Question

B. Calculate the number of moles of NaOH in
i) 60 g
ii) 20 g of the compound
(Average atomic masses of Na = 23,0 = 16, H = 1)​

Answer 1

Answer:

1)60/40 = 1•5

2)20/40 = 0.5

Answer 2

Given :

• 60g of NaOH

• 20g of NaOH

• ‎ Atomic mass of Na = 23

• Atomic mass of O = 16

• Atomic mass of H = 1

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To :

• Calculate the number of moles of NaOH in 60g and 20g

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Concept :

In order to calculate the number of moles we would use a formula as follows :

$\bf\color{teal}{Number~of~moles~=~\frac{Gram~weight}{Molar~Mass}}$

So using this formula is simple as we are given the weight in grams but we need to calculate the molar mass.

For molar mass we would add up the atomic masses of all the atoms present in NaOH i.e., atomic mass of Na , atomic mass of O and atomic mass of H .

Hope am clear let's do it :D~

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Solution :

Calculating the Molar mass of NaOH -

$\sf\:Molar~Mass~=~Atomic~mass~of~(Na+O+H)$

Plugging the given atomic masses of Na , O and H

$\sf\twoheadrightarrow\:Molar~Mass~=~23+16+1$

$\small{\mathfrak{\twoheadrightarrow\:Molar~Mass~=~40g~per~mol}}$

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Question (i) :

60 g

$\sf\:Number~of~moles~=~\frac{Gram~Weight}{Molar~Mass}$

Substituting the values

$\sf\to\:Number~of~moles~=~\frac{60}{40}$

Reducing the fraction to lower terms

$\sf\to\:Number~of~moles~=~\frac{6\cancel{0}}{4\cancel{0}}$

$\sf\to\:Number~of~moles~=~\cancel{\frac{6}{4}}$

$\sf\to\:Number~of~moles~=~\frac{3}{2}$

$\small{\underline{\boxed{\mathrm{\to~Number~of~moles~=~1.5~moles}}}}$ ★

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Question (ii) :

20g

$\sf\:Number~of~moles~=~\frac{Gram~Weight}{Molar~Mass}$

Substituting the values

$\sf\to\:Number~of~moles~=~\frac{20}{40}$

Reducing the fraction to lower terms

$\sf\to\:Number~of~moles~=~\frac{2\cancel{0}}{4\cancel{0}}$

$\sf\to\:Number~of~moles~=~\cancel{\frac{2}{4}}$

$\sf\to\:Number~of~moles~=~\frac{1}{2}$

$\small{\underline{\boxed{\mathrm{\to~Number~of~moles~=~0.5~moles}}}}$ ★

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Therefore :

❒ Number of moles in 60g = $\small\fbox\red{1.5~moles}$

❒ Number of moles in 20g = $\small\fbox\red{0.5~moles}$

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