[BioExpert]

Hello, I have a chemistry test on Friday and am confused on how to do these problems on the review.

1.) Answer the following question about a pure compound that contains only carbon, hydrogen, and oxygen.

    A.) A 0.7549 sample of the compound burns in O₂ to produce 1.9061g of CO₂ and 0.3370g of H₂0.
          I. Calculate the individual masses of C, H, and O in the 0.7549 sample.

         II. Determine the empirical formula for the compound.

2.) Answer the following questions that relate to the analysis of chemical compounds.

    A.) A compound containing the elements C, H, N and O is analyzed. When 1.2359g saple is burned in excess oxygen, 2.241 of CO₂ is formed. The combustion analysis also showed that the sample containing 0.0648 g of H.

         I. Determine the mass, in grams, of C in the 1.2359 sample of the compound.

        II. When the compound is anylyzed for N content only, the mass percent of N is found to be 28.84%.
             Determine the mass, in grams, of N in the original 1.2359 g sample of the compound.

       III. Determine the mass of O in the original 1.2359 g sample.

       IV. Determine the empirical formula of the compound.

3.) For the reaction between iron(III) chloride and hydrosulfuric acid to form iron (III) sulfide and hydrochloric acid.

    A.) Write the balanced chemical reaction

    B.) Determine the theoretical yield of Iron(III) sulfide if 100. g of iron (III) chloride reacts with 50.0 g of hydrosulfuric acid.

    C.) If 58.3 g of iron(III) sulfide was actually collected, what is the percent yield?


      Can anyone help me with these problems on my chapter review. Please show correct significant figures and steps.

                                                                                                                                     Thank-You

[Arkcon]

In the nine separate questions you posted, can you do any of them?  For example, can you write the balanced chemical reaction asked in the third one?

Let's start with 1. A. I -- Can you use the masses of products to determine the masses of the elements in the compound?

And I'm going to expect that you can make an attempt at the correct number of significant figures yourself.

[Kudo89]

Hint :
- write the balanced chemical reaction
- remember that amount of mass before and after reaction are always same
- don't be afraid to use some assumption for anything you still don't know

that's you need to answer these question
good luck

[BioExpert]

I have done number 1 based on what I know. I do not know if this is correct, if not can you please tell me where I went wrong?

1.) % C = [(C)(100%)] / (CO2) = [(12.011)(100%)] / (44.009) = 27.292144%
 
(1.9061 g)(0.27292144) = 0.5202154 g of C
 
% H = [(H2)(100%)] / (H2O) = [(2.016)(100%)] / (18.015) = 11.190674%
 
(0.3370 g)(0.11190674) = 0.0377125 g of H
 
mass of oxygen = (0.7549 g) – (0.5202154 g) – (0.0377125 g) = 0.196972 g
 
C = (0.5202154 g) / (12.011 g/mol) = 0.0433115 mol
 H = (0.0377125 g) / (1.008 g/mol) = 0.374131 mol
 O = (0.196972 g) / (15.999 g/mol) = 0.0122957 mol
 
B.)

C = (0.0433115 mol) / (0.0122957) = 3.5224916 mol
H = (0.374131 mol) / (0.0122957) = 3.0427791 mol
 O = (0.0122957 mol) / (0.0122957) = 1 mol
 
C = (3.5224916 mol) × 2 = 7.0349706 mol = 7 mol
 H = (3.0427791 mol) × 2 = 6.0769092 mol = 6 mol
 O = (1 mol) × 2 = 2 mol
 
C7H6O2

Is this correct?

                                                                                                                                  Thank-You

[Borek]

C₇H₆O₂ it is.