QOTD 5/14/14
Please have out to be checked off:
• Soap reading/prelab Qs
• p. 59 Qs
QOTD: Rank the following solutions in order of most acidic to
least acidic and explain why.
• 1 M vinegar (weak acid)
• 1 M HCl (strong acid)
• 0.5 M HCl (strong acid)
• 1 M NaOH (strong base)
• 1 M NH3 (weak base)
• Pure water
QOTD Answer
QOTD: Rank the following solutions in order of most acidic
to least acidic and explain why.
1. 1 M HCl (strong acid)
100% ions (excess H+)
2. 0.5 M HCl (strong acid) 100% ions (excess H+)
3. 1 M vinegar (weak acid) less than 100% ions (~1%)
4. Pure water
neutral
5. 1 M NH3 (weak base)
less basic than a strong base
6. 1 M NaOH (strong base) strong base = most basic
= least acidic
Answers Homework Qs!
(p. 59)
Check-in Questions:
1. You have a 1.0 M solution of a strong acid (HCl) and 1.0 M of a
weak acid (acetic acid). Predict which will have a lower pH, and
explain why:
The 1.0 M HCl because it dissociates
completely…more H+ means lower pH
Check-in Questions:
2. How is the Bronsted-Lowry definition of acid/base theory
different from Arrhenius?
The Bronsted-Lowry theory says that a base
can accept a proton (H+) (in addition to
donating a OH-).
Homework Questions:
1. Label the following substances as acids or
bases. In each case, list the ions you would
expect to form in solution:
+, IAcid,
H
a. Hydroiodic Acid, HI
b. Rubidium Hydroxide, RbOH Base, Rb+, OHc. Selenous acid, H2SeO4 Acid, 2 H+, SeO 24
+
d. Phosphine, PH3 Base, PH4 , OH
e. Calcium hydroxide, Ca(OH)2 Base, Ca2+, 2 OHf. Perchloric acid, HClO4 Acid, H+, ClO4-
2. Consider a solution of hydrobromic acid, HBr. If you drew a particle view of HBr in water
that contained 10 H+ ions, how many Br- ions would you need? Explain your thinking:
10 Br- ions (to cancel out the 10 H+ ions)
3. Consider a solution of mangnesium hydroxide, Mg(OH)2. If you drew a particle view of
this substance with 10 Mg2+ ions, how many hydroxide (OH- ) ions would you need to draw?
20 OH- ions
4. The CO32- ion is a weak base. Explain, using Bronsted-Lowry theory, what makes this
substance a base:
It can accept a proton (H+)
Challenge: Some solutions conduct electricity better than other solutions. Use your
knowledge about the different kinds of acids and bases to explain why a 1.0 M
hydrochloric acid solution is a better conductor of electricity than a 1.0 M acetic acid
solution.
The strong acid dissociates completely, making
it easier for electricity to flow through the
solution . (more ions = more moving charges)
Acids and Bases Notes
PLEASE SEND A GROUP MEMBER TO
GRAB NOTES SHEETS!
Arrhenius Theory
• Acid: A substance that adds hydrogen ions,
H+, to an aqueous solution
• Base: A substance that adds hydroxide ions,
OH-, to an aqueous solution
• Not the best definition…
Bronsted-Lowry Definition
• Acid: Any chemical that donates a hydrogen
ion, H+
• Base: Any chemical that accepts a hydrogen
ion into their structure
+
Acid
Base
Proton
donor
Proton
acceptor
BAAD
• Bases Accept, Acids Donate
Example:
Acid Base
HCl + H2O  Cl- + H3O+
H+
Base Acid
NH3 + H2O  NH4+ + OHH+
Other terms to know
• Hydronium ion: H3O+
• Hydroxide ion: OH• Amphoteric (or amphiprotic) : Water can act
as both an acid and a base in different
situations
Your Turn (partner talk)
H2O + HBr  Br- + H3O+
Which compound is acting as an acid?
Which is acting like a base?
H2O
HBr
Your Turn (Partner talk)
H2O + SO42-  OH- + HSO4Which of the compounds is acting as a base?
SO42-
Your Turn (partner talk)
• Predict the products when phosphoric acid
(H3PO4) is added to water:
H3PO4 + H2O  H2PO4- + H3O+
Properties of Acids
• Corrosive
• Sour taste
• Contains hydrogen ions (H+) when dissolved in
water
• pH < 7
• Electrolytes (conduct electricity)
• Neutralize bases
http://qldscienceteachers.tripod.com/junior/chem/acid.html
Examples of Acids
•
•
•
•
•
•
•
•
Hydrochloric acid (HCl) in gastric juice
Sulphuric acid (H2SO4)
Nitric acid (HNO3)
Carbonic acid in soft drinks (H2CO3)
Uric acid in urine
Ascorbic acid (Vitamin C) in fruit
Citric acid in oranges and lemons
Acetic acid in vinegar
http://qldscienceteachers.tripod.com/junior/chem/acid.html
Properties of Bases
• Taste bitter
• Slippery
• Electrolytes (conduct electricity)
• Base + fat = soap
• Neutralize acids
• Corrosive
http://qldscienceteachers.tripod.com/junior/chem/acid.html
Examples of Bases
• Sodium hydroxide (NaOH)
• Calcium hydroxide ( Ca(OH)2 ) or limewater
• Ammonium hydroxide (NH4OH) or ammonia
water
• Magnesium hydroxide ( Mg(OH)2 ) or milk of
magnesia
• Many bleaches, soaps, toothpastes and
cleaning agents
http://qldscienceteachers.tripod.com/junior/chem/acid.html
Indicators
• Substances that change color when exposed
to an acid or base
• Can be used to identify acids and bases, even
their strength
• Usually a weak acid or base
Examples of indicators
• Litmus paper: Red for acid, blue for base
• pH paper: universal indicator, compare colors
to known pH
• Cabbage juice: color changes in response to
concentration of H+ ions
• Phenolphthalein: color is clear/cloudy in an
acid and pink in a base
Solutions
• Acidic solution: the hydronium ion
concentration is higher than the hydroxide ion
concentration [H+] > [OH-]
• Basic solution: hydroxide ion concentration is
higher than the hydronium ion concentration
[H+] < [OH-]
• Neutral solution: concentration of hydronium
and hydroxide ions is the same
[H+] = [OH-]
– Ex. Pure water
– Created when equal quantities of an acid and
base are combined
pH
• pH: Measures the concentration of H3O+ ions
• pH scale: A numeric scale used to describe
the acidity of a solution from 0 to 14
• Draw the scale below
0
Increasing strength
Acids
7
Increasing strength
Neutral
Bases
(water)
14
pH Scale
Acidic
Neutral solution
Basic
http://staff.jccc.net/pdecell/chemistry/phscale.html
Strong vs. Weak Acids and Bases
• Strong Acid or Base: all of the molecules
dissociate (split apart) into ions
• Weak Acid or Base: Only some of the
molecules actually dissociate
– Not as many H+ or OH- ions in solution
Strong base
Weak base
Soap!
• Let’s review the soap procedure…
• SAFETY! What will you use to protect yourself?
GOGGLES FOR EVERYONE!
Gloves for the person who pours the NaOH and mixes it.
• How hot will you make the NaOH and Oils?
50 degrees! They both need to be around 50 (+ or – a couple
degrees)