Question

. Acetic acid contains carbon, hydrogen and oxygen. 4.24g of sample of acetic
acid on complete combustion gave 6.21g of CO2 and 2.54 of H20. The
molecular mass of acetic acid is 60. Find (i)Empirical formula of acetic acid and
(ii) Molecular formula of acetic acid.​

Answer 1

Answer:

make the table it's too boring I use to do I. my tenth it looks like

elements. molecular mass. percentage composition/molecular mass divide by lowest no. to get whole no. ratio

H.

O

C

Answer 2

Answer:

(i)  Empirical formula of acetic acid is  CH₂O.

(ii)  Molecular formula of acetic acid is CH₃COOH.

Explanation:

Mass of carbon in the carbon dioxide $= \frac{12}{44}\times6.21= 1.693g$

Mass % of carbon in the sample of acetic acid$=\frac{ 1.693}{4.21}\times100= 40\%$

Mass of hydrogen in the water$= \frac{2}{18}\times2.54= 0.282g$

The percentage of hydrogen in the sample $=\frac{ 0.282}{4.21}\times 100= 6.7\%$

Mass percentage of oxygen = 100 - (40 + 6.7) = 53.3%

Now, mass percentage of C, H and O are 40, 6.7 and 53.3 respectively.

$Element\\\\C\\\\H\\\\O$      $Mass\%\\\\40\\\\6.7\\\\53.3$        $Atomic\; mass\\\\12\\\\1\\\\16$      $mass\%/At. mass\\\\\frac{40}{12}=3.33\\ \\\frac{6.7}{1}=6.7\\ \\\frac{53.3}{16}=3.33$       $Simple \;ratio\\\\1\\\\2\\\\1$  

Therefore, the empirical formula of the acetic acid is CH₂O.

The empirical formula mass of acetic acid = 12 + 2 + 16 = 30g

Given, the molecular mass of the acetic acid = 60g/mol

n = molar mass/ empirical formula mass

$n = \frac{60}{30} =2$

Therefore, molecular formula of acetic acid is (CH₂O)₂ or CH₃COOH.

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