Analytical Chemistry (midterm)

1. A type of coprecipitation in which a compound is trapped within a pocket formed rapid crystal growth

• surface adsorption

• mixed crystal formation

• occlusion

• mechanical entrapment

A type of coprecipitation in which crystal lie together during growth and doing trap a portion of solution in tiny pocket

• mechanical entrapment

• occlusion

• surface adsorption

• mixed crystal formation

What element can be analyzed by the use of dimethylglyoxime in weakly alkaline solution

• Nickle

• Magnesium

• Zinc

• Cadmium

Which of the following is not a property of reference materials in titration and in other analytical methods?

• Established methods for confirming purity should be available

• Absence of hydrate water so that the composition of the solid does not change

• Reasonably low molar mass so that relative error associated with weighing with the standard is minimized

• Modest cost

1. In an acid base titration using phenolphthalein indicator, the equivalence point is manifested by the appearance of what color?

• yellow

• blue

• orange

• purple

1. In the reaction Zn_(s) + 2H⁺_(aq) à Zn⁺²_(aq) + H_2(g), what is the oxidizing agent?

• Zn

• Zn^2

• H⁺

• H₂

1. Which of the following is true in this reaction

3NO^2- + Cr₂O₇^2- + 8H⁺ à 2Cr⁺³ + 3NO^3- + 4H₂O

• N of NO^2- is reduced, Cr of Cr₂O₇^2- is oxidized

• N of NO^2- oxidized, Cr of Cr₂O₇^2- is reduced

• O of NO^2- oxidized, Cr of Cr₂O₇^2- is reduced

• Cr⁺³ is reduced, N of NO²- is oxidized

In the laboratory, a student measured the pH of a 0.599 M aqueous solution of ethylamine, C₂H₅NH₂ (a weak base), to be 12.192. Use the information she obtained to determine the K_b for this base.

• 2.41 x 10^-11

• 10^-1.88

• 4.15 x 10^-4

• 1.56 x 10^-2

When a weak acid is titrated with a strong base, the pH at the equivalence point is ALWAYS

• 7

• <7

• >7

• <1

1. Which of the following aqueous solutions are good buffer systems?

I. 0.20 M calcium hydroxide + 0.20 M calcium chloride

II. 0.35 M ammonia + 0.32 M ammonium nitrate

III. 0.10 M hypochlorous acid + 0.14 M hydrobromic acid

IV. 0.33 M barium iodide + 0.27 M sodium iodide

V. 0.29 M hydrochloric acid + 0.19 M sodium chloride

• II III, and IV

• II and V

• II

• all are good buffers