[xskaternickx]

Hi, I've been trying to figure these homework problems out but just can't seem to understand what i'm supose to do. Can anyone show me how to find the answers?

1.
      CH4 + 2O2 ---> CO2 + 2H2O
1 mole of CH4 reacts with ___ Moles of O2 to form ___ moles CO2 and ___ moles H2O

2.
An unknown compound is found to contain 27.0g Ca, 21.6g O and 1.37g H. What is it's empirical formula?

3.
       H3PO4 + 3NaOH ---> 3H2O + Na3PO4
How many moles of Na3PO4 will be produced from 1.7 moles of NaOH in the presence of excess H3PO4?

4.
      2AgNO3 + CaBr2 ---> 2AgBr + Ca(NO3)2
A chemist wishes to obtain 59.5g AgBr from the above reaction. How many grams of AgNO3 and how many grams of CaBr2 should be reacted?

5.
A chemist performs the following experiment:
    2FeCl3 + 3CaCO3 ---> Fe2(CO3)3 + 3CaCl
If he starts with 105g FeCl3 and excess CaCO3 how many grams of CaCl2 will he obtain?

6.
How many moles of CaCl2 is this? (the answer from #7)

7.
A compound has an empirical formula of CHO2. It's molarmass is 90g 1 mole. What is the molecular formula of the compound?


any help would be appreciated, Thank you so much!

[Arkcon]

OK, many of these problems involve converting moles to grams and vice versa.  Do you recall from classes how that's done?  Do you know the definition of moles?

[xskaternickx]

Yes, i do. I just don't understand what steps you have to do... I think i got the 2nd question is it CaO2H2?

[Arkcon]

Yes, i do. I just don't understand what steps you have to do... I think i got the 2nd question is it CaO2H2?

Good.  Now how to you calculate it.  And as an aside, how would you rewrite your formula, using conventional formula writing rules?  It's kinda like math, can you 'combine the terms' O2H2 into something simpler?

Likewise, this one:

7. A compound has an empirical formula of CHO2. It's molarmass is 90g 1 mole. What is the molecular formula of the compound?

What is the molar mass of CHO2?  How different is it from 90 g 1 mole?  (Hey that's you notation, not mine.)  What is the difference?  And are you noticing that all these questions are pretty much the same basic idea?

[xskaternickx]

So to simplify it what do you mean like Ca+2HO?
So #7 is pretty much doing the opposite as #2? So they are looking for C2H2O4?

[Arkcon]

Good.  Show your work if you have problems with the others.