For a lab at school, we are given six substances which we have to separate and purify. The substances are benzoic acid, stearic acid, salt, sand, sawdust, and iron. We took out the iron with a magnet already, and got the sawdust out using a balloon and static electricity. However, my group is having trouble separating the rest of the mixture, and we only have one more class period to work on this lab. Also, we have many materials in class, but for safety reasons we cannot do something like heating alcohol (ethanol, acetone, etc.) at a high temp because of the flammability of the liquid. We really need some help and advice so we can complete the lab tomorrow!

salt RO filter or evaporation, sand filter paper

Do you have access to any solvents? I know you said you cant heat anything, but can you at least boil water? Stearic acid is not soluble in water. So you could add water to the mixture, and the stearic acid will float to the top. At that point you just scoop it off. Now, the NaCl and Benzoic acid are soluble in water, so you're best bet would be to boil off the water..but this will only get you a mixture of NaCl and Benzoic Acid. Benzoic acid may be less soluble in cold water. So after you remove the stearic acid, cool the water considerably..around 4-5 Celsius. The benzoic acid should precipitate at the bottom and the NaCl should be relatively soluble still so it should pour off with the water (use a filter for this part as well). That's your best bet.

salt RO filter or evaporation, sand filter paper

yes, i forgot this part, do this too.

Edited September 22, 20169 yr by Elite Engineer

benzoic acid,

stearic acid,

salt,

sand,

sawdust,

and iron

 

1st - magnet to remove iron filings

2nd - balloon to get out saw dust.

3rd - nice hot water (over 70 deg C and your stearic acid will liquify and your benzoic acid will dissolve) - stearic acid will form layer on the top, pour off or take off with pipette

4th - filter paper to remove sand

5th - cool water down - Benzoic Acid is has low solubilty in cold water. It will precipitate out and you can refilter for it

6th - boil water off to leave salt

 

just recapping what others said really - but wanted to get straight in my own head. Interested to see what any of our professional chemists say

benzoic acid,

stearic acid,

salt,

sand,

sawdust,

and iron

 

1st - magnet to remove iron filings

2nd - balloon to get out saw dust.

3rd - nice hot water (over 70 deg C and your stearic acid will liquify and your benzoic acid will dissolve) - stearic acid will form layer on the top, pour off or take off with pipette

4th - filter paper to remove sand

5th - cool water down - Benzoic Acid is has low solubilty in cold water. It will precipitate out and you can refilter for it

6th - boil water off to leave salt

 

just recapping what others said really - but wanted to get straight in my own head. Interested to see what any of our professional chemists say

this is what i said, yet no +1 for me. I'm not mad tho

Thanks for your advice, it worked!! But now my lab group is trying to figure out how we got benzoic. The day before, we had heated up some acetone with a mixture of benzoic and salt. Then we put it away in our drawer, and some of the acetone had evaporated. The next day, we found benzoic acid by itself, and we have no idea how it happened. Please help explain!!!