Chemical buffers prevent sudden changes in a solution's acidity. Buffer solutions keep a certain pH level nearly constant during the course of biological reactions and are crucial for many physiological processes. All laboratory experiments in biochemistry or biophysics require buffer solutions. Citric acid is an organic acid that can efficiently maintain pH range from 3 to 6.2. In this example, you would make 200 ml of a citric acid buffer solution with the concentration 0.1 molar and pH 5.5.
Things You'll Need
- Citric acid
- pH meter
- Magnetic stirrer
- Stir bar
- Beaker (250 or 500 ml)
- Graduated cylinder (250 or 500 ml)
- Distilled water
- Plastic pipette
- Solution of sodium hydroxide (NaOH) 3 molar
Calculate the mass of citric acid needed to make the buffer solution using the following formula: mass(citric acid)=192.12 x molarity (solution) x volume (solution)/1,000 ml. (The molar mass of citric acid is 192.12 g/mole.)
In our example, mass(citric acid)=192.12 g/mole x 0.1 M x 200 ml/1,000 ml= 3.842 g.
Weigh citric acid on the scale and place the chemical in the beaker. Pour the distilled water into the beaker. The volume of the water added should be about 10 ml less than the final volume. In our example, you would add 190 ml.
Place a stir bar in the beaker with the solution. Put the beaker on the magnetic stirrer and turn it on to start stirring the solution.
Place the glass electrode of the pH meter in the solution and wait 20 to 30 seconds. Read the pH displayed by the instrument. It should be below 3.
Fill the plastic pipette with the sodium hydroxide solution.
Add three to five drops from the plastic pipette to the solution in the beaker. Wait 20 to 30 seconds.
Read the value displayed by pH meter and compare it with the desired pH.
Repeat Steps 6 and 7 until the pH of the solution reaches the designated value. In our example, it is 5.5.
Switch off the magnetic stirrer and take off the pH glass electrode.
Pour the solution into the graduated cylinder and add the distilled water to the final volume. In our example, add water to the mark “200 ml.”
- Chemistry; K.W. Whitten, R.E. Davis, L. Peck, and G.G. Stanley; 2009
How to Make Sodium Citrate Anticoagulant
Sodium citrate is a salt produced through the reaction of sodium carbonate with citric acid that serves as an anticoagulant for fractionated...
How to Make a Citric Acid Solution
One of the most common acids in the world, citric acid is responsible for giving fruits like lemons and limes their characteristic...
Preparation of Buffer Solutions
A buffer solution using citric acid and monopotassium citrate will have a pH of 3.1. ... preparation of the buffer solution is...
How to Make a Citrate Buffer
Citric acid is an organic acid commonly present in citrus fruits, but also in various animals and bacteria. A buffer consists of...
Examples of Acidic Buffers
A buffer solution of citric acid can be prepared by adding trisodium citrate, a salt of citric acid, to the solution.
How to Prepare Acetate Buffers
To prepare a 0.1M sucrose, ... How to Prepare Citric Acid Buffers; How to Prepare Buffers; How to Change Buffer Capacity in...