Question

calculate the molality of 1 M Nacl solution having density 1.10 g cm (Molar mass = 58.5g /mole)​

Answer 1

Answer:

Correct option is

B

0.86 mol kg

−1

in this question 1M solution of NaNO

3

,

By definition if Molarity we know that it is the no. of moles present in per litre of solution. = 1M molar solution has 1 mole of NaNO

3

for 1000ml of solution.

Therefore, mass of solute is mass of 1 mole of NaNO

3

= 23+14+48 = 85 gm.

volume of solution = 1000 ml as per definition.

Now,Given that density is 1.25 g/cm3

Therefore, mass = 1.25×1000 (m = density X volume)

=> mass = 1250 gm (solution mass)

Mass of solvent = mass of solution - mass of solute

= 1250 - 85= 1165gm.

Molarity is the no. of mole of solute per kg of solvent

=> m =

1165

1

×1000 =

1165

1000

=0.85m

Answer 2

Given:

Molarity of NaCl solution $=1M$

Density of NaCl solution $\[ = 1.10\,gc{m^{ - 3}}\]$

Molar mass of NaCl $58.5g /mole$

To Find: Molality of 1 M NaCl solution

Solution:

Since molarity is the number of moles of solute present in $1l$ (1000 ml) of a solution, therefore, 1 M NaCl solution means it contains 1 mole of NaCl in 1000 ml of solution.

Therefore, the volume of the solution $=1000 ml$

Thus, the mass of NaCl solution can be given as:

$\[Mass = Volume \times Density\]$

$\[Mass = 1000ml \times 1.10gc{m^{ - 3}}\]$

$\[Mass = 1,100g\]$

As the solution contains 1 mole of NaCl, therefore, the mass of NaCl can be given as:

$\[Mass = No.\,of\,moles \times molar\,mass\]$

$\[Mass = 1\,mol \times 58.5g/mol\]$

$\[Mass = 58.5g\]$

Therefore, the mass of solvent will be

Mass of solvent $\[ = 1,100g - 58.5g\]$

Mass of solvent $\[ = 1,041.5g\]$

Thus, the molality of the solution can be calculated as:

$\[Molality = \frac{{moles\,of\,solute}}{{mass\,of\,solvent(in\,g)}} \times 1000\]$

$\[Molality = \frac{1}{{1,041.5g}} \times 1000\]$

$\[Molality = 0.96\,moles\,/kg\]$

Hence, the molality of 1 M NaCl solution having density $\[1.10gc{m^{ - 3}}\]$ is $\[0.96\,moles\,/kg\]$.