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

$18*y = 4.6*6.10^{23}$

$18y = 2.76*10^{24}$

$y = \frac{2.76*10^{24}}{18}$

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

Answer 2

Answer: The number of molecules present in given amount of water are $1.54\times 10^{23}$

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:

$\text{Moles of water}=\frac{4.6g}{18.0g/mol}=0.255mol$

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 $0.255\times 6.022\times 10^{23}=1.54\times 10^{23}$ number of molecules.

Hence, the number of molecules present in given amount of water are $1.54\times 10^{23}$