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.