Question

How many atoms in each element?

5CH3CO2H
C:
H:
O:

4(NH2)2CO
N:
H:
C:
O:

4C3H5(OH)3
C:
H:
O:

Answer 1

`5CH_3CO_2H`
`C: 10`
`H: 20`
`O: 10`

`4(NH_2)_2CO`
`N: 8`
`H: 16`
`C: 4`
`O: 4`

`4C_3H_5(OH)_3`
`C: 12`
`H: 32`
`O: 12`

Explanation:

When determining how many atoms of an element are in a compound from the chemical formula, we need to keep in mind two things:

• The subscript, which is where the `x` is in `A_x`. This tells us how many atoms of that specific element or group are in the compound.
  So, for example, in `H_2O`, there are `2` hydrogen atoms.
  In `Be(NO_3)_2`, there are `2` `NO_3^-` ions. It also means that there's `2xx3=6` atoms of oxygen.
• The coefficient, which is where the `x` is in `xA`. When we put a coefficient in front of something, we're multiplying the entire thing by that number.
  For example, in `2CO_2`, there are `2` `CO_2` molecules. It also means that there's `2xx2=4` atoms of oxygen.

Let's get on with the questions! :)

`5CH_3CO_2H`

`C`: Carbon appears twice in this formula. In both cases, they don't have subscripts. That means that there are `2` carbon atoms if we don't look at the coefficient. After looking at the coefficient, though, there's `2xx5=10` atoms of carbon.
`H`: There's `3+1=4` atoms of hydrogen without the coefficient (it appears once as `H_3` and once as `H`), so there's `4xx5=20` atoms of hydrogen with the coefficient.
`O`: `2xx5=10` atoms.

`4(NH_2)_2CO`
`N`: The bracket around `NH_2` has a subscript of `2`, so that means there's `2` nitrogen atoms if we're not counting the coefficient. Again, counting the coefficient, there's `4xx2=8` atoms of nitrogen.
`H`: `2xx2xx4=16` atoms of hydrogen.
`C`: It only appears once and without a subscript, so `1xx4=4`.
`O`: Like carbon, it's `1xx4=4`.

`4C_3H_5(OH)_3`
`C:` `3xx4=12` atoms.
`H:` Ignoring the coefficient, we know there's `5+3=8` atoms of hydrogen. The coefficient multiplies that by `4`, so we get `8xx4=32` atoms of hydrogen.
`O:` `3xx4=12` atoms.