Transcript Chemistry -- Acids and Bases

Chemistry
Acid//Base Chemistry
I. Introduction
We’ve learned about:
- formation
- decomposition
- combustion
Now, we will learn about acid/base reactions
II. Acids & Bases
A. What is an acid?
1. Release a hydrogen ion (H+) in water (conduct
electricity when added H2O)
2. Neutralize bases in a neutralization rxn
3. Corrode active metals (releasing H2 gas)
4. Turn blue litmus paper red
5. Taste sour
Notes on the properties of
acids…
Don’t taste!
Conduct electricity
– ionic compounds conduct electricity
-- Acids are special covalent compounds that conduct
electricity when added to H2O
Litmus
--an indicator
Indicator: a substance that turns one color in the presence of
acids and another color in the presence of bases
Most acids are weak acids (dissociate poorly)
6 strong acids to memorize: Strong acids dissociate
completely in water (H+ + __-)
HCl
HNO3
HClO4
H2SO4
HBr
Everything else is weak!
HI
Acetic
v. HCl
B. What is a base?
1. Release hydroxide ion in water
2. Neutralize acids in neutralization rxns
3. Denature proteins (feel slippery to the
touch)
4. Bases turn red litmus paper blue
5. Taste bitter (Do NOT taste!)
Strong bases to memorize:
-- Easy: the hydroxides of the alkali metals
and barium (alkaline earth metal)
LiOH NaOH
KOH
RbOH
CsOH Ba(OH)2
III. The Chemical Definition
of Acids and Bases
Acid: a molecule that donates H+ ion(s)
Bases: a molecule that accepts H+ ion(s)
For example:
HCl + H2O → H3O+ + ClWhich is the acid and which is the base?
Important note about H3O+
-- Called the hydronium ion
-- Most often written as H+
-- As H+, just referred to as H+, hydrogen
ion, or a proton
-- H3O+ and H+ are the really the same
thing and are used interchangeably
Another acid/base reaction:
H2O(l) + NH3(aq) → NH4+(aq) + OHWhich is the acid and which is the base?
Water can be both an acid or a base –
depending on what it reacts with
Amphiprotic compounds: Compounds that can
act as either an acid or a base
Examples:
Which is acid and which is base?
H2SO4(aq) + CaCO3(aq) →
Ca2+(aq) + HSO4-(aq) + HCO3-(aq)
HCl(aq) + NaOH(aq)→H2O(l) + NaCl(aq)
2HNO3(aq) + Mg(OH)2(aq) →
Mg(NO3)2(aq) + 2H2O(l)
OYO’s
Determine the acid and base in the
following reactions:
10.1 HBr(aq) +NH3(aq)→NH4+(aq)
+ Br -(aq)
10.2 3C2H4O2(aq) +Al(OH)3 →
Al(C2H3O2)3(aq) + 3H2O(l)
10.3 H3PO4(aq) + 3KOH(aq) →
3H2O(l) + K3PO4(aq)
IV. Recognizing and Naming
Acids and Bases from their
Formulas
A. Recognizing - General Trends (not
strictly true):
-- Acids start with “H” in the formula
except C2H4O2 (aka CH3COOH and
HC2H3O2)
-- Bases that are ionic compounds and
have “OH” in formula
(2 notable exceptions: H2O and NH3)
Acid, base, or neither?:
HF
CH4
RbOH
CH3OH
HNO3
H2SO4
NaOH
B. Naming acids and bases
1. Acids
-- ions that end in “-ide”
hydro______ic acid (e.g., HCl)
-- ions that end in “-ate”
__________ic acid (e.g., H2SO4)
-- ions that end in “-ite”
__________ous acid (e.g., HNO2)
2. Bases
-- Normal ionic naming rules
(e.g., Sr(OH)2 – strontium hydroxide)
V. Predicting the Reactions that
Occur between Acids and Bases
A. How many protons can an acid donate
H3PO4 can donate up to 3 H+
-- “more than one” – “proton”
Polyprotic acid: An acid that can donate more
than one proton
Triprotic acid: An acid that can donate up to 3
protons
Diprotic acid: An acid that can donate up to 2
protons
B. Acids and Ionic Bases
Hydrofluoric acid and potassium hydroxide
HF + KOH → ?
Steps to solving:
1. Write acid and base as individual ions
2. Combine the negative acid ion with the
positive base ion, put the H+ with the negative
base ion
3. Balance (if necessary)
Acid + Ionic base → Salt + water
HCl + NaOH → NaCl + H2O
(You think of “salt” and NaCl – but a salt is
any ionic compound that formed because
an ionic base reacted with an acid!)
Examples:
Hydrochloric acid and rubidium hydroxide
Sulfuric acid and sodium hydroxide
Nitric acid and aluminum hydroxide
OYO’s
10.4 Give the chemical equation that
represents the reaction between each of the
following:
a. HClO3 and KOH
b. HBr and Ca(OH)2
c. H3PO4 and Mg(OH)2
Everyday example of acids and
bases:
Drain uncloggers contain base
;
-- proteins contain amino acids (hair, food)
Acid + Ionic base→ Salt + water
All-purpose Cleaners contain bases
-- most spills are acidic
Toilet bowl cleaners (contain acid)
--lime stains (CaO) are a common problem
-- CaO reacts with water in toilet to become CaOH
-- acid neutralizes
B. Acids and Covalent Bases
So…Acid + Ionic Base → Salt + water
…but when an acid is reacts with a
covalent base (and it always does –
because it is in aqueous solution) –
ions result
H2SO4 + H2O → 2H3O+ + SO42Acid + Covalent Base → ions
Examples:
H3PO4 + 3NH3 →
3NH4+ + PO43HOCl + H2O →
H3O+ + ClO-
OYO’s
10.5 What is the chemical equation that
describes the reaction between H2SO4 and
ammonia (NH3)?
10.6 What reaction occurs between HI and
water?
V. Molarity
(a.k.a. concentration)
Density = g/mL
Concentration in Chemistry:
moles/L = Molarity (M)
Example: The Works is 3% HCl; muriatic
acid is 30% HCl
What is the M of 1400.0 grams of muriatic
acid in 4.00 L of water?
What is the M of HCl in The Works?
More Examples:
What is the M of NaOH when 2.6 moles of
NaOH are dissolved in 534 mL?
124.3 g of HNO3 are dissolved in 250.0mL.
What is the M?
OYO’s
10.7 Determine the concentration for the
following acids and bases:
A. 2.1 moles HCl in 346 mL solution
B. 6.78 g KOH in 150.0 mL
C. 20.1 g H2SO4 in 3.4 L
VI. Dilution
Chemists don’t usually measure grams of acid or
base solution to make certain concentrations…
They dilute! (Always add acid TO water – if you
add water to acid, the acid may splash on you)
Here’s the formula (memorize):
C1V1 = C2V2
C1 = M of thing you are diluting
V1 = Volume of initial thing (how much of it
you will use (can be in mL or L – as long
as V2 is measured in the same units)
C2 = M you want in the end
V2 = Final volume of new concentration
(important: this is V1 + water to get to V2)
water you add = V2 – V1
Examples:
Chemist wants to dilute 12.0M HCl to get
500 mL of 3.5M HCl solution
Chemist makes 2.4L of 5.6M NaOH and
adds water to 10.0 L. New concentration?
Dilution equation not only applies to acids
and bases, but to all chemicals!
OYO
10.8 Chemist needs 750.0 mL of 3.5M
H2SO4. Has 10.0M H2SO4. Write out how
you would do the dilution.
VII. Using Concentration in
Stoichiometry
You can use the M of an acid or base to
find out how many grams of product
2HCl +
2H2O
100 mL
6.18M
Ba(OH)2 →
excess
BaCl2 +
?g
Example:
Sodium sulfate can be made by reacting
H2SO4 with sodium hydroxide. How many
grams of sodium sulfate can be produced
if 500.0 mL of 1.6M sodium hydroxide is
reacted with excess sulfuric acid?
OYO
10.9 Barium hydroxide is often used to clean
up toxic acid spills in industrial settings. If
10.0 L container of 12.0 M nitric acid is
broken, how many grams of barium
hydroxide will be needed to clean up the
spill?
VIII. Acid/Base Titrations
Titration: The process of slowly reacting a
base of unknown concentration with an
acid of known concentration (or vice
versa) until just enough acid has been
added to react with all of the base (the
endpoint has been reached).
Just stoichiometry with acids and bases!
OYO
10.10 125mL of nitric acid with unknown M
is titrated against magnesium hydroxide
with a concentration of 2.3 M. If 35.4 mL
of base are required in order to reach the
endpoint, what was the concentration of
the acid?