Science Buddies: "Ask an Expert"

Hi I'm doing the science project on how to measure the density of salt water and i got the idea from this website. and the idea was an "Eggsperiment to measure the density of salt water" but I don't get what the relative salt concentration is and how you find it. Also i do not get what is the absolute salt concentration and how you find it too. Last but not least, i dont understand what this equation is for and how to use it : new concentration = vol. stock / (vol. stock + vol. water). . Oh and if possible can you please tell me how you get the density of salt water from all this? Thanks!

Can anyone please help me? I'm DESPERATE! Anyone?

Hi,

This forum is a message board, not a chat room--please expect the experts to take at least 24 hours and perhaps 48 hours to answer your question; assigned experts only check the forums once per day.

Absolute concentration can be expressed in grams per liter. The directions for the experiment say that a cup of salt is 292 grams, and a quart of water is .946 liter. Thus, to get the salt concentration in the stock solution, you divide 292 by 0.946. To get the new concentration in each dilution, you use the formula provided: volume of the stock solution you add to the cup in liters divided by that volume plus the volume of water you add. Remember to keep your units the same--you can convert cups to liters using this website: http://www.sciencemadesimple.com/conversions.html .

For the relative concentrations, assume that your stock solution has a concentration of 1. It looks like they have you mix equal amounts of the previous solution with tap water each time, so each time you are decreasing the concentration by a factor of two. In other words, in cup two the relative concentration is 1 divided by 2 = 1/2, or 0.5. The next will be 0.5 divided by two, and so on.

Hope this helps!

Thanks you did help except you still didn't answer my question of how you get the density of salt water from that.

P.S sorry, i'm a procrastinator so when i need to finish things quickly i kinda worry

Whoops, I'm sorry! In order to measure the density of the salt water, you will need to know the density of the raw egg. There are instructions on how to get that, here: https://www.sciencebuddies.org/mentorin ... p007.shtml. Then, you know the density of the salt water solution in which the egg floated. Since you also know that the density of tap water is about 1 kg/L or 1 g/mL, you can make some fairly good estimates of the density of some of the other solutions, sea water, etc.

Does that make sense?

The easiest way to find the density of a liquid is to weigh a measuring cup or other volume measuring container recording this "tare" weight. Then fill the measuring cup to one of its known volume lines and weigh it again. Subtract the "tare" weight from the total weight to get the weight of the liquid. Divide the weight of the known volume of liquid by the volume measured to get the density in (scale weight units) / (measuring cup volume units). You will probably want to convert this density to scientific units using the conversion constants in the project write-up.