Select all the correct answers.
A sample of an unknown compound has a percent composition of $52.14 \%$ carbon, $13.13 \%$ hydrogen, and $34.73 \%$ oxygen. Which compounds could the sample be?
$CH _3 CH _3 CH _2 O _2$
$C _2 H _5 OH$
$C _4 H _{10} O _2$
$C _4 H _{12} O _2$
Answer (2)
Calculate the percent composition of C 2 H 6 O and find it matches the given composition.
Calculate the percent composition of C 3 H 8 O 2 and find it does not match the given composition.
Calculate the percent composition of C 4 H 10 O 2 and find it does not match the given composition.
Calculate the percent composition of C 4 H 12 O 2 and find it matches the given composition.
The compounds that match the given percent composition are C 2 H 6 O and C 4 H 12 O 2 . Therefore, the answer is C 2 H 5 O H , C 4 H 12 O 2 .
Explanation
Analyze the problem and data We are given the percent composition of an unknown compound: 52.14% carbon, 13.13% hydrogen, and 34.73% oxygen. We need to determine which of the given compounds could have this composition. The compounds are:
C H 3 C H 3 C H 2 O 2 which is C 3 H 8 O 2
C 2 H 5 O H which is C 2 H 6 O
C 4 H 10 O 2
C 4 H 12 O 2
Outline the solution To solve this, we will calculate the percent composition of each compound and compare it to the given composition. We'll use the molar masses: C = 12.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol.
Calculate percent composition of C2H6O
C 2 H 6 O :
Molar mass = 2 ( 12.01 ) + 6 ( 1.008 ) + 1 ( 16.00 ) = 24.02 + 6.048 + 16.00 = 46.068 g/mol %C = 46.068 2 ( 12.01 ) × 100 = 46.068 24.02 × 100 = 52.14%
%H = 46.068 6 ( 1.008 ) × 100 = 46.068 6.048 × 100 = 13.13%
%O = 46.068 1 ( 16.00 ) × 100 = 46.068 16.00 × 100 = 34.73%
Calculate percent composition of C3H8O2
C 3 H 8 O 2 :
Molar mass = 3 ( 12.01 ) + 8 ( 1.008 ) + 2 ( 16.00 ) = 36.03 + 8.064 + 32.00 = 76.094 g/mol %C = 76.094 3 ( 12.01 ) × 100 = 76.094 36.03 × 100 = 47.35%
%H = 76.094 8 ( 1.008 ) × 100 = 76.094 8.064 × 100 = 10.60%
%O = 76.094 2 ( 16.00 ) × 100 = 76.094 32.00 × 100 = 42.05%
Calculate percent composition of C4H10O2
C 4 H 10 O 2 :
Molar mass = 4 ( 12.01 ) + 10 ( 1.008 ) + 2 ( 16.00 ) = 48.04 + 10.08 + 32.00 = 90.12 g/mol %C = 90.12 4 ( 12.01 ) × 100 = 90.12 48.04 × 100 = 53.31%
%H = 90.12 10 ( 1.008 ) × 100 = 90.12 10.08 × 100 = 11.19%
%O = 90.12 2 ( 16.00 ) × 100 = 90.12 32.00 × 100 = 35.51%
Calculate percent composition of C4H12O2
C 4 H 12 O 2 :
Molar mass = 4 ( 12.01 ) + 12 ( 1.008 ) + 2 ( 16.00 ) = 48.04 + 12.096 + 32.00 = 92.136 g/mol %C = 92.136 4 ( 12.01 ) × 100 = 92.136 48.04 × 100 = 52.14%
%H = 92.136 12 ( 1.008 ) × 100 = 92.136 12.096 × 100 = 13.13%
%O = 92.136 2 ( 16.00 ) × 100 = 92.136 32.00 × 100 = 34.73%
Compare and conclude Comparing the calculated percent compositions to the given composition (52.14% C, 13.13% H, 34.73% O), we find that C 2 H 6 O and C 4 H 12 O 2 match the given composition.
Final Answer Therefore, the compounds that could be the sample are C 2 H 5 O H and C 4 H 12 O 2 .
Examples
Percent composition is a fundamental concept in chemistry that helps us identify and characterize different compounds. For example, if you're working in a lab and synthesize a new compound, you can determine its percent composition to confirm its identity or purity. Similarly, in environmental science, knowing the percent composition of pollutants helps in assessing their impact and devising strategies for remediation. Imagine you're analyzing a soil sample to determine the amount of organic matter present. By determining the percent composition of carbon, hydrogen, and oxygen, you can estimate the amount of organic material in the soil, which is crucial for understanding soil fertility and health.
The compounds that match the given percent composition of the unknown compound are C 2 H 5 O H and C 4 H 12 O 2 . Both compounds have the same carbon, hydrogen, and oxygen percentages as provided. Thus, the final answer includes these two options.
;
