Serotonin (molar mass 176 g/mol) is a compound that conducts nerve impulses in brain and muscle. It contains 68.2% C, 6.86% H, 15.9% N and 9.08% O. What is the molecular formula?

Question

Serotonin (molar mass 176 g/mol) is a compound that conducts nerve impulses in brain and muscle. It contains 68.2% C, 6.86% H, 15.9% N and 9.08% O. What is the molecular formula?

1 Answer

Impact of this question

15029 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2017-02-16T22:48:57

$Serotonin \equiv C_{10} H_{12} N_{2} O$ $"Serotonin"-=C_10H_12N_2O$

Explanation:

As with all these problems, we ASSUME $100 \cdot g$ $100*g$ of compound, and we work out the percentages of each element on a molar basis:

$Moles of carbon$ $"Moles of carbon"$ $=$ $=$ $\frac{68.2 \cdot g}{12.011 \cdot g \cdot m o l^{- 1}} = 5.68 \cdot m o l$ $(68.2*g)/(12.011*g*mol^-1)=5.68*mol$ .

$Moles of hydrogen$ $"Moles of hydrogen"$ $=$ $=$ $\frac{6.86 \cdot g}{1.00794 \cdot g \cdot m o l^{- 1}} = 6.81 \cdot m o l$ $(6.86*g)/(1.00794*g*mol^-1)=6.81*mol$ .

$Moles of nitrogen$ $"Moles of nitrogen"$ $=$ $=$ $\frac{15.9 \cdot g}{14.01 \cdot g \cdot m o l^{- 1}} = 1.14 \cdot m o l$ $(15.9*g)/(14.01*g*mol^-1)=1.14*mol$ .

$Moles of oxygen$ $"Moles of oxygen"$ $=$ $=$ $\frac{9.08 \cdot g}{15.999 \cdot g \cdot m o l^{- 1}} = 0.568 \cdot m o l$ $(9.08*g)/(15.999*g*mol^-1)=0.568*mol$ .

Note that normally the analyst would not give you $% O$ $%O$ ; you would be expected to work it out by difference.

And now we divide thru by the SMALLEST molar quantity, that of oxygen, to give an empirical formula of:

$C_{10} H_{12} N_{2} O$ $C_10H_12N_2O$ .

And this is the empirical formula, the simplest whole number ratio defining constituent atoms in a species.

Now the molecular formula is ALWAYS a multiple of the empirical formula. That is $Molecular formula \equiv {(empirical formula)}_{n}$ $"Molecular formula"-="(empirical formula)"_n$ .

Thus the molecular mass must show this proportionality:

${(C_{10} H_{12} N_{2} O)}_{n} = 176 \cdot g \cdot m o l^{- 1}$ $(C_10H_12N_2O)_n=176*g*mol^-1$

So $n \times (10 \times 12.011 + 12 \times 1.00794 + 2 \times 14.01 + 15.999) \cdot g \cdot m o l^{- 1} = 176 \cdot g \cdot m o l^{- 1}$ $nxx(10xx12.011+12xx1.00794+2xx14.01+15.999)*g*mol^-1=176*g*mol^-1$

Clearly, $n = 1$ $n=1$ , and the $empirical formula$ $"empirical formula"$ is the same as the $molecular formula$ $"molecular formula"$ .

This approach is standard, however, most of the time you would not be quoted a percentage oxygen composition. You would be expected to calculate this yourself by difference.

Science

Math

Humanities

... and beyond

Serotonin (molar mass 176 g/mol) is a compound that conducts nerve impulses in brain and muscle. It contains 68.2% C, 6.86% H, 15.9% N and 9.08% O. What is the molecular formula?

1 Answer

Explanation:

Related questions

Impact of this question