# Preparation of Solutions and Buffers

Preparation of Solutions and Buffers

Objectives:

1. To learn and understand the theory, principle and formula behind buffers and solutions preparation. 2. To learn the methods for buffers and solutions preparation.

Introduction:

(Wikipedia, 2013) Solute is a substance dissolved in another substance. Solvent is a substance in which the solute is dissolved by it. Solution is a mixture of two or more substances. The amount of solute dissolved in a solvent is called concentration and it can be expressed in several different ways.

First and foremost, the expression of concentration can be in term of molarity. Molarity is the number of moles of solute per liter of solution. The unit of molarity is M and is read as molar. Molarity = moles of soluteliter of solution

(Normality, 2012) Normality (N) is another way of expressing the concentration of a solution. It is based on an alternate chemical unit of mass called the equivalent weight. The normality of a solution is the concentration expressed as the number of equivalent weights (equivalents) of solute per liter of solution. The equivalent weight of a substance is depend on the reaction that the substance undergoes. In acid-base chemistry, the equivalent weight is the weight of a substance that donates or accepts 1 mole of protons. On the other hand, in oxidation-reduction reactions, the equivalent weight is the weight of a substance that loses or gains 1 mole of electrons. N = Number of equivalents of soluteLiter of solution

where

Number of equivalents of solute = Grams of soluteEquivalent weight of solute

The third type of concentration expression is percent composition (% w/w). Percent composition is the percent of weight of solute in the total weight of the solution. It is expressed in grams of solute per 100 g of the solution. Percent composition (% w/w) = Weight of solute (g)Weight of solution (g) X 100 %

Percent concentration of weight/volume (% w/v) is usually used when the solution is made by one solid and one liquid. It is defined as percent of weight of solute in the total volume of solution. It is expressed in grams of solute per 100 ml of the solution. Percent concentration (% w/v) = Weight of solute (g)Volume of solution (ml) X 100 %

Furthermore, volume percent (% v/v) is also one way of representing the concentration unit. It is most often used when preparing solutions of liquids. It is defined as percent of volume of solute in the total volume of solution. It is expressed in milliliters of solute per 100 ml of the solution. Volume percent (% v/v) = Volume of solute (ml)Volume of solution (ml) X 100 %

Dilution is the process of making a substance or solution less concentrated by adding a solvent. Generally, stock solutions are prepared and then diluted to the desired concentration. Thus, an equation is used to calculate the total volume of solvent need to be added into the stock solution. Concentration within the equation may refers to molarity, percent, normality, etc. C1 X V1 = C2 X V2

where

C1 = the original concentration of stock reagent

V1 = the volume to be taken from the stock reagent

C2 = the desired dilution concentration

V2 = the desired volume of diluted solution

Materials:

Sodium chloride powder (NaCl), volumetric flasks, glass pipettes, pipettors, distilled water, 1 M sodium hydroxide solution, 95 % ethanol solution, 1 M Tris-HCl pH 4 solution, 1 M Tris-HCl pH 7 solution, media storage bottles.

Results:

A. Preparation of Solution

(1)

10 % (w/w) = Weight of NaCl100 g X 100 %

Weight of NaCl = 0.1 X 100 g

= 10 g

Firstly, a weight of 10 g NaCl powder was weighted out and transferred to a volumetric flask. Little amount of distilled water was added to dissolve the powder. The volumetric flask was swirled several times to ensure the solid dissolved and mixed. Then, the solution was massed up with distilled water to a total weight of 100 g.

(2)

4 % (w/v) = Weight of...

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