Don't understand a step in the procedure in my science proj.

[irock333]

https://www.sciencebuddies.org/science- ... w&from=TSW
*Heres the link to the topic.
Experimental Procedure

Salinity and Mixing

You'll need to keep track of which containers have salt added and which ones do not, so start by labeling your containers while everything is still dry. Mark one container and two bottles "+ salt." Mark the other container and two bottles "fresh."
Add tap water to each container.
Add salt to the "+ salt" container and stir until it dissolves. How much salt? You decide! Use the following information to assist you with your calculations:
The salinity map in the Introduction shows that deep ocean salinity ranges from 32 to 37.5 parts per thousand (ppt or 0/00). As an example, 32 ppt would mean 32 g of salt per 1000 g of seawater.*That means how much salt do I use ?
At 25°C, the maximal solubility of NaCl in water is about 357 g/l.
For making measurements in a typical American kitchen, the following facts will be helpful. A cup of table salt is approximately 292 g (GourmetSleuth.com, 2001). There are 16 tablespoons per cup, and 3 teaspoons per tablespoon. Finally, a cup of water is the same as 236.6 ml.
Optional: if you have a hydrometer, measure the density of each solution. Rinse off the hydrometer and wipe the outside dry between measurements so that you don't transfer one solution to the other.
Add about 3 drops of food coloring to each container. Use one color for "+ salt" and a different color for "fresh." Note which is which in your lab notebook. (You'll want your notebook handy, but off to the side in case of spills.)
Completely fill a "+ salt" bottle with colored salt water.
Completely fill a "fresh" bottle with colored fresh water.* I don't understand this part....
Use the two remaining bottles for color samples of each solution for comparison as the experiment proceeds.
Now comes the tricky part. You are going to invert one bottle and put it on top of the other, without spilling. It doesn't matter which one you choose to flip over first, because you'll be doing the experiment both ways. It's a good idea to practice this maneuver first with plain tap water until you get the hang of it, so you don't waste your solutions. Here's how:
Use the card (or plastic) to cover the top of the bottle you're going to invert.
Hold the bottle near the base with one hand while holding the card against the opening with two fingers of the other hand.
Slowly and carefully flip the bottle over, keeping the card pressed tightly against the opening. For plastic bottles, try not to squeeze the bottle as you do this, since squeezing will push water out of the bottle. Holding near the bottom of the bottle where it is stiffer will help.
Place the inverted bottle on top of the other bottle (the card remains in place, so it is between the openings of the two bottles).
Line up the two bottles so that the inverted bottle is balanced on top.
Note the time, and then carefully slide the card out from between the two bottles.
With practice, you'll be able to do this without spilling more than a few drops.
Observe what happens to the two solutions. Write your observations in your lab notebook. Remember to the note the time as you make your observations. Here are some things to look for:
Do you see any evidence of mixing (e.g., color changes, or schlieren lines)? Note: schlieren lines are wavy lines caused by changes in the index of refraction of the solution. Since the two solutions have different densities, they will also have different indices of refraction. Where the two solutions mix, schlieren lines may be apparent. You may have seen schlieren lines before on a hot summer day in the air over hot asphalt pavement. In this case the lines are the result of rising hot air mixing with cooler air above.
How does the color of solution in each bottle compare to the original color?
Is the color uniform throughout each bottle?
Note anything else of interest.
Optional: if you have a hydrometer, measure the density of the water in each bottle at the conclusion of the experiment.
Confirm your results by repeating the experiment. You should perform at least three trials with salt water in the top bottle and fresh water in the bottom bottle, and at least three trials with fresh water in the top bottle and salt water in the bottom bottle.

[donnahardy2]

Hi,

Thanks for posting the link to this experiment. I had not noticed this project before, but it looks like an excellent project on densities. I see that it is an open-ended project and does not tell you exactly how much salt to use to make the high density solution, but encourages you to experiment. However, I can understand that you need a specific suggestion. I recommend that you make a very dense solution, so this would be 1 cup of salt in a liter (about a quart) or water. It is important to write down exactly how much you use, so we can calculate the concentration of salt (if you are interested). If you have access to a metric balance, you can weigh out 290 grams of salt and add it to a liter of water. If your bottles are smaller or larger, you can scale up or down and maintain the same relative proportion of salt.

If you are working at home, use tap water for the fresh (low density) water and the 290 gram/liter salt for the salt (high density) water. Use different food coloring for each sample of water.

I hope this will help you get started. Let me know if you have had any chemistry so I can show you how to calculate the concentration of salt in the salt water sample.

Please let us know if you have any other questions.


Donna Hardy

[Qua're Jones]

Why does ponds freeze faster than oceans?
What does salt contain?

[Qua're Jones]

Why does ponds freeze faster than oceans?
What does salt contain?

[donnahardy2]

Hi,

Yes, ponds to freeze faster than oceans because of the difference in salt concentration.

Are you planning to do a scence project? Here is one that would be fun to do that explores the effect of ice on freezing point.

https://www.sciencebuddies.org/science- ... p023.shtml

Here's a website that includes additional information onthe topic.

http://www.worsleyschool.net/science/fi ... water.html

Donna Hardy