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General Chemistry Lab, need some help

  1. Aug 24, 2011 #1
    I'm curious if I'm doing this chemistry lab correctly or not. If you open the link below, you can see the lab. Basically, my job right now is to write a well formulated procedure on how to perform this lab.

    So, for this lab, am I supposed to be calculating the mass of the substance (h2o in this case) in the provided methods for 3 trials? What I don't quite get is how to verify that the mass is directional proportional to its volume. I feel very unsure about my procedures I wrote. So if anyone can, would they mind checking the lab and steer me in the right direction or atleast verify if what I'm doing is right?

    Thanks in advance.

    https://viewer.zoho.com/docs/uaBiK" [Broken]
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Aug 24, 2011 #2
    This is just a study of density, which is a property of a substance. The density is how much mass for a given volume, thus having units of grams per milliliter (g/mL = g/cm^3). At the same temperature and pressure this property is always constant provided the substance is chemically the same every time (i.e. no other chemicals were added during trials 2 and 3).

    For water at 1 atm and 25 C the density is approximately 1.0 g/mL.

    Verifying that the mass is always proportional to the volume is easy. You are just measuring the density at different volumes and if they are the same then you've succeeded.

    For example, first get the mass of a graduated cylinder and then pour 10 mL water into it and take the mass again. Now you have [(Mass water & cylinder) - (Mass Cylinder)]/10 mL = Density of water g/mL.
    Next repeat this using 7 mL of water and then 9 mL. You will get the approximately the same number!

    Maybe you will get
    trial 1 = 0.995 g/mL
    trial 2 = 0.990 g/mL
    trial 3 = 0.998 g/mL
    Which is correct! You should be somewhere in this range!
     
  4. Aug 27, 2011 #3
    Thanks, I was right :) I even asked the teacher, he confirmed it. Also, there's this odd question...

    "What does it mean when you a piece of glassware that is "graduated" or has "graduations" on it?" Couldn't we describe graduations as precise measuring marks?
     
  5. Aug 28, 2011 #4

    Borek

    User Avatar

    Staff: Mentor

    We can, just note that you can have a single volume or multiple volumes calibrated glass.

    Compare http://www.titrations.info/pipette-burette for more details about calibrated glass.
     
  6. Aug 28, 2011 #5
    Just curious, but why are we dividing by 10? FYI, I'm taking the temperature in Fahrenheit.
     
    Last edited: Aug 28, 2011
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