CHAPTER 8- ACIDS, BASES, & SALTS

DEFINITIONS

•

Acids

– – Ionize to form

hydronium ions

(H 3 O + ) in water (Arrhenius) Donates a proton to the base (Bronsted) – Accepts a pair of electrons from base (Lewis)

HCl + H

2

O



H

3

O

+

+ Cl

–

DEFINITIONS

•

Bases

– – – Dissociate or ionize to form

hydroxide ions

(OH ) in water (Arrhenius) Accepts a proton from acid (Bronsted) Donates pair of electrons to acid (Lewis)

NH

3

+ H

2

O



NH

4 +

+ OH

-

DEFINITIONS

•

Indicator

– substance that changes color in an acid or base • Examples: – litmus - red/blue – phenolphthalein - colorless/pink – goldenrod - yellow/red – red cabbage juice - pink/green

PROPERTIES

• • • • • • sour taste corrosive Electrolytes (solns that conduct electricity when dissolved in water) turn blue litmus paper red react with metals to form H 2 pH below 7 gas • bitter taste • corrosive • electrolytes • turn red litmus paper blue • slippery feel • Many contain –OH groups • pH above 7

• • Ionize completely in water Strong electrolyte – Solutions of these acids have as many hydronium atoms as the acid can possible form • • Do not ionize completely in water Weaker electrolyte – Some acid molecules will combine with water to form ions – Some of these ions will recombine to form molecules of the weak acid

USES

• H 3 PO 4 - soft drinks, fertilizer, detergents • H 2 SO 4 - fertilizer, car batteries • HCl - gastric juice, swimming pools • HC 2 H 3 O 2 - vinegar

• • Metal + OH All IA and IIA hydroxides are strong • Dissociate completely in water into ions • Strong electrolyte • Do not dissociate completely in water • Weaker electrolyte

USES

• NaOH - lye, drain and oven cleaner • Mg(OH) 2 - laxative, antacid • NH 3 - cleaners, fertilizer • Ca(OH) 2 - treating acid soil, cement, mortar

• •

SAFETY

Any acid or base can be very dangerous in concentrated form Always wear goggles and gloves if you must work with these!!!!

PH SCALE

•

pH

– – – a measure of the concentration of H 3 O + ions in solution measured with a pH paper, pH meter or an indicator with a wide color range Ranges from 0-14 I

NCREASING ACIDITY NEUTRAL

I

NCREASING BASICITY

PH SCALE

pH of Common Substances

• •

CALCULATING PH

Can calculate using the molarity of H+ ions Equation is as follows: • pH= -log ([H+]) • Type in negative sign, press log button, left parenthesis, H+ concentration, right parenthesis Example: Determine the pH of an HCl solution with a concentration of 0.0001 M pH= -log ([H+]) pH= -log (0.0001) pH= 4

CONCEPTEST

• Which of the following "molecular" pictures best represents a concentrated solution of the weak acid HA?

A B

CONCEPTEST

• Is the following statement TRUE or FALSE?

– A strong acid has a lower pH than a weak acid.

– FALSE - Strong/weak refers to amount of ionization whereas pH refers to concentration of H + .

COMMON CHEMICALS

SOAP & DETERGENT

• • •

Chemical composition

Improve water’s ability to clean Soaps are salts of potassium and fatty acids, basic with –COO chains Detergents are salts of sodium, potassium, and sometimes ammonium, basic with –SO 3 chains •

How they work

Negatively charged ends dissolve in water, other end dissolves in oil, dirt, and grease

HOUSEHOLD CLEANERS

• •

Ammonia

Ammonia is a weak base [OH ] concentration low, but there is enough ions to help emulsify thin layers of dirt and fingerprints NH 3 + H 2 O  NH 4 + + OH • •

Bleach

A strong disinfectant – A chemical substance that kills harmful bacteria or viruses Changes stains to colorless form because of the oxygen atom in the hypochlorite ion, ClO -

Ammonia and Bleach should not be mixed because noxious chloramine gas, NH 2 Cl is formed!!!

HEALTHCARE

• •

Antacids

We will see how these work in labs Made of magnesium hydroxide or sodium bicarbonate • • •

Shampoo

pH balanced between 5-8 If shampoo is too basic, will cause strands of hair to swell Shampoo that is too acidic dries out hair

• • •

THE REFRIGERATOR TRICK

The apple was cut at the same time One side was moistened with lemon juice Why does this work?

– The citric acid in lemon juice helps antioxidants in the apple that react with oxygen can react with other substances in the apple

REACTIONS WITH ACIDS AND BASES

NEUTRALIZATION REACTION

• • Chemical reaction between an acid and a base.

Products are a salt (ionic compound) and water.

NEUTRALIZATION REACTION

ACID + BASE



SALT + WATER HCl + NaOH



NaCl + H

2

O

=

Neutralization does not always mean pH = 7.

NEUTRALIZATION REACTION

KOH + HNO

3



H

2

O + KNO

3

Acid?

HNO

3

Base?

KOH Salt?

KNO

3

• • • •

NEUTRALIZATION REACTIONS

Not all produce neutral solutions final pH depends on amounts and strength of acids and bases that are combined If a strong acid reacts with an equal amount of weak base, the resulting solution will still be acidic If a strong base reacts with an equal amount of weak acid, the resulting solutions will still be basic

TITRATION

•

Titration

– Process in which a standard solution is used to determine the concentration of an unknown solution.

standard solution unknown solution

TITRATION

•

Equivalence Point

– Point at which equal amounts of H 3 O + and OH have been added.

– Determined by… • indicator color change • dramatic change in pH

• •

EQUIVALENCE POINT

• The equivalence point is not always neutral When strong base reacts with strong acid, EP is neutral When strong base reacts with a weak acid or strong acid reacts with weak base, EP will not be at pH 7

EQUIVALENCE POINTS

Weak Acid titrated with strong base Weak base titrated with strong acid

• •

SALTS

Origin of NaCl in US – Underground deposits from dried up ancient seas Uses of NaCl – Sodium in your diet – Seasoning and preserving food – Ceramic glazes – Soap – Water softeners – De-icing of highways – Fire extinguishers