Consider the titration of 100.0 mL of a solution that contains a mixture of 0.050 M H2 SO4 and 0

Consider the titration of 100.0 mL of a solution that...

Key Concepts

Acid-Base Titration

Acid-base titration is an analytical technique in which a solution of known concentration (titrant) is slowly added to a solution containing an analyte to determine its concentration. This process relies on the neutralization reaction between acids and bases, and by tracking the pH change, one can determine key points such as the equivalence point, where stoichiometric amounts of acid and base have reacted.

Stoichiometry in Neutralization Reactions

Stoichiometry in neutralization reactions involves calculating the moles of acid and base involved in the reaction to determine how far the reaction has proceeded at any stage of a titration. This is critical for understanding when an analyte is fully neutralized, remains in excess, or when there is leftover titrant, all of which directly influence the pH of the solution.

Polyprotic Acid Behavior

Polyprotic acids are capable of donating more than one proton, often in a stepwise manner with each proton having its own dissociation constant. This behavior complicates titration curves because each deprotonation event can result in distinct equivalence points and alter the overall acid-base reaction stoichiometry.

pH Calculation in Titrations

Calculating the pH during a titration requires assessing the concentration of hydrogen ions or hydroxide ions at different stages of the titration. This involves understanding the contributions from strong and weak acids (or bases), using equilibrium expressions where necessary, and correctly applying relationships such as pH = -log[H+], while also considering water's autoionization in extreme conditions.

Buffer Formation

Buffer formation occurs when a weak acid and its conjugate base (or a weak base and its conjugate acid) are present in appreciable amounts, resulting in a solution that resists drastic changes in pH upon the addition of small amounts of strong acid or base. This phenomenon is particularly important in titrations, as it can create a buffer region that affects the pH transition around the half-equivalence point.

Transcript

00:01 In answering this question, before we actually add any sodium hydroxide into our acetic acid, remember the ph is equal to negative log, the concentration of hydrogen ions.

00:15 Now for the first part of the question, remember, we are looking at acetic acid dissolving into solution to produce ch3c0 the conjugate base plus h3 h3o plus ions.

00:33 The ka is equal to the concentration of h3 plus ions divided by the concentration of ch3 c0 or h.

00:43 He will multiply by ch3 c0 the conjugate base and this should give us 1 .8 by 10 to or negative 5.

00:53 Now we've got initial concentrations.

00:57 Let's just isolate this.

00:58 We've got initial concentration, which is 0 .202.

01:04 We've got 0 here and we've got 0 here before it starts dissociating.

01:11 And then as for the change, if this decreases by x, it means the conjugate base will increase by x and this will also increase by x since they are in the ratio of 1 is to 1.

01:23 What this means is at equilibrium we've got 0 .202 minus x we've got x and we've got x.

01:31 Now if we substitute into the k a expression what we are saying is x multiplied by x divided by 0 .202 minus x should give us 1 .8 by 10 to the 0 .5.

01:43 And if we solve for x we've got x being equal to 1 .907 by 10 to 0 .907 by 10 to 0 .2 negative 3 and this is equal to the of h plus ions.

01:56 So the ph is going to be negative log 1 .907 by 10 to the power negative 3, which gives us a ph of 2 .72.

02:05 And then we start adding sodium hydroxide.

02:09 So for us to do this, we need these concentrations right here, the initial, the change and the equilibrium.

02:16 So what we need to do is to convert these concentrations into the concentrations when we mix these two.

02:24 So the number of more, remember, concentration equal to number of moles divided by the volume.

02:31 Now, the new volume here, it is not the original volume, but it is going to be the total volume of the acid plus the base.

02:40 So we are saying the total volume is going to be 0 .04 liters plus 0 .055 liters, which gives us a total of 0 .0595.

02:52 So we now need to determine the concentration of the acid and the concentration of the sodium hydroxide, the initial concentrations.

03:01 And we do this, the volume is 0 .059.

03:06 So to determine the number of moles, remember, number of moles is equal to volume by concentration...

Please give Ace some feedback