Acids and BasesSection A2.4

Unit AScience 10

Objective ChecklistAt the end of this lesson, will be able to:

Identify and classify acids and bases based on their properties

Name acids and bases

Acids and BasesImportant Control digestion in our bodies (stomach acid

and activation and deactivation of enzymes)Found in foods and used in industry

Acid or a Base?Taste:

Acids- sour (ex. Lemons- citric acid)Bases- bitter (ex. Soap)

Touch:Bases- slippery to the touch and corrosive to the

skin What does corrosive mean?

Acids- not slippery and corrosive to the skinReaction with Metal:

Acids- react; forms H2 gas (bubble formation)Bases- don’t react

Using pHWhat is pH used for?What does the scale look like?What substance is considered neutral?Where do the following substances place on

the scale?Acid rain, normal rain, lemon juice, stomach

juicesBaking soda, human blood, oven cleaner,

window cleaner (ammonia)

ConductivityBoth acids and bases have or form ions in

solutionIn solution, these ions can conduct electricity,

so they are electrolytesCan you think of any everyday items that

contain an acid or a base (alkali) to conduct electricity?

IndicatorsTo determine pH and whether something is

an acid or base, we use indicatorsIndicators change color depending on pHLitmus paper is created through extracting

the chemical from lichens Acid: blue litmus paper turns red (BRA)Base: red litmus paper turns blue (RBB)Neutral: paper stays same color

ACID RED BASE BLUE

DemonstrationWhat color should the acid (lemon juice,

citric acid) turn the blue litmus paper? Red litmus paper?

What color should the base (bleach) turn the red litmus paper? Blue litmus paper?

How do we test whether the unknown is an acid or base? If blue litmus stays blue, can we conclude that it is a base? Why or why not?

Recognizing AcidsIn acids, the formula often has a “H”

(hydrogen ion – may be more than one) on the left side of the formula (ex. HCl)Can also appear on the right side as “-COOH”

(organic acid group) (ex. CH3COOH) They are bonded to an anion (one or more

non-metals)

To identify acids from formulas, look for “H” on the left or “-COOH” on the right

Recognizing AcidsWhich of the following are acids?

HBr(aq) NaCl(aq)H2SO4(aq) HCOOH(l)

NaOH(aq) H2O(l) HNO3(aq)C6H5COOH(l)

K2SO4(aq)

Naming AcidsIUPAC method: name as an aqueous ionic

compound What would HCl be using these rules?

Another method:1) When containing hydrogen and non-metallic

element (anion name ends in –ide):Use prefix “hydro” and suffix “ic”Ex. HCl becomes hydrochloric acid

What would HF be using this rule?

Naming Acids cont…2) When acid contains oxygen (ex. H2SO4(aq)),

name based on the anion What is the anion in H2SO4(aq)?

If anion ends in “ate”, name of acid ends in “ic”

Ex. H2SO4(aq) contains sulfate anion (SO42-) and is then named sulfuric acid

What is the acid name of H3PO4(aq)? How do we approach naming it?

Naming Acids cont…3) if anion ends in “ite”, name of acid ends

in “ous”H2SO3 (aq)contains the anion sulfite (SO3

2-), so the acid is named sulfurous acid

What is the name of the acid HNO2(aq)?

PracticeAcid Formula Name

HNO3(aq)

chromic acid

HI(aq)

hydrobromic acid

HClO(aq)

nitric acid

H2CrO4(aq)

hydroiodic acid

HBr(aq)

hypochlorous acid

For your reference

Back of periodic table sheet

Recognizing BasesOften, bases are identified by presence of

“OH-” (hydroxide ion) with a metal ion or the ammonium ion (NH4

+)It is more complicated than this, but for now:

Any compound with high solubility and an OH on right is a base

Name base as would name an ionic compound What would NaOH be named using rules we

already know?

PracticeBase Name

KOH(s)

ammonium hydroxide

calcium hydroxide

Mg(OH)2(s)

aluminium hydroxide

potassium hydroxide

NH4OH(aq)

magnesium hydroxide

Al(OH)3(s)

Ca(OH)2

NeutralizationReaction between acid and a base which

produces water and a saltThe acidic and basic properties disappearWhy would this be important? Give an

exampleEx. A bee’s sting contains methanoic acid

which dissolves nerve endings in the skin (lots of pain!). Sting creams containing ammonia limit the pain as the ammonia neutralizes the acid

Neutralization DemoWhat pH is water?Is vinegar an acid or a base?What color do we observe initially?If I add alka-seltzer (a base) predict the color

changeWhat do we observe as I add the base?Explain why this occurred