Determine whether the mixing of each pair of solutions...

Determine whether the mixing of each pair of solutions results in a buffer. a. 100.0 $\mathrm{mL}$ of $0.10 \mathrm{M} \mathrm{NH}_{3} ; 100.0 \mathrm{mL}$ of 0.15 $\mathrm{M} \mathrm{NH}_{4} \mathrm{Cl}$ b. 50.0 $\mathrm{mL}$ of $0.10 \mathrm{M} \mathrm{HCl} ; 35.0 \mathrm{mL}$ of 0.150 $\mathrm{M} \mathrm{NaOH}$ c. 50.0 $\mathrm{mL}$ of $0.15 \mathrm{M} \mathrm{HF} ; 20.0 \mathrm{mL}$ of 0.15 $\mathrm{MNaOH}$ d. 175.0 $\mathrm{mL}$ of $0.10 \mathrm{M} \mathrm{N} \mathrm{N}_{3} ; 150.0 \mathrm{mL}$ of 0.12 $\mathrm{MNaOH}$ e. 125.0 $\mathrm{mL}$ of $0.15 \mathrm{M} \mathrm{NH}_{3} ; 150.0 \mathrm{mL}$ of 0.20 $\mathrm{M} \mathrm{NaOH}$

Determine whether the mixing of each pair of solutions results in a buffer.
a. 100.0 $\mathrm{mL}$ of $0.10 \mathrm{M} \mathrm{NH}_{3} ; 100.0 \mathrm{mL}$ of 0.15 $\mathrm{M} \mathrm{NH}_{4} \mathrm{Cl}$
b. 50.0 $\mathrm{mL}$ of $0.10 \mathrm{M} \mathrm{HCl} ; 35.0 \mathrm{mL}$ of 0.150 $\mathrm{M} \mathrm{NaOH}$
c. 50.0 $\mathrm{mL}$ of $0.15 \mathrm{M} \mathrm{HF} ; 20.0 \mathrm{mL}$ of 0.15 $\mathrm{MNaOH}$
d. 175.0 $\mathrm{mL}$ of $0.10 \mathrm{M} \mathrm{N} \mathrm{N}_{3} ; 150.0 \mathrm{mL}$ of 0.12 $\mathrm{MNaOH}$
e. 125.0 $\mathrm{mL}$ of $0.15 \mathrm{M} \mathrm{NH}_{3} ; 150.0 \mathrm{mL}$ of 0.20 $\mathrm{M} \mathrm{NaOH}$

Key Concepts

Role of Strong vs. Weak Acids/Bases

The nature of the acids and bases involved (whether they are strong or weak) determines the outcome of mixing them. A strong acid or base will completely dissociate and react, while a weak acid or base only partially dissociates. This difference is critical when forming buffers since an ideal buffer requires the presence of a weak acid/base and its conjugate, not an overwhelming amount of strong acid or base.

Neutralization Reactions

Neutralization reactions involve the reaction of acids and bases to form water and a salt, often converting a weak acid to its conjugate base or a weak base to its conjugate acid. Understanding the extent of these reactions is crucial in determining if enough of the conjugate pair remains to produce a buffer system.

Acid-Base Reaction Stoichiometry

Stoichiometry in acid-base reactions is used to calculate the number of moles of acids and bases present and to predict the outcome of mixing them. By determining the limiting reactant and the extent of neutralization, one can assess whether the remaining species constitute a conjugate acid-base pair necessary for a buffer.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs consist of a weak acid and its corresponding conjugate base, or a weak base and its conjugate acid. In a buffer, this pair coexists in solution and reacts with added acids or bases to minimize changes in pH by neutralizing added protons or hydroxide ions.

Buffer Solutions

A buffer solution is a mixture that resists changes in pH when small amounts of acid or base are added. It typically contains appreciable amounts of a weak acid and its conjugate base or a weak base and its conjugate acid. Buffers are crucial in many chemical and biological systems, allowing them to maintain a stable pH under various conditions.

Transcript

00:01 This question is asking us whether or not, that is we are trying to predict whether a buffer solution is going to form.

00:10 And for us to answer this question, we have to first of all define what a buffer is.

00:14 So when we are looking at a buffer, we are saying this is a solution that resists, that resists ph change when small amounts of acid or base is added.

00:26 So what results in this resistance in change in ph is the existence of, an acid and conjugate base or a weak base and its conjugate acid and remember what is important here is the word small we are saying a buffer solution is a solution that resists p exchange when small amounts of acids and base are in are added into that it's not just any amount of acid or base, but a small amount of base, because there is a certain ph range that must be maintained that can be handled by a buffer solution.

01:16 And for a buffer solution to be called a buffer or to be able to buffer, the concentrations of the base and the acid must not be greater than by a factor of 10.

01:28 So as long as, number one, these are met and the concentrations of the acid and the base are not.

01:35 Not greater than the factor of 10 a buffer solution can handle its purpose of being a buffer.

01:46 So we just look at what we've been given and see if these conditions are met.

01:51 So if we look at the first one, we've been given nh3, we've been given nh3 and we've been given nh4 plus.

02:02 So if we look at this already we've met this part where we've got a weak base and a conjugate asset...

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