Question

Determine the percentage by mass of each element in the following compounds. (Round your answers to one decimal place.)(a)ammonia, NH3N:____%H:_____%(b)washing soda, Na2CO3Na:____%C:_____%O:_____%

Answer 1

To determine the mass percentage of each element in the compounds, we are going to use the following formula:

`\%\text{ m/m = }\frac{mass\text{ of the element}}{mass\text{ of the compound}}*100`

In the case of the last element of each compound, we are going to make the subtraction of 100% minus the addition of the other elements.

We are going to assume that we have 1 mole of every substance.

First, we have to determine the molecular weight of each substance:

a. NH3

`M.W\text{ NH}_3\text{ = 14+1*3 = 17 g/mol}`

If we have 1 mole of ammonia, then we have 17 g. Then, we can calculate the nitrogen mass percentage as follows:

`\%\text{ m/m N = }\frac{14\text{ g }}{17\text{ g}}\text{ *100}=\text{ 82.4}\%\text{ }`

Then, we make the subtraction to determine the hydrogen percentage:

`\%m/m\text{ H = 100-82.4 = 17.6\%}`

Then, the answer is that the nitrogen mass percentage equals 82.4% and the hydrogen one is 17.6%

b. Na2CO3

We repeat the same steps that we did with the ammonia.

`M.W\text{ Na}_2CO_3\text{ = 23*2+12+16*3= 106 g/mol }`

`\%\text{ m/m Na = }\frac{46\text{ g }}{106\text{ g}}*100=\text{ 43.4 \%}`
`\%\text{ m/m C = }\frac{12\text{ g}}{106\text{ g }}*100\text{ = 11.3\%}`
`\%m/m\text{ O= 100-\lparen11.3+43.4\rparen=45.3\%}`

Then, the answer is that the sodium mass percentage equals 43.4%, the carbon is 11.3%, and the oxygen one is 45.3%