Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: missbrokensmile on March 24, 2010, 11:20:31 PM
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I'm really confused about the data processing I have to do for an experiment. I'm hoping someone can *delete me*
What I'm ultimately trying to do is find the rate: rate=concentration/time
My experiment is the iodine clock reaction (hydrogen peroxide variation) and I'm investigating the relationship between temperature and reaction rate.
But to find the reaction rate, I need to find concentration and I'm confused about how to go about finding this concentration.
The equation of the reaction is:
2I- (aq) + H2O2 (l) + 2H+ (aq) --> I2 (g) + 2H2O (l)
I2 (g) + 2S2O3-2 (aq) --> S4O62- (aq) + 2I- (aq)
[is there a third reaction with the colour change? would that be signficant in what I'm trying to calculate?]
The chemicals I used are:
Distilled water
3% Hydrogen peroxide (H2O2)
Potassium iodide (KI)
Sodium thiosulfate (NaS2O3)
Soluble starch (freshly prepared)
Sulfuric acid (2.5M)
My question is, which one am I supposed to use to figure out the concentration? The products/rectants? The actual chemicals used or equation of reaction? Do I add all the chemicals/ions used and use a single concentration? And how exactly should I calculate the concentration?
I'd appreciate any sort of *delete me*
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Is it all? Or perhaps you did some measurements during the experiment?
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Well, I mixed up a "solution A" (made up from Distilled water, Potassium iodide (KI), Sodium thiosulfate (NaS2O3), Soluble starch, Sulfuric acid (2.5M)) and a "solution B" (made from hydrogen peroxide and distilled water). And I basically used them as stock solutions (not sure if that is the right word) for each repeat/temperature change.
Basically, I poured a small amount of solution A and B together in a conical flask and timed the time taken for the colour to occur.
In the experiment, I recorded the time taken for the dark blue colour to appear. So the only measurements I have are time (plus temperature and I could *possibly* calculate moles or whatever)
Independent: Temperature
Dependent: Time taken for the colour to occur
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I poured a small amount of solution A and B together in a conical flask
Random volume, or have you measured the volume taken?
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I measured it
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Sorry, I mixed up solution A. The potassium iodide is supposed to be in solution B
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So, if you have measured volume, can you calculate number of moles of substances that were present in the measured volume?
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I can calculate the moles. But, how do I calculate concentration? As in, which part of the equation/chemicals do I use?
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You know moles then.
Can you calculate volume of the mixture?
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I can.
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So you know number of moles, you know the volume, can you calculate concentration?
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I know that to calculate concentration, it's: c=n/v, but I don't what parts of the chemicals to calculate concentration from. Do I calculate a single chemical, ie. sodium thiosultfate, or do I calculate all the products/reactants, and I also don't understand how the experimental concentration is supposed to fit into the half equation of the equations of the clock reaction
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Each substance separately.
I also don't understand how the experimental concentration is supposed to fit into the half equation of the equations of the clock reaction
No idea what you mean, please elaborate.