Question

How many molecules are in each sample?4.6 g H2O

Answer 1

Hello!

We have the following data:

m (mass) = 4.6 grams
MM (molar mass) of H2O
H = 2 * 1 = 2 amu
O = 1 * 16 = 16 amu
--------------------------
MM (molar mass) of H2O = 2 + 16 = 18 g/mol

Solving:

Establishing a relation with Avogadro's number (6.10²³) we have:

18 g of H2O --------------- 6.10²³ molecules
4.6 g of H2O --------------- y molecules


`18*y = 4.6*6.10^(23)`


`18y = 2.76*10^(24)`


`y = (2.76*10^(24))/(18)`


`\boxed{\boxed{y \approx 1.53*10^(23)\:molecules}}\end{array}}\qquad\quad\checkmark`

Answer 2

Answer: The number of molecules present in given amount of water are
`1.54* 10^(23)`

Step-by-step explanation:

To calculate the number of moles, we use the equation:

`\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}`

Given mass of water = 4.6 g

Molar mass of water = 18.0 g/mol

Putting values in above equation, we get:

`\text{Moles of water}=(4.6g)/(18.0g/mol)=0.255mol`

According to mole concept:

1 mole of a compound contains
`6.022\time 10^(23)` number of molecules.

So, 0.255 moles of water will contain
`0.255* 6.022* 10^(23)=1.54* 10^(23)` number of molecules.

Hence, the number of molecules present in given amount of water are
`1.54* 10^(23)`