Homework Help: Chemistry

Posted by anon on Thursday, February 28, 2008 at 8:05pm.

Please Help me with my chemistry Review I have a test tommorow?
Please help me with my review my test average is low and i need at least a b to pass the class for the six weeks I am freaking out!!!! I care more about showing work i dont want answers I just want help on how to do each of them if you want to give me the answer thats fine but once again i care about the work!!!!

1.How many gramsof Ca(OH)2 are needed to nuetralize 52.3 g of HNO3?
balanced equation:

2. When exactly 61.9 g of silver nitrate react with magnesium, how many grams of Ag are prepared?
Balanced equation:

3. How many grams of CaCO3 are required in the preparation of exactly 73.5 g of CO2?

---CaCO3> ---CaO + ---CO2

4. Phosphorous trichloride, PCl3, reacts with water to form phosphorous acid, H3PO4, and hydrocholoric acid:

PCl3+ 3H2O> H3PO3+3HCL

a. what is the limiting reactant when 10.0g of PCl3 is mixed with 12.4 g of H2O?

b.what mass of HCl is formed?

C. how much excess reactant remains after the reaction stops?

5. DDT is an insecticide banned by the U.S Government because it is a hazard to fish, birds, and humans. 710 g of DDT is actually isolated in the reaction. the theoretical yield for this reaction was calculated to be 725 g. what is the percent yield for this reaction?

6.Answer the following questions about BaC2O4 and its hydrate:
A. calculate the mass percent of carbon in the hydrated form of the solid that has the fromula BaC2O4 * 3H2O

Chemistry - DrBob222, Friday, February 29, 2008 at 12:17am
1.How many gramsof Ca(OH)2 are needed to nuetralize 52.3 g of HNO3?
balanced equation:
Write the equation.
Ca(OH)2 + 2HNO3 ==> Ca(NO3)2 + 2H2O

2. Convert what you have (in this case HNO3) into mols. mols = g/molar mass
mols HNO3 = 52.3/63 = 0.83

3. Using the coefficients in the balanced equation, convert mols of what you have (in this case HNO3) to mols of what you want (in this case Ca(OH)2).

mols Ca(OH)2 = 0.83 mols HNO3 x (1 mol Ca(OH)2/2 mols HNO3) = 0.42 mols Ca(OH)2. Notice how the unit we don't want (mols HNO3 cancel to leave mols we want, Ca(OH)2.

4. Now convert mols from step 3 to grams.
g = mols x molar mass = 0.42 x 74 = ??

All of the stoichiometry problems are worked this way and I notice you have a number like this. I have worked this in detail and you can use it as a template for the others. I have estimated the molar masses; please go back through and redo them if you need more accuracy. You would have done better to make one problem per post.

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