acids and bases. the basics… acids and bases are a group of compounds that share similar chemical...
TRANSCRIPT
Acids and Bases
The basics…• Acids and bases are a group of compounds
that share similar chemical properties. • There are a few ways that this group can be
classified.
Lewis Acids and Bases
Brønsted-Lowry Acid and Bases
Arrhenius Acid and Bases
Arrhenius Acids and Bases
• Arrhenius’ is the most common definition of acidic and basic compounds.
• Acid: Releases an H+ (hydronium) ion in solution– HA H+ + A-
• Base: Releases an OH- (hydroxide) ion in solution– BOH B+ + OH-
or H3O+
Common Arrhenius Acids and Bases
HCl H+ + Cl-
Ca(OH)2 Ca2+ + 2OH-
Regents Question
H-
H+
H3O+
OH-
BOH B+ + OH-
An Arrhenius Acid will produce which positively charged ion in solution?
1. Hydronium ion2. Hydride ion3. Hydroxide ion4. Hydrogen
In the following neutralization reaction, which compound is considered an
Arrhenius base? HCl + NaOH H2O + NaCl
1. HCl2. NaOH3. H2O
4. NaCl
Brønsted-Lowry Model
• While Arrhenius was H+ and OH-, Brønsted-Lowry focused exclusively on the H+.
• Brønsted-Lowry Acid: Donates an H+ ion• Brønsted-Lowry Base: Accepts an H+ ion
HCl + NH3 NH4+ + Cl-
Donates H+
Accepts H+
Who is the Brønsted-Lowry Base?HF + H2O H3O+ + F-
1.HF2.H2O
3.H3O+
4.F-
Who is the Brønsted-Lowry Acid?H3O+ + Cl- H2O + HCl
1.HCl2.H2O
3.H3O+
4.Cl-
Lewis’ Model: Acids and Bases• Lewis’ Model further expands the definition of
acids and bases• Lewis Acid: Electron-Pair Acceptor• Lewis Base: Electron-Pair Donor
LewisAcid
LewisBase
Accepts Electrons
DonatesElectrons
Strengths of Acids and Bases
• Ionize: To break apart into ions in solution• A strong acid/base will break apart completely • A weak acid/base will produce fewer ions
HCl H+ + Cl-
HF HF + H+ + F-
CompletelyIonizes
PartiallyIonizes
pH Scale• We measure the strength of Arrhenius acids
using the pH scale.
Neutral
BaseAcid
pH Scale• pH measures the concentration of H+ ions in solution• An increase of 1 pH means a 10 times increase in OH-
(or a 10 time decrease in H+)• At a pH of 7 (neutral) there are equal amounts of H+
and OH- in solution. • Acids have more H+ in solution• Bases have less H+ in solution
Which of the following compounds is an Arrhenius Acid?
1.NaOH2.NH3
3.CaCl2
4.H2SO4
In the following equation, which compound is the Brønsted-Lowry base?
HCl + H2O H3O+ + Cl-
1.Cl-
2.H3O+
3.H2O
4.HCl
Measures of Concentration
Concentration
• The amount of a solute in a solvent is something that we can quantify (assign a number to).
• We measure this in terms of molarity:
SolutionofLiters
SoluteofMolesMolarity
__
__
Moles
• Remember we can always determine moles from a given mass using the formula:
Calculating Molarity
• Consider the following statement: In a 500L solution, 50 moles of NaCl are dissolved.
Calculating Molarity
• Consider the following statement: 30 moles of KCl are disssolved in 60 L solution.
Significant Figures
http://blog.swivel.com/weblog/2007/02/ode_to_numbers.html
Not All Numbers Were Created Equal
When we are measuring an
object, we always guess a little
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Guessing
2 . 4 5Definite
Definite
Guess
Remember, you can only guess
on one number.
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Sig Figs Rules
• When adding or subtracting measurements, your answer can have no more decimal places than the measurement with the fewest decimal places. 45.6
54.65324.93425.18425.2
+
Sig Figs Rules
• When multiplying or dividing measurements, your answer can have no more numbers than the fewest number of significant (definite) figures. 48.3
296.6100
1 Sig Fig
The Rules of Zero
Atlantic
Right
Pacific
Left
The Rules of Zero
AtlanticAbsentRight
PacificPresentLeft
How many significant figures?
1.0450
Determine if there is a decimal present or absent.
The Rules of Zero
Atlantic
Right
Pacific
Left
How many significant figures?
Start counting with the first non-zero number.
1.0450
The Rules of Zero
AtlanticAbsentRight
PacificPresentLeft 1.0450
How many significant figures?
5 Sig Figs
The Rules of Zero
AtlanticAbsentRight
PacificPresentLeft 98700
How many significant figures?
3 Sig Figs
The Rules of Zero
AtlanticAbsentRight
PacificPresentLeft 98.70
How many significant figures?
4 Sig Figs
Acid-Base Titrations
Classic Part II Question
What we know…
• An Arrhenius acid is one that produces H+ or H3O+ in solution.
• When an acid reacts with a base, a neutralization reaction occurs.
• A neutralization reaction produces a salt and water each and every time.
Neutralization Reactions
• In a neutralization reaction, acid reacts with base to produce salt and water.
• Neutralization reactions are a type of double replacement reaction
HCl + Ca(OH)2 H2O + CaCl2
Acid Base Water Salt
Titration reaction
• Titration reactions are used to determine the concentration of an unknown acid.
MAVA = MBVB
Moles H+ = Moles OH-
• We can calculate the amount needed to neutralize any solution.
Titration• How many milliliters of 3M NaOH are needed
to neutralize 400mL of 2M HCl?
How much 4M NaOH is needed to neutralize 50mL of 2M HCl?
How much 6M HCl are needed to neutralize 100mL of 3M NaOH?
Titrating an Unknown Solution
• If we combine the information we have about titrations and indicators, we can determine the concentration of an unknown solution.
• We will need to use an indicator that has a changing point that is close to the neutral point.
Titration
Acid of Unknown
Concentration
Base
When the indicator changes color, all of the H+ has been neutralized.
If we know the VA, the MB and VB of the system we can back calculate the concentration of the acid.
VA
VB
MB
Titration• What is the concentration of 50mL of an acid
that is titrated to neutrality with 75mL of 3M NaOH?
Titration• What is the concentration of 80mL of a base
that is titrated to neutrality with 40mL of 2M HCl?
A student neutralized 16.4 milliliters of HCl by adding 12.7 milliliters of 0.0620 M KOH. What was the molarity of the
HCl acid?