Unit 17- Acids/Bases/Salts

General properties Taste sour Turn litmus React with active metals React with bases Taste bitter Turn litmus Feel soapy or slippery (react with fats to make soap) React with acids blue to redred to blue

Acids have a pH less than 7

Acids React with Carbonates and Bicarbonates HCl + NaHCO 3 NaCl + H 2 O + CO 2 Hydrochloric acid + sodium bicarbonate salt + water + carbon dioxide An old-time home remedy for relieving an upset stomach

Effects of Acid Rain on Marble (marble is calcium carbonate) George Washington: BEFORE acid rain George Washington: AFTER acid rain

Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH) 2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH) 2 MgCl H 2 O Magnesium salts can cause diarrhea (thus they are used as a laxative) and may also cause kidney stones.

Naming Acids are composed of hydrogen (H + ) followed by an anion (negative ion). If the acid formula contains oxygen in the anion, such as in H 2 SO 4, it is known as an oxyacid.

3 Rules To Naming Acids If H + anion ending in –ide: Acid name is “hydro_____ic acid” –Take the root from the anion name and fill in the blank. H + anion ending in –ate: Acid name is “_____ic acid” –Take the root from the anion name and fill in the blank. –“What I ATE was ICky” H + anion ending in –ite: Acid name is “_____ous acid” –Take the root from the anion name and fill in the blank. –“Don’t bITE; it’s infectiOUS”

Exceptions Sulfate (SO 4 2- ) –Root is not sulf, but sulfur Sulfuric acid Phosphate (PO 4 3- ) –Root is not phosph, but phosphor Phosphoric acid

Svante Arrhenius He was a Swedish chemist ( ), and a Nobel prize winner in chemistry (1903) one of the first chemists to explain the chemical theory of the behavior of acids and bases

Arrhenius Definition Acids produce hydrogen ions (H 1+ ) in aqueous solution (HCl → H 1+ + Cl 1- ) Bases produce hydroxide ions (OH 1- ) when dissolved in water. (NaOH → Na 1+ + OH 1- ) Limited to aqueous solutions. Only one kind of base (hydroxides) NH 3 (ammonia) could not be an Arrhenius base: no OH 1- produced.

Brønsted-Lowry A broader definition than Arrhenius Acid is hydrogen-ion donor (H + or proton); base is hydrogen-ion acceptor. Acids and bases always come in pairs. HCl is an acid. –When it dissolves in water, it gives it’s proton to water. HCl (g) + H 2 O (l) ↔ H 3 O + (aq) + Cl - (aq) Water is a base; makes hydronium ion.

Acids and bases come in pairs A “conjugate base” is the remainder of the original acid, after it donates it’s hydrogen ion A “conjugate acid” is the particle formed when the original base gains a hydrogen ion Thus, a conjugate acid-base pair is related by the loss or gain of a single hydrogen ion.

Definitions Acids – produce H + Bases - produce OH - Acids – donate H + Bases – accept H + Arrehenius Bronsted-Lowry only in water any solvent

When life goes either way Amphiprotic substances HCO 3 - H 2 CO 3 CO H + - H + Acting like a base Acting like an acid accepts H + donates H +

Strong and Weak Acids/Bases Strong acids/bases – 100% dissociation into ions HClNaOH HNO 3 KOH H 2 SO 4 Weak acids/bases – partial dissociation, both ions and molecules CH 3 COOHNH 3

Strong Acids Prechloric Acid HClO 4 Sulfuric Acid H 2 SO 4 Hydriodic Acid HI Hydrobromic Acid HBr Hydrochloric Acid HCl Nitric Acid HNO 3

Strong Bases Lithium hydroxide, LiOH Calcium hydroxide, Ca(OH) 2 Sodium hydroxide, NaOH Strontium hydroxide, Sr(OH) 2 Potassium hydroxide, KOH Barium hydroxide,Barium hydroxide, Ba(OH) 2 Magnesium hydroxide,Magnesium hydroxide, Mg(OH) 2

Salt Hydrolysis A salt is an ionic compound that: –comes from the anion of an acid –comes from the cation of a base –is formed from a neutralization reaction –some neutral; others acidic or basic “Salt hydrolysis” - a salt that reacts with water to produce an acid or base

Salt Hydrolysis Hydrolyzing salts usually come from: 1.a strong acid + a weak base, or 2.a weak acid + a strong base Strong refers to the degree of ionization A strong Acid + a strong Base = Neutral Salt How do you know if it’s strong? –Refer the list on your notes

Salt Hydrolysis To see if the resulting salt is acidic or basic, check the “parent” acid and base that formed it. Practice on these: HCl + NaOH  H 2 SO 4 + NH 4 OH  CH 3 COOH + KOH  NaCl, a neutral salt (NH 4 ) 2 SO 4, acidic salt CH 3 COOK, basic salt

Ionization constant of Water Water ionizes, or falls apart into ions: H 2 O ↔ H 1+ + OH 1- Called the “self ionization” of water Occurs to a very small extent: [H 1+ ] = [OH 1- ] = 1 x M Since they are equal, a neutral solution results from water K w = [H 1+ ] x [OH 1- ] = 1 x M 2 K w is called the “ion product constant” for water

Ion Product Constant K w is constant in every aqueous solution: [H + ] x [OH - ] = 1 x M 2 If [H + ] > then [OH - ] < If [H + ] If we know one, other can be determined If [H + ] > 10 -7, it is acidic and [OH - ] < If [H + ] –Basic solutions also called “alkaline”

If [H 3 O+] > [OH– ‑ ] the solution is acidic. If [H 3 O+] < [OH– ‑ ] the solution is basic. If [H 3 O+] = [OH– ‑ ] the solution is neutral.

Acid/Base/Salts Part 2

pH Expressing hydrogen ion concentration in numbers can be cumbersome. A widely used system for expressing [H3O+] is the pH scale. Whether or not a solution is acidic, basic, or neutral depends on the balance of H + and OH - ions: Neutral: [H + ] = [OH - ] Acid: [H + ] > [OH - ] Base:[H + ] < [OH - ]

pH pH is the negative base 10 logarithm of the hydronium ion concentration: pH = - log [H 3 O + ]

Measuring pH Why measure pH? 4Everyday solutions we use - everything from swimming pools, soil conditions for plants, medical diagnosis, soaps and shampoos, etc. Sometimes we can use indicators, other times we might need a pH meter

pH Remember, for pure water, [H 3 O + ] is 1 x 10-7 M. So what’s the pH of pure water? Ex: What is the pH of a solution with a hydronium ion concentration of 1.0 x M?

Note that as pH increases, [H 3 O + ] decreases and [OH – ‑ ] increases. Note the relationship between [H 3 O + ] and [OH – ‑ ]. Remember, the product of these must always equal 1 x for aqueous solutions. Note that as pH increases, [H3O+] decreases and [OH– ‑ ] increases. Note the relationship between [H3O+] and [OH– ‑ ]. Remember, the product of these must always equal 1 x for aqueous solutions.

pOH = - log [OH - ] pH + pOH = 14

Example Find the pH, the pOH = 5.3  pH + pOH = 14 pH = pH = 8.7

pH calculations Use the reverse of the equation to calculate the [H + ] when pH is known.  [H 3 O + ] =10 (-pH) *** 2 nd log on the calulator! = 10 -pH

pH calculations Use identical process for [OH - ] when pOH is known.  [OH - ] = 10 (-pOH)

Acid/Bases/Salts Neutralization/Titrations

A. Neutralization Chemical reaction between an acid and a base. Products are a salt (ionic compound) and water. Note in the reaction above, the acid:base mole ratio is 1:1. However, in the reaction between H 2 SO 4 and NaOH: it takes 2 moles of base to neutralize 1 mole of acid. The reacting ratios of acid and base will be important in solving problems related to neutralization reactions.

A. Neutralization ACID + BASE  SALT + WATER HCl + NaOH  NaCl + H 2 O HC 2 H 3 O 2 + NaOH  NaC 2 H 3 O 2 + H 2 O –Salts can be neutral, acidic, or basic. –Neutralization does not mean pH = 7. weak strong neutral basic

B. Titration Titration –A laboratory technique that uses a neutralization reaction to determine the concentration of an unknown acid or base. standard solution unknown solution

An indicator is used to show when neutralization has occurred. changes color in response to changes in pH. actually weak acid or base that change color in response to pH change. In acidic solutions, indicators act as Bronsted-Lowry base. As the indicator molecules accept H+, they change color. In basic solutions, indicators act as Bronsted-Lowry acid. As the indicator molecules donate H+, they change color.

End Point – –point at which an indicator changes color during a titration Equivalence point –Point at which equal amounts of H 3 O + and OH - have been added. –when mole ratio exactly equals mole ratio required by reaction –Determined by… indicator color change B. Titration dramatic change in pH

B. Titration moles H 3 O + = moles OH - M  V  n = M  V  n M:Molarity V:volume n:# of H + ions in the acid or OH - ions in the base

B. Titration 42.5 mL of 1.3M KOH are required to neutralize 50.0 mL of H 2 SO 4. Find the molarity of H 2 SO 4. H3O+H3O+ M = ? V = 50.0 mL n = 2 OH - M = 1.3M V = 42.5 mL n = 1 MV# = MV# M(50.0mL)(2)=(1.3M)(42.5mL)(1) M = 0.55M H 2 SO 4