Question

What is the mass of `3.34xx10^23` `"water molecules"`?

Answer 1

`6.022140857xx10^23` water molecules have a mass of `(15.999+2xx1.008)*g` `~~` `18.0*g`

Explanation:

The number `6.022140857xx10^23` is `N_A`, Avogadro's number. If I have precisely this number of atoms, or molecules, I have, by definition, A MOLE of such ATOMS or MOLECULES. You have `3.34xx10^23` individual water molecules; you have slightly over `1/2` `xx` `N_A`, i.e. `9-10` `g`.

Answer 2

the mass of `3.34xx10^23` water molecules is 9.911 grams

Explanation:

Okay so firstly, you want to be converting the number of molecules of water you have into number of moles
As you probably know
Number of Particles = Number of Moles x Avogadro's constant
thus, no of moles = number of particles/Avogadro's constant
`=3.34xx10^23//6.02xx10^23`
`=0.55`
Thus 0.55 Moles
Now number of moles = mass/molar mass
We have to calculate the mass, thus
Mass = Number of Moles x Molar Mass
The molar mass of `H_2O` is
H - 2(1.01) = 2.02
O- 16
18.02
Thus, the molar mass is 18.02 g/mol
Therefore, now we have the required values to find the mass
Mass = `0.55 xx 18.02`
Mass = `9.911`
Thus, the mass of `3.34xx10^23` water molecules is 9.911 grams