Questions & Answers

Question

Answers

A. 52.14%

B. 13.13%

C. 16%

D. 34.73%

Answer

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We know that the molecular formula of ethanol is ${{C}_{2}}{{H}_{5}}OH$. We can find the molecular mass of ethanol using the following steps:

- Consider the atomic masses of each element

- Multiply the atomic masses by the number of atoms of that element found in the molecule based on the molecular formula. For example, here, 6 atoms of hydrogen are present, so multiply the atomic weight of hydrogen with 6 to get the total weight of hydrogen present.

- Add the total weights of all the elements present to get the molecular formula.

Thus, the molecular weight of ethanol is:

$\left( 12\times 2 \right)+\left( 5\times 1 \right)+\left( 1\times 16 \right)+\left( 1\times 1 \right)=46gmo{{l}^{-1}}$

There is only one oxygen in this ethanol. So, mass percent of oxygen will be$\dfrac{16}{48}\times 100=33%\cong 34.72%$.

- We can find out the mass percent of carbon in ethanol in this same way. That is,$\dfrac{\left( 2\times 12 \right)}{48}\times 100=50%$. In the options, there is 52.14%.

- Also, we can find the mass percent of hydrogen in this ethanol in this same way. That is,

$\dfrac{\left( 6\times 1 \right)}{48}\times 100=12.5%$. There is an option 13.13% which is approximately the mass percent of hydrogen in ethanol.

- Mass percent is one method to express the concentration of a substance in the particular mixture. The composition of solution also can be expressed in the same way by mass of solute present in the given mass of solution.