Answer to Question #142930 in General Chemistry for Amber

Question

From a 0.5 M NaCl solution, prepare a 0.1M NaCl solution in a 250cm3 flask. Show all calculations

Answer 1

Q142930

From a 0.5 M NaCl solution, prepare a 0.1M NaCl solution in a 250cm3 flask. Show all calculations

Solution:

0.5M NaCl solution is our stock solution and we have to prepare 250cm³ of 0.1M NaCl from it.

Method 1:

We can use the dilution equation, M_i V_i = M_f V_f and find the volume of stock solution required for preparing the dilute solution.

M_i = concentration of solution before dilution ( concentration of stock solution ) = 0.5 M NaCl

V_i = volume of stock solution required ( This is unknown to us) = ?

M_f = concentration of solution after dilution ( concentration of diluted solution ) = 0.1M NaCl

V_f = volume of diluted solution = 250cm³ .

Substitute all this information in the dilution formula we have

0.5 M NaCl * V_i = 0.1M NaCl * 250cm³ ;

divide both the side by 0.5 M NaCl, we have

0.5 M NaCl * V_i / 0.5 M NaCl = 0.1M NaCl * 250cm³ /0.5 M NaCl

V_i = 50 cm³ ;

Hence we will take 50 cm³ of 0.5 M NaCl solutuion in a 250 mL volumetric flask and dilute it with

distilled water upto the mark.

Method 2:

Here we will follow two steps.

Step 1: We can first find the moles of NaCl present in the 250 cm³ of 0.1M NaCl solution by using

formula of molarity.

Step 2: In this step we will again use the formula of molarity and find the volume using moles of NaCl and molarity of stock solution of NaCl .

Convert 250cm³ to 'L' using 1L = 1000 cm³ ;

volume of diluted solution in 'L' = 250cm³ * 1L/1000cm³ = 0.250 L;

Step 1: To find moles of NaCl required for preparing solution.

molarity = moles of NaCl / volume of NaCl in 'L'

0.1M = moles of NaCl / 0.250L ;

multiply both the side 0.250L, we have

0.1mol/L * 0.250L = moles of NaCl * 0.250L / 0.250L ;

0.0250 mol = moles of NaCl ;

Hence moles of NaCl required for preparing solution is 0.0250 moles

Step 2 : To find the volume of stock solution using moles and molarity of stock solution.

molarity = moles of NaCl / volume of NaCl in 'L' ;

0.5 M = 0.0250 moles / V_i ;

Solve this equation for V_i we have

V_i = 0.0250moles / 0.5mol/L = 0.050 L;

which in cm³ = 0.050 L * 1000cm³ / 1L = 50 cm³ ;

Hence we will take 50cm³ of stock solution in a 250 mL volumetric flask and divide it upto the mark.