What is the identity of the two species in each set (strong acid/strong base/wea

Question

What is the identity of the two species in each set (strong acid/strong base/weak acid/weak base/salt/other) and explain your reasoning. Identify if there is anything in common between the two species in each set and underline that portion. How do you think the two species in each set are related to each other? Justify your answer. If there is a weak acid or a weak base present (NOT a significant conjugate acid or a significant conjugate base) ? If there is write out the equation relating the two species in each set. If applicable, label the species your equation as a weak acid and its conjugate base or a weak base and its conjugate acid. Determine the Ka for the acid species (if you are dealing with a weak base how could you possible find a ka for the acid species in the equation?) Could this mixture possible be a buffer? why? a) benzoic acid, HC_7H_5O_2 and potassium benzoate, KC_7H_5O_2 Ethylamine, C_5H_5NH_2 and ammonium chloride, NH_4CL

Explanation / Answer

a)Benzoic acid C6H5COOH potassium benzoate C6H5COOK

1)

Benzoic acid - weak acid (It is a weak acid and so only slightly dissociated in aqueous solution. Benzoic acid has a Ka value of 6.4 x 10^–5)

Potassium benzoate – salt (It is the potassium salt of benzoic acid

C6H5COOH + NaOH = C6H5COONa + H2O)

2) Both have common C6H5COO^-

3) One species is acid and other is its salt.

4) C6H5COOH (aq) <=> C6H5COO- (aq) + H+ (aq)

C6H5COOH+NaOH<-------> C6H5COONa + H2O

5) Conjugate Acid = H+

Conjugate base C6H5COO-

and

Conjugate Acid= H20

Conjugate base=C6H5COONa

6) For a conjugate acid-base pair

Ka × Kb = Kw

If Ka is the larger, the Kb is smaller. That is, the stronger the acid, the weaker the conjugate base.

7) Benzoic acid potassium benzoate is buffer, because solution contains substantial amounts of a compound in both its protonated and deprotonated forms. If we wanted to make a buffer with a pH around 3.2, we would then like a compound with a pKa near this value. Benzoic acid has a pKa of 3.18 so this would be a good choice.

a) Ethylamine C2H5NH2 Ammonium chloride NH4Cl

1) This equation shows that ethylamine is a weak base.

Ammonium chloride is a salt

2) Nothing common

3) One species is base and other is its salt.

4) C2H5NH 2(l) + H2O (l) <--->C2H5NH3+(aq) + OH-(aq)

NH4Cl(s) + H2O(l) = [NH4]+(aq) + [Cl]-(aq)

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