Chemistry Questions Help (NOT HW QUESTIONS)!!!! (Over all aspects of Chemistry)?

Here are a couple questions I don't get --- its for AP Chem but I don't remember them: 4. An unknown organic contains only carbon and hydrogen and has a molar mass of 78.1 g/mol. Analysis shows the compound to be 7.69% hydrogen by mass. a. Find the empirical formula for this compound. b. Determine the... show more Here are a couple questions I don't get --- its for AP Chem but I don't remember them:
4. An unknown organic contains only carbon and hydrogen and has a molar mass of 78.1 g/mol. Analysis shows the compound to be 7.69% hydrogen by mass.
a. Find the empirical formula for this compound.
b. Determine the molecular formula for the compound
c. When the compound reacts with oxygen the products are carbon dioxide and water. Write and balance the equation for the combustion reaction described.

5. Sodium carbonate decomposes upon heating, producing sodium oxide and carbon dioxide.
a. Write a balanced chemical equation for this reaction.
b. How many grams of sodium oxide will be produced after 17.05 grams of sodium carbonate are completely decomposed.
c. How many sodium ions are produced in the mass of sodium oxide calculated in part b?

6. Hydrochloric acid is added to solid zinc producing hydrogen gas and aqueous zinc chloride.
a. Write a balanced chemical equation for this reaction.
b. Calculate the number of moles in 18.0 grams of zinc.
c. If .745 mol of hydrochloric acid react with the amount of zinc in part b, determine the limiting reactant.
d. Calculate the percent yield if .195 mol of zinc chloride is actually recovered in lab.

7. Gallium consists of two naturally occurring isotopes with masses of 69 and 71 amu.
a. How many protons and neutrons are in the nucleus of each isotope.
b. Gallium reacts with oxygen in a redox, synthesis, reaction; write the balanced equation for this reaction.
c. If the atomic mass of gallium is 69.72 amu, calculate the percent abundance of each isotope of gallium.
d. When 14.00 grams of gallium reacts completely with oxygen, what mass of oxygen has been consumed?
e. What volume of oxygen gas would have reacted at STP in part d.
Update: please provide explanations too! I practically self taught Chem Honors to myself.
Update 2: Is 4 a CH?
I did this: 7.69*78.1=600.589 ---- 600.589/100 (cause it was a percent) = 6.00589 ---- that divided by one = about 6 Hydrogens...

then did the same for Carbon and got 6 carbons to get C6H6 - CH
Update 3: Ok just to see if Im on the right track so far: 4a. CH 4b. C6H6 4c.2C6H6(l)+15O2 (g) - 12CO2(g) + 6H2O(g) 5a.Na2CO3 - Na2O + CO2 5b. 9.97 grams of Na2O 5c. 2 Sodium Ions 6a.2HCl(l) + Zn(s) - H2(g) + ZnCl2(aq) 6b. 1.0836x10^25 6c.Zn= Limiting Reagent 7a.31 protons 38 neutrons ---- 31 protons 40 neutrons 7b. I dont... show more Ok just to see if Im on the right track so far:
4a. CH
4b. C6H6
4c.2C6H6(l)+15O2 (g) - 12CO2(g) + 6H2O(g)
5a.Na2CO3 - Na2O + CO2
5b. 9.97 grams of Na2O
5c. 2 Sodium Ions
6a.2HCl(l) + Zn(s) - H2(g) + ZnCl2(aq)
6b. 1.0836x10^25
6c.Zn= Limiting Reagent
7a.31 protons 38 neutrons ---- 31 protons 40 neutrons
7b. I dont get redox
2 answers 2