Question

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day - sem 1 - toronto dsb
question 8 (1 point)
which of the following statements is correct?
\\(\mathrm{ch}_3\mathrm{coo}^- (aq)\\) is a stronger conjugate base of weak acid \\(\mathrm{ch}_3\mathrm{cooh}(aq)\\)
\\(\mathrm{ch}_3\mathrm{coo}^- (aq)\\) is a weaker conjugate base of weak acid \\(\mathrm{ch}_3\mathrm{cooh} (aq)\\)
\\(\mathrm{ch}_3\mathrm{coo}^- (aq)\\) is a stronger conjugate base of strong acid \\(\mathrm{ch}_3\mathrm{cooh}(aq)\\)
\\(\mathrm{ch}_3\mathrm{coo}^- (aq)\\) is a weaker conjugate base of strong acid \\(\mathrm{ch}_3\mathrm{cooh}(aq)\\)
\\(\mathrm{ch}_3\mathrm{coo}^- (aq)\\) is a stronger conjugate base of weak base \\(\mathrm{ch}_3\mathrm{cooh}(aq)\\)
question 9 (1 point)
in which of the following reactions does \\(\mathrm{nh}_3\\) act as bronsted acid?
\\(\mathrm{nh}_3(aq) + \mathrm{hcl} (aq) \
ightarrow \mathrm{nh}_4\mathrm{cl} (aq)\\)
\\(\mathrm{nh}_3 (aq) + \mathrm{h}^+ (aq) \
ightarrow \mathrm{nh}_4^+ (aq)\\)
\\(\mathrm{nh}_3 (aq) + \mathrm{na} (s) \
ightarrow \mathrm{nanh}_2 (aq) + \frac{1}{2}\mathrm{h}_2 (g)\\)
\\(\mathrm{nh}_3 (aq) + \mathrm{h}_2\mathrm{o} (l) \
ightarrow \mathrm{nh}_4^+ (aq) + \mathrm{oh}^- (aq\\)
\\(\mathrm{nh}_3(g)\\) can never act as acid.
question 10 (1 point)
use the following information to answer the next question.

Explanation:

Question 8

To determine the correct statement, we recall the relationship between acids and their conjugate bases: the weaker the acid, the stronger its conjugate base. $\ce{CH3COOH(aq)}$ (acetic acid) is a weak acid (it does not dissociate completely in solution). The conjugate base of $\ce{CH3COOH}$ is $\ce{CH3COO^-}$. Since $\ce{CH3COOH}$ is weak, its conjugate base $\ce{CH3COO^-}$ should be a stronger conjugate base (compared to the conjugate base of a strong acid, which would be weak). Let's analyze each option:

• Option 1: States $\ce{CH3COO^-(aq)}$ is a stronger conjugate base of weak acid $\ce{CH3COOH(aq)}$. This matches the acid - conjugate base relationship (weak acid $\implies$ stronger conjugate base).
• Option 2: Claims it is a weaker conjugate base, which is incorrect as weak acids have stronger conjugate bases.
• Option 3: Says $\ce{CH3COOH}$ is a strong acid, but $\ce{CH3COOH}$ is weak, so this is wrong.
• Option 4: Incorrectly classifies $\ce{CH3COOH}$ as a strong acid and also claims the conjugate base is weaker, which is double - wrong.
• Option 5: $\ce{CH3COOH}$ is an acid, not a base, so this is incorrect.

A Brønsted acid is a substance that donates a proton ($\ce{H^+}$). Let's analyze each reaction:

• Option 1: $\ce{NH3(aq) + HCl(aq) -> NH4Cl(aq)}$. In this reaction, $\ce{NH3}$ accepts a proton from $\ce{HCl}$ ( $\ce{HCl}$ donates $\ce{H^+}$ to $\ce{NH3}$ to form $\ce{NH4^+}$), so $\ce{NH3}$ acts as a Brønsted base here.
• Option 2: $\ce{NH3(aq) + H^+(aq) -> NH4^+(aq)}$. $\ce{NH3}$ accepts a proton, so it is acting as a Brønsted base.
• Option 3: $\ce{NH3(aq) + Na(s) -> NaNH2(aq) + \frac{1}{2}H2(g)}$. In this reaction, $\ce{NH3}$ donates a proton ( $\ce{H^+}$) to $\ce{Na}$. The reaction can be thought of as $\ce{NH3 + Na -> NaNH2 + \frac{1}{2}H2}$, where $\ce{NH3}$ loses a proton (the $\ce{H^+}$ combines with $\ce{Na}$ - related species to form $\ce{H2}$). So here, $\ce{NH3}$ is donating a proton, which means it is acting as a Brønsted acid.
• Option 4: $\ce{NH3(aq) + H2O(l) -> NH4^+(aq) + OH^-(aq)}$. $\ce{NH3}$ accepts a proton from $\ce{H2O}$ ( $\ce{H2O}$ donates $\ce{H^+}$ to $\ce{NH3}$ to form $\ce{NH4^+}$), so $\ce{NH3}$ acts as a Brønsted base.
• Option 5: Claims $\ce{NH3}$ can never act as an acid, but from option 3, we see it can donate a proton, so this is incorrect.

Answer:

1. $\boldsymbol{\ce{CH3COO^-(aq)}}$ is a stronger conjugate base of weak acid $\ce{CH3COOH(aq)}$

Question 9