How to Prepare a Standard Buffer Solution

You can make your own standard buffer solutions.

Acidity or alkalinity is measured in pH on a logarithmic scale from 0 to 14. A pH value of 7 is neutral. Values below 7 are increasingly acid, and values above are increasingly basic. You can determine a substance's pH with a pH meter. Standard buffer solutions calibrate these meters. A buffer solution is a water-based solution whose pH does not change when a small amount of either an acid or a base is added. A standard buffer solution is one whose pH is known for a specific temperature range. You can prepare a standard buffer solution of 1L of 0.01 molarity borax, or use the same method to prepare solutions from your own choice of chemicals.

Things You'll Need

• Chemistry reference book
• Protective gear -- lab apron, gloves and goggles
• Scale
• Nonreactive containers -- 1L glass beaker, one plastic weighing boat
• Distilled water -- 1L
• Chemicals -- 3.812 g borax
• Glass or other nonreactive stirring rod

Instructions

1. Look up a standard buffer solution in your chemistry reference for the temperature and pH range you want. For example, 0.01 molarity borax has a pH ranging from 8.83 at 95 degrees Celsius to 9.463 at 0 degrees Celsius.

2. Calculate the molecular weight of each chemical you need. In this example, borax --sodium tetraborate, decahydrate -- has two sodium atoms, four boron atoms, seven oxygen atoms and 10 water molecules. Its molecular weight is 2(23.0) plus 4(10.8) plus 7(16.0) plus 10(18.0) equals 381.2.

3. Calculate the mass of each chemical you need, using the formula "mass equals molarity times volume times molecular weight." For the borax solution, you need 0.01 moles per liter times 1L times 381.2 g per mole equals 3.812 g.

4. Obtain the chemicals you need. In this case, you already know how much borax you need.

5. Don protective gear.

6. Use the scale to measure an amount of distilled water equal to the amount of standard buffer you need into a clean nonreactive container. For the borax solution, measure 1L water into a glass beaker.

7. Use the scale to measure the required amount of the first chemical you need into a clean nonreactive container. Add it to the water and stir. Repeat for any additional chemicals one at a time, stirring after each. Measure 3.812 g of borax into a plastic weighing boat, add it to the water and stir.

Tips & Warnings

• Some chemistry references give recipes for some standard buffer solutions, specifying the amount of each chemical needed for a specific volume of water. If you can find one of these to meet your needs, the only calculation you need to do is a volume adjustment.

• Molarity calculators are available on the Internet.

• Before starting, read up on the hazards and precautions for each chemical you will use.

• Use the necessary protective gear and adhere to the recommended safety procedures.

References

• University of Wisconsin-Platteville: UW GenChem Pages, Glossary
• "CRC Handbook of Chemistry and Physics, 45th Edition"; Robert C. Weast, Ph.D., ed.; 1964
• Selleck Chemicals: Molarity Calculator