Acids and Bases

An Introduction

Chapter 7

What do you already know about acids and bases?

What r some common acids?

Deoxyribonucleaic acid (DNA)

Ribonucleaic acid (RNA)

Amino acids (building blocks of protein)

Lactic acid (build-up →sore muscles; by-product of cell metabolism and insufficient oxygen)

Boric acid (antiseptic)

Acetic acid ( in vinegar)

Citric acid (in fruits)

What is an acid?

“an acid is a substance that produces hydrogen ions in solution” – Arrhenius 1884

HCl (aq) → H+ (aq) + Cl- (aq)

What r some common bases?

Most soaps/detergents

Most drain cleaners

Most window cleaners

What is a base?

“ a substance that produces hydroxide ions in solution” – Arrhenius

NaOH (aq) →Na+ (aq) + OH- (aq)

Distinguishing between acids and bases

Most solutions of both acids and bases are clear and colourless.We need an indicator to tell them apart.An indicator is a chemical which changes colour as the concentration of H+ (aq) and OH- (aq) changes.Two common indicators are litmus and phenolpthalein

Which compounds are acids and which are bases?

Acids: Formulas begin with one or more hydrogen atoms (ex. HCl (aq) or H2SO4 (aq))

Names have the word “acid” in them (ex. Hydrochloric acid or sulfuric acid)

Bases: Formulas end with one or more “OH” (ex. NaOH (aq) or Ca(OH)2 (aq))

Names end in hydroxide (ex. Sodium hydroxide or calcium hydroxide)

Characteristics of acids

Sour taste (never taste lab chemicals)Stinging feeling on mucous membranesStrong acids will burn your skinAggressive reactions with metalsConduct electricityTurns blue litmus redPhenolpthalein remains colourlessForms carbon dioxide when reacting with carbonates and non metal oxides when reacting with water

Characteristics of bases

taste bitter feel slippery (soap and many drugs are bases)caustic on organic matterconduct electricity Strong bases will burn your skinTurn red litmus blueTurns phenolpthalein pinkDoes not react with carbonates but forms metallic oxides when reacting with water

Oxides of Elements

Acids and bases are formed when oxides of elements react with water.

An oxide is a binary compound formed with an element and oxygen e.g. CO, CO2 , Al2O3, N2O5

H2O (l) + CO2 (g) → H2CO3 (aq)

pH : a “powerful” scale ( courtesy of Sørensen – a Danish biochemist)

Really means the power or concentration of hydrogen ions in solutionThe lower the pH the greater the concentration of H+ (aq) and the more acidic the solutionThe higher the pH, the greater the concentration of OH- (aq) and the more basic the solutionThe scale goes from 0-14 with a midpoint of 7Solutions with a pH of 7 are neutral

Ways to measure pH

pH paper

pH meters

pH probes

How is pH calculated?

You need not know this but for future reference:pH = -log [H+]E.g. suppose that your concentration was 0.010 , enter this in your calculator and press the log button, change the sign, your answer should be 2.0Home work text p. 218 1-4, p. 225 1-5

Properties of Acids and Bases

Two factors determine how many H+ ions are contained in a solution: concentration and percent ionizationConcentration refers to the amount of pure acid dissolved per litre of waterPercent ionization refers to the number of molecules that will ionize per 100 that dissolve.Strong acids ionize completely whereas weak acids do not. E.g. sulfuric is strong and acetic is weakStrong bases also ionize completely whereas weak bases do not e.g. NaOH is a strong base but NH3 is not

Strong Acids and Bases

Name Formula

Sulfuric acid H2SO4

Hydrochloric acid HCl

Nitric acid HNO3

Carbonic acid H2CO3

Sodium hydroxide NaOH

Potassium hydroxide KOH

Calcium hydroxide Ca(OH)2

Magnesium hydroxide Mg(OH)2

ammonia NH3

Neutralization reactions

When an acid and a base react together to form a new compound, the word equation is Acid + Base → Salt + WaterA salt is an ionic compound produced when an acid and base reactThe reaction is also known as a neutralization reaction

HNO3 (aq) + KOH (aq) → KNO3 (aq)+ H20 (l)

Chemistry of Swimming Pools

Acids, bases, and neutralization reactions help maintain water in swimming pools.Water is chlorinated to kill bacteria and algae but chlorine gas is toxic so we use sodium hypochlorite insteadThe following reactions describe how the pH of pools are adjustedHOCl (aq) +NaOH (aq) → NaOCl (aq) + H2O (l) NaOCl (aq) + H2O (l) →HOCl (aq) + Na+ (aq) + OH- (aq)HOCl (aq) → H+ (aq) + OCl- (aq) Acidic water may be neutralized by adding sodium carbonateBasic water may be neutralized by adding hydrochloric acid

Next up

Acid Rain

Purple Rain

Rain on Me