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Two things are given to us: The "molar mass" of NaOH and the number of molecules of NaOH. 

The molar mass is different from "mass"; 1 mole of NaOH is equal to 40.0g/mol.
When the question asks, what is the mass? It is referring to how many grams there are. 

First, we are going to convert the molecules to atoms using Avogadro's number (=6.02 x 10^23)

(2.50 x 10^22 molecules) x (6.02 x 10^23 atoms) = 0.042 mol

Next, we are going to convert from moles to grams.

 0.042 mol of NaOH x 40.0 g of NaOH/1 mole = 1.68g of NaOH.

There are 1.68 grams in 2.50 x 10^22 molecules of NaOH.



dexteright02

Hello!

What is the mass of 2.50 ×1022 molecules of NaOH (Molar mass = 40.0 g/mol)?

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 -------------------- 2.50*10²² molecules

[tex]\dfrac{1}{y} = \dfrac{6.02*10^{23}}{0.250*10^{23}}[/tex]

Product of extremes equals product of means

[tex]6.02*10^{23}*y = 0.250*10^{23}*1[/tex]

[tex]6.02*10^{23}\:y = 0.250*10^{23}[/tex]

[tex]y = \dfrac{0.250*10^{23}}{6.02*10^{23}}[/tex]

[tex]\boxed{y \approx 0.042\:mol}[/tex]

Solving: Find the mass value now

40 g ----------------- 1 mol of NaOH

x g ------------- 0.042 mol of NaOH

[tex]x = 40*0.042[/tex]

[tex]\boxed{\boxed{x = 1.68\:g}}\end{array}}\qquad\quad\checkmark[/tex]

Answer:

The mass is 1.68 grams

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I Hope this helps, greetings ... Dexteright02! =)

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