[asraiblu]

I am not sure how to calculate the number of atoms in the following chemical formulas. The parentheses are confusing me. Thanks for your help:

CH3(CH2)16COOH (stearic acid)
C3H5(C17H33COO)3 (triolein)

[rudi_in]

NO, NO, NO


For stearic acid

CH3(CH2)16COOH

This is a long chain

a CH3

followed by 16 CH2

then the COOH

The 16 refers to only the number of CH2 in the chain it is kind of a short hand instead of writing it all out like this...

CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH 2COOH

We should break this up into each atom

Carbon

Hydrogen

Oxygen

We can determine the number of each atom as you suggested by breaking up the segments of the formula

CH3

(CH2)16

COOH

In the first segment we have 1 carbon and 3 hydrogen

In the second segment we have 16 carbon and 32 hydrogen

In the third segment we have 1 carbon, 1 hydrogen,and 2 oxygen

This gives a total of

18 carbon
36 hydrogen
2 oxygen

and 56 total atoms


For this one...

C3H5(C17H33COO)3

you have
C3H5

and

(C17H33COO)3

that means 3 of everything in the parentheses

3-C17 = 51 carbon
3-H33 = 99 hydrogen
3-C = 3 carbon
3-O = 3 oxygen
3-O = 3 oxygen

add this to the 3 carbon and 5 hydrogen from the first part to get
57 carbon
104 hydrogen
6 oxygen

total of 167 atoms

[Evil dead]

O sorry my mistake, I got the numbers mixed up