Mixing Calculations and Chemical Reaction

Chemicals come usually in a concentrated form and have to be mixed with other chemicals or water to create the desired solution. The process of mixing different solutions together is called dilution. There are two ways to calculate the amount of solution needed to create a dilution. The first method is by using percentages and the second one is by using molarity.

Based on percentages

Mixing Calculations and Chemical Reaction solutions based on percentages may be quoted as percent volume (v/v), or percent weight (w/v). To dilute a solution based on percentages, you need to know the percentage of each component in the original solution, otherwise, you wouldn’t carry out a successful chemical experiment.

The first step is determining how the percent solution is given, i.e. whether v/v or w/v. Normally, a solid solute dissolved in a solvent is given as w/v, whereas a liquid solute in a solvent is given as v/v.

If the solution is given as v/v, use the relation C1V1=C2V2, where C represents the concentration, V represents volume, and subscripts 1 and 2 refer to the initial and final concentrations, respectively.

For example: You have 500 mL of a 5% v/v solution of acetic acid. You want to make a 2% v/v dilution. What volume of water must you add?

C1V1=C2V2

5%*500 mL=2%*V2

0.05*500 mL=2%*V2

25 mL=2%*V2

V2=1250 mL-500 mL=750 mL

Therefore, you would add 750 mL of water to 500 ml of the 5% solution to make a 2% solution.

If the solution is given as w/v, you need to consider that the solute contributes to the final volume of the solution. When making such a solution, first pour the solute into the volumetric flask before adding the solvent.

For example, a 10% w/v NaCl solution means that 10 grams of NaCl are dissolved in water to make 100ml of solution.

Based on Molarity

Molarity is the number of moles of solute per liter (L) of solution and is represented by the symbol M. To dilute a solution based on molarity, you need to know the molarity of the original solution.

The equation for diluting a solution based on molarity is M1V1=M2V2, where M represents molarity, V represents volume, and subscripts 1 and 2 refer to the initial and final molarities, respectively.

For example: You have 500 mL of a 0.1 M NaOH solution. You want to make a 0.01 M dilution. What volume of water must you add?

M1V1=M2V2

0.1M*500 mL=0.01M*V2

50 mL=0.01M*V2

V2=5000 mL-500 mL=4500 mL

Therefore, you would add 4500 mL of water to 500 mL of the 0.1 M solution to make a 0.01 M solution.

Both methods are useful for creating chemical solutions for different chemical reactions, but you need to know which one to use depending on the information given.