How Salty Does the Sea Have to Be for an Egg to Float?

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magsv
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Joined: Mon Jan 16, 2023 10:35 pm
Occupation: Parent

How Salty Does the Sea Have to Be for an Egg to Float?

Post by magsv »

Hello, my son is doing the "How Salty Does the Sea Have to Be for an Egg to Float?" experiment as stated on your website, but we have a question about variables. The amount of salt in each cup is Independent Variable, and the height that the eggs float is the dependent varible, correct? The experiment calls for using 5 eggs, so we did that and were planning on each egg being a seperate "trial". We only made the stock solution once and used the same serial dilutions in cups for each egg/trial we ran. In using a different egg for each trial, but not using a new batch of the stock solution/serial dilutions did we inadvertantly add a second varible (different eggs). If not can you explain why? My son is trying to write his research paper and we just don't understand this. I will write the procedure we used below in case that is helpful.

1. Made the stock solution according Science Buddies instructions
2. Labeled cups 1-5
3. Measured 200 mL of tap water into cups 2-5 (cup 5 is the control)
4. Measured 200 mL of stock soulution into cup 1
5. Performed the serial dilution in cups 2-4 according to Science Buddies instructions
6. Trial 1: placed egg one into each cup, beginning with cup 5 and working to cup 1 measuring the dependent variable if applicable
7. Trial 2: placed egg two into each cup, beginning with cup 5 and working to cup 1 measuring the dependent variable if applicable
8. Trial 3: placed egg three into each cup, beginning with cup 5 and working to cup 1 measuring the dependent variable if applicable
9. Trial 4: places egg four into each cup, beginning with cup 5 and working to cup 1 measuring the dependent variable if applicable
10. Trial 5: placed egg five into each cup, beginning with cup 5 and working to cup 1 measuring the dependent variable if applicable
11. Calculate the mass concentration of the stock solution and serial dilutions
12. Calculate the relative salt concentrations for cups 2-4
13. Calculate the egg's densities.

The thing that alerted us to the fact that we may have a second variable was when in Trial 3 the egg (egg 3) floated in cup 3 and that was the only time that happened in our experiement. When we calculated the egg's densities we found that egg 3 was not the least dense egg, so there must have been another factor that led to it floating.

We are grateful for any help you can give us!

Maggie
koneill18
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Posts: 188
Joined: Thu Aug 06, 2020 8:22 am
Occupation: Other Adult

Re: How Salty Does the Sea Have to Be for an Egg to Float?

Post by koneill18 »

Hello!

You're correct that the independent variable is the amount of salt in each cup and the dependent variable is whether or not the egg floats. You're also spot on in making each egg a separate trial. The purpose of using different eggs is to see if the results that you observed with your first egg also apply to other eggs. You can't be confident in stating how much salt is required to get an egg to float unless you've tested multiple different eggs! It's totally normal for one of your trials to have weird results compared to the other trials. That happens in my experiments all the time! It's possible that one of the eggs was slightly different from the other ones in some way. When your son writes up his report, he can just record his best guess for why he thinks that one egg floated while the other ones didn't. It's okay not to have a firm answer. That's a normal part of science!

I hope this helps! Please let us know if you have any more questions or need more clarification.
magsv
Posts: 4
Joined: Mon Jan 16, 2023 10:35 pm
Occupation: Parent

Re: How Salty Does the Sea Have to Be for an Egg to Float?

Post by magsv »

Thank you so much for helping me understand! You've been so helpful.

Maggie
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