1) pyridine is a weak base that is used in the manufacture of pesticides and plastic resins. it is also a component of cigarette smoke. pyridine ionizes in water as follows: c5h5n+h2o< -> c5h5nh++oh? the pkb of pyridine is 8.75. what is the ph of a 0.305m solution of pyridine? express the ph numerically to two decimal places. benzoic acid is a weak acid that has antimicrobial properties. its sodium salt, sodium benzoate, is a preservative found in foods, medications, and personal hygiene products. benzoic acid ionizes in water: c6h5cooh< -> c6h5coo? +h+2) the pka of this reaction is 4.2. in a 0.66m solution of benzoic acid, what percentage of the molecules are ionized? express your answer to two significant figures and include the appropriate units.
3 )ammonia, nh3, is a weak base with a kb value of 1.8

1) pH = 9.37

2) α = 0.97%

Explanation:

1) Pyridine is a weak base that ionizes in water as follows:

C₅H₅N(aq) + H₂O(l) ⇄ C₅H₅NH⁺(aq) + OH⁻(aq)

Since pKb is 8.75, we can find the equilibrium constant Kb using the following expression:

pKb = -log Kb

Kb = antilog (-pKb) = antilog (-8.75) = 1.78 × 10⁻⁹

If we know Kb and the initial concentration of the base (Cb) we can find [OH⁻] using the following expression:

[OH⁻] = √(Kb × Cb)

[OH⁻] = √(1.78 × 10⁻⁹ × 0.305) = 2.33 × 10⁻⁵ M

Then, we can find pOH and pH.

pOH = -log [OH⁻]

pOH = -log (2.33 × 10⁻⁵) = 4.63

pH + pOH = 14

pH = 14 - pOH = 14 - 4.63 = 9.37

2) Benzoic acid is a weak acid that ionizes in water as follows:

C₆H₅COOH(aq) ⇄ C₆H₅COO⁻(aq) + H⁺(aq)

Since pKa is 4.2, we can find the equilibrium constant Ka using the following expression:

pKa = -log Ka

Ka = antilog (-pKa) = antilog (-4.2) = 6.3 × 10⁻⁵

If we know Ka and the initial concentration of the acid (Ca) we can find [H⁺] and [C₆H₅COO⁻] using the following expression:

[H⁺] = [C₆H₅COO⁻] = √(Ka × Ca)

[H⁺] = [C₆H₅COO⁻] = √(6.3 × 10⁻⁵ × 0.66) = 6.4 × 10⁻³ M

The percentage of ionized molecules (α) is:

the answer is b because, investigating whether another species of moth also drinks tears might be interesting, but it would not directly explain why this species of moth does.

to explain why this species of moth drinks tears, the scientist could ask: "what nutrients that moths need are in elephant tears? "

the scientist could experiment with moth repellent or oter ways to keep the moths away, but that would not answer his original question.