Question

A chemist needs to prepare 30.00 L of a 0.250 M solution of NaOH.
What mass of NaOH does she need to make the solution?

Answer 1

Answer:-

Given:-

Volume of the solution = 30.00 L

Molarity of the solution = 0.250 M

We know that,

Molarity = No. of moles of solute (n)/Volume of the solution (V)

So,

⟹ n/30.00 = 0.250

⟹ n = (0.250)(30.00)

⟹ n = 7.5 mol

Now,

We know that,

Number of moles (n) = Given mass/Molecular weight

• Molecular weight of NaOH = 23 + 16 + 1 = 40 g/mol.

Let the mass of NaOH be m g.

Hence,

⟹ 7.5 = m/40

⟹ (7.5)(40) = m

⟹ 300 g = m

∴ The Chemist needs 300 g of NaOH for preparing the solution.

Answer 2

Answer:

Given :-

• A chemist needs to prepare 30.00 L of a 0.250 M solution of NaOH. .

To Find :-

• What is the mass of NaOH does she need to make the solution.

Solution :-

First, we have to find the moles of Solute :

As we know that :

$\clubsuit$ Molarity Formula :

$\footnotesize\bigstar\: \: \sf\boxed{\bold{\pink{Molarity =\: \dfrac{Mole\: Of\: Solute}{Volume\: Of\: Solution\: (Litres)}}}}\: \: \bigstar$

Given :

• Molarity of the solution = 0.250 M
• Volume of Solution (Litres) = 30.00 L

According to the question by using the formula we get,

$\implies \sf 0.250 =\: \dfrac{Moles\: Of\: Solute}{30.00}$

By doing cross multiplication we get,

$\implies \sf Moles\: Of\: Solute =\: 30.00(0.250)$

$\implies \sf Moles\: Of\: Solute =\: 30.00 \times 0.250$

$\implies \sf\bold{\purple{Moles\: Of\: Solute =\: 7.5\: Moles}}$

Now, we have to find the mass of NaOH :

As we know that :

$\clubsuit$ Number Of Moles Formula :

$\footnotesize\bigstar\: \: \sf\boxed{\bold{\pink{No\: .Of\: Moles =\: \dfrac{Mass}{Molecular\: Weight}}}}\: \: \bigstar$

First, we have to find the molecular weight of NaOH :

$\implies \sf Molecular\: Weight_{(NaOH)} =\: 23 + 16 + 1$

$\implies \sf\bold{\green{Molecular\: Weight_{(NaOH)} =\: 40\: g/mol}}$

Now, we have to find the mass of NaOH :

Given :

• Number of Moles = 7.5 Moles
• Molecular Weight = 40 g/mol

According to the question by using the formula we get,

$\longrightarrow \sf 7.5 =\: \dfrac{Mass}{40}$

By doing cross multiplication we get,

$\longrightarrow \sf Mass =\: 40(7.5)$

$\longrightarrow \sf Mass =\: 40 \times 7.5$

$\longrightarrow \sf\bold{\red{Mass =\: 300\: g}}$

${\footnotesize{\bold{\underline{\therefore\: The\: mass\: of\: NaOH\: does\: she\: need\: to\: make\: the\: solution\: is\: 300\: g\: .}}}}$