Acids and Bases

Acids and Bases

Acids and BasesText Chapter 8Previous knowledge Naming Acids and Bases (Gr. 11)Acid and BasesAcidBaseSourElectrolytesGritty feelpH 0 - 6.9Blue litmus redReact with bases to form a salt and waterPut H+ into solutionMade by reaction of oxides and water and binary covalent molecules and water

BitterElectrolytesSlippery feelpH 7.1 14Red litmus blueReact with acids to form a salt and waterPut OH- into solutionMade by metallic oxides and water

Acid and Base NamesAcids

Contains one or more hydrogen atoms

General formula

HnX

H hydrogen atomn number of hydrogen atoms (subscript)X monoatomic or polyatomic anion

HCl

H2SO4

Acid and Base NamesWhen the name of the anion ends in ide (X), the acid is a binary acid, and the prefix is hydro and the ending is ic

When there is a polyatomic ion, that makes up (X), the acid is a ternary acid. If the ion ends in ite, the ending for the acid is ous

When the polyatomic ion ends in ate, the ending for the acid is icAcid and Base NamesHint If the name of the anion is ate, and the acid is ic, one less oxygen, the acid is ous, one more less oxygen, the acid is prefix hypo and ending is ous

If there is one more oxygen than the ate polyatomic ion, the name is, prefix per and ending ic

Some organic acids, you just have to memorize the name. Ex. Ethanoic Acid CH3COOHAcid and Base NamesHClH2SO4H2SO3HCNHClO3HClO4HClOH3PO4

Cl- - chlorideBinary hydro stem - icHydrochloric acidSO4 -2 - SulfateTernary stem - icSulfuric AcidSO3-2 - sulfiteTernary stem - ousSulfurous AcidAcid and Base NamesBasesNamed the same as ionic compoundsSome you just have to memorize (ie. Ammonia)

Positive ion cation (+)Negative ion anion (-)NaOHSodium hydroxideMagnesium hydroxide

Aluminum hydroxideAcid Base TheoriesArrhenius Acids and BasesHydrogen containing compounds that ionize (ions wanderers to produce H+ are acids

Hydroxide containing compounds that produce OH- ions in solution are called bases

Not all substances that contain hydrogen atoms or hydroxide will be acidic or basic. It depends on electronegativity and polarity between the acidic / basic unit and the bonded atoms.Acid Base TheoriesBronsted Lowry Acid and BasesAcid hydrogen ion donorBase hydrogen ion acceptor

Substance that accepts the hydrogen is the conjugate acidSubstance that donates the hydrogen is the conjugate base

Used for those exceptions that cannot be explained by ArrheniusTruer theory as a naked hydrogen ion is very unlikely and unstable. Hydronium ion is most likelyAcid Base TheoriesWater can behave as both a conjugate base and acid (can accept and donate)

Called Amphoteric substance (behave as an acid and a base)

Strengths of Acids and Bases Based upon structure Greater the EN difference, the greater the ionization and dissociation, means the more product is formed, and more H+ or OH- goes into solution

Therefore, stronger acid and base (Keq greater than 1)

First ionization is the strongestSecond and subsequent ionizations are weaker. (p.607)

Acid Base TheoriesThe number of hydrogens will determine whether it is monoprotic, diprotic or triprotic acids.

Structure will determine the strength of the acid.

Rule the greater the EN difference, the greater the polarity, the greater the dissociation (ionization) and strength of the acid or base.Rule For ternary acids, if the Oxygens out number the hydrogens by more than 2, the acid will be strongGreater net pull, according to the first rule.

Strengths of Acids and BasesKeq for an acid is called Ka, and is the measure of how much of the acid ionizes (H+ or H3O+ and X) and how much stays together (HnX)

Keq for a base is called Kb, and is the measure of how much OH- and + ion is in solution and how much stays together.HXH+ + X-H2XOyH+ + H XOy-M(OH)zM+ + Z( OH-)Strengths of Acids and BasesThe amount that dissociates, or ionizes, is in equilibrium with the acid that stays as a whole

If the Keq is greater than 1, it favours product

For Acids and Bases, the Keq greater than 1, means it dissociates 100%, and all of the reactant (acid or the base) goes to ions.Strengths of Acids and BasesFor example

H2SO4 Ka = 1.00 x 103

H2SO4H+ + H SO4-

Therefore, if the concentration of the acid is 2.0 M, the concentrations of ions will be:

H2SO4H+HSO4 -2I2.000C2.0 -2.00 + 2.00+2.0E02.02.0Therefore, the concentration of the hydronium ion is 2.0 M.Strengths of Acids and BasesTherefore, when a strong acid or base dissociates, 100% turns into ions.

What would be the OH- for a sodium hydroxide solution with a molarity of 0.5 M?Solution sodium hydroxide is a strong base, therefore, it dissociates 100%

NaOHNa+ + OH-0.5 MO.5 M 0.5 M

Strengths of Acids and Bases

Strengths of Acids and BasesWhat about weak acids and bases?

We need to solve for the concentrations of ions, using Ka or Kb values because they do not dissociate 100%

Ka or Kb values are less than 1, favouring the acid or base to stay together and little ionize.

They may only dissociate 50% or 10%, leaving the majority of the acid or base as a whole and very little in ion form

Strengths of Acids and BasesExample What is the [H+] concentration in a 1.0 M solution of carbonic acid? (Ka = 4.3 x 10-7)Hint Look at the Ka value. It is less than 1. Therefore, it will not dissociate 100% and is a weak acid. We need to use equilibrium to determine the concentration of the [H+].Note In your text, the Keq expression is written using Bronsted /Lowry. You can use either, as long as you remember that there are some exceptions in which the ionization cannot be shown using Arrhenius. Also, the Keq expression uses water, then omits it. Keep in mind, water always has a concentration of 1 M. Concentration of water?!!!!Strengths of Acids and BasesWhy are we finding the H+ or OH-?

pH

power of hydrogen or potential of hydrogenHydrogen Ions and pHBased upon waterHighly polar Made up of hydronium ion and hydroxide ionSelf Ionization of water (Kw)

Hydrogen Ions and pHEach ion has a value of 1 x 10 -7 M, which, when multiplied together forms the Keq or Kw, which is 1 x 10 -14

Both are equal to each other in terms of their concentrations, and therefore form a neutral substance (pH = 7)

If the concentration of H+ is greater than 1 x 10 -7 M, the solution is acidic (ie. More H+ and less OH-), since all solutions are in water.

If the concentration of H+ is less than 1 x 10 -7 M, the solution is basic (ie. Less H+ and more OH-), since all solutions are in water.Hydrogen Ions and pHpH = potential hydrogen

pH scale is based upon the [H+] found in a solution.

If the [H+] is greater than 1 x 10 -7 M, the solution will be acidic and the pH will be less than 7.

If the [H+] is less than 1 x 10 -7 M, the solution will be basic and the pH will be greater than 7.

pH is the negative log of the hydrogen ion concentration.pH Scale

Measuring pH Acid Base IndicatorsIndicator usually a weak acid that accepts hydrogen ions, and in doing so, changes its chemical structure, which facilitates a colour change.

Litmus changes from red to blue at pH of 7, or 1 x 10 -7 M

Bromothymol Blue is yellow below 1 x 10 -7 M, green at 1 x 10 -7 M, and blue over 1 x 10 -7 M

Phenopthlalein changes color at a pH of 7-9 (the hydrogen ion concentration of 1 x 10 -7 M to 1 x 10 -9 M)Measuring pH Acid Base IndicatorsHIn (aq)H+(aq) + In-(aq)Acid FormBase FormColor #1Color #2

OH- H+The change is caused by the removal of a hydronium ion to form the Base form and the addition of a hydronium ion for the acid form.Measuring pH Acid Base IndicatorsIndicator papers are impregnated with the indicator solution and when exposed to the hydrogen ion, change color, depending on the concentration

Universal Indicators show all pH levels. What do you think they are made up of?Neutralization Reactions and TitrationIf we have high levels of acid in our stomach, we take an antacid (base) to control it.

In our small intestine, the acidic chyme, is neutralized by the bile (basic) to make sure we do not ulcerate our intestine

Why does it neutralize?We make a salt and water, that does not necessarily work out to a pH of 7 (more later)We could bring the solution to a pH of 7.

Neutralization Reactions and Titration[H+] = [OH-]1 x 10-7 M = 1 x 10-7 M

Ex. If you react a strong acid and a strong base, the ions in solution will cancel each other out, producing a neutral solution. The products are always, regardless of the product pH, a salt and water. HCl(aq) + NaOH(aq)NaCl(aq) + H2O(l)Neutralization Reactions and TitrationThe point where the number of moles of hydronium ion equals the number of moles of hydroxide ion, is called the equivalence point. (not necessarily pH =7)

Salt

The compound formed by the cation of the base bonding with the anion of the acid.Neutralization Reactions and TitrationTitrationThe process of adding a known amount of solution of known concentration to determine the concentration of another solution

When the color changes, this is called the end point, which is the point of neutralization

There is only salt and water at this point, if both were strong acids and bases.Neutralization Reactions and TitrationAnimation of Titration

Lab Primer

The idea is to calculate the concentration or number of moles for an unknown solution, using the equivalence point to determine neutralizationNeutralization Reactions and TitrationTitration Curves

SaltsSalts are the combination of the cation from the base and the anion from the acid and are the products of neutralization reactions

Salts can be acidic, basic or neutral, depending on the strength of the acid and base that formed it.

Buffers are an equilibrium condition which consists of the weak acid and conjugate base (salt) in solution, or a weak base and its conjugate acid (salt) keeping pH stable

SaltsGenerally, if a strong acid reacts with a strong base, the resulting salt will be neutral (pH=7) (ie. The equivalence point is 7)

For salts formed from weak acids with a strong base, or weak bases with a strong acid, the salt will not be neutral

This is called by salt hydrolysis, as the cations or anions from a dissociated salt remove or add hydrogen ions to water, creating either H+, or OH- in solution

SaltsAnother way to determine the acidity or basicity of a salt is to look at the net ionic equation and remembering that strong bases and acids dissociate 100%, while weak acids and bases do not.

In generalAcidic salts produce positive ions that release protons into waterBasic solutions produce negative ions that attract protons from waterSaltsStrong Acid + Strong BaseNeutral solutionStrong Acid + Weak BaseAcidic SolutionWeak Acid + Strong BaseBasic SolutionBuffersBufferA substance in which the pH remains constant, when small amounts of acid or base is added.It contains the weak acid and one of its salts (anion conjugate base) or the weak base and one of its salts (cation conjugate acid)

Pure water is not a buffer, as when you add acid (H+) or base (OH-), the concentrations increase, changing the pHBuffersA buffer is like a sponge

When hydrogen ions are added, they are absorbed by the negative ion, forming the whole weak acid, that does not dissociate 100%, lowering the acidity, and raising the pH to neutral

When hydroxide is added, they react with the acid to form the negative ion and water, lowering the basicity, and lowering the pH to neutral

BuffersAnimation of Buffering

Common buffers, keep the pH at a stable level

Ethanoic acid maintain pH 4.76Carbonic acidmaintain pH 6.5 (blood)Ammoniamaintain pH 9