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Topic: Rate Law (Magnesium + HCl) Lab  (Read 13448 times)

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Offline shahrukh1

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Rate Law (Magnesium + HCl) Lab
« on: December 22, 2011, 06:00:55 PM »
In our lab we reacted Mg+HCl and measured pressure as time progresses.
After graphing, and getting the initial rate I am left with as follows:

The [Mg] remained constant, we used a 2cm long strip of Mg, and it was not weighed.

[] is measured in mols/L
Initial Rate:           [HCl]              [Mg]
1.591 x10-1            0.5                 -
4.795 x10-1            1                    -
6.966 x10-1            1.5                 -
1.32                      2                   -

Now we had to get the rate law using the above data

Rate = k[Mg]^m[HCl]^n
1.32/4.795E-1 = (2/1)^n
3 = 2^n      n = log3/log2= 2
n = 2

I am stuck as to how do I get the value of M and K, as I am stuck

Also, I have to propose a rate mechanism (the thing with the elementary steps and what not)
I am totally stuck, and have no idea how to get the elementary steps.
Please help

Offline not_a_frog

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Re: Rate Law (Magnesium + HCl) Lab
« Reply #1 on: December 22, 2011, 07:48:02 PM »
To determine m and k, plug in your initial rates and reactant concentrations into the rate law equation that you have. You will then have simultaneous equations, which you can use to solve for both k and m. Two equations to determine the values of k and m should be sufficient, then plugging in the result into a third equation to double-check.

As a hint for proposing a rate mechanism, take note that the rate law is based on the stoichiometric coefficients of the rate-limiting step of your mechanism. Once you've worked out the rate-determining step, the other steps should follow quite easily.

Offline Borek

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Re: Rate Law (Magnesium + HCl) Lab
« Reply #2 on: December 23, 2011, 05:16:10 AM »
To determine m and k, plug in your initial rates and reactant concentrations into the rate law equation that you have. You will then have simultaneous equations, which you can use to solve for both k and m.

Better to use a linear regression.
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