stuck on this for a few hours now, How would you set up the stoichiometry? thanks in advance to anyone who can help

For, #1 would I have to convert the grams to moles then multiply by the molecular weight? For the second problem, I'm really not sure where to start the stoichemetric problem
« Last Edit: September 08, 2007, 02:07:31 PM by Bunsen Burner »

#### macman104

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##### Re: Chemistry Review Help
« Reply #1 on: September 08, 2007, 02:06:26 PM »
Pure Calcium is added to water
CaO+2H20-----> Ca(OH)2 + H2 gas
You need to fix your equation here.  is pure calcium CaO?  Fix that, and your stoichiometry will work out.

1)  How many moles is 4.5645g of pure calcium?  For every mole of Ca in the reaction, how many moles of Ca(OH)2 will be made?

2)  This one has me a little confused.  You should know how many moles of Ca(OH)2 were made.  However, you don't know the molarity, so, I'm not sure how to proceed here.  Unless they're saying the concentration is 1 x 10-5...

#### Bunsen Burner

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##### Re: Chemistry Stoicheometry Review Help
« Reply #2 on: September 08, 2007, 02:22:20 PM »
Hi Macman104, Thanks for your response!

1.) Should I convert the 4.5654 to mol then multiply by 2 then multiply by molecular weight? Geez, I must sound really dumb

2.) I think the 1.0 x 10 to the -2 M is the concentration

#### macman104

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##### Re: Chemistry Stoicheometry Review Help
« Reply #3 on: September 08, 2007, 02:26:52 PM »
Hi Macman104, Thanks for your response!

1.) Should I convert the 4.5654 to mol then multiply by 2 then multiply by molecular weight? Geez, I must sound really dumb
Why are you multiplying by 2?  2 moles of Ca(OH)2 are produced for every mole of Ca reacted?
Quote
2.) I think the 1.0 x 10 to the -2 M is the concentration
Just to clarify, you mean -5?

#### Bunsen Burner

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##### Re: Chemistry Stoicheometry Review Help
« Reply #4 on: September 08, 2007, 02:32:07 PM »
Yeah, sorry it is -5

#### Bunsen Burner

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##### Re: Chemistry Stoicheometry Review Help
« Reply #5 on: September 09, 2007, 12:28:22 AM »
I think I figured out #1, can someone tell me how to set up the answer for just #2? Thanks again to anyone who can help out.