Acids and Bases

Acids Definition : latin meaning sour “Acidus” Lots of acids –Dangerous Nitric Acid, Sulfuric Acid –Essential Ascorbic Acid –Dietary Acetic Acid (ethanoic acid) (vinegar), Citric Acid, Carbonic Acid –Odd Stearic Acid, Benzoic Acid

info Turns blue Litmus paper Red React with metals to produce hydrogen gas H 2 SO 4 + ZnZnSO 4 + H 2 React with Carbonates to produce CO 2

Arrhenius Theory An acid is a substance that dissociates in water to produce H + ions –Svante Arrhenius (nobel prize 1903)

Add HCl to water and we get H + ions and Chlorine Nitric and Sulfuric acid behave the same HClH + +Cl HNO 3 H + +NO 3 H 2 SO 4 2H + +SO 4 2-

When we add a solution of Hydrogen chloride to water we call it Hydrochl o ric acid Mono basic: HClH + +Cl Di Basic H 2 SO 4 2H + +SO 4 2- Tri Basic H 3 PO 4 3H + +PO 4 3- Dependant on the number of hydrogen ions donated

Strong and weak acids Sulfuric and nitric are strong as they dissociate fully in water but acetic acid is weak as it only partially dissociates

Hydronium Ion The H + ion....just a proton Cannot exist independently in solution so the Hydronium ion is born The oxygen atom allows an electron to form a dative covalent bond with the hydrogen atom

Hydrogen ion reacts with water to form Hydronium Ion H 3 O + O HXHX H+H+ XHXH.... HXHX H+H+ XHXH.. O.. +

Hydronium Ion For accuracy we should use HA +H 2 OH 3 O + + A - HCl +H 2 OH 3 O + + Cl - Many chemists simply say the hydrogen ion

Importance of water If we add pure Hydrogen Chloride or acetic acid into a solvent like benzene (no water) we do not get either H + or Hydronium ion formation and blue litmus paper stays blue Shows that Hydrogen Chloride or acetic acid is only acid when water is present

Bases Behave in the opposite manner to acids Turn Red litmus paper blue Example: –Sodium Hydroxide (NaOH) –Magnesium Hydroxide ([Mg(OH) 2 ]) –Calcium Hydroxide ([Ca(OH) 2 ])

Info Many bases have a soapy feel Used as degreasers in household detergents Act by converting the oil into soap which washes away more easily

Arrhenius Theory A base is a substance that dissociates in water to produce OH - ions The OH - ion is called the hydroxide ion When added to water it dissociates completely into Sodium ions and hydroxide ions NaOH Na + + OH -

Arrhenius Theory Similarly for Magnesium Hydroxide and Calcium Hydroxide [Mg(OH) 2 ]Mg OH - [Ca(OH) 2 ]Ca OH -

Strong and Weak bases Strong bases include Sodium Hydroxide because they dissociate almost completely in water but....Magnesium Hydroxide and Calcium Hydroxide do not and are referred to as weak bases

A number of flaws to the Arrhenius Theory Hydronium ions are present not bare hydrogen ions Arrhenius theory limited to aqueous solutions and not all acid base reactions are water based NH 3 +HClNH 4 Cl Baseacidammonium chloride

Brønsted -Lowry Update needed to reflect more accurately the reactions that occur 1923 Johannes Bronsted (Danish) & Thomas Lowry (English) – working independently came up with the same theory

Brønsted -Lowry Definition of an Acid –An acid is a proton donor Definition of a base –A Base is a proton acceptor

Detail HCl +H 2 OH 3 O + + Cl - Acidbase Donatesaccepts a protona proton Therefore these obey the B/L definition

Ammonia Gas NH 3 +H 2 ONH OH - baseacid accepts Donates a protona proton Therefore these obey the B/L definition

What to learn Water can act as an acid or a base - amphoteric

Can be applied to non aqueous reactions HCl+ NH 3 NH 4 + +Cl - Acidbase Brønsted –Lowry broadens the definition of what can act as an acid or a base

Homework Questions 12.1 in textbook and 12.1 in workbook

Conjugate acid-base pairs Add acetic acid (ethanoic acid) to water CH 3 COOH+ H 2 OCH 3 COO - + H 3 O The reaction works in both directions

Conjugate acid-base pairs Add acetic acid (ethanoic acid) to water CH 3 COOH+ H 2 OCH 3 COO - + H 3 O Donatesaccepts A protona proton

Conjugate acid-base pairs Add acetic acid (ethanoic acid) to water CH 3 COO - + H 3 O CH 3 COOH+ H 2 O AcceptsDonates A protona proton The water is behaving like an acid

Conjugate acid-base pairs Add acetic acid (ethanoic acid) to water CH 3 COOH+ H 2 OCH 3 COO - + H 3 O The reaction works in both directions so we call each conjugate pairs CH 3 COOH is a conjugate acid of CH 3 COO - CH 3 COO - is a conjugate base of CH 3 COOH

An acid changes into a conjugate base when it donates a proton CH 3 COOHCH 3 COO - H + acidConjugate proton base A base changes into a conjugate acid when it accepts a proton CH 3 COO - H + CH 3 COOH baseproton conjugate acid

Every acid has a conjugate base and every base has a conjugate acid... We call this an conjugate acid - base pair A conjugate acid – base pair is any pair consisting of an acid and a base which differs by one proton

Important The definition says that the pair must involve a single proton so...the conjugate pair of H 2 SO 4 HSO 4 -

Example What is the conjugate acid and the conjugate base of HC 2 O 4 - To change into its conjugate the base must accept a proton...so HC 2 O 4 - +H + H 2 C 2 O 4 HC 2 O 4 - +H + H 2 C 2 O 4 baseconjugate acid

Example What is the conjugate acid and the conjugate base of HC 2 O 4 - To change into its conjugate the acid must donate a proton...so HC 2 O 4 - C 2 O H + HC 2 O 4 - C 2 O H + Acidconjugate base

Tell me Which is the acid and which is the base HNO 3 + H 2 F 2 H 2 NO 3 + HF 2 Also mark out the pairs

HNO 3 + H 2 F 2 H 2 NO 3 + HF 2 Conjugate acid-base pair Acid Base

Neutralisation Neutralisation is the reaction between an acid and a base to form salt and water

Neutralisation Acids and base in the correct proportions cancel each other out This means they lose their characterisitics,the acid is no longer behaving like and acid and vice versa The resulting solution has a neutral effect on litmus paper

example HCl + NaOHNaCl+ H 2 O The word salt simply refers to the fact that the hydrogen in the acid is replaced by a metal or ammonium ion

What’s Happening? HCl + NaOHNaCl+ H 2 O In soln: H + + Cl - + Na + + OH - Na + + Cl - = H 2 O Lets ignore the spectator ions

H + + Cl - + Na + + OH - Na + + Cl - = H 2 O The hydrogen (hydronium) ions from the acid are reacting with the hydroxide ions from the base to form water which results in a neutral solution

Everyday examples Stomach HCL neutralised by NaHCO 3 –In other words...by an antacid (bioSodol) containing sodium hydrogencarbonate HCl + NaHCO 3 NaCl + H 2 O + CO 2 Another example (Maalox) 2HCl + Mg(OH) 2 MgCl + H 2 O

Everyday examples Calcium Oxide (lime) spread on soil to neutralize the acid conditions CaO + H 2 O Ca(OH) 2 Lime + waterCalcium Hydroxide Calcium Hydroxide can neutralize acidity as follows Ca(OH) 2 + H 2 SO 4 CaSO 4 + 2H 2 O Calcium hydroxide plus Sulfuric Acid becomes Calcium Sulfate and Water

Everyday examples Limestone added to lake water to neuralise the effects of acid rain CaCO 3 + H 2 SO 4 CaSO 4 + 2H 2 O + CO 2 Calcium carbonate plus Sulfuric Acid becomes Calcium Sulfate and Water and Carbon Dioxide

Homework Questions 12.2 – 12.6 in textbook and 12.2 – 12.4 in workbook