Chapter 14 - Acids & Bases

There are two main factors that determine whether a molecule containing an X-H bond will behave as an Bronsted-Lowry acid:

- the polarity of the bond - the strenth of the bond

In the denominator of the acid dissociation constant, sometimes the unknown variable can be substituted with

0. for ex: (4.5*10^-2) [CN-] / 1.00 - x (4.5*10^-2) [CN-]/1.00

What are the two ways to calculating the pH of sulfuric acid?

1. (Only works for 1.0 M H2SO4) dissociate it into 1.0 M H+ and 1.0 M HSO4. Then use the the equation HSO4 dissociating into H+ and SO4-. You can ignore the 5% rule because a large amount comes from the first step of dissociation. 2. (Only works if H2SO4 is less than 1.0 M and diluted) Do the same thing in #1 and split 0.1 M H+ and 0.1 HSO4. THIS TIME YOU HAVE TO TAKE INTO ACCOUNT OF 5% rule; demoninator cannot be set to 0.

Thus at only 25 degrees, Kw=

1.0 * 10^-14

How much conjugate acid base pairs are there in the general reaction that occurs when an acid is dissolved in water?

2 conjugate acid base pairs: HA and A- , H3O+ and H2O

A strong acid yields a strong or weak conjugate base?

A strong acid yields a weak conjugate base. (the conjugate base has a low affinity to the proton as opposed to water's high affinity)

YOU CAN ONLY WRITE Ka= [H+][A-]/[HA] for general reactions in which a proton is removed from HA to form conjugate base

A-.

14.2

Acid Strength

14.8

Acid-Base Properties of Salts

14.10

Acid-Base properties of Oxides

What was the Broasted-Lowry model?

Acids were hydrogen ion(proton) donors, while bases were hydrogen ion(proton) acceptors.

The first theory to observe the essential nature of acids and bases was Arhenius. What was the Arhenius concept?

Acids would produce H+ ions in AQUEOUS solution. Bases would produce OH- ions in aqueous solution.

Always remember the equation for aluminum(showing its strong acidity):

Al(H2O)6+3 + H2O -> Al(H2O)5(OH)+2 + H+

What is another name for bases?

Alkalis

What are the strong bases?

All group 1 cations, and Barium, Calcium, Strontium

What are the 7 strong acids?

B I C P e N S HBr, HI, HCl, HClO4(Perchloric acid), HNo3, H2SO4,

What is the general reaction equation when a BASE reacts with water?

B(aq) + H2O(l) acid -> BH+(aq conj acid) + OH- <-

14.6

Bases

How would you calculate the pH and pOH for 1.0 M OH+ at 25 degrees celsius.

Because OH+ can be looked at as H+, we just use 1.0 M as H+ and Kw=1.0*10*-14 to solve for OH-, then plug into pOH, etc.

How come in a Ka table, strong acids are not shown?

Because when a strong acid such as HCl is placed in solution, the equilibrium position lies so far to the right that it cannot be measured due to its denominator being so small.

How do we calculate the pH of Weak acid solutions?

By drawing an ICE table.

How come molecules containing C-H bonds display no acidic properties? (ex: CHCl3, CH3NO2)

C-H bonds are non polar and thus there is no tendency to donate protons. The bond strength is strong and non polar.

14.4

Calculating the pH of Strong Acid Solutions

14.5

Calculating the pH of Weak Acid solutions

How come when anions such as Cl- and NO3- are placed in water, it has no effect on the pH?

Cl- is a weak conjugate base given HCl is a strong acid. Cl- as a base dissociates to such an insignifigant amount(less than the autoionization of water) and does combine with H+ that we simply look at only the water; it has no effect on the pH.

Def. Acidic Oxides

Covalent oxides that will produce an acidic solution when dissolved in polar water.

Def. Basic Oxides

Covalent oxides that will produce an basic solution when dissolved in polar water.

Define Conjugate base.

Everything leftover after an proton is removed from the acid.

What structural properties of a molecule cause it to behave as an acid or base?

For acids, any molecule containing a hydrogen ion will POTENTIALLY be an acid.

Most ionic oxides, such as those of _________ will produce basic solutions when dissolved in water.

Group 1A and 2A metals. (not electronegative)

H3O+ can also be represented as

H+

In a 1.0 M HCl what are the major species?

H+, Cl-, and H2O because it is a very acidic solution.

Given bond polarity+bond strength: H-F > H-Cl > H-Br > H-I Why is H-F the least acidic and H-I the most acidic?

H-F is the strongest bond, and thus has difficulty dissociating completley.

What is the skeleton of an oxyacid?

H-O-X(central atom)

Why is (H3PO4) a triprotic acid, but phosphorus acid(H3PO3) a diprotic acid, and hypohphsphorous acid(H3PO2) a monoprotic acid?

H3PO3 is diprotic because when you draw out the lewis structure, there are two O-H bonds (meaning two acidic H+) and only one H+ attached(not acidic). Same with H3PO2, there is one O-H bond

From the general reaction identify, HA, H2O, H3O+, A- as an acid, base, conjugate acid, conjugate base

HA is an acid. H2O is a base. A- is an conjugate base. H3O+ is an conjugate acid.

The general reaction that occurs when an acid dissolves in water is the following:

HA(aq) + H20(l) -> H30+(aq) + A-(aq) <-

Examine base strength with an example(ex: HCN)

HCN + H2O -> CN- + H+ <- CN- appears to be a strong conjugate base. However... CN- + H2O -> HCN + OH- <- Kb for CN- = 1.6 *10^-5 The Kb value for CN- is small because you have to remember that CN- is competing with OH- for the proton. Strength of OH- base > anion from weak acid > H2O

For two strong bases: 1.0 M LiOH and 0.1 M NaOH, how would you find pH?

INSTEAD of choosing the largest Ka, you would take both into consideration. SO ADD 1.0 M and 0.1 M together and use pOH=-log[1.1]

How would you calculate the pH of strong bases? ex: calculate the pH of a 5.0 * 10^-2 M NaOH solution

Identify major species; strong acids or bases will always have dissociated substance + water. Plug the value into [OH-][H+]= 1.0*10^-14

If X has a high electronegativity in H-O-X, will the oxide produce an acid or base when dissolved in water? Explain

If X has an high electronegativity, a acid will be produced because O-X bonds will remain intact(strong and covalent), while H-O bonds will tend to break and release protons.

Acid Dissociation constant

Ka

Various ways to describe acid strength

Ka value(large Ka= strong acid small Ka= weak acid Position of dissociation equilibrium(far to right is strong acid, left is weak acid) EQUILIBRIUM concentration of H+ compared with original concentration of HA ( [H+] = [HA]initial is a strong acid) ([H+] <<[HA]initial is a weak acid) Strength of conjugate base with that of water A- is weaker than H2O -> strong acid A- is stronger than H2O-> weak acid

If given the acid dissociation constant(Ka), how do we find Kb?

Ka*Kb=Kw(1.0*10^-14)

For a typical weak polypro tic acid, Ka1 >

Ka2 > Ka3

What is the equation for the acid dissociation constant?

Ka= ([H3O+][A-]) / (HA) or Ka= ([H+][A-])/(HA)

Instead of Ka, what do we use to express how much a base ionizes?

Kb= [BH+][OH-] / [B]

The auto ionization reaction for water 2H2O(l) -> H3O+(aq) + OH-(aq) <- leads to the equilibrium expression

Kw= [H3O+][OH-]=[H+][OH-]

14.11

Lewis Acid-Base Model

In an aqueous solution sodium acetate(NaC2H3O2) the major species are

Na+, C2H3O2-, H2O Na+ has no effect and C2H3O2- is a strong conjugate base which disocciates.

In 1.0 M HCl what are the minor species?

OH-, HCl

14.7

Polyprotic acids

14.12

Strategy for Solving Acid-Base Problems

The general reaction in which HA forms a conjugate base A- is called

The Acid Dissocation(ionization) reaction.

14.9

The Effect of Structure on Acid Base properties

14.1

The Nature of Acids and Bases

What does the pH scale represent?

The acidity of the solution.

According to Bronsted-Lowry, if HCl(g) dissolved in water, which would be the acid and which substance would be the base?

The bronsted lowryacid would be HCl because each HCl molecule donates a proton to the water. Because water accepts protons, it is a bronsted lowry base.

Explain why it is important to distinguish Bronsted-Lowry versus Arhenius in the reaction: NH3(g) + HCl(g) -> NH4Cl(s) <-

The bronsted-lowry definition works here because HCl acts as a proton donor while NH3 accepts a proton. Thus HCl is an bronsted lowry acid while NH3 as an bronsted lowry base. Arhenius's definiton wouldn't work in this case because an acid does not produce hydrogen ions in AQUEOUS solutions in this case. Similarly, Nh3 and Hcl are gases not aqueous solutions.

Why does acid strength increase when oxygens increase in an oxyacids?

The extra oxygens are able to draw the electron density away from the central atom and the O-H bond which weakens the bond strength of the O-H.

What determines whether an oxide with skeleton structure H-O-X will form an acid or a base?

The nature of the O-X bond.

14.3

The pH scale

Why was the Arrhenius concept limited?

The theory only worked for bases producing OH- ions and only aqueous solutions.

What is really happening in terms of equilibrium position for the general reaction of an acid dissolving in water?

There is a competition between the two bases: H2O and A-(the conjugate base). If H2O is a stronger base, the equilibrium position will shift to the right; conversely if A- is a stronger base the equilibrium position will shift to the left.

True or false; the Lewis Acid-Base model encompasses the Bronsted Lowry model, but not the other way around.

True.

Why is water not included in the acid dissociation constant despite being in the general equation?

We can assume that the concentration of liquid water remains constant even when acid is dissolved. Liquids and Solids are also not included in equilbrium expression.

What are the two key things you should ask yourself when solving an acid-base problem?

What are the major species in the solution? Which equation is domininating the equilibrium(which one affects pH the most)?

Can auto ionization occur in other liquids besides water?

Yes, take NH3 for instance. NH3 + NH3 will yield an acid and a base

How do you calculate the pH of solutions including two or more acids?

You only create the ICE table for the larger Ka.

Write the simple dissociation reaction (omitting water) for hydrated aluminum(III)ion [Al(H2O)6]3+ and Ammonium(NH4+)

[Al(H2O)6]3+(aq) -> H+ + Al(H2O)5(OH)+2 <- NH4+ -> NH3 + H+ (aq) <- (aq) (aq)

At 60 degreses celsius Kw is 1*10^-13, find [H+] and [OH-]

[H+] * [OH-] = 1*10^-13 [H+]=[OH-]=3*10^-7 M

In the percent dissociation formula, Amt dissociated also means

[H+] or [OH-]

ONLY WHEN AT 25 degrees celsius in pure water,

[H+]=[OH-]=1.0 * 10^-7 M

Define Conjugate acid

a base that accepts an proton.

Define amphoteric and give an example

a substance that can behave as an acid or base

Define weak acid

a weak acid yields an equilibrium position to the left. Most of the acid originally placed in the solution is still present as HA in equilbrium. (dissociates to a very small extent)

SO3(g)+ H2O(l) will produce an ____ because..

acid it is an acidic oxide; Sulfur is electronegative enough to form strong bonds with oxygen.

Species such as Na+, K+, Li+, Cl-, NO3- has neither

acidic or basic properties(no effect on pH)

Salts in which the cation is from a weak base, and the anion is from a strong acid is(ex: NH4Cl)

acidic.

Define monoprotic acids

acids having only one acidic proton.

Lewis proposed that

acids were electron pair acceptors, bases were elctron pair donors.

Under certain conditions salts can behave as either

an acid or base

What are oxyacids?

an acid that contains oxygen.

Define hydrohalic acids

an acid with a proton attached to a halogen.

What is inductive effect?

an electronegative atom can affect the bond polarity two or three atoms away. ex: for oxyacids above.

For solutions of any weak acid HA, [H+] decreases as

as [HA]0 decreases, but the percent dissociation increases as [HA]0 decreases.

The acidicty of the water molecules attached to the metal ion(Al+3) is increased by the

attraction of the electrons to the positive metal ion.

Define Strong bases

bases that dissociate completely

A cation from a strong base and an anion from a weak acid will be(ex: NaF, NaNO2)

basic - the anion is a strong conjugate base.

PO4-3 + H2o -> HPO4-2 + OH- HPO4-2 + H2O-> H2PO4- +OH- H2PO4- +H2O-> H3PO4 + OH- means that PO43- will produce three hydroxides HPO42- will produce two hydroxides H2PO4- will produce one hydroxide. Thus in the hydrolysis of salt, Na2Co3 is more ___ than NaHCO3

basic because of the behavior shown above.

Bases taste and feel

bitter and slippery

How can you tell water is an amphoteric substance?

by looking at the auto ionization of water, involving the transfer of a proton from one water molecule to another water molecule producing a hydroxide and hydronium ion.

Percent dissociation increases as an acid is

diluted.

The electron deficiency for ex: of boron trifluoride makes it very reactive towards any

electron pair donor.

Using a table arrange the following species according to their strengths as bases: H2O, Cl-, CN-(given lower value of Ka), NO2-(given higher value of Ka)

from least to greatest base strength Cl-, H2O, NO2-, CN- a lower value of Ka(weaker acid) will give you a higher conjugate base.

In terms of equilibrium position, as strong acid is one that..

has its equilibrium position far on the right.

A second type of salt that produces an acidic solution is one that contains a

highly charged metal ion ex: AlCl3 Although Al+3 itself is not a bronsted lowry acid, its hydrated form Al(H2O)6 + H2O is a bronsted lowry acid. Aluminum polarisez OH bonds making the hydrogens in the water molecule more acidic than those in free water.

The pH decreases as [H+] ...

increases

Salt is simply another name for

ionic compound

A cation from a STRONG ACID and a anion from a strong base will be(ex: NaCl, KBr)

neutral(pH=7). WEAK CONJUGATE ACID + WEAK CONJUGATE BASE

alkaline earth hydroxides (group 2) are _ soluble.

not very.

What is the percent dissociation formula?

percent dissociated= 100 * (Amt dissociate [M])/ (Intial concentration [M])

Percent dissociation is also known as

percent ionization

What are examples of weak acids(acids that do not dissociate fully)?

phosphoric acid(H3PO4), nitrous acid (HNO2), and hypochlorous acid(HOCl)

Acids that can furnish more than one proton are called

polyprotic acids

When both the cation and anion are from weak acids and bases(for a salt), we can only determine whether it is acidic or basic through

quaitative observations (Ka > Kb , Ka = Kb, Ka< Kb)

The hydration of a metal ion, such as Al3+ can be viewed as an Lewis acid-base

reaction

Calcium hydroxide is often also called

slaked lime

When dealing with an acid-base equilibria, we must focus on the

solution components and their chemistry.

The next step with dealing an acid-base equilibria is to only focus on MAJOR SPECIES. What are major species?

solution components present in relatively large amounts.

Acids taste

sour (ex: citric acid)

What is a general rule to remember strengths regarding acids and bases?

stronger acids and stronger bases -> weaker conjugate bases and weaker conjugate acids

Give an example of a diprotic acid.

sulfuric acid (H2SO4) -> H+ + HSO4- (HAS two acidic protons)

What are the 7 main strong acids?

sulfuric acid(H2SO4), Hydrobromic acid(HBr), Hydroiodic acid(HI), hydrochloric acid (HCl), nitric acid(HNO3), and perchloric acid(HClO4), HClO3(chloric acid)

How would you determine which substance is a stronger acid in an oxyacid? ex: HClO4 & H3PO4 & H2SO4

the MORE electronegative the central atom is, the longer the bond length between O-H. Thus Cl is the most electronegative and HClO4 is the strongest acid.

What is the strength of an acid defined by?

the equilibrium position of dissociation

What is Kw called?

the ion-product constant or the dissociation constant for water.

How would you determine which substance is a stronger acid in a binary acid? ex: H2S, H2Se

the less electronegative central atom is the stronger acid because the bond length is longer

The greater the charge on the metal ion

the more acidic the hydrated ion becomes.

Acid strength increases in an oxyacid as ...

the number of oxygen atoms attached to the central atom increases.

What is the sig fig rule for logarithms?

the number of sig figs plugged into the logarithms is the number of DECIMAL places in the final pH.

If X has a low electronegativity in H-O-X, will the oxide produce an acid or base?

the oxide will produce a base because O-X bonds will be ionic and subject to being broken in water.

Calculate the pH of 1.0 *10^-10 M HCl

the pH=7 because the HCl exists in such a small amount in water, that the pure water is simply seen as neutral. We know this because the concentration of HCl is less than 1.0*10^-7

organic acids are usually weak acids. True or false?

true. they contain a carboxyl group with carbon in its backbone.

Define Conjugate acid-base pair

two substances related to each other by the donating and accepting of A SINGLE proton.

What is slaked lime used for?

used in industry for scrubbing stack gases to remove sulfur dioxide from the exhaust of power plants and factories.

If [H+] = [OH-]

you have a neutral solution

If [H+] > [OH-]

you have an acidic solution

If [H+] < [OH-]

you have an basic solution