Chem hmwrk?

Question

-While working in the lab, you find a bottle of white powder labeled "meat preserver (antioxidant)". Since the original investigator neglected to record the identity of the substance, you decide to perform a combustion analysis to identify the compound. You have a 48.6 g sample that when burned produces 131 g CO2 and 38.9 g H2O. What is the formula of this compound? (The compound consists of only C, H, and O.)

-Multivitamins are one source of many biologically important elements. One of these elements is zinc, which can be found in vitamins in zinc oxide. One tablet, having a weight of 1.4096 g, is dissolved and 0.0187 g ZnO is recovered. What is the weight percent of zinc in this tablet?

-Silicon carbide, SiC, is used as an abrasive for many industrial processes. If you want to produce 1.00 kg of silicon carbide from the reaction of SiO2 and carbon, what is the minimum amount of SiO2 that is needed?
SiO2(s) + 3C(s)-->SiC(s) + 2CO(g)

Answer 1

1. Find oxygen added to sample to react.
(131+38.9 - 48.6). Call result O(add) in grams
2. Take 131 g CO2 and divide by 12/44 to get mass of carbon.
3. Take 38.9 g H2O and divide by 2/18 to get mass of hydrogen.
4. Take the remainder mass from 2 and 3 (which is oxygen in the burnt products).
5. Subtract out O(add), this gives you the mass of oxygen.
6. Now divide the carbon mass by 12, the hydrogen mass by 1, and the oxygen mass by 16. Call these results CM, HM and OM
7. Take the smallest of CM, HM or OM, and divide 1 by that variable. Call the result SU (scaleup)
8. The formula will be C1, HM*SU ,OM*SU

1. Find mol wt of ZnO. Call it Mzox
2. Find atomic wt of Zn. Call it Mz
3. multiply 0.0187 by Mz/Mzox. This gives you grams of zinc.
4. Divide g of zinc by tablet weight and multiply by 100 for answer.

1. Find mol wt of SiC. Call it MWsc
2. Divide 1000 g by Msc to get moles of SiC
3. From reaction, moles of SiO2=moles of SiC
4. Find mol wt of SiO2. Call it MWso
5. Multiply MWso by moles of SiC. That's your answer.