ACIDS AND BASESUnit VII

I ELECTROLYTES

An electrolyte is a compound, that when dissolved in water, conducts electricity How?

Ions (charges) produced are free to move Movement of charge is conductivity

Examples Acids Bases “Salts”

Soluble Ionic compounds

II PROPERTIES

Acids Good conductors Dissolve metals

Table J--Metals above “H2” dissolve in acid

Taste sour Turns litmus paper red Turns phenolphthalein clear

II PROPERTIES

Bases Good conductors Dissolve fats

Feels slippery Taste bitter Turns litmus paper blue Turns phenolphthalein pink

III DEFINITIONS

A. Arrhenius Acids

An Arrhenius acid contains H+ ions When dissolved in water these H+ ions

combine to form hydronium ion (H3O+) Examples: HCl H2SO4 HC2H3O2

Bases An Arrhenius base contains OH- ions

(hydroxide ion) bonded to NH4+ or a metal

Examples: NaOH Ca(OH)2

III DEFINITIONSB. Brönsted-Lowry

Acids A Brönsted-Lowry acid loses or donates

protons to its conjugate (substance that differs by an H+) HCl + NH3 → Cl - + NH4

+

HCl and Cl- are conjugate pairs; HCl is the acid and Cl - is its conjugate base

Bases A Brönsted-Lowry base gains or accepts protons

from its conjugate HCl + NH3 → Cl - + NH4

+

NH3 and NH4+ are conjugate pairs; NH3 is

the base and NH4+ is its conjugate acid

IV NOMENCLATURE

A. Naming Compounds Binary Acids

A binary acid contains hydrogen and a nonmetal To name a binary acid

Use “hydro-” Add nonmetal root word End with “ic acid”

Ex. HCl Hydrochloric acid

Ex. H2O

Hydroxic acid

IV NOMENCLATURE Ternary Acids

A ternary acid contains hydrogen and a polyatomic ion To name a ternary acid

Determine the polyatomic that is present using Reference Table E

If the polyatomic ion ends in “ate” change the ending to “ic”

If the polyatomic ion ends in “ite” change the ending to “ous”

Ex. HClO3 Chlorate becomes Chloric acid (no hydro

is used)

Ex. HNO2 Nitrite becomes Nitrous acid

IV NOMENCLATURE

Bases To name a base, name as you would any

compound Write the first element Write the polyatomic Add a Roman numeral if needed

Ex. NaOH Sodium hydroxide

Ex. Cu(OH) 2 Copper II hydroxide

IV NOMENCLATURE

B. Writing Formulas- Acids

• If binary • Write H+ and the other element present• Assign charges and criss-cross

Ex. Hydrochloric acid

H+1 Cl-1

HCl

IV NOMENCLATURE

• If ternary • Identify the polyatomic present using

ending• Write H+ and the polyatomic ion• Assign charges and criss-cross

• Ex. Chloric acid• chloric comes from chlorate

ClO3-1

• H+1 ClO3-1

• HClO3

V REACTIONS

A Neutralization Mixing of acid and base

HCl + NaOH → Makes salt and water

Break (ionize) the acid and base H+1 Cl-1 Na +1 OH-1

Join H to OH (H2O) Join metal to nonmetal (assign charges and

crisscross)

HCl + NaOH → H2O + NaCl

Lab technique for neutralization is called Titration Occurs when moles of acid equals moles of

base For 1:1 acid–base reactions

Moles acid = Moles base MAVA = MBVB

EXAMPLES OF TITRATION PROBLEMS Given the balanced equation:

HCl + NaOH → H2O + NaCl How many milliliters of 3.0M NaOH are needed to

neutralize 20 milliliters of 2.5M HCl? MB= 3.0M NaOH MA= 2.5M HCl VA= 20 mLs HCl

Ratio is 1:1 so MAVA = MBVB can be used 2.5M x 20 mLs = 3.0M x VB

50 = 3VB

VB=16.7 mLs NaOH

EXAMPLES OF TITRATION PROBLEMSGiven the balanced equation:

H2SO4 + 2 NaOH → 2 H2O + Na2SO4

How many milliliters of 1.2 M NaOH are needed to neutralize 23 milliliters of 1.9 M H2SO4?

MB= 1.2 M NaOH

MA= 1.9 M H2SO4

VA= 23 mLs H2SO4

Ratio is NOT 1:1 so MAVA = MBVB CANNOT be used23mL H2SO4 x 1L x 1.9 mole H2SO4 x 2 mole NaOH x 1L x 1000

ml

1000 mL 1 L 1 mole H2SO4 1.2 mole NaOH 1L

VB= 72.8 mLs NaOH

IV REACTIONS

B Hydrolysis Mixing of salt and water

Makes parent acid and base of the salt

NaCl + HOH → HCl + NaOH

Reverse of neutralization

VI STRENGTH

Acid and base strength depend on number of ions in solution More ions; stronger acid or base

Some acids ionize 100% (strongest acids) HCl HBr HI H2SO4 HNO3 HClO4

Some bases ionize 100% (strongest bases) LiOH NaOH KOH RbOH CsOH NH4OH

A. pH

Every aqueous solution contains H + and OH-

• Acids have more H+ than OH-

• Bases have more OH- than H+

pH represents the amount of H + in a solution

1 7 14

Strong Weak Neutral Weak Strong

acid acid base base

Most H+ Equal H+ and OH- Least H+

Least OH- Most OH -

pH Scale is logarithmic•Values change by factors of 10

• ex. pH = 3 vs. pH = 5• Difference in pH• 2 units

• 10 x 10• pH 3 is 100 times stronger than pH 5• pH 5 is 1/100th as strong as pH 3

B. Acid Base Indicators Compounds that change color over pH ranges

Table M Common Acid–Base Indicators• methyl orange 3.2–4.4 red to yellow• bromthymol blue 6.0–7.6 yellow to blue• phenolphthalein 8.2–10 colorless to

pink• litmus 5.5–8.2 red to blue• bromcresol green 3.8–5.4 yellow to

blue• thymol blue 8.0–9.6 yellow to blue