Science Buddies: "Ask an Expert"

Hi, I am helping my 5th grader. she chose to test dissolved oxygen levels in different water sources and temperatures. school only allows to have one independent variable and one dependent variable. but her teacher approved the hypothesis, which to me includes two independent variables. water sources and temperatures, am I thinking right? or it is still one of each variables? can i add option of aerated and nonaerated?
secondly i need help with choosing a catchy title and some attractive board ideas.
third I am confused with the oxygen testing kits, there are many on Amazon, not sure how they work and which one is better? some talk about dissolving other liquids and then noting the findings and some show wands we can add liquid to. so please help.

Hello!

Thank you for your question!
If you were to change levels of the temperature and sources of water simultaneously in your experimental groups, you would have two independent variables at hand. Having two variables being manipulated at the same time renders it very challenging to elucidate which variable the results can be attributed to. I suspect that might be why the school is allowing only one independent variable.

If you still want to test dissolved oxygen levels in water samples of different temperatures and from different sources, I would recommend a blocking approach. You would separate your samples into “blocks” by water source, and within each block, change the temperatures (ensuring to use the same temperature changes for each block to keep that variable constant).

For example, if you have 3 water sources (source A, B, and C) and 3 temperatures to test (60, 80, 100 degrees Fahrenheit), you would have 3 blocks based on water sources, and have the following experimental groups:
- Block A: source A at 60 F, source A at 80 F, source A at 100 F
- Block B: source B at 60 F, source B at 80 F, source B at 100 F
- Block C: source C at 60 F, source C at 80 F, source C at 100 F

You would then compare the results of each block to each other. This way, you are separating the effects of water source and temperature and can properly propose explanations for the results based on the effects of each variable.

To answer your second question, Science Buddies has great resources for creating a board! Here is a reference page that might be helpful: https://www.sciencebuddies.org/science- ... lay-boards.

To answer your third question, Science Buddies also has a very similar project idea with a materials directory and links to oxygen testing kits! I’d highly recommend checking out the following:
- https://www.sciencebuddies.org/science- ... emperature
- https://www.sciencebuddies.org/science- ... f-air-rust

Hope this helps! Please don’t hesitate to reach out if you have more questions.

Anika

Hi, so i have chose three different sources and chose 32degrees for cold temperature and 100 degree for hot and sectioning it baseline temperature at the source and hot and cold and measure dissolved oxygen levels at all three temperatures. Using double cooling and double heating methods for cooling and heating the water.
My table will look like this
Temperature/sources: Ocean water Creek water Tap water

Baseline dissolved Oxygen levels: 5mg. 5mg. 5mg
32 degrees dissolved Oxygen Levels: 5mg. 5mg. 5mg
100 degrees dissolved Oxygen Levels: 3mg. 3mg. 3mg

These levels are just imaginary numbers for showing the table look like and then i would make a graph based on it.

Do you think i am on the right track? I ordered the dissolved oxygen wand and it has electrolyte solution in it trying to figure out how to use, as it seems easier than the adding solution and finding the saturation.
Please suggest if i am doing it right

Hello!

Thanks for your response!

This table layout looks great. Blocking the sources by 3 standardized temperature levels is the right way to go!

As for your final graphs, if you would like to plot all 3 sources vs. all 3 temperatures on the same graph, I would recommend using a bar plot with 3 different bars/colors per water source, a stacked bar plot, OR a line plot with 3 different lines to represent the 3 sources. You can also plot each source as its own graph, if you so prefer.

Let me know if you have more questions!