Question

What is the mass of 2.70 ×10^22 molecules of NaOH (Molar mass = 40.0 g/mol)?

Answer 1

Data:
Molar Mass of NaOH = 40 g/mol

Solving: According to the Law Avogradro, we have in 1 mole of a substance, 6.02x10²³ atoms/mol or molecules

1 mol -------------------- 6.02*10²³ molecules
y mol -------------------- 2.70*10²² molecules

6.02*10²³y = 0.270*10²³ 
$y = \frac{0.270*\diagup\!\!\!\!\!\!10^{\diagup\!\!\!\!\!\!23}}{6.02*\diagup\!\!\!\!\!\!10^{\diagup\!\!\!\!\!\!23}}$
$\boxed{y \approx 0.04\:mol}$


Solving: Find the mass value now

40 g ----------------- 1 mol of NaOH
x g ------------- 0.04 mol of NaOH

$x = 40*0.04$
$\boxed{\boxed{x = 1.6\:g}}\end{array}}\qquad\quad\checkmark$

Answer:
The mass is 1.6 grams