TBR Chemistry I Passage IV Question 22?

[dartmed]

The questions states 1 gram of which of the above acids required exactly 30.0 mL of 0.20 M NaOH to reach equivalence?

Without looking at the options, this was what was going to going through my head- because all of the acids are weak, I would need twice as many number of moles of the weak acid than whatever the moles of strong base that I have. I have 0.006 moles of strong base (30.0mL/1000mL * 0.20 M = 0.006), so I would need 0.012 moles of weak acid in order for pH = pKa. However, none of the options have this as the option.

A. Acetic acid, MW = 60
B. Trichloroacetic acid, MW = 151.5
C. p-nitro benzoic acid, MW = 167
D. Benzoic acid MW = 122

---

Members don't see this ad.

 

[TieuBachHo]

The questions states 1 gram of which of the above acids required exactly 30.0 mL of 0.20 M NaOH to reach equivalence?

Without looking at the options, this was what was going to going through my head- because all of the acids are weak, I would need twice as many number of moles of the weak acid than whatever the moles of strong base that I have. I have 0.006 moles of strong base (30.0mL/1000mL * 0.20 M = 0.006), so I would need 0.012 moles of weak acid in order for pH = pKa. However, none of the options have this as the option.

A. Acetic acid, MW = 60
B. Trichloroacetic acid, MW = 151.5
C. p-nitro benzoic acid, MW = 167
D. Benzoic acid MW = 122

I don't have TBR book but I think you confuse equivalent point to neutrality. If it's a monoprotic acid, then it's 1:1 ratio.

 

[LoLCareerGoals]

The questions states 1 gram of which of the above acids required exactly 30.0 mL of 0.20 M NaOH to reach equivalence?

Without looking at the options, this was what was going to going through my head- because all of the acids are weak, I would need twice as many number of moles of the weak acid than whatever the moles of strong base that I have. I have 0.006 moles of strong base (30.0mL/1000mL * 0.20 M = 0.006), so I would need 0.012 moles of weak acid in order for pH = pKa. However, none of the options have this as the option.

A. Acetic acid, MW = 60
B. Trichloroacetic acid, MW = 151.5
C. p-nitro benzoic acid, MW = 167
D. Benzoic acid MW = 122

Huh? Why twice? I mean you treat weak and strong as if they were some discrete binary quantities. You do realize acid strength is a continuous quantity and where we draw the strong vs weak boundary is not set in stone.

Now on to the molage required to neutralize an acid:
As the poster above mentioned # of protons is what matter whether you need to multiply anything by a factor of 2 or 3. Example:
A: HC2H3O2 + NaOH -> NaC2H3O2 + H20 (all coeffs 1s), but 1/60 = 0.016 moles!=0.006

I have no idea what other acids look like, but I would assume they are all monoprotic.
Given that C is the answer.