You take an aspirin tablet (a compound consisting solely of carbon, hydrogen, an
ID: 481551 • Letter: Y
Question
You take an aspirin tablet (a compound consisting solely of carbon, hydrogen, and oxygen) with a mass of 1.00 g, burn it in air, and collect 2.20 g of carbon dioxide and 0.400 g water. The molar mass of aspirin is between 170 and 190 g/mol. What is the molecular formula of aspirin?
Based on the information given above, fill the table below. It will help you solve this problem. Please show your calculation in the second page after the table.
Mass of aspirin tablet sample
C
Mass of CO2 collected
Mole of CO2 collected
Mole of C in the sample of aspirin tablet
Mass of C in the sample of aspirin tablet
H
Mass of H2O collected
Mole of H2O collected
Mole of H in the sample of aspirin tablet
Mass of H in the sample of aspirin tablet
O
Mass of O in the sample of aspirin tablet
Mole of O in the sample of aspirin tablet
Mole ratio of C, H and O in the sample of aspirin tablet
The simplest whole number mole ratio of C, H, and O in the sample of aspirin tablet
Empirical formula of aspirin
Molecular formula of aspirin
Mass of aspirin tablet sample
C
Mass of CO2 collected
Mole of CO2 collected
Mole of C in the sample of aspirin tablet
Mass of C in the sample of aspirin tablet
H
Mass of H2O collected
Mole of H2O collected
Mole of H in the sample of aspirin tablet
Mass of H in the sample of aspirin tablet
O
Mass of O in the sample of aspirin tablet
Mole of O in the sample of aspirin tablet
Mole ratio of C, H and O in the sample of aspirin tablet
The simplest whole number mole ratio of C, H, and O in the sample of aspirin tablet
Empirical formula of aspirin
Molecular formula of aspirin
Explanation / Answer
Mass of aspirin tablet sample
1 g
C
Mass of CO2 collected
2.20 g
Mole of CO2 collected
0.0500 mol
Mole of C in the sample of aspirin tablet
0.0500 mol
Mass of C in the sample of aspirin tablet
0.601 g
H
Mass of H2O collected
0.400 g
Mole of H2O collected
0.022 mol
Mole of H in the sample of aspirin tablet
0.044 mol
Mass of H in the sample of aspirin tablet
0.0444 g
O
Mass of O in the sample of aspirin tablet
0.354 g
Mole of O in the sample of aspirin tablet
0.0221 mol
Mole ratio of C, H and O in the sample of aspirin tablet
0.0500:0.044:0.0221
The simplest whole number mole ratio of C, H, and O in the sample of aspirin tablet
2.25:2:1
Empirical formula of aspirin
C2.25H2O
Molecular formula of aspirin
C9H8O4
Calculation and explanation:
Given, mass of CO2 collected = 2.20 g
Mole of CO2 = 2.20 g/ 44.009 g/mol
= 0.0500 mol
And Mole of C in the sample of aspirin tablet = mole of CO2 collected
= 0.0500 mol …………………..….…1
Therefore, mass of C in the sample of aspirin tablet = 0.0500 mol x 12.011 g/mol=0.601 g
Also given, the mass of H2O collected = 0.400 g
Mole of H2O collected = 0.400 g/18.02 g/mol
= 0.022 mol
And, mole of H in the sample of aspirin tablet = 2 x mole of H2O collected
= 2 x 0.022
= 0.044 mol ……………………………2
Therefore, mass of H in the sample of aspirin tablet = 0.044 mol x 1.008 g/mol
= 0.0444 g
It is also mentioned in the question that the mass of aspirin tablet sample = 1 g
Therefore, mass of O in the sample of aspirin tablet = 1.00 – (mass of H and C)
= 1.00 - ( 0.0444 + 0.601)
= 1.00 -0.6454
= 0.354 g
Hence, Mole of O in the sample of aspirin tablet = 0.354 g/15.999 g/mol
= 0.0221 mol………………………….3
From 1, 2 and 3, the molar ratio of C, H and O in the sample of aspirin tablet i.e.,
C: H: O = 0.0500: 0.044: 0.0221
Dividing it by 0.0221, we get the simplest whole number molar ratio of C, H, and O in the sample of aspirin tablet = 2.25: 2: 1
Hence, the empirical formula of aspirin = C2.25H2O
And multiplying the empirical formula by 4 we get the molecular formula of aspirin = C9H8O4
Thus, the molar mass of aspirin =180g/mol
Mass of aspirin tablet sample
1 g
C
Mass of CO2 collected
2.20 g
Mole of CO2 collected
0.0500 mol
Mole of C in the sample of aspirin tablet
0.0500 mol
Mass of C in the sample of aspirin tablet
0.601 g
H
Mass of H2O collected
0.400 g
Mole of H2O collected
0.022 mol
Mole of H in the sample of aspirin tablet
0.044 mol
Mass of H in the sample of aspirin tablet
0.0444 g
O
Mass of O in the sample of aspirin tablet
0.354 g
Mole of O in the sample of aspirin tablet
0.0221 mol
Mole ratio of C, H and O in the sample of aspirin tablet
0.0500:0.044:0.0221
The simplest whole number mole ratio of C, H, and O in the sample of aspirin tablet
2.25:2:1
Empirical formula of aspirin
C2.25H2O
Molecular formula of aspirin
C9H8O4
Calculation and explanation:
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