Question

Question 1.12 If the density of methanol is 0.793 kg L–1, what is its volume needed for making 2.5 L of its 0.25 M solution?

Class XI Some Basic Concepts of Chemistry Page 23

Answer 1

concept : In case of dilution, volume is calculated with help of molarity equation .
e.g.,
$M_1V_1=M_2V_2$
where, M₁ , M₂ show molarity of initial and final .
V₁ , V₂ shows volume of initial and final .

Here, Given, d = 0.793 Kg/L = 0.793 × 10³ g/L
V₂ ( final volume ) = 2.5 L
M₂ ( final molarity ) = 0.25 M
M₁ ( initial molarity) = ?
V₁ ( initial volume ) = ?

Molar mass of CH₃OH = 12 + 3 × 1 + 16 + 1
= 32 g/mol

$Molarity = \frac{density}{molar \: mass}$
Molarity (M₁ ) = 0.793 × 10³/32 = 24.781 mol/L

now,
$M_1V_1=M_2V_2\\\\24.781\times\:V_1=0.25\times\:2.5\\\\V_1=\frac{0.625}{24.781}=0.02522L=25.22mL$