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04-15-2009   #1 (permalink)
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Default [Chemistry] Identifying Sources of Error

I did a lab experiment in class a couple of weeks ago. We had to use calcium chloride and sodium carbonate to create chalk. The materials used were:
  • three 250 mL beakers
  • ring stand
  • 2.5 grams sodium carbonate
  • one Funnel
  • 2 Stirring rods
  • filter clamp
  • distilled water
  • 25 mL graduated cylinder
  • electronic balance
  • filter paper
  • 2.2 grams calcium chloride
I'm kind of stumped on identifying sources of error. We aren't allowed to identify human errors as experimental sources of error. I already mentioned a few sources of error, such as:
  • Loss of product (chalk) during the filtration process
  • Impure reactants and side reactions
Also, my chemistry teacher says calibration of tools (balances, thermometers, etc) and measurement errors are not valid.
What other kinds of sources of error could there possibly be?
 
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04-15-2009   #2 (permalink)
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Cross contamination? You never know if the beakers you used and other equipment used to hold the compounds were properly cleaned by other students or not.
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04-15-2009   #3 (permalink)
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Possibly... when you said side reactions, I interpreted it as the compounds reacting to atmospheric conditions (i.e. gases present during the procedure).
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04-15-2009   #4 (permalink)
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Edit: Nevermind D:

Missed the part where measurement errors aren't allowed.
 
04-15-2009   #5 (permalink)
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Quote:
Originally Posted by Pathos
I did a lab experiment in class a couple of weeks ago. We had to use calcium chloride and sodium carbonate to create chalk. The materials used were:
  • three 250 mL beakers
    beakers are a pretty imprecise method of measuring volume. A graduated cylinder is much more precise. I don't think this is a measurement error, b/c its a result of the device, not (for example) human error in misreading the numbers on the beaker.
  • filter paper
Whenever you filter stuff out, some of the precipitate inevitably gets stuck on the filter paper. Possible error?
edit: you already listed this. woops.

[/font]
Comments are underlined. Otherwise, you might consider the effects of limiting reagents, and whether you would receive optimal yield from the reaction, especially if you've only measured to 2 sig figs on each.
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04-16-2009   #6 (permalink)
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hmm.. let me get my chem book.. we had this type of experiments.. @_@
apparently its hard to know errors if you don't know the procedure..


~~~~i dont know how to subscript here~~~~~
CaCl2 + Na2CO3 ------heat and H2O------> CaCO3 (white precipitate) + 2NaCl

so from that only.. i can say
heat can be part of the error. @_@
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Last edited by GrayMatter; 04-16-2009 at 04:03 AM.
 
04-16-2009   #7 (permalink)
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Quote:
Originally Posted by badna0
beakers are a pretty imprecise method of measuring volume. A graduated cylinder is much more precise. I don't think this is a measurement error, b/c its a result of the device, not (for example) human error in misreading the numbers on the beaker.
The beakers weren't used to measure anything. We weighed 2.2 grams of the calcium chloride and 2.5 grams of the sodium carbonate. Then we added each of those compounds in two separate 250 mL beakers. The graduated cylinder was used to measure the distilled water, which was added to each 250 mL beaker.

EDIT: Gray, according to the formula my teacher gave me, there's no catalyst that speeds up the reaction.


Last edited by Pathos; 04-16-2009 at 12:56 PM.
 
04-16-2009   #8 (permalink)
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Heat and Water is just present to allow for the reaction to occur.

Anyways, even though Calcium carbonate is a precipitate, depending on the temperature, there is still a certain amount of it dissolved in the water. Not sure if you can say it's error though, since it's inevitable as it is always at equilibrium
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04-17-2009   #9 (permalink)
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hmm. i was thinking calcium chloride and sodium carbonate in solid form as you have distilled water in the materials..

so.. assuming that both calcium chloride and sodium carbonate are in liquid form.. they just form precipitate directly and just use heat for more precipitate..

so errors..
hmmm
-not following instruction?
-wrong chemicals used?
-error in calculating the exact grams on how much precipitate was formed (quantitative and qualitative analysis)
@_@ kinda stucked..
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