Chemistry Unit 7

Acids and Bases

Acids

An acid is a substance that produces positive hydrogen ions when placed in water. (H+)The strength of an acid depends on how completely the substance ionizes. Strong acids completely ionize in water. Weak acids ionize only slightly.

Base

A base is a substance that produces negative hydroxide ions when placed in water. (OH-)The strength of a base depends on how completely the substance dissociates into metal ions and hydroxide ions in water. Strong bases dissociate completely. Weak bases do not.

Basic Acidic Neutral

H+

H+

H+OH-

OH-

OH-

Solution Solution Solution

Which solution is Acidic? Basic? Neutral???

Acids and Bases

Produce H+ ions in waterHave a sour tasteBreak down metalsFormula starts with HPoisonous and corrosive to skinpH less than 7

Produce OH- ions in waterHave a bitter taste and a slippery feelBreak down fats and oilsFormula ends with OHPoisonous and corrosive to skinpH greater than 7

Acids and Bases

ACIDSExamples: vinegar,

lemon juice, aspirin, stomach acid, battery acid, cola, milk

BASESExamples: soap,

shampoo, ammonia, drain cleaner, antacids

Neutral SubstancespH = 7Safe to ingest and leave on skinConcentrations of H+ ions and OH-

ions are equalExamples: dH2O, salts, most

cosmetics, lotions, eye drops, etc.

Naming Acids (This should be review!)

Every acid formula starts with H, a cation. To name an acid, look at the anion the hydrogen is bonded to.H2S anion = chloride ion

H2SO3 anion = sulfite ion

H2SO4 anion = sulfate ion

Naming Acids1) If the name of the anion ends in –

ide, the acid name begins with the prefix hydro- The stem of the anion is given then the suffix -ic is added and is followed by the word acid.

H2S (anion sulfur) hydro + stem + ic +

acid Hydrosulfuric

Acid

Naming Acids

2) If the name of the anion ends in –ite, the acid name is the stem of the anion with the suffix –ous and is followed by the word acid.

H2SO3

(anion Sulfite) stem + ous + acid Sulfurous Acid

Naming Acids

3) If the name of the anion ends in –ate, the acid name is the stem of the anion with the suffix –ic and is followed by the word acid.

H2SO4

(anion Sulfate) stem + ic + acid)Sulfuric Acid

Does the formula contain Oxygen?

Hydro “stem”ic acid Anion end in __ ?

No Yes

“stem”ous acid“stem”ic acid

“ate” “ite”

Naming Acids

Writing Formulas for Acids

If the name starts with “hydro”Hydrosulfuric Acid

Write the hydrogen ion with charge.H+1

Write the anion with the proper charge.S-2

Balance the charges using subscripts. H2S

Writing Formulas for AcidsIf the name contains the suffix –ous

Sulfurous AcidWrite the hydrogen ion with charge.

H+1

Look up the polyatomic ion (sulfite) and write it with the correct charge.

SO3-2

Balance the charges using subscripts. H2SO3

Writing Formulas for AcidsIf the name contains the suffix –ic without the prefix hydro

Sulfuric AcidWrite the hydrogen ion with charge.

H+1

Look up the polyatomic ion (sulfate) and write it with the correct charge.

SO4-2

Balance the charges using subscripts.H2SO4

Writing Formulas/Naming Acids

Remember the following statements…

“I ate it and it was icky.” -ate becomes -ic

“Rite ous” -ite becomes -ous (Righteous)

Naming Bases

Bases are named using the traditional ionic naming system. Metal name + polyatomic ion name

Examples:Ca(OH)2 = calcium hydroxideNaOH = sodium hydroxideAl(OH)3 = aluminum hydroxide

Writing Base FormulasBase formulas are written using the traditional ionic system.Look up the metal ion. Write the symbol with the proper charge. Ca+2

Look up the polyatomic ion. With bases, this will always be hydroxide, OH-1.Balance the charges using subscripts.

Ca(OH)2

Neutralization Reactions

When an acid is added to a base, the end products are always salt and water. (neutral)A salt is defined as the neutral end product of an acid/base reaction.

ACID + BASE SALT + WATER H2S + Ca(OH)2 CaS + H2O

What is wrong with this equation???

Balance the final equation!

H2S + Ca(OH)2 CaS + H2O

1 Ca 11 S 14 H 22 O 1

H2S + Ca(OH)2 CaS + 2 H2O

Neutralization ReactionsTry another example:Acid + Base Salt +

Water

H2SO4 + NaOH Na2SO4 + H2O

1 Na 21 SO4 1

3 H 21 O 1

H2SO4 + 2 NaOH Na2SO4 + 2 H2O

Take it one step further…Sulfurous acid and sodium hydroxide

yields sodium sulfite and water.

H2SO3 + NaOH Na2SO3 + H2O

1 Na 21 SO3 1

3 H 21 O 1

H2SO3 + 2NaOH Na2SO3 + 2H2O

One Last StepHydrosulfuric acid and calcium

hydroxide yields what??? H2S + Ca(OH)2

1) One product will always be water. H2S + Ca(OH)2 H2O + 2) The other product will be the + ion

of the base bonded with the – ion of the acid.

H2S + Ca(OH)2 2H2O + CaS

pH Scale

pH – a number used to denote the hydrogen ion concentration, or acididty, of a solution

pH Scale Typically runs from 0 – 14

0 7 14Acidic BasicNeutral

pH IndicatorsA chemical substance that changes color in the presence of an acid and/or a base.

1) pH paper – Dip the paper, match color to scale on vial to determine numeric pH.pH<7 = acid, pH>7 = base, pH = 7 neutral

2) Litmus – Dip one red and one blue paper.Red stays red, blue turns red AcidBlue stays blue, red turns blue BaseRed stays red, blue stays blue Neutral

pH Indicators3) Bromthymol Blue – Add a few drops of

bromthymol blue to the substance. If the blue color turns to yellow AcidIf the blue color stays blue Base4) Phenolphthalein – Add a few drops of

phenolphthalein to the substance.If the clear liquid turns to pink BaseIf the clear liquid remains clear Acid

Concentration Strength of an acid or base is determined by the amount of ionization. Concentration is determined by the amount of water added to the substance.

Molarity (M)

The number of moles of solute dissolved in each liter of solution.

Molarity = moles of solute

liters of solution

Example Problem #1

If 1.00 liter of sugar water contains exactly 1.00 mole of sugar, what is its molarity?Molarity = 1.00 mol

1.00 LMolarity = 1.00 M

Example Problem #2

If 1.00 liter of sugar water contains exactly 2.00 mole of sugar, what is its molarity?Molarity = 2.00 mol

1.00 LMolarity = 2.00 M or 2.00 mol/L

(Twice as concentrated…)

Example Problem #3

What is the molarity when 0.75 mol is dissolved in 2.50 L of solution?

Molarity = 0.75 mol = 0.30 mol/L or 0.30M

2.50 L

In Lab, grams are typically used in place of moles.If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need? First, calculate the molar mass of the acid.H 1 x 1.00795 = 1.00795Cl 1 x 35.453 = 35.453

36.46095 = 36.461

If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need?

First, calculate the molar mass of the acid.

HCl contains 36.461 g/mol

It would take 36.461 g of HCl to make 1 liter of a 1M HCl solution. How many grams would it take to make 2L of a 1M solution?

2 x 36.461g = 72.922g

If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need?

It takes 72.922g of HCl to make 2 liters of a 1M solution. How much would it take to make 2 liters of a 6M solution?

6 x 72.922g = 437.532 g

Try One MoreSuppose you wanted to make 2 liters of a 0.5 M solution of HCl. How much HCl would you need?Each mole of HCl is equal to 36.461gFor a 0.5 M solution, you would need half that much. 36.461 x 0.5 = 18.2305g.However, you want to make 2 liters, so double that amount. 18.2305 x 2 = 36.461g.