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The Effect of Acids and Alkalis on Bacterial GrowthFeatured science projectScience project video


The purpose of this experiment is to find out whether bacterial growth is inhibited by either strong acids or strong alkalis, or even both. It is important for us to know about bacteria inhibition in order to develop more efficient antimicrobials.


The stronger the alkali or acid, the higher the inhibition of bacterial growth.

Scientific Terms

Microccus luteus, Serratia marcesceus, ions, pH


What is acid/alkali?

An acidic solution contains a higher than usual proportion of Hydrogen ions (H+), while an alkaline solution contains a higher than usual proportion of Hydroxide ions (OH-). This occurs because compounds can exist as free moving ions in liquid state.

pH is a type of scale used to measure the acidity or basicity (alkalinity) of a solution. It ranges from 1 to 14. As the pH of a solution decreases, it becomes more acidic. When the pH increases, the solution becomes more alkaline. Hence, When an acid is dissolved in water, the pH will be less than 7 and when an alkali is dissolved in water, the pH will be greater than 7. Pure water has an acidity of about 7.

What are Bacteria?

A bacterium is a unicellular organism, and found in all shapes and sizes. They can be round, rods, or spirals. Though Anonie van Leeuwenhoek first observed them in 1676, the hardy bacteria have been around for billions of years. As the first organism to have life on earth, the bacteria has evolved over the years and there are now approximately five nonillion (5 x 10^30) bacteria on earth.

Bacteria can be beneficial to man. Louis Pasteur showed how bacteria can be used to create vaccines and has paved the way for medical progress and breakthroughs.

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Complexity level:
Project cost ($):
Time required:
1 hour to prepare, 24 hours incubation period, 30 minutes to observe and record findings.
Material availability:
All materials should be provided by the biology laboratory. However, students should prepare their own goggles and lab coat.
Safety concerns:

Safety concerns: All biohazard material should be disposed into the sharps bin. Students must put on safety goggles and lab coat at all times throughout this experiment. Teachers must be on standby especially when students are removing the bacteria culture out of the bottle. Disinfectants must also be prepared in case of any bacteria culture spills.