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Unformatted text preview: s and Bases Salt Prediction:
acidic, basic or
neutral? General Chemistry I and II Lab Manual pH Acidic, basic or
neutral? Strongly or
weakly? Observations: Dakota State University page 1 42 of 232 Experiment 11: Acids and Bases General Chemistry I and II Lab Manual Pre-lab Questions:
1. We are making a serial dilution of HCl and NaOH; what does this mean?
2. How do you suppose we will decide if a solution is “strongly” or “weakly” acidic or basic? Dakota State University page 1 43 of 232 Experiment 11: Acids and Bases General Chemistry I and II Lab Manual Post-lab Questions:
1. What was the biggest surprise to you in the household items?
2. Some salts you could predict the pH of in solution, some you could not. Why? Dakota State University page 1 44 of 232 Experiment 12: Le Chatliere’s Principle General Chemistry I and II Lab Manual Experiment 12: Le Chatliere’s principle
Purpose: To gain experience with Le Chatliere’s principle
Purloin: To steal
See “Using the Pasco System” and
“Basic Laboratory Procedures”; Pipettes
Equilibia are critical to life. I mean, if chemical reactions were not reversible, we would
be one-shot machines. Our metabolism, which is nothing more than the series of chemical
reactions that keep us alive, would run through their cycle one time, and we would expire. This
does not happen, because most of the reactions in our metabolic pathways are reversible; what is
used up in one step, is regenerated in the next.
Le Chatliere tells us that, when it comes to equilibria, we are allowed to be bullies. We
can push the equilibrium to the reactants by adding products, or to the products by adding
reactants. We can even push the equilibrium around by changing the conditions, such as
Today, we will be playing with what is probably one of the most important equilibria to
us as humans; acid/base equilibria. Essentially, we are going to create a buffer solution, and play
with it for a bit. We’ll be using an (unknown) organic acid; the general equilibria will be
HA (aq) ß à H+ (aq) + A- (aq)
We are using an organic acid because they are all weak, and therefore appropriate choices for
creating a buffer solution. Recall the equilibrium constant, and equilibria calculations as you’ve
learned them in class, and we will see, I hope, some of these principles come to life.
You will need to start the Pasco system with the pH probe. Use the standard methods for starting
the system; you will want to choose manual data collection.
Part I: Determination of the equilibrium constant Ka
You will find two bottles in the lab, one of an unknown organic acid, and one of its
corresponding salt. Both of these are the same concentration which will be provided for you in
class. Using the pipettes provided, thoroughly mix 20.00 mL of each of these solutions into a
Dakota State University page 1 45 of 232 Experiment 12: Le Chatliere’s Principle General Chemistry I and II Lab Manual clean, dry flask. Determine the pH of...
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