How to Make pH Buffers
A buffer is a special kind of chemical solution that many kinds of laboratories use to ensure that their solutions maintain a constant pH level. As such, one of its unique features includes the ability to maintain one pH, which is why scientists use them to sustain cells' lives, to dissolve other kinds of chemicals and to store DNA. Scientists can make buffers by raising or lowering its alkalinity or acidity levels.
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Things You'll Need
- Digital pH meter
- Unadjusted buffer
- Rubber bulb
- Washable glass dropper
- Chemical hood
- Magnetic plate
- Magnetic stirrer
- Solvent
- pH standard solutions (with pH 4, 7 and 10)
- Glass beaker
- Triple-distilled water
- Kimwipes
Instructions
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1
Perform the proper laboratory procedures before beginning. For instance, obtain the necessary bookings for using a magnetic stirrer or pH meter. Autoclave any glassware and the water. Don protective equipment, including eye masks and gloves. Work only inside a chemical hood.
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2
Measure out the amount of reagent necessary with total accuracy. Accurately measure out powders when placing them into weighting containers. Precision is required for this procedure, since an error can alter the pH of your buffer. Calculate whether your final concentration is expressed as a molarity or a percentage.
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3
Dissolve the concentrated reagent in your solvent. Ideally, this would be made with a sterile solution in a glass beaker of over 50 percent of the volume being prepared than the buffer. Clean the stirrer prior to putting it into the solution. Dissolve using the plate and stirrer. Stir thoroughly.
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4
Calibrate your pH meter. Take out the electrode in your storage and rinse it off with the triple-distilled water. Allow the water to drain into a beaker as you are rinsing the electrode. Do not let the buffer be contaminated.
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5
Cover the tip of the now-rinsed electrode with small aliquots of each of the three pH standards in containers that are wide enough to support the electrode. Power on your pH meter, and switch it so that it is either set to "standardize" or "calibrate." Submerge the electrode into the pH 4 standard so only the tip is inserted.
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6
Return the meter to "standby" mode. Remove the electrode and rinse it with the distilled water again. Submerge the tip into the pH 7 standard. Repeat this for the pH 10 standard. Do not skip any step to ensure accuracy.
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Measure the pH level of your buffer. Adjust, if necessary, using recommended alkali or acid chemicals. Move your stirring plate beside the pH meter. Place the container that is holding the buffer and put it on top of the plate. Place the stirrer and put it in the beaker. Set the speed knob of your stirring plate until it reaches zero. Power it on.
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Turn the knob up until you notice the stirrer in the beaker spinning. Keep turning it to whatever speed you feel most comfortable. However, most scientists keep turning it until the stirrer spins as fast as possible without being flung from the plate.
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Thoroughly rinse the tip of the electrode once more. Immerse it into the buffer, ensuring it does not touch the stirrer in any way. Touching it may cause damage to the electrode.
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10
Switch the meter to "measure" and wait for it to stabilize. Include concentrated acid if the pH measures too high. Include concentrated alkali if the pH measures too low.
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Properly label your buffer. Write down its pH level, chemical composition, name, your name and when you prepared it. Store it in an appropriate temperature if necessary.
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Tips & Warnings
Take great care regarding what kind of alkali or acid you use; some may not safely be mixed together and can become explosive, or they may emit high temperatures and toxic fumes.
References
Resources
- Photo Credit chemistry image by david hughes from Fotolia.com
