Chemistry
posted by Sara on .
O.k. I am confused. So here is what I did.
Mass of empty flask plus stopper: 37.34g
mass of stoppered flask plus water: 63.67g
Mass of stoppered flask plus liquid:
52.01g
Mass of water:
63.67  37.34= 26.33
Volume of Flask(density of H20 at 25*C, 0.9970 g/cm^3:
(37.34g)/(0.9970g/cm^3)=37.45cm^3
Mass of Liquid:
52.01g  37.34g= 14.67g
Density of Liquid:
(14.67)/(0.9970)=14.72g/cm^3
That was part 1 (density of unknown Liquid) Here comes part 2 density of unknown metal.
Mass of stoppered Flask plus metal:
61.28g
Mass of stoppered Flask + Metal+ Water:
78.19g
Mass of metal:
61.28g  37.34g= 23.94g
(Note that 37.34 is the mass of the stoppered Flask from before)
Mass of water:
78.19g  61.28g=16.91g
Volume of water:
(16.91)/ (0.9970)=16.96cm^3
Volume of metal:
???????????
I did the following:
(23.94g)/(0.9970g/cm^3)= 24.01cm^3
then using this answer I need to caculate the Density of the Metal:
(23.94g)/(24.01cm^3)= 0.9970 g/cm^3
But why would the Density for water at 25*C, which was given, be the same as the density of the metal? Shouldn't it be different? So I came to the conclusion that in the end I must be doing something wrong because my answer is like walking around in circles...(The last two caculations), so I either don't really get the concept or I made a mistake from the get go...or I am using the wrong numbers, to calculate certain parts. so, this is were i need your help. I hope it's clearer whemn I show you exactly what I did.

You are getting confused with the numbers.
Go back to square 1.
You were correct before that
mass H2O = 26.33 g.
mass liquid = 14.67 g.
volume of H2O = 26.33/0.9970 = 26.409 cc = volume of the liquid.
so density of liquid = mass/volume =14.67/26.409 = 0.55549 which rounds to 4 significant figures as 0.5555
Your original error was in miscalculating the volume of the liquid. The volume of the liquid is the same as the volume of the water and the volume of water is the mass of water divided by the density of water to give the volume of water. 
Mass of empty flask plus stopper: 37.34g
mass of stoppered flask plus water: 63.67g
Mass of stoppered flask plus liquid:
52.01g
Mass of water:
63.67  37.34= 26.33
Volume of Flask(density of H20 at 25*C, 0.9970 g/cm^3:
You are ok to here.
(37.34g)/(0.9970g/cm^3)=37.45cm^3
You have used the mass of the EMPTY flask. The volume of the flask is the grams H2O in the flask divided by the density of the water which is 26.33 (your figures from above)/0.9970 (the density of the water at the temperature at which the experiment was conducted) = 26.409 cc = volume of flask.
Mass of Liquid:
52.01g  37.34g= 14.67g
OK here
Density of Liquid:
(14.67)/(0.9970)=14.72g/cm^3
No, the density of the liquid is the mass of the liquid (14.67 is correct) divided by the volume of the liquid. The volume of the liquid is the same as the volume of the water that was in the flask which is 26.409 cc. That's why you went through the whole process of determining the volume of the flask by weighing the water and using the density of water to calculate the volume of the water which also is the volume of the flask. So,
density of liquid = 14.67/26.409 = 0.55549 g/cc which to 4 significant figures is 0.5555 g/cc.
Let's get the first part straight before tackling the second part. I will let you see what you were doing incorrectly for the first part> then using that knowledge work through the density of the metal. Repost that part if you get stuck. Thanks for showing your work. It makes it easier to catch what is going wrong.
That was part 1 (density of unknown Liquid) Here comes part 2 density of unknown metal.
Mass of stoppered Flask plus metal:
61.28g
Mass of stoppered Flask + Metal+ Water:
78.19g
Mass of metal:
61.28g  37.34g= 23.94g
(Note that 37.34 is the mass of the stoppered Flask from before)
Mass of water:
78.19g  61.28g=16.91g
Volume of water:
(16.91)/ (0.9970)=16.96cm^3
Volume of metal:
???????????
I did the following:
(23.94g)/(0.9970g/cm^3)= 24.01cm^3
then using this answer I need to caculate the Density of the Metal:
(23.94g)/(24.01cm^3)= 0.9970 g/cm^3