How well do disinfectants work? Questions

[deleted-333777]

Hi, I did this how well do didinfectants work experiment with my son, i was just wondering if the results I got were correct.
Lysol-3 colonies
Baking soda mixture-6 colonies
Corax mix-2 colonies
Spic and span-2 colonies
409-1 colony

Also, what do you think the results wouldve been for bleach micture and pinesol
Also why do you think some disinfectants work better than other.

Thanks, I'm rally looking forward to hearing from you.

[SciB]

Hi,

In science there are no 'correct' answers. When an experiment is done you get data. As long as the experiment was done properly with several replicates and controls it is up to you to interpret the results and use that information to plan the next experiment. Meaningful research is done through a series of interrelated repeatable experiments.

You tested a lot of different products--Lysol, Clorox, Spic 'n Span, and 409 along with sodium bicarbonate. The one test I did not see was the control with sterile distilled water or with nothing added. You need to know the baseline number of colonies that you get with just water. That is what you should compare all the tests to.

The other important factor in this experiment is how much of each product was used. How did you do the experiment? Is your project this one: https://www.sciencebuddies.org/science- ... #procedure

I would make a list of the ingredients from each product and identify which ones are antibacterial and which ones are there for other purposes. Try to get an idea of the concentration of the antibacterial ingredients in each product relative to the amount recommended for use. Clorox, for example, contains sodium hypochlorite which is a very strong oxidizing disinfectant and a 10% solution will kill just about all bacteria and fungi except for spores. Cleaners like 409 have strong detergents that can destroy the membranes that surround bacterial cells and kill them that way.

I hope this helps. If you have more questions. let us know.

Sybee

[deleted-333777]

Ok, thank you very much, my control was a plain petti dish without any disinfectant used. The control had 37 colinies. It would really be helpful if you told me how many colonies I shouldve received for toilet bowl cleaner and bleach. Thanks for the help

[SciB]

I am trying to make it clear to you that these experiments do not have one 'answer'. This is not an exam where you either get it right or wrong. In science you make a prediction about what you think will happen under certain conditions. That is your hypothesis. Did you do that? What is your hypothesis?

Then you set up experiments to test the hypothesis. This is where you have to be creative and careful because omitting certain controls or performing the experiments incorrectly can invalidate your data.

In your experiment you exposed bacteria to various antibacterial agents that will kill them, so you would predict that the test Petri dishes would have fewer colonies than the control dish that got only water. It is impossible to say how many colonies you should or should not get with a particular product because they are not equivalent. One product might be a better killer of bacteria than another but in order to prove that you would have to test them many times under different conditions.

Did you repeat your experiment? Did you get the same result? It is always best to perform an experiment at least three times and then average the results. Then you can be more confident that your data are showing a real affect and not something that happened by chance. In the lab we do experiments over many times and in different ways with lots of controls. In fact we try hard to disprove our hypothesis. If we cannot do it then we begin to believe our results. But only when several other labs have replicated and built on our results do we really start to have confidence that we are on the track to the truth.

I hope this helps, but if you still have questions let us know.

Sybee

[deleted-333777]

Ok, thank you that makes a lot more sense. Just have one more question , I know all answered are fifer the but I was just wondering if bleach would have cleansed the cutting board better tan 409 or would it have been less powerful. Also same with pinesol, I was wondering if pinesol would be better have cleansed better than bleach and 409 or would it have been less powerful. Thanks

[SciB]

Just do the experiment and report the results. In comparing the different cleansers you need to describe exactly how much you used because obviously the antibacterial effects are a result of amount as well as potency.

For example, did you use straight Clorox or a dilute solution? Did you use one spray of 409 or several? Etc, etc.

I asked you before if you repeated the experiment. Did you do that?

If you want to be able to trust the results of an experiment it has to be repeated. You have to take the average of at least three colony counts. Only that way can you have any confidence in the outcome.

Sybee