Calculating Density of Unknown Liquid in Chemistry Lab

[njblaha]

In the lab for my chemistry class we were doing the density of an unknown liquid using a microliter syringe.We had to fill the syringe with water and then weigh it.Then we had to fill it with the unknown liquid and weigh it again.to make a long story short,one of the questions is can another liquid other than water be used.Knowing nothing about chemistry I have no idea.Can someone help me?

 

[mrjeffy321]

I would say Yes, you could substitute any other liquid you wanted for water, proving you knew what its density was.

I think how the experiment went is you first fill the syringe with water, of a given volume, weight it. Since you know what the density of water is, 1 gram / mililter, then you can easily calulate the weight of the liquid inside, and then from that, the weight of the syringe.
Then you fille the syringe with the unknown liquid, wieght it, then subtract out the weight of the syringe. Now you have the weight of the unknown liquid, and you know the volume. Densisty = mass / volume, and you have it.

but the first step is to find the weight of the syringe, (why the complicate it with the water, I don't know, you could have just weighed the empty syringe). and you could in theory do it with any known liquid.

 

[njblaha]

Actually,we had to weigh the syringe first then fill it with the water.Then we took the temperature of the same water that was in a beaker.From the temperature we figured out the density from a chart.then we took the unknown liquid in the syringe and weighed that and did all the calculations.Don't ask me why we did it this way,it was a pain in the neck and took a really long time.

Does this change your answer?

 

[mrjeffy321]

well, I fail to see the point of the water then now.
but it seems like you were going for a really exact number on density, hense the temperature and chart, but I think as long as you could still find the density of whatever liquid you substtitute, it would be OK.
This whole experiment seems to me to be over complicated.

 

[dextercioby]

This whole experiment seems to me to be over complicated.

I'm sorry but i have to disagree.I think the experiment went by the book without any operation being done uselessly.I would have done it the same way...

Daniel.

P.S.There's been a while since performing any experiments in a chemistry lab,but i still remember a few things...

 

[njblaha]

The numbers were very exact but the whole process was just so painful,for the lack a better word.

Now that I look at the lab book they also want to know if any liquid other than water can be used to find the density of an unknown solid.I think you can use any liquid if you're just going to drop the solid into it to find the volume,right?

 

[dextercioby]

Sure,just as long as u have tabulated density chart for the liquid (density as a function of temperature,assuming constant atmospherical pressure),it can be done.However,(distilled) water is preferred due to the nice number 1000Kg/cubic meter or 1g/cubic centimeter.Plus the fact that another liquid might chemically interact with the solid...

Daniel.

 

[njblaha]

I didn't have to take the temperature when I took the density of the metal,so it would have nothing to do with it.

 

[dextercioby]

You have to take the temperature of both the fluid & the solid,because the density of each is temperature dependent and thus you avoid heat exchange when putting them in contact.

Daniel.


P.S.Things are really subtle...

 

[njblaha]

The lab didn't require that the temperature be taken of the liquid of the solid or the liquid.the only time I had to worry about the temperature was when I did the test with the microsyringe.

 

[dextercioby]

That's one thing.Correct procedure to minimize subjective errors is another...

Daniel.

 

[njblaha]

I didn't make up the experiment,I only did it.

 

[dextercioby]

My remark was meant more like an advice for future experiments,in which u have to take all possible measures to reduce sujective errors...

Daniel.