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Questions 1 - 10

Which of the following is a classic example of a first-order reaction?

Radioactive decay

A collision between 2 reactant molecules

A change in temperature

None of the other answers

Explanation

First order reactions have rates that are directly proportional to only 1 reactant. In radioactive decay, the rate of decrease of a radioactive material is proportional only to the amount of the material.

A buffer using acetic acid (pKa=4.76) is titrated with NaOH. What is the pH at half the equivalence point?

2.38

4.76

7.00

9.52

12.36

Explanation

The pH at half the equivalence point is equal to the pKa of the acid.

Which of the following compounds is insoluble in water?

$\small CaCO_{3}$

$\small Ca(NO_{3})_{2}$

$\small Na_{3}PO_{4}$

Explanation

Unless paired with an alkali metal, carbonate compounds are generally insoluble. Compounds that contain nitrate or an alkali metal will generally be soluble in water, and hydroxides are soluble when paired with heavier alkaline earth metals (such as calcium).

Put the following acids in order of their INCREASING acid strength: HI, HCl, HBr, HF.

HI, HCl, HBr, HF

HF, HCl, HBr, HI

HI, HBr, HCl, HF

HF, HBR, HI, HCl

HCl, HBr, HI, HF

Explanation

Larger halogen size leads to greater acidity because of weaker H-X interactions.

Put the following acids in order of their INCREASING acid strength: HI, HCl, HBr, HF.

HI, HCl, HBr, HF

HF, HCl, HBr, HI

HI, HBr, HCl, HF

HF, HBR, HI, HCl

HCl, HBr, HI, HF

Explanation

Larger halogen size leads to greater acidity because of weaker H-X interactions.

Which of the following is a classic example of a first-order reaction?

Radioactive decay

A collision between 2 reactant molecules

A change in temperature

None of the other answers

Explanation

$Fe_{(s)} + 2HCl_{(aq)} \rightarrow FeCl_{2(aq)} + H_{2(g)}$

For the redox reaction shown, which of the following half reactions occurs in the anode?

$Fe \rightarrow Fe^{2+} + 2e^{-}$

$Fe \rightarrow Fe^{3+} + 3e^{-}$

$Fe^{2+} + 2e^{-} \rightarrow Fe$

$2H_{2} + 2e^{-} \rightarrow H_{2}$

Explanation

Recall that oxidation always occurs at the anode (in both the electrochemical and galvanic cells). loses two electrons in this case to become $Fe^{2+}$ . The presence of $Fe^{2+}$ is hinted by the ionic compound .

Given the following equation (2A+B --> 3C). Which of the following correctly displays the rate of the reaction?

I. -Δ\[A\]/2Δt

II. Δ\[B\]/Δt

III. Δ\[C\]/3Δt

I only

II only

I and III only

II and III only

I, II, and III

Explanation

The rate based on concentration is related to the coefficients in front of the compounds. Based on the reactants the rate should be negative (because change in concentration for the forward reaction will be negative) and based on the products should be positive. This means that II is incorrect. The rate for each compound in the reaction should be divided by it's coefficient to make it all related to 1M, showing that I and III are correct.

Where does the flattest region of a titration curve of the titration of a weak acid with a strong base occur?

At the pKa of the acid

At the pKb of the base

At a pH greater than 7

At a pH of 7

Explanation

In this question, titration curve would graph the pH of acid solution versus the amount of base added. Since the base is strong and the acid is weak, we can conclude that the pH will be slightly greater than 7 at the equivalence point. The equivalence point is found in the steepest region of the curve.

The half-equivalence point is the flattest region of the titration curve and is most resistant to changes in pH. This corresponds to the pKa of the acid. Within this region, adding base (changing the x-value) results in very little deviation in the pH (the y-value). This region is also the buffer region for the given acid.

A buffer using acetic acid (pKa=4.76) is titrated with NaOH. What is the pH at half the equivalence point?

2.38

4.76

7.00

9.52

12.36