Since there is now more strong base than weak acid in the solution, the remaining amount of strong base alone will dictate the pH.

By converting concentration to moles, we can determine that we started with 0.01 moles of weak acid.

Using the same equation, we can determine that 0.012 moles of base was added.

After neutralization, that leaves us with 0.002 moles of strong base. This strong base is the only value we will use to determine the pH. Since the final volume is 110mL, the concentration of remaining sodium hydroxide is calculated as

Finally, we can solve for the pH by first finding the pOH, then subtracting from 14.

A generic acid-base reaction involves the production of salt and water. The amount of products depends on the strength of the reactants. Recall that a strong acid completely dissociates into hydrogen ions and conjugate base in water. Similarly, a strong base completely dissociates into conjugate acid and hydroxide ions in water. A salt (like ) is formed from the conjugate base ( from ) and conjugate acid ( from ); therefore, to get the highest yield of salt we need complete dissociation of acid and base into their respective conjugates. Since they completely dissociate and form conjugates, strong acid and strong base will yield the highest concentration of salt (in this question solution A).

Solution B will also form salt; however, since acetic acid is a weak acid only few molecules of conjugate base (acetate) will be produced, thereby decreasing the amount of salt produced.

The pH is a measure of the concentration of hydrogen ions in solution. An increase in pH corresponds to lower hydrogen ion concentration whereas a decrease in pH corresponds to higher hydrogen ion concentration. Recall that a strong base dissociates completely into conjugate acid and hydroxide ions whereas a weak acid doesn’t dissociate completely into conjugate base and hydrogen ions. Since there is an excess of hydroxide ions in a weak acid/strong base solution, the hydroxide ions will react with and consume the hydrogen ions from weak acid. This will decrease the hydrogen ion concentration and, subsequently, increase the pH. On the other hand, a weak base doesn’t produce as many hydroxide ions; therefore, not as much hydrogen ions will be consumed (pH will be decreased).   

The pKa is a measure of the strength of an acid. The lower the pKa the stronger the acid. The extent of dissociation of acid into hydrogen ions and conjugate base depends on the strength; therefore, pKa determines how much hydrogen ion will be produced.

A strong acid and strong base will completely dissociate into their respective conjugates. This means that if equal amounts of strong acid and strong base are added, equal amounts of hydrogen ions and hydroxide ions are produced. Since there are equal amounts of them, hydrogen ions and hydroxide ions will react with each other and form water. Recall that water has a pH of 7; therefore, a strong acid/strong base solution will always have a pH of 7 (if equal amounts of strong acid and strong base are added). The definition of pH is:

If we solve for hydrogen ion concentration:

Therefore, the hydrogen ion concentration in a strong acid/strong base solution is:

The relationship between hydrogen ion concentration and hydroxide ion concentration is:

If we solve for :

The buffer region occurs when the pH of the solution equals the pKa of the acid. This means that the pKa of the acid is 4; therefore, this acid is a weak acid. Recall that buffer regions occur during titration when a weak component (acid or base) is added to a strong component (acid or base). For example, buffer regions can be seen when a weak acid is added to a strong base. Since we already determined that the acid is weak, the other component in the solution must be a strong base. Note that titration with two strong agents (strong acid and strong base) does not produce a buffer region.

Equivalence point is the point at which the amount of acid or base added is equal to the amount of its counterpart. In a strong acid-strong base titration, the equivalence point occurs when the pH is equal to 7. In a weak acid-strong base titration, the equivalence point occurs at a higher pH. This is because at equivalence point all of weak acid is converted to conjugate base, increasing the concentration of hydroxide ions. Endpoint is the end of titration. This typically occurs at the equivalence point; therefore, strong acid-strong base titration has a lower pH at endpoint.

Reduction reactions are characterized by a gain of electrons whereas oxidation reactions are characterized by a loss of electrons. Recall that elements on the right side of the periodic table have the tendency to gain electrons to complete the octet. Groups such as chalcogens (group VI) and halogens (group VII) have six and seven valence electrons, respectively; therefore, they only need a few electrons to have eight valence electrons and complete the octet. Since halogens tend to gain electrons, they typically undergo reduction.

Alkaline earth metals (group II) and transition metals have few valence electrons; therefore, they tend to lose electrons and undergo oxidation. Noble gases are nonreactive elements and do not undergo reduction or oxidation.

For this problem, we need to figure out the oxidation states of manganese in each compound. Oxygen typically has an oxidation number of  and potassium has an oxidation number of . For Compound A, there are two oxygen molecules; therefore, oxygen contributes a total charge of . Since manganese dioxide is a neutral molecule, the manganese in it will have an oxidation number of . For Compound B, four oxygen atoms contribute a charge of  whereas one potassium atom contributes a charge of ; therefore, the manganese in potassium permanganate will have an oxidation number of . Conversion of manganese from Compound A to manganese in Compound B involves the removal of electrons—three electrons, specifically, because its charge has to change from  to ; therefore, this reaction is characterized as an oxidation reaction.

A reaction that has both reduction and oxidation half reaction is called a redox reaction. It involves one or more atoms gaining electrons (reduction) and one or more atoms losing electrons (oxidation). Recall that single displacement reactions involve the replacement of an element in a compound with another element. An example of single replacement reaction is shown below:

In this reaction, a sodium atom replaces a calcium atom in calcium sulfate. If we calculate the oxidation numbers for sodium and calcium, we can see that sodium loses an electron (the oxidation state goes from  to ) whereas the calcium ion gains two electrons (goes from  to ); therefore, this is a redox reaction. All single displacement reactions follow this general trend and are characterized as redox reactions.

Reaction of sodium chloride and calcium sulfate is as follows:

If we calculate the oxidation state of each atom we will notice that oxidation number doesn’t change; therefore, this isn’t a redox reaction.

Oxidation involves a loss of electrons whereas reduction involves a gain of electrons. This means that oxidation generates electrons as products whereas reduction consumes electrons as reactants. Note that oxidation and reduction reactions can be distinguished by looking at oxidation states. If the oxidation state of an atom becomes more positive, then it underwent an oxidation reaction, and if the oxidation state becomes more negative, then that atom underwent a reduction reaction.

An electrolytic cell utilizes energy to facilitate a nonspontaneous redox reaction. This is different from a galvanic cell, which releases energy from a spontaneous redox reaction. A shared characteristic of both cells is that the oxidation half-reaction always happens at the anode and the reduction half-reaction always happens at the cathode. Note that a redox reaction always has an oxidation half-reaction and a reduction half-reaction.

The entropy of the reaction is typically negative for a nonspontaneous reaction. This is not true for all cases; therefore, the entropy could be positive or negative for an electrolytic cell. Electroplating involves reduction reactions that convert metal ions into solid metal. This solid metal is coated onto a metal plate. Since this involves a reduction reaction, it occurs at the cathode.