Question

Calculate the molarity of a 10 (w/w) solution of naoh if density is 1.2

Answer 1

Answer :

Given -

• The w/w % of the solution = 10%
• Density of the solution of NaOH = 1.2 g/ml

To Find -

• Molarity ?

Solution -

We are given, w/w % = 10%.

Hence, 10 g of NaOH is in 100 g of solution.

Now, Density = Mass/Volume.

⇒ 1.2 = 100/Volume

⇒ Volume = 100/1.2

⇒ Volume = 83.33 mL = 8.33/1000 = 0.08333 L

Molar mass of NaOH = 23 u + 18 u + 1 u = 40 u = 40 g/mol.

Now, Molarity = No. of moles of solute/Volume of solution in litres.

⇒ Molarity = (Total mass/Molar mass)/Volume of solution in L

⇒ Molarity = (10/40)/0.08333

⇒ Molarity = (1/4)/0.08333

⇒ Molarity = 0.25/0.08333

⇒ Molarity = 3.0001

⇒ Molarity = 3 M.

Answer 2

Given :-

❤Molarity% ($\frac{w}{w}$) = 10 %

• $\frac{ Mass~of~Solute}{ Mass~of~Solution}$ × 100

Let,

❤ Mass of solution (M) = 100 gm

❤ Mass of NaOH = 10 gm

✨ Molar mass of NaOH = 23 u + 18 u + 1 u

• 40 u
• 40 g/mol

❤ Number of NaOH = $\frac{10}{40}$ = $\frac{1}{4}$ mol

❤ Volume of solution = $\frac{M}{S}$

• $\frac{10}{1.2}$ ml

• $\frac{100}{1.2~×~1000}$ litre

☃️ Mass = $\frac{No.~of~NaOH}{Volume~of~solution~(litre) }$

• $\frac{1~×~1.2~×~1000}{100~×~4}$ M

• $\frac{12}{4}$ M

• 3 M