HC2H3O2 + NaOH --> NaC2H3O2 + H2O?
a. when the titration is only half over, what species are present in the reaction flask
b. what can be said about the pH at this point when the titration is half over?
c. what is the pH at the equivalence point of this titration? 7, >7, <7
where are the answers?!?!
a. When the titration is only half over, there will be a mixture of reactants and products present in the reaction flask. Specifically, there will be HC2H3O2 (acetic acid) and NaOH (sodium hydroxide) still remaining, as well as some amount of the product NaC2H3O2 (sodium acetate) and H2O (water) that has been formed.
b. At this point, when the titration is half over, the pH of the solution can be determined based on the properties of acetic acid and its conjugate base (acetate ion). Acetic acid is a weak acid and its conjugate base acetate ion is a weak base. In the presence of a strong base like NaOH, the acetic acid will be partially neutralized, leading to the production of acetate ion.
Since acetate ion is a weak base, it will react with water to form a small amount of hydroxide ions (OH-) and shift the equilibrium slightly to the right. This will result in a slight increase in the pH of the solution but it will still be slightly acidic, as acetic acid is a weak acid. Therefore, the pH at this point when the titration is half over will be slightly above 7, but still acidic.
c. The equivalence point of the titration is reached when the moles of acid (HC2H3O2) and base (NaOH) are present in a 1:1 ratio. At this point, all of the acid has been completely neutralized by the base, and the resulting solution contains only the salt, NaC2H3O2, and water (H2O).
NaC2H3O2, being the salt of a weak acid (acetic acid), will hydrolyze in water to produce acetate ions (C2H3O2-) and hydroxide ions (OH-), which makes the resulting solution slightly basic. Therefore, the pH at the equivalence point of this titration will be greater than 7, indicating a basic solution.
To answer these questions, we need to understand the process of titration and the reaction between acetic acid (HC2H3O2) and sodium hydroxide (NaOH).
a. When the titration is only half over, we can assume that half of the acetic acid has reacted with the sodium hydroxide. At this point, there will be a mixture of acetic acid (HC2H3O2) and its conjugate base acetate ion (C2H3O2-) present in the reaction flask. Additionally, there will be some unreacted acetic acid and sodium hydroxide remaining.
b. The pH at this point when the titration is half over can be determined by the presence of the conjugate acid-base pair in the solution. Acetic acid is a weak acid, and its conjugate base, acetate ion, is a weak base. During the titration, when half of the acetic acid reacts with sodium hydroxide, we have a buffer system consisting of both the weak acid and its conjugate base.
A buffer solution resists changes in pH when small amounts of strong acid or base are added. In this case, since acetic acid and acetate ion constitute a buffer system, the pH will remain relatively constant. The pH will be close to the pKa of acetic acid, which is around 4.75. Therefore, at this point, the pH will be approximately 4.75.
c. The equivalence point of a titration occurs when the moles of the acid and base are in a 1:1 ratio. In this reaction, acetic acid and sodium hydroxide react in a 1:1 ratio. At the equivalence point, all the acetic acid has reacted with sodium hydroxide to form sodium acetate and water.
Since sodium acetate is a salt of a weak acid (acetic acid) and a strong base (sodium hydroxide), when it dissolves in water, it hydrolyzes to produce hydroxide ions (OH-) and acetate ions (C2H3O2-). This hydrolysis reaction makes the solution basic. Therefore, at the equivalence point, the pH will be greater than 7, indicating a basic solution.
a. When half over, you have some HC2H3O2 not yet titrated, you have some extra water produced, some NaC2H3O2 (the sodium acetate salt) produced (present as Na^+ and C2H3O2^-).
b. When half over, the pH = pKa
c. The pH at the equivalence point is determined by the salt present; i.e., one has only water and the salt at that point. The pH of NaC2H3O2 (the salt of a strong base and a weak acid) is basic so the pH is >7 (about 8.5 or so).