Question

Find the approximate atomic mass of a water molecule (h2o). give your answer in atomic mass units rounded to the nearest whole number.

Answer 1

Answer: 18 amu

Explanation:

The atomic mass of hydrogen is 1.008 or 1 (rounded to the nearest whole number)

The atomic mass of oxygen is 15.999 or 16 (rounded to the nearest whole number)

There are 2 hydrogen atoms and one oxygen atom in water.

1+1+16= 18 amu

Answer 2

First step is to get the mass of water molecule in grams:
From the periodic table:
molar mass of hydrogen is 1
molar mass of oxygen is 16

molar mass of a water molecule = 2(1) + 16 = 18 gm

Now, to convert the gm into amu, all you have to do is multiply the gm you got by Avogadro's number as follows:
mass of water molecule = 18 x 6.22 x 10^23 = 1.1196 x 10^25 amu which is approximately 1 x 10^25 amu