105b Lab Study Guide - (1-4)

What reaction was studied in Lab 1 of Kinetics I?

The catalyzed decomposition of hydrogen peroxide: 2H2O2(aq) ⟶ 2H2O(l) + O2(g).

What acts as a catalyst in the decomposition of hydrogen peroxide?

Aqueous iodide (I⁻) via forming and consuming hypoiodite, IO⁻.

What is the empirical rate law derived from the reaction studied in Lab 1?

Rate = k[H2O2]^n[I⁻]^m.

How does changing the concentration of [H2O2] or [I⁻] affect the rate constant?

It affects the orders n and m in the rate law.

What is the primary goal of Lab 1?

To derive the empirical rate law for the iodide-catalyzed decomposition of hydrogen peroxide.

What does the Arrhenius equation relate to in Lab 1?

The temperature dependence of reaction rates.

In Lab 2, what was the primary compound involved in the spectrophotometric determination?

FD&C Blue #1 dye.

Why was OCl⁻ kept in large excess in Lab 2?

To treat the dye's disappearance as a pseudo-'nth'-order process.

What method was used to determine the reaction order of the dye in Lab 2?

Integration rate-law plots such as [Blue #1] vs. t, ln[Blue #1] vs. t, and 1/[Blue #1] vs. t.

What was the objective of Lab 3: Le Chatelier's Principle?

To observe qualitative changes in equilibria under various stresses.

How do you demonstrate Le Chatelier's Principle using color changes?

By adding/removing reactants or products, changing pH, or altering temperature to see the shifts in color.

What observation was made with the chromate to dichromate reaction?

Adding NaOH caused the solution to shift from yellow to orange, indicating a right shift.

What pH indicator was studied in Lab 4?

Bromothymol blue (BTB).

What was the method to measure the acid dissociation constant (K_IN) for BTB?

Measuring absorbance at two wavelengths across a series of buffer solutions of known pH.

What key equation is related to spectrophotometry in Lab 4?

Beer–Lambert Law: A = εℓc.

How is pK_IN extracted from the Henderson-Hasselbalch plot?

The intercept of the plot log([In⁻]/[HIn]) vs. pH gives -pK_IN.

What is the relationship between absorbance and concentration according to Beer-Lambert Law?

Absorbance (A) is directly proportional to the concentration (c) of the absorbing species.