Acids and Bases Chapter 16

A special solution Acids and bases are ALWAYS in a water solution. Your body has water in it so they are always dangerous to living things. Bases are just as dangerous as acids. In low concentrations they are not that dangerous and found all over your house.

Acids and Bases Aci Re less than 7 sour metals and bases ase lue more than 7 bitter and feel slippery oils and acids Although they can be dangerous, acids and base do not react with or “eat” everything. Neither has an effect on glass for example. turn litmus paper have a pH taste react with DB

Common places to find acids and bases Acids Vinegar- acetic acid citrus fruits- citric acid carbonated drinks- carbonic acid Your stomach- hydrochloric acid Bases Antacid tablets (calcium hydroxide) Windex- ammonia Oven cleaner- sodium hydroxide Draino – sodium hydroxide

Homework Using the litmus paper provided in class check to see if two common items found in your house are acidic or basic. Report your findings on a piece of paper, and staple the litmus paper with it. You need to report what the items are and if they are acidic or basic. Please exercise caution and common sense. Do NOT test anything dangerous!

Definitions Acid- a proton (H + ) donor [force feeder] Acids produce H 3 O + (hydronium) in water Base- a proton (H + ) acceptor [thief] Bases produce OH - (hydroxide) in water

Heat of solution Normally dissolving a substance is an exothermic process. You are normally increasing the state of entropy (measure of disorder) Which normally means you will release heat. There are exceptions, dissolving ammonium nitrate is an endothermic process

Always do what you oughta … Always add acid to water Dissolving the acid in water releases heat If you have a lot of acid and a little water on top, the water typically boils quickly causing the hot acid to spray out. A lot of water on the bottom typically doesn’t boil if the acid is added slowly enough.

Self dissociation of water. Some water will dissociate itself H 2 O +H 2 O  H 3 O + +OH - in “pure” water you will find H 3 O + has concentration of 1 x M OH - has concentration of 1 x M The product of the conc. of H 3 O + and OH - is always 1 x [ ]-conc. [H 3 O + ] [OH - ] = 1 x

pH In any solution the H 3 O + and OH - concentration is always very small. pH- method of representing the H 3 O + concentration in a solution. pH = -log [H 3 O + ] So the pH of water is… pH = - log 1 x10 -7 pH = 7

What is a log log stands for logarithm ~we can use them to solve for an exponent. log x y = y log x For example log 1 x10 -7 = -7 the log key on your calculator is log 10 meaning it will cancel out a 10^. To reverse a log 10 raise the whole thing to the 10 th power (10 ^ ), this is an antilog The reversed pH equation is [H 3 O + ] = 10^(-pH)

pH values pH of 7 is neutral- equal [H 3 O + ] and [OH - ] below 7 is acidic, higher [H 3 O + ] than [OH - ] above 7 is basic or alkaline, higher [OH - ] than [H 3 O + ]

Acid Base Equations [H 3 O + ] [OH - ] = 1 x pH = -log [H 3 O + ] [H 3 O + ] = 10^(-pH)

Sig Figs and pH The number of decimal places in the log value, pH value, is equal to the number of significant figures in the number that we took the logarithm of, concentration. So [H 3 O + ] = 2.45 x10 -4 M 3 sig figs pH = -log 2.45 x10 -4 M = decimal places

Reversing that Having a pH of 4.32 (2 decimal places) gives you a hydronium concentration of… [H 3 O + ] = 10^(-4.32) = 4.8 x10 -5 M (2 sig figs)

pH problems What is the pH of a 2.4 x M H 3 O + ? pH = - log 2.4 x pH = 3.62 What is the OH - concentration? [H 3 O + ] [OH - ] = 1 x x10 -4 [OH - ] = 1 x [OH - ] = 4.2 x M

Backwards problem What is the [H 3 O + ] and [OH - ] of a solution with a pH of 8.75? [H 3 O + ] = 10^(-pH) [H 3 O + ] = [H 3 O + ] = 1.8 x M 1.78…x10 -9 [OH - ] = 1 x [OH - ] = 5.6 x M

Last one What is the pH and [H 3 O + ] of a solution with a [OH - ] conc. of 2.9 x10 -4 M?

Homework What is the pH and [H 3 O + ] of a solution with a [OH - ] of 5.92 x10 -5 M?

Neutralization of an acid or base.

Mixing acids and bases ~creates water H 3 O + + OH -  2 H 2 O this is called neutralizing the solution a neutralized solution is no longer dangerous. The point where neutralization is complete is called the equivalence point

Salts ~the byproduct of an acid and a base. NaOH + HCl  H 2 O + NaCl (base) (acid) (water) (salt) there are several more than just table salt. HNO 3 + NH 4 OH  H 2 O + NH 4 NO 3 Acid Base water salt

Gases can be created this depends on the reactants (not all will) sodium bicarbonate (baking soda) will pretty much always release a gas NaHCO 3 + H 2 SO 4  H 2 O + NaHSO 4 + CO 2 Gas Salt

Titration ~mixing an acid and base perfectly to make a neutral solution. You normally need some kind of indicator for this. Phenolphthalein- when in solution turns red if basic and is clear if acidic. You can also use a pH probe

Graph of titration Volume strong base added pH equivalence point

Using math To neutralize a solution you will need to add an equal amount of H 3 O + / OH - to what was already present. so that mol H 3 O + = mol OH - This is used if and only if you are at the equivalence point (completely neutral solution)!

Problem If 94 mL of 4.0 M NaOH neutralizes 6.0 L of an unknown strong acid, what was the H 3 O + concentration of the unknown? 4 M NaOH x.094 L =.376 mol NaOH.376 mol H 3 O + / 6.0 L =.063 M H 3 O +

Another problem If 127 mL of 2.0 M NaOH neutralizes 4.1 L of an unknown acid, what is the initial concentration of the acid? 2.0M(.127 L) =.254 mol NaOH =.254 mol OH - =.254 mol H 3 O L =.062 M

Equilibrium Chapter 17

Rates of reaction Different reactions happen at different speeds. There are ways to speed up or slow down a reaction. Changing the surface area of the reactants Powders react more quickly than “chunks” Changing the amount/concentration of reactants More reactant speeds up the reaction Changing the temperature Warmer reactions tend to go faster Amount of rate change depends on the reaction.

Catalysts and Inhibitors Catalyst- something that increases the rate of a reaction without changing the products of the reaction. Catalytic converter speeding the reaction of emissions of a car to less dangerous products Inhibitor- something that slows or stops a reaction -food preservatives

Catalyst example 2 O 3  3 O 2 Ozone will decompose into elemental oxygen, however this process is very slow. Chlorine acts as a catalyst as shown in this two step reaction 2 O Cl 2  6 ClO 6 ClO  3 O Cl 2 ClO is an intermediate, something formed in the middle of the reaction that is later consumed. Chlorine is a catalyst because it is a reactant in the first step, but a product in the last step. So it isn’t used up during the reaction.

Forwards and backwards Most reactions can go forwards or backwards Neutralization equation H 3 O + + OH -  2 H 2 O Self ionization of water 2 H 2 O  H 3 O + + OH -

Equilibrium In water, both of those reactions are occurring simultaneously. Equilibrium is when the forward and backward reactions are occurring at the same rate. This will cause a stable amount of product and reactant to be present. No net change is occurring when it is at equilibrium. (dynamic equilibrium) The amount of product and reactant do NOT have to be equal!

Representing equilibrium It is normally represented with a double arrow 2 H 2 O H 3 O + + OH - This reaction comes to equilibrium when [H 3 O + ] = 1 x10 -7 M and [OH - ] = 1 x10 -7 M (assuming the solution is neutral) you won’t have to calculate this.

Le Châtelier’s Principle ~whenever stress is applied to a system at equilibrium, a new equilibrium will be obtained to relieve this stress. stress is a change in temperature, pressure, or concentration of some component. This will change the rate of reaction of either the forward or backward reaction So you will see an increase in the concentration of the substances on one side of the equation, and a decrease on the other. This will “shift” the equation to the right or left.

Examples Endothermic reactions absorb heat, i.e. they need heat to react. If the solution is heated prior to the reaction (stress)… It will react more quickly So the equation will be forced to the right (product side) If the reaction is cooled, it will be forced to the left (reactant side)

Equilibrium

Systems at equilibrium are still dynamic (changing). However, no NET CHANGE will be observed. A system is at equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction.

Changing concentration 2 H 2 O  H 3 O + + OH - If I add more water It will force the reaction to the right Which means more hydronium and hydroxide will be produced This is dilution (making the ratio of hydronium/hydroxide closer)

Equilibrium Add water 2 H 2 O  H 3 O + + OH - Stress + X 0 0 Shift -2y +y +y Final +X - 2y + y +y Since the stress was added to the left we must take from the left and give to the right to relieve the stress *where X is the amount of H 2 O added and larger than 2y

That means… Add water 2 H 2 O  H 3 O + + OH - Final + X - 2y + y +y We increased water because X is always larger than y (with any coefficent). We increased H 3 O + because +y is an increase We increased OH - because +y is an increase

The only equilibrium calculation That you will have to do with numbers is: [OH - ] [H 3 O + ] = K w K w is the equilibrium constant for water, it equals 1 x M We have already used the equation

More Le Châtelier’s If I add an acid to the equilibrium… 2 H 2 O  H 3 O + + OH - Stress 0 +X 0 Shift +2y -y -y Final + 2y +X- y -y    *Where X is larger than 2y so adding acid will decrease the [OH - ], only slightly increase the[H 3 O + ], and increase water.

2 H 2 O  H 3 O + + OH - If I remove hydroxide from the solution… 2 H 2 O  H 3 O + + OH - Stress 0 0 -X Shift -2y +y +y Final - 2y + y -X +y    *Where X is larger than 2y So removing hydroxide increases [H 3 O + ], only slightly decreases [OH - ], and decrease the water

Different equation Adding hydrogen to the equilibrium 2 NH 3  3 H 2 + N 2 Stress 0 +X 0 Change +2y -3y -y Final +2y +X-3y -y    *where X is larger than 3y Increases the amount of NH 3 decreases the amount of N 2 and only slightly increases H 2

With heat If I cool the following equilibrium Heat+ Co Cl -  CoCl 4 2- stress -x Shift +y +4y -y Final +y +4y -y    So cooling the solution will cause more Co 2+ & Cl - and less CoCl 4 2- to form

Conjugate acids and bases

Different definitions of acids and bases Acids are proton donors (Brønsted Lowry definition) they generate H 3 O + in water (Arrhenius definition) Bases are proton acceptors they generate OH - in water which is an acid/base? HF + H 2 O  H 3 O + + F - NaHCO 3 + H 2 O  Na + +H 2 O + CO 2 + OH -

Follow the proton HF + H 2 O  H 3 O + + F - NaHCO 3 + H 2 O  Na + + H 2 O+CO 2 +OH - Joining equilibrium to acid base…What about the reverse reaction? H+H+ H+H+ H+H+ H+H+

Conjugate acids and bases When you run the reverse reaction you find the products are also acids and bases. The acids and bases that are formed are called conjugate acids or bases H 2 O + HF  H 3 O + + F - base acid conjugate acid conjugate base NaHCO 3 + H 2 O  Na + +H 2 O + CO 2 +OH - base acid CA CB

Label Acid, Base, Conjugate Acid, Conjugate Base HClO 3 + H 2 O  ClO 3 - +H 3 O + A B CB CA ClO - + H 2 O  HClO + OH - B A CA CB HSO H 2 O  SO H 3 O + A B CB CA LiOH + H 2 O  Li + + H 2 O + OH - B A CA CB

Conjugate acids and bases … Conjugate acids and bases determine if an acid or base is strong or weak. If the conjugate acid/base readily reacts to run the reverse reaction it is a weak acid/base. If it does not react in the reverse reaction the acid or base is strong.

Strong acids Acidformula Nitric AcidHNO 3 Sulfuric AcidH 2 SO 4 Hydrochloric acid HCl

Strong Bases NameFormulaNameFormula Sodium Hydroxide NaOHCalcium Hydroxide Ca(OH) 2 Potassium Hydroxide KOHStrontium Hydroxide Sr(OH) 2 Barium Hydroxide Ba(OH) 2 these make a lightning bolt on the periodic table!

More with conjugate acids/bases H 2 SO 4 + H 2 O  H 3 O + + HSO 4 - Sulfuric acid is a strong acid so its conjugate base, HSO 4 -, will not run the reverse reaction. HSO 4 - is actually an acid in water. HSO H 2 O  H 3 O + + SO 4 2- SO 4 2- will run the reverse reaction, so it is a weak acid

Other weak acids and bases Weak Acids Acetic Acid (vinegar) Citric Acid Ascorbic Acid (vitamin C) Boric Acid Carbonic Acid Weak Bases Sodium Bicarbonate Ammonia Sodium Hypochlorite (bleach)

Danger!!! Strong and Weak acids and bases do NOT necessarily tell you how dangerous they are. Concentration is the most important factor for determining danger. Ammonia is a weak base, if it is highly concentrated it can burn you. Dilute hydrochloric acid (less than 1 M) is not particularly dangerous

What is water Water is either an acid or base depending on the situation. Anything that is either an acid or a base is called amphoteric. Several things are amphoteric, like parts of you.

Donating Protons Hydrochloric acid (HCl) can donate 1 proton, so it is called a monoprotic acid. Sulfuric acid (H 2 SO 4 ) can donate 2 protons, so it is called a diprotic acid. Phosphoric acid (H 3 PO 4 ) can donate 3 protons, so it is called a triprotic acid.

Indicators

Weak acids and bases can act as an indicator can be forced the other way So ammonia… NH 3 + H 2 O NH 4 + +OH - Ammonia is a gas with a distinct odor Ammonium and hydroxide are both odorless. If base is added to the solution you will smell ammonia, if hydroxide is removed you won’t.

Pet Stain Problem Urine has ammonia in it. Most cleansers are basic NH 3 + H 2 O ⇌ NH 4 + +OH - If I stress this equilibrium by adding a base… It shifts to the left causing more ammonia to form. Animals sense of smell is better so they fine the same spot and mark it again. That is why there are special cleansers (acidic) for pet stains

Indicators Indicators are a substance that change color in the presence of (whatever they check for) They do this because of Le Châtelier’s principle. All you need an equilibrium reaction with different colored products and reactants. The pen used to check for counterfeit money is a starch indicator

How an acid base indicator works A generic indicator will follow this reaction, HId is the reactant indicator, and Id - is its product HId + H 2 O H 3 O + + Id - The color differences are important in an acidic solution (high H 3 O + ) you see reactant HId + H 2 O H 3 O + + Id - in a basic solution (low H 3 O + ) you see product HId + H 2 O H 3 O + + Id -

Acid Base indicators Acid base indicators change color at certain pH levels They don’t have to change at 7 (most don’t) Universal indicator solution (phenolphthalein, bromthymol blue and methyl red dissolved in ethanol and water) changes color at each integral pH value

Other pH indicators Litmus and phenolphthalein are indicators Red cabbage has a pigment that changes colors at different pH values

Buffers Buffers are solutions that don’t change in pH when acids or bases are added. They use weak acids/bases and Le Châtelier’s principle. WA = weak acid HWA + H 2 O  H 3 O + + WA -

How? pH is determined by the concentration of H 3 O + Concentration is measured by mol /L Moles of H 3 O + / L (primarily of) H 2 O

What it does adding H 3 O + should increase [H 3 O + ] However, this forces the equation to the left, decreasing H 3 O + and increasing H 2 O so the [H 3 O + ] remains constant Removing H 3 O + (adding a base) should decrease [H 3 O + ] However, this forces the equation to the right, increasing H 3 O + and decreasing H 2 O So again, there is no change to [H 3 O + ] There is a breaking point where the pH will change.

What does this have to do with my life? Your blood is a buffered solution The pH must remain between Outside of that range can kill you below this range is called acidosis above is called alkalosis

Buffered Products medications (Bufferin) Shampoos, body soaps All are buffered to be near your body pH so they won’t cause a major disruption.