Chapter 10: Acids and Bases Flashcards by Dwight Faszer

What is the Arrhenius definition of an acid or base? Is water considered an Arrhenius acid?

The most specific of the definitions, and thus more restrictive, the Arrhenius definition describes acids will dissociate to form an excess H+ in solution, and a base will dissociate OH- into solution. These definitions are generally limited to aqueous acids and bases.

Water is not considered an Arrhenius acid as it does not donate an excess of H+ to solution, but is considered an Bronsted-Lowry because it will donate H+ to other species.

Easily identified:

HCL, HNO3, H2SO4 are all Arrhenius acids by definition as they contribute H+ to solution.

NaOH, Ca(OH)2, and Fe(OH)3 are all Arrhenius bases by definition as the contribute OH- to solution.

How well did you know this?

Not at all

Perfectly

What is a Bronsted-Lowry acid or base? Is water considered a Bronsted-Lowry acid?

Side note: most acid base chemistry reactions on the MCAT will involve transfer of H+ ions in accordance with the Bronsted-Lowry definition.

Bronsted-Lowry acids and bases are a more inclusive definition of acids and bases where Bronsted-Lowry acids donates H+ ions, while Bronsted-Lowry bases is any species that accepts the H+ ions.

Water is considered a Bronsted-Lowry acid because it will donate H+ to other species.

Every Arrhenius acid or base can also be classified as a Bronsted-Lowry acid or base, every Bronsted-Lowry acid can be classified as an Arrhenius acid, but some Bronsted-Lowry bases (such as NH3) are not considered Arrhenius bases (because NH3 does not contribute OH- to solution, but will accept H+ in solution).

Examples OH-, F-, and NH3 are all Bronsted-Lowry bases but not Arrhenius bases (as they do not contribute OH- to solution).

How well did you know this?

Not at all

Perfectly

Why do Bronsted-Lowry acids and bases always occur in pairs? What are conjugate base pairs? Example?

Bronsted-Lowry acids and bases always occur in pairs because the definitions require the transfer of a proton from the acid to the base. Known as CONJUGATE BASE PAIRS.

For example, in the authorization of water, H30+ is the dominate acid and OH- is the citrate base like the image:

How well did you know this?

Not at all

Perfectly

What is a Lewis definition of acid and base? How does the Lewis definition of acids and bases differ from the Bronsted-Lowry definition of acids and bases?

A Lewis acid is an electron pair acceptor, a Lewis base is an electron pair donor.

Lewis acid and base focus on the electron forming coordinate covalent bonds whereas the Bronsted-Lowry definition follow the exchange of protons (H+).

How well did you know this?

Not at all

Perfectly

What is the most inclusive definition of acids and bases? Briefly describe the three and why that is. In what study might you find this most inclusive definition applied.

Lewis acid base definition is the most inclusive. Every Arrhenius acid is also a Bronsted-Lowry acid is also a Lewis acid (and likewise for bases). This is not always true for the converse.

For example, BF3 and AlCl3 are species that can each accept an electron pair, which qualifies them as a Lewis acid, but they lack H+ ions to donate, disqualifying them as Bronsted-Lowry or Arrhenius acids.

You may encounter Lewis acids in the context of organic chemistry reactions because Lewis acids are often used as catalysts.

How well did you know this?

Not at all

Perfectly

What are amphoteric species? What is amphiprotic? What is a good example of an amphoteric species?

An amphoteric species is one that reacts like an acid in a basic environment and acts like a base when in an acidic environment. (In a Bronsted-Lowry sense, an amphoteric species can either gain or lose a proton, making it amphiprotic)

Water is the most common example of an amphoteric species.

How well did you know this?

Not at all

Perfectly

Think of a partially dissociated conjugate base of a polyvalent acid. Is it amphoteric?

How about species that can act as oxidizing and reducing agents. Amphoteric?

How well did you know this?

Not at all

Perfectly

Recall what a zwitterion is. Are they considered amphoteric?

Zwitterions (aka dipolar ions) are a molecule with an equal number of positive and negative charges, resulting in a net charge of zero. The charges of most zwitterions depend on pH, so in some cases the compound may not be a zwitterion. For example, when amino acids are in a solution with a low pH, the amino group accepts a lot of H+ ions, making the molecule positively charged.

Yes they are considered amphoteric.

How well did you know this?

Not at all

Perfectly

Acid-Base Nomenclature. Recognize these and know these.

How well did you know this?

Not at all

Perfectly

Concept check 1.1 1 properties of acids and bases page 368

How well did you know this?

Not at all

Perfectly

Concept check chapter 1.1 2 properties of acids and bases page 369

How well did you know this?

Not at all

Perfectly

Concept check 1.1 3 properties of acids and bases page 369

How well did you know this?

Not at all

Perfectly

What is the chemical equation for the autoionization of water? Is water amphoteric? What are the name of the products of the autoionization of water?

How well did you know this?

Not at all

Perfectly

What is the water dissociation constant (Kw)? Can the water dissociation constant change? What causes this change? Talk about it a little bit.

How well did you know this?

Not at all

Perfectly

What happens to Kw when temperature increases? Why? What happens to Kw when pressure increases?

The water dissociation constant (Kw=10^-14) increases with increased temperature because autoionization of water is an endothermic process (absorbs heat).

Increasing pressure will have no effect on Kw. THE ONLY WAY TO CHANGE Kw IS BY CHANGING THE TEMPERATURE. The product of the respective concentrations of H+ and OH- will always be 10^-14 when the temperature of the solution is 298K.

How well did you know this?

Not at all

Perfectly

What happen when the an acidic species is introduced to pure water (regarding Le Chatelier’s principle)? Relate that to Kw.

If a species donates hydrogen ions to pure water, the H+ ion concentration will increase, causing the system to shift toward the reactants in the autoionization process. The result is a decrease in the OH- concentration and return to an equilibrium state. The shift away from the products necessarily decreases the OH- concentration (and increases H+ concentration) such that the product of the concentrations of dissolved ions equals Kw.

How well did you know this?

Not at all

Perfectly

What is a p scale? What are the logarithmic scale of pH and pOH? What are the equations for pH and pOH?

A p scale is defined as the negative logarithm of the number of items.

The pH and pOH scale are logarithmic scales for the concentration of hydrogen and hydroxide ions, respectively. The reactivity of an acidic solution is not a function of hydrogen ion concentration, but instead of the LOGARITHM OF THE HYDROGEN ION CONCENTRATION.

How well did you know this?

Not at all

Perfectly

What are the H+ and OH- concentrations at 298K for the following:

pH+pOH=14

This comes from log(xy)=logx+logy

How well did you know this?

Not at all

Perfectly

How can you get a relatively close approximation of a p scale value if the nonlogarithmic value is written in proper scientific notation n x 10^-m?

Example being if Ka of acid is 2.3x10^-5, what would be pKa?

How well did you know this?

Not at all

Perfectly

Example of logarithm approximation of scientific notation page 373. Also perform this calculation for Ka=6.3x10^-12, 8.9x10^-12, 2.1x10^-3, 4.6x10^-4.

How well did you know this?

Not at all

Perfectly

Example question page 373 calculating pH

How well did you know this?

Not at all

Perfectly

What is a strong acid or strong base? What is a good example of a strong base? Strong acid?

Strong acids or bases completely dissociate into their component ions in aqueous solutions.

An example of a strong base would be NaOH, strong acid would be HCl.

How well did you know this?

Not at all

Perfectly

What is the definition of a logarithm? What is the equation for what a logarithm is defined as.

What is log1?
log10?
log(10^-7)?

How well did you know this?

Not at all

Perfectly

What are some common strong acids and bases found on the MCAT? Why is it important to recognize a strong acid or base?

How well did you know this?

Not at all

Perfectly

Example pH of solution calculation page 374. What is that acid called? Is it a strong acid?

Why should we refer to the concentration of acids and bases as concentrated or dilute rather than strong or weak, respectively?

Strong and weak refer to the tendency for an acid or base to dissociate. Strong or weak acids or bases completely dissociate into aqueous solutions such that the 1 M of a strong acid or base will produce 1 M of its constituent ions (assuming 1N). It is more accurate to say concentrated or dilute when referring to the concentrations of solutes as we don’t want to get that mixed up with “strong or weak” in the dissociative sense.

What are weak acids and bases? What will be the equilibrium state of a weak monophonic acid, HA, dissolved in water (equation)?

Weak acids and bases only partially dissociate in aqueous solutions.

What is Ka? What is Kb? What are the equations for Ka and Kb? What does a small Ka mean? Large Ka? That does a small Kb mean? Large Kb? What number is generally accepted as the benchmark for weak acids and bases?

Ka is the acid dissociation constant. Kb is the base dissociation constant.

Describe conjugate acid base pairs. What is a conjugate acid, what is a conjugate base? Which kind of acid produces conjugate acid base pairs? What variety of base will a strong acid produce? What variety of base will a weak acid produce? Use carbonate to produce a chemical equation for a conjugate acid base pairing along with the Ka equation and Kb equation. Relate these two to Kw of water.

Relate Ka and Kb of the acid base reaction of HCO3- and water to Kw and how this is an important understanding for the fluctuations and calculations of Ka and Kb.

Relate the bicarbonate buffer system to what we are learning about conjugate acid base pairing.

Weak acid and bases tend to have weak conjugates.

What is the concept of induction regarding strength of acids? How does induction affect the strength of an acid? The book uses butyric acid (butanoic acid) as an example. Talk about that.

The effect of induction on acid strength of an acid is the understanding that the presence of an electronegative species on a molecule can impact the strength of an acid by pulling electron density out of the bond holding the acidic proton. This weakens proton bonding and facilitates dissociation. Thus, electronegative elements nearer to acidic hydrogens are stronger than those that do not.

What does a high Ka mean regarding strength of an acid? What does a high pKa mean regarding strength of an acid? Gotta know this well.

Example concentration of acid calculation page 377

What are the four combinations of strong and weak acids and bases? Page 379

A noteworthy standout here would be the combination of strong acid and weak base. No water will be produced because weak bases typically do not contain hydroxides and therefore won’t produce water. Might be handy to remember this.

Describe the neutralization reaction, or condensation reaction, of peptide bonds in proteins.

The peptide bonds of proteins are created from the reaction of a carboxyl group (acid) and in amino group (base), while forming a water molecule. The salt in this reaction is the polypeptide itself; breaking it apart, requires hydrolysis.

Concept check 10.2 page 380 properties of acids question 2

A high Ka indicates a strong acid and will completely dissociate in aqueous solution. A low Ka indicates a weak acid and will only minimally dissociate in aqueous solution.

Concept check 10.2 page 380 properties of acids question 3

High Kb indicates a strong base and it will dissociate complete in solution. Kb slightly greater than water means the base is weak and will only minimally dissociate in solution.

Concept check 10.2 page 381 properties of acids question 4

Concept check 10.2 page 381 properties of acids question 5

Concept check 10.2 page 381 properties of acids question 6

Concept check 10.2 page 381 properties of acids question 7

What is an acid equivalent? What is a base equivalent? What is polyvalence? What is polyprotic and what definition of an acid would be polyprotic? What’s a good example of a polyprotic acid?

An acid equivalent is equal to one mole of H+ (or more properly H3O+) ions. A base equivalent is equal to one mole of OH- ions. Some acids and bases are polyvalent, meaning each mole of the acid or base liberates more than one acid or base equivalent. Under Bronsted-Lowry definition of acid and base, such acids and bases could also be termed polyprotic. Sulfuric acid and phosphoric acids are good example of polyvalent (or polyprotic) acids.

The quantity of acidic or basic capacity is indicated by the solutions normality. Describe.

Normality is the amount of equivalents per liter (eq/L). A polyprotic acid has many equivalents per mole, meaning that its normality is greater than its molarity because it contributes more equivalents per liter.

Concept check 10.3 page 382 polyvalence and normality question 1

Acids: moles of H+ ions (H3O+ ions) Bases: moles of OH- ions

Concept check 10.3 page 382 polyvalence and normality question 2

What is titration? How are titrations done?

Titration is a procedure used to determine the concentration of an unknown reactant in a solution. There are different types including acid – base, oxidation – reduction, and complexometric. Titrations are performed by adding small volumes of a solution of known concentration (the titrant) to a known volume of a solution of unknown concentration (the titrand) until completion of the reaction is achieved at the equivalence point. Acid base and redox are frequently tested on the MCAT. Complexometric won’t be on the MCAT.

What is a tirtant and what is a titrand?

Tirtant is the solution of known concentration that is added to the titrand, the volume of a solution of unknown concentration.

When is equivalence point reached? What is the equation for calculating the unknown concentration of the titrand?

Equivalent point is reached when the number of acid equivalents present in the original solution equals the number of basic equivalents added, or vice versa. The equation for calculating the unknown concentration of a titrand is:

How do indicators change color? How do you select an ideal indicator?

Indicators change color due to small structural changes that leads to a change in the absorption spectrum of the molecule. The indicator must always be a weaker acid or base than the acid or base being treated otherwise the indicator will be titrated first. The at which the indicator changes to its final color is not the equivalent point but rather the endpoint. Any question involving the selection of an ideal indicator will require you to know what the pH of the reaction at the equivalent point will be, whether graphically or mathematically. Once you have determined where the equivalent point is, select the indicator that has the closest pKa value to it.

Describe the graph of a titration of a strong acid and a strong base.

Describe the graph of a weak acid and a strong base.

Describe the graph for a strong acid and weak base (weak base titand and strong acid titrant).

Describe the graph for a weak acid weak base titration curve.

What is the Henderson-Haasselbalch equation for a weak acid buffer solution, weak base buffer solution?

The Henderson-Haasselbalch equation is used to estimate the pH or pOH of a buffer solution.

Rearrange the acid dissociation constant to derive the Henderson-Haasselbalch equation.

What is buffering capacity? What happens to buffering capacity when the concentrations of the acid and conjugate base are increased proportionally (so that the reaction doesn’t change but the concentrations increase)?

Buffering capacity is the ability to which the system can resist changes in pH. The pH of the solution would not change with increasing the concentrations of the the acid and conjugate base, but the buffering capacity of the system will increase. Changing the ratio of acid to base will change the pH of the system.

Example pH and titration (Henderson-Haasselbalch and equivalents) page 391

Concept check general principles of acids and bases 10.4 page 392 question 1

Concept check general principles of acids and bases 10.4 page 392 question 2

Concept check general principles of acids and bases 10.4 page 392 question 3

What is the purpose of a buffer solution?

A buffer solution is designed to resist changes in pH and has optimal buffering capacity within one pH point from its pKa. Buffer solutions consist of a mixture of a weak acid and its conjugate salt or a weak base and its conjugate salt; they resist large fluctuations in pH.

Concept check general principles of acids and bases 10.4 page 392 question 5

Pay attention to the calculation in a few spots. First, recognize that the calculation became more simple by plugging everything into the HH equation and simplifying a commonality between the concentrations. Second, you need to be able to apply long division. It’s killing your calculations. Notice how we calculated 1/50 by using long division. Third. The HH equation has a sign flip due to the negative exponent on the +log portion.