2. Make predictions and fill in the first column of Part A of this experiment 13

Question

2. Make predictions and fill in the first column of Part A of this experiment 13o 3. hat is the approximate expected pH of a 0.030 M HNO, solution? 4. What is the final pH after 1 drop (o.o5 mL) of 6 M HCI is added to 1.0Lof freshly prepared pure water that was originally at a pH of 7.0. Is there a significant pH change? 5.1 A mul 5. a. What is the molarity of pure water at 20eC? b. Does the concentration of water change significantly (from the value in 4-a) when enough acetic acid is added to make the solution 0.1 M acetic acid?

Explanation / Answer

b) No the concentration of water does change significantly when enough acetic acid is added to make the solution 0.1 M acetic acid. The Ka is very small .For the Ka (Kw) for water is 1 x –14. This is usually a factor of at least 1 x 10^-6 times smaller than the Ka values for the weakest acids (for example, Ka(CH3COOH) = 1.8 x 10^-5) and so the contribution of the ionization of water to the proton concentration can be ignored.

c)

HA (aq) + H2O(l) <====>      H3O+(aq) + A-(aq)

When writing an equilibrium constant expression for this homogeneous equilibrium, we leave out the concentration of the liquid water.

The equilibrium constant for this expression is called the acid dissociation constant

Ka =[ H3O+ ] [ A- ]/[ HA]

Ka is acid dissociation constant

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