Method & Calculations for Preparation of Chemical Solutions
There are three types of solutions,

1. % (W/V) called as Percent Weight by Volume

2. % (W/W) called as Percent Weight by Weight

3. % (V/V) called as Percent Volume by Volume

Where numerator stands for quantity of the Solute and denominator stands for the quantity of the solution not the solvent.

Therefore,

  • 2% (W/V) = 2gm of solute present in per 100ml of solution
  • 2% (W/W) = 2gm of solute present in per 100gm of solution
  • 2% (V/V) = 2gm of solute present in per 100ml of solution

METHOD OF MIXING TWO DIFFERENT CONCENTRATIONS OF SOLUTION TO GET THE REQUIRED CONCENTRATION

If we have x% and y% solution and have to prepare z% solution.

Solution mixing methodThen, write the % of the available solutions on the left hand side, and the required amount of % to be written in the centre, then in the top-right and bottom-right positions their difference is to be written, as shown in the fig. Now find the ratio of the two differences, i.e.,

Ratio of two concentrations for mixing


HOW TO FIND THE WEIGHT OF THE SOLUTE PRESENT IN (OR REQUIRED TO MAKE) 500ML OF X% SOLUTION ?

Let consider 7% solution as 7gms of solute in 100ml of solution

It means, in 100ml –> 7gm of solute is present

Therefore, in 500ml –> 500*7/100 = 35gm of solute is present.


QUESTION #1

How will you prepare 500ml of 10gpl NaOH Solution ?

STEP 1: First calculate the amount of NaOH required in 500ml,

10gpl means, in 1000ml –> 10gms of NaOH

       Therefore, in 500ml –> 500*10/1000 (by Cross multiplication)

                                       = 5gms of NaOH is required

STEP 2: Now, weigh 5gms of NaOH and dissolve it in 50-60ml of water

STEP 3: Transfer the solution into the measuring cylinder, then go on adding water till it comes to the 500ml mark.

This solution so obtained is the required 500ml of 10gpl NaOH solution.


QUESTION #2

How will you prepare 300ml of 3gpl NaCl Solution ?

STEP 1: First calculate the amount of NaCl required in 300ml,

3gpl means, in 1000ml –> 3gms of NaCl

       Therefore, in 300ml –>300*3/1000 (by Cross multiplication)

                                       = 0.9gm of NaCl is required

STEP 2: Now, weigh 0.9gm of NaCl and dissolve it in 50-60ml of water

STEP 3: Transfer the solution into the measuring cylinder, then go on adding water till it comes to the 300ml mark.

This solution so obtained is the required 300ml of 3gpl NaCl solution.


QUESTION #3

How will you prepare 50ml of 2% (w/v), 2% (w/w), 2% (v/v) Solutions ?

*For 2% (w/v)

STEP 1: First calculate the amount of solute required in 50ml,

2% means, in 100ml –> 2gms of Solute

       Therefore, in 50ml –>50*2/100 (by Cross multiplication)

                                       = 1gm of Solute is required

STEP 2: Now, weigh 1gm of solute and dissolve it in 20-30ml of water.

STEP 3: Transfer the solution into the measuring cylinder, then go on adding water till it comes to the 50ml mark.

This is the required 50ml of 2% (w/v) solution.

*For 2% (w/w)

STEP 1: First calculate the amount of solute required in 50gm of the solution and then from this calculate the amount of solute required in 50ml (because 50gm of a solution may not be exactly equal to 50ml of that solution)

Now,

2% means, in 100gms –> 2gms of Solute

   Therefore, in 50ml –>50*2/100 (by Cross multiplication)

                                       = 1gm of Solute is required

Hence, 1gm of solute + 49gm of solvent is required for 50gm of solution. But the volume of the solution is not exactly equal to 50ml, therefore consider this volume as ‘V’ ml.

         for V ml –> 1gm of solute is required

then, for 50ml –> 50*1 / V = W gm of solute is required

STEP 2: Now, weigh ‘W’ gm of solute and dissolve it in 20-30ml of water.

STEP 3: Transfer the solution into the measuring cylinder, then go on adding water till it comes to the 50ml mark.

This is the required 50ml of 2% (w/w) solution.

*For 2% (v/v)

STEP 1: First calculate the amount of solute required in 50ml,

2% means, in 100ml –> 2ml of Solute

       Therefore, in 50ml –>50*2/100 (by Cross multiplication)

                                       = 1ml of Solute is required

STEP 2: Now, measure 1ml of solute and mix it in 20-30ml of water.

STEP 3: Transfer the solution into the measuring cylinder, then go on adding water till it comes to the 50ml mark.

This is the required 50ml of 2% (v/v) solution.


QUESTION #4

How will you prepare 500ml of 4% Solution from 6% and 2% Solutions ?

Calculation for solution mixing
Calculation method for mixing of solutions

Since the ratio is 1:1, therefore 1ml of 6% solution and 1ml of 2% solution is to be mixed together to give 2ml of required solution.

     it means, in 2ml –> 1ml of 6% solution

therefore, in 500ml –> 500*1/2 = 250ml of 6% solution

and equal quantity of 2% solution i.e., 250ml will be added to give 500ml of the required 4% solution.


QUESTION #5

How will you prepare 700ml of 5% Solution from 7% Solution ?

Method for Mixing of chemical solutionsSince the ratio is 5:2, therefore 5ml of 7% solution and 2ml of 0% solution that is water is to be mixed together to give 7ml of required solution.

     it means, in 7ml –> 5ml of 7% solution

therefore, in 700ml –> 700*5/7 = 500ml of 7% solution

and the remaining 200ml of water. Therefore, 500ml of 7% and 200ml of water are mixed to prepare 700ml of 5% solution.


QUESTION #6

How will you prepare 1500ml of 5% Solution from 7% & 4% Solutions ?

Since the ratio is 1:2, therefore 1ml of 7% solution and 2ml of 4% solution is to be mixed together to make 3ml of required solution.

     it means, in 3ml –> 1ml of 7% solution

therefore, in 1500ml –> 1500*1/3 = 500ml of 7% solution

and the remaining 1000ml of 4% solution are mixed to prepare 1500ml of 5% solution. Therefore, 500ml of 7% and 1000ml of 4% solution are mixed to prepare 1500ml of 5% solution.


QUESTION #7

150ml of 5%, 100ml of 3% and 50ml of 1% dye solution are mixed together what will be the concentration of the resultant solution ?

150ml of 5% solution means, in 100ml –> 5gm of dye is present

therefore, in 150ml of solution –> 150*5/100 = 7.5gm of dye is present

Similarly,

100ml of 3% solution means, in 100ml of soln –> 3gm of dye is present

Similarly,

50ml of 1% solution means, in 100ml of soln –> 1gm of dye is present

therefore, in 50ml of solution –> 50*1/100 = 0.5gm of dye is present

After mixing, the total volume of liquor = 150 + 100 + 50 = 300ml

and the corresponding amt. of dye present in solution = 7.5 + 3 + 0.5 = 11gm

Therefore, 100ml of solution contains –> 100*11/300 = 3.66%

Hence, the concentration of the resultant solution is 3.66%


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