Practical Exam Survival Guide
* Know to create a calibration curve: What are the labels for the axes? (Absorbance on y-axis, concentration on the x-axis.)
* Know how to use the data from a calibration curve to find (1) slope and (2) equation of the line.
* How are absorbance and transmittance related? We discussed several equations: A = log (100/%T)
A = (I0/IT)
T = (IT/I0) x 100%
A = 2 – log (%T) * What is Beer’s law and what does it describe?
Rates of Reaction
* How is the concentration of a solution determined? (M = n/V is the equation, but what does it mean?) How does dilution affect the number of moles of a substance?
* What is the general form of a rate law? Rate = k[A]order – what is an order? Can you solve for k given rate, [A], and order of A?\
* What does a rate order of zero mean?
Equilibrium Constants and Le Chatelier’s Priciple
* What is Le Chatelier’s principle? What does it describe?
* Be able to use chemical reactions to show Le Chatelier’s principle in action. Example question: The two different colored Co(II) complex ions, [Co(H2O)6]2+ and [CoCl4]2-, exist together in equilibrium in solution in the presence of chloride ions: [Co(H2O)6]2+ (aq, pink) + 4 Cl- (aq) ⇌ [CoCl4]2- (aq, blue) + 6 H2O (l) This equilibrium can be disturbed by changing the chloride ion concentration or by changing the temperature. The colour changes accompanying the changes in equilibrium position are as predicted by Le Chatelier’s principle. * Be able to write the equilibrium constant expression for a weak acid, a weak base, and a sparingly-soluble salt.
* What is the difference between endpoint and equivalence point? Are they different? (Yes!) How so? (Equivalence point is reached when moles of analyte (what’s in the flask) equal the amount of titrant (what’s in the buret). Another way we stated this during the HCl/NaOH experiment was “moles of acid (the analyte) = moles of...
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