Science Buddies: "Ask an Expert"

My son, Quinn, is trying to complete his 1st Science Fair Project. He wanted to experiment with which type of water will make a boat float the best- pond water, salt water, sugar water or vinegar water.

He is just starting the project and we are looking for ideas on where to begin researching. He has come up with a prediction but does not have a scientific reason. He thinks the pond water will make the boat float the best because he sees boats floating in the pond or lake water very often.
(Remember, this is our first project!)

Does anyone have any suggestions on how we can handle the research or narrow our topic? After we do the experiment, how can I help him research WHY the salt water worked the best without just giving him the answers?

Any ideas would be helpful. It seems that everyone here is way ahead of us but I'm sure someone out there was in 2nd grade once!

Thanks in advance for any responses!

Quinn 123 wrote:My son, Quinn, is trying to complete his 1st Science Fair Project. He wanted to experiment with which type of water will make a boat float the best- pond water, salt water, sugar water or vinegar water.

He is just starting the project and we are looking for ideas on where to begin researching. He has come up with a prediction but does not have a scientific reason. He thinks the pond water will make the boat float the best because he sees boats floating in the pond or lake water very often.
(Remember, this is our first project!)

Does anyone have any suggestions on how we can handle the research or narrow our topic? After we do the experiment, how can I help him research WHY the salt water worked the best without just giving him the answers?

Any ideas would be helpful. It seems that everyone here is way ahead of us but I'm sure someone out there was in 2nd grade once!

Thanks in advance for any responses!

What exactly are you measuring? Are you just floating toy boats on the water? Maybe you could actually measure the density- and show that some of these solutions are "heavier" than others. When you make the solutions of salt and water, I would definitly emphasize the _adding_ of salt.

Most of the stuff on boyancy is written at a very high level. I'll keep thinking about this. Someone else may pop in with a better idea though.

Louise

The difference between salt or sugar water and regular water may be too small to measure for a 2nd grade experiment (but maybe not -- I don't have any kids, and it's been a long time since I was 7). Your toy boat will float very well in all these fluids. My gut reaction is that you would have to add a lot of salt to change the density enough so that you would be able to reliably measure a change in the water line on the boat. I hope you are using a really big boat. I agree that the important thing to measure would be how much salt you added.

You could also rig it so that the boat sinks under certain circumstances (people always like to see engineering failure). Maybe add more and more "people" (lead weights?) in the boat, so your son can see that a denser fluid supports more weight.

There must be an age-appropriate discussion of Archimedes (guy in the bathtub, displacing volumes of water with his body) out there on the web somewhere too. That could give you some extra discussion material too.

Thank you both for your quick and kind replies.

Louise: Yes, we are using a toy boat (approx. 5 inches long) and we have measured 8 cups of water in a clear plastic container for our boat to practice floating. So far, we have not created our salt, sugar or creek water. How much salt do you recommend using to make a difference in the way the boat will float in the water? Is there a known concentration for the Dead Sea? Could we use this?

Lucinda: If we added weights (where would we purchase these?), would the lesson be about how much weight each type of water could support before the boat sank? Would the scientific question be one of density and comparing the density of each type of water?

Can either of you suggest a website that might explain density on a 2nd grader's level? I'm trying to be helpful without doing the project for him. This is a fine line and I certainly don't want to cross it. Obviously, he would need to understand it quite well to understand why the boat is floating differently. He would also need to be able to explain this to persons visiting the science fair and to the judges themselves.

Can you tell I'm NOT a scientist??? Thanks again for your help....

Quinn 123 wrote:Thank you both for your quick and kind replies.

Louise: Yes, we are using a toy boat (approx. 5 inches long) and we have measured 8 cups of water in a clear plastic container for our boat to practice floating. So far, we have not created our salt, sugar or creek water. How much salt do you recommend using to make a difference in the way the boat will float in the water? Is there a known concentration for the Dead Sea? Could we use this?

Lucinda: If we added weights (where would we purchase these?), would the lesson be about how much weight each type of water could support before the boat sank? Would the scientific question be one of density and comparing the density of each type of water?

Can either of you suggest a website that might explain density on a 2nd grader's level? I'm trying to be helpful without doing the project for him. This is a fine line and I certainly don't want to cross it. Obviously, he would need to understand it quite well to understand why the boat is floating differently. He would also need to be able to explain this to persons visiting the science fair and to the judges themselves.

Can you tell I'm NOT a scientist??? Thanks again for your help....

I think the Dead Sea is a great idea- I found this- "The salt concentration in the dead sea is ten times higher than other seas (for example: the salt concentration in the Dead Sea is 34%, while the concentration in the Mediterranean sea is only 3.5%). This high salt concentration makes floating in its waters effortless."

So, maybe you could make "regular" ocean and "dead sea" ocean and try Lucinda's experiment. I think you should certainly see a difference.

For weights, you might be able to use something small like quarters or some other coins. Either look up the weight of the coins and use this as a standard value, or weigh them on a food scale.

I haven't see good sites for younger students, but I am looking. I'll post if I find anything.

As for the science, I think you are doing fine. I think this is a great experiment and your son can learn alot. If you can help him discover how something works, and show him how to test things with simple experiments, this will be a very useful leason!

Louise

I found this site which (once you get past the actual experiment) describes Archimedes' principle to kids: http://www.madsci.org/experiments/archi ... 58.Ph.html. Problem is, it really doesn't talk about how the liquid itself affects buoyancy. Still, you might take a look and see if it helps any.

Thank you again to all responders!

I have researched on-line this afternoon to find an appropriate website to direct Quinn to regarding buoyancy and/or density. I have not been successful. I did like the one that Melissa (?) referred me to on the MadSci Network, but it was only one experiment.

How can he make a hypothesis about which water will do better if he has no scientific research under his belt? Sigh.

What if we do the experiment, add an enormous amount of salt to the salt water sample and then slowly add the coins to see how much weight it will take to sink the boat in each of the different waters? This is very similar to the experiment on MadSci. Would it take quite a few MORE coins to sink the boat in the salt water? I'm assuming so. Scientists......answer?

Then, could he look at research I have already found (on his level) that explains WHY the salt water had this result?

Maybe we could then have a picture of the Dead Sea or an article on the Dead Sea at the science fair to help him explain?

"How can he make a hypothesis about which water will do better if he has no scientific research under his belt? Sigh. "

Well, I think at this level the hypothesis does not have to be all that sophiscated. As long as he can come up with some reason behind his hypothesis, I think it will be fine. Even something very simple like "all water will be the same" or the "the water will be different". I don't think anyone expects a 2nd grader to correctly predict the density of several solutions.

What is more important is that he understands the results when he does the experiment.



"What if we do the experiment, add an enormous amount of salt to the salt water sample and then slowly add the coins to see how much weight it will take to sink the boat in each of the different waters?"

Yes. I think this is perfect.


"Would it take quite a few MORE coins to sink the boat in the salt water? I'm assuming so."


Yes. Look at the wikipedia entry on the dead sea:
http://en.wikipedia.org/wiki/Dead_Sea

At several different points it mentions how easy it is for people to float on the dead sea.

The density of the dead sea is: 1.17 kg/L

Also, there is apparently there is one other hypersaline lake that is saltier than the Dead Sea. The Dead Sea is 8-9 times saltier than the ocean, this one is 18 times more salty. [This came from wikipedia] So I guess you can make _very_ salty water.

"Then, could he look at research I have already found (on his level) that explains WHY the salt water had this result?"

Yes, I think being able to explain his results afterwards is much more important than having a complicated hypothesis to start.

"Maybe we could then have a picture of the Dead Sea or an article on the Dead Sea at the science fair to help him explain?"

You may be able to bring two small tanks (plain water and super salty) and have them in front of the board.

Louise

Thank you Louise! I'm beginning to feel much better about HIS project. I just really wanted him to enjoy the project, like the process, etc. so that he will want to continue his interest in science!

Do you have a suggestion as to how much salt we should put in the 8 cups of water to make the Dead Sea water? Your numbers regarding percentages and density levels make my head swim (no pun intended).

Should we just use plain non-iodized salt from the store?

Thanks again!

Quinn's Mom

Quinn 123 wrote:Thank you Louise! I'm beginning to feel much better about HIS project. I just really wanted him to enjoy the project, like the process, etc. so that he will want to continue his interest in science!

Do you have a suggestion as to how much salt we should put in the 8 cups of water to make the Dead Sea water? Your numbers regarding percentages and density levels make my head swim (no pun intended).

Should we just use plain non-iodized salt from the store?

Thanks again!

Quinn's Mom

Actually Epsom salt (magnesium sulfate) is recommended for a lot of these experiments, maybe because it is cheaper? Not that table salt is that expensive, but epsom salt is usually sold in larger boxes. The ocean (or the Dead Sea) isn't pure sodium chloride (table salt) but actually a mixture of many different mineral salts, so neither salt is really "accurate" to make the ocean. On the other hand, makin a mixture of 10 different salts doesn't really change the results, so pure table salt or epsom is fine.

What kind of scale do you have? Do you have a food scale with gm and oz? [A scale would be best] Or will you need to use measuring cups? I'll walk you through the calculations if you tell me what units you will be using.

I think I used food coloring to make carnations different colors for my second grade science fair- so I'm very impressed with this project!

And I think what you said about enjoying the process is really important... the science fair can become a really hideous event if the students do not have a passion for their projects or if mom and dad end up doing the whole thing so it is "perfect". Then the students learn to hate science!

Louise

I have a food scale but I think it would be worthless as it only measures up to 16 oz. (for diet purposes).

It would probably be easier to use measuring cups and then use the scale for measuring the weight of the coins/weights.


Thank you!

P.S. I think the carnation trick is a great one! We did this one at home and the kids were wow'ed!! We also have done the salt/pepper separation with oil (or was it dish soap?).

Quinn 123 wrote:I have a food scale but I think it would be worthless as it only measures up to 16 oz. (for diet purposes).

It would probably be easier to use measuring cups and then use the scale for measuring the weight of the coins/weights.

Feel free to e-mail me if it would be easier than to continue posting the replies.

Thank you!

P.S. I think the carnation trick is a great one! We did this one at home and the kids were wow'ed!! We also have done the salt/pepper separation with oil (or was it dish soap?).

We aren't allowed to email you- we have so many children posting here it is much safer for them if the rules are never give your email out on a forum- never let anyone on the forum try to contact you- etc.

I think the food scale is fine for the salt.

The dead sea is 30-35 % salt. Water weighs 1 g/ mL (notice this is a density-and a very easy one to remember- 1! and the units are grams and mililiters, which is 1/1000 of a liter) . Thankfully, google does unit conversion if you aren't good at them. To find out how many mL are in 8 cups, you can type in the search bar "number of mL per 8 cups" and get:
8 US cup = 1 892.7059 mL

This means you have 1893 mL or 1893 grams of water in your tank (or 67 ounces or about 4 lbs). So, to make a solution that is approximately similar to the dead sea, you would take roughly 1/3 of that (33%)- which is 568 grams. Using google again, we find that it is about 20 ounces, which you could measure in two batches on your scale.

This isn't exactly the correct way to calculate this percent, but it is close. The actual correct way to calculate this value is that the percent salt is the percent of the TOTAL mass (total is the weigh of salt+ water- not just the weight of the water which is what we did above). So the more accurate value is:
33%= (x grams of salt)/(x grams of salt + 1893 grams of water) and solve for x. This gives a salt weight of 848 grams, which is about 30 oz. If you don't follow this, don't worry about it (unless you are very interested, in which case, ask!). I just like to put the more correct answer down as well, in case somebody else needs to know this at a more accurate level.

So, you should be able to put 20-30 oz of salt in your water.

The ocean has a salinity of about 8-9 times less, so I would divide what we calculated above by 8 for the ocean.

I don't know if your family has ever been to Salt Lake City, Utah, but that is named because of one of these hypersaline lakes. For a very long time, this type of lake was a significant source of salt. Either you dried sea water to get salt, or you gathered salt from salt pans/shores of hypersaline lakes. The percentage of salt in the Great Salt Lake in Utah "is highly variable, and depends on the lake's level; it ranges from 5 to 27%" [1] So, if your son has seen this lake, or been to Salt Lake City, this might be a better example than the Dead Sea.

One last bit of math. Water has a density of 1 gm/mL, which is the same as 1 kg/L. So, you can see that even though the Dead Sea has a ton of salt, the density is only 1.17 kg/L. Even though these numbers look very close to each other, it is actually a pretty large change in density which you will see with your experiment.

I think your son will love this project. Not only do you get to play with water, but you get to sink boats too!


Louise
[1] from the wikipedia- you may want to use a "real" encylopedia to double check the numbers. Wikipedia is pretty good on a lot of things, but most teachers like a more permanent reference.

Yes, I agree that Quinn is going to have fun with this project, and the key isn't for him to have the "correct" hypothesis right away, it's for him to design and observe the experiment. I think his hypothesis that boats will float best in lake water, because he has seen that before, is a perfectly good one. He is using his past experience to try to predict what will happen, which is something many scientists do. And it is even better to have your hypothesis disproven, because that leads to more questions, and the quest for answers is what science is all about! Science is most definitely not about having the right answer ahead of time. (Also, maybe he is thinking about salt water as ocean water, and since there are lots of waves at the beach, maybe he thinks small boats won't float as well in the ocean. In that case, he would be confusing the effects of waves with the effects of density, which is perfectly understandable. This is another problem that faces scientists -- we try to study one single phenomenon for simplicity, but we quickly realize that all of our past experience with that phenomenon is closely coupled with another more complicated and not really related phenomenon.)

One caveat about trying to achieve a hypersaline solution: You are going to have to mix that salt in really well for it to stay in suspension -- it doesn't do any good to add four cups of salt to a gallon of water (I can't remember the exact ratios, so I am just making the numbers up) if only two cups of salt dissolve and the rest just sits at the bottom of the pan. Then your density would really be 2 cups/gallon, instead of the 4 cups/gallon you were aiming for. I'm sure you'll find this out as you go. But I imagine Quinn might have fun stirring the salt up between experiments too...

LucindaS wrote: One caveat about trying to achieve a hypersaline solution: You are going to have to mix that salt in really well for it to stay in suspension -- it doesn't do any good to add four cups of salt to a gallon of water (I can't remember the exact ratios, so I am just making the numbers up) if only two cups of salt dissolve and the rest just sits at the bottom of the pan. Then your density would really be 2 cups/gallon, instead of the 4 cups/gallon you were aiming for. I'm sure you'll find this out as you go. But I imagine Quinn might have fun stirring the salt up between experiments too...

This is a good cavaet, though I'm guessing these ratios aren't going to be a problem, since there is a lake in antartica (somewhere colde, anyway...) with 18 times the salinity of the ocean. So 8-9 times probably isn't a saturated solution. Hypersaline with regard to lakes seems to be anything saltier than the ocean, and nothing to do with the saturation limit of the water (which is how a chemist or engineer might think hypersalinity is defined).


Time to test. 30 g table salt in 100 mL water (cold/from the tap). It all goes in... though I had to swirl a bit. When you first dump it in, it looks like it won't dissolve all of the salt... but then the solution clears and the salt all goes in. So, I think the amounts above should be fine. It took maybe thirty seconds of swirling to get it in. (And I have to say, I'm not happy with the performance of my dishwasher. I don't usually stare intently at my dishes, but upon careful inspection the measuring cup is not as sparkling as I might like! The salt is dissolved though!)


Louise

Louise wrote:

LucindaS wrote: One caveat about trying to achieve a hypersaline solution: You are going to have to mix that salt in really well for it to stay in suspension -- it doesn't do any good to add four cups of salt to a gallon of water (I can't remember the exact ratios, so I am just making the numbers up) if only two cups of salt dissolve and the rest just sits at the bottom of the pan. Then your density would really be 2 cups/gallon, instead of the 4 cups/gallon you were aiming for. I'm sure you'll find this out as you go. But I imagine Quinn might have fun stirring the salt up between experiments too...

This is a good cavaet, though I'm guessing these ratios aren't going to be a problem, since there is a lake in antartica (somewhere colde, anyway...) with 18 times the salinity of the ocean. So 8-9 times probably isn't a saturated solution. Hypersaline with regard to lakes seems to be anything saltier than the ocean, and nothing to do with the saturation limit of the water (which is how a chemist or engineer might think hypersalinity is defined).


Time to test. 30 g table salt in 100 mL water (cold/from the tap). It all goes in... though I had to swirl a bit. When you first dump it in, it looks like it won't dissolve all of the salt... but then the solution clears and the salt all goes in. So, I think the amounts above should be fine. It took maybe thirty seconds of swirling to get it in. (And I have to say, I'm not happy with the performance of my dishwasher. I don't usually stare intently at my dishes, but upon careful inspection the measuring cup is not as sparkling as I might like! The salt is dissolved though!)


Louise

Looking up the reported solubility for table salt- LucindaS is right, you are near the solubility limit, though it looks like you should be able to get 38 g/ 100 mL of water in at 68 degrees.

Epsom salt is even more soluble in water, you can dissolve more than 71 g/ 100 mL water (at 68 degrees).

So, if you use table salt, use the lower end of 20-30 oz per 8 cups. If you use epsom salt, you can use the higher end.

Louise

Well..... Quinn did the experiment and, luckily, the boat took approximately 2-3 more quarters to sink in the "Dead Sea" salt water. We also ended up with 2 cups more total water solution of the sugar water AND the salt water. Also an interesting finding!

He tied for 3rd place (out of 19 competitors!!) in the 2nd Graders Science Fair last week. He was THRILLED! He talks density like a pro and loves to tell everyone about his findings.

Thanks so much to each of you who responded. Your help was invaluable and we will be returning for next year's project!

Quinn's Mom!

Quinn 123 wrote:Well..... Quinn did the experiment and, luckily, the boat took approximately 2-3 more quarters to sink in the "Dead Sea" salt water. We also ended up with 2 cups more total water solution of the sugar water AND the salt water. Also an interesting finding!

He tied for 3rd place (out of 19 competitors!!) in the 2nd Graders Science Fair last week. He was THRILLED! He talks density like a pro and loves to tell everyone about his findings.

Thanks so much to each of you who responded. Your help was invaluable and we will be returning for next year's project!

Quinn's Mom!

That is great news! I'm glad the project was fun and successful.

As for the volume change- all that "stuff" has to fit somewhere. Small amounts won't change the volume too much, but at high %s the change will be dramatic (as you saw).

Louise

Congrats on a well done project! Sorry I missed all the discussions.