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Bases

Strong bases are hydroxide salts

For now, only important weak base is NH3

Ionization of weak acid produces a weak base

If the oxalate anion (C2O4-) reacts in an acid-base reaction,

which of the following can’t it make?

1 2 3

28%

53%

19%

1. H2C2O4

2. HC2O4-

3. 2CO2

Acid Base Reactions

Acid Base Reactions

Strong Acid + Strong Base

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) acid base “salt” water

What do we get if we mix:

HBr (aq) + LiOH (aq)

Acid Base Reactions

Diprotic acids or bases

H2SO4(aq) + NaOH(aq)

H2SO4(aq) + Ba(OH)2(aq)

HCl(aq) + Ba(OH)2(aq)

Acid Base Reactions

Strong Acid + Weak Base

HCl(aq) + NH3(aq)

What do we get if we mix:

HNO3(aq) + NH3(aq)

Acid Base Reactions

Weak Acid + Strong Base (like strong acid+strong base)

HCN(aq) + NaOH(aq) NaCN(aq) + H2O(l) acid base “salt” water

What do we get if we mix:

HCOOH (aq) + KOH (aq) formic acid

Net Ionic Equations

1. Write a balanced chemical equation Molecular equation

1. Write out all the ions Total ionic equation

2. Cancel out anything that appears on both sides

Net ionic equation

Net Ionic Equations

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

What really happens:

H+(aq) + OH-(aq) H2O(l)

Sodium ion and chloride ion are “spectator ions”

Reactions Involving a Weak Base

Molecular equation:

HCl(aq) + NH3(aq) NH4Cl(aq)

Total ionic equation:

H+(aq) + Cl-(aq) + NH3(aq) NH4+

+ Cl-(aq)

Net ionic equation:

H+(aq) + NH3(aq) NH4+ (aq)

What is the net ionic equation for:

HNO3(aq) + NH3(aq) NH4NO3(aq)

CH3CO2H(aq) + NaOH(aq)

1 2 3

33% 33%33%1. CH3CO2H2

+(aq) + NaO(aq)

2. CH3CO2-(aq) + H2O(l) + Na+(aq)

3. CH4(g) + CO2(g) + H2O(l)

20

HCN(aq) + NH3(aq)

1 2 3

33% 33%33%

20

1. NH4+(aq) + CN-(aq)

2. H2CN+(aq) + NH2-(aq)

3. C2N2(s) + 3 H2(g)

The pH Scale

Quantitative measure of solution acidity

Remember solution concentration:

[NaCl]=0.25M means 0.25 moles of NaCl are in 1L of solution

solventL

solutemolesMolarity

1

#

The pH Scale

In pure water, some molecules ionize to form H3O+ and OH-

H2O + H2O OH– + H3O+

In acidic and basic solutions, these concentrations are not equal

acidic: [H3O+] > [OH–]

basic: [OH–] > [H3O+]

neutral: [H3O+] = [OH–]

The pH Scale

pH scale= measure of [H3O+]pH < 7.0 = acidicpH > 7.0 = basicpH = 7.0 = neutral

Measure of H3O+ concentration (moles per liter) in a solution

As acidity increases, pH decreases

The pH Scale

The pH scale is logarithmic100100 101022 log(10log(1022) = 2) = 21010 101011 log(10log(1011) = 1) = 111 101000 log(10log(1000) = 0) = 00.10.1 1010–1–1 log(10log(10–1–1) = –1) = –10.010.01 1010–2–2 log(10log(10–2–2) = –2) = –2

pH = –log [HpH = –log [H33OO++]]

pH if [HpH if [H33OO++] = 10] = 10–5–5? 10? 10–9–9??

Acidic or basic?Acidic or basic?

pH if [HpH if [H33OO++] = 0.000057 M?] = 0.000057 M?

Finding [H3O+] from pH

[H[H33OO++] = 10] = 10-pH-pH or [H or [H33OO++] = log] = log-1-1 (-pH) (-pH)

Finding the inverse log (or log Finding the inverse log (or log -1-1)of a number )of a number on your calculator:on your calculator:

Enter the number, press the inverse (inv) or shift button, Enter the number, press the inverse (inv) or shift button, the press the log button (it might be labeled 10the press the log button (it might be labeled 10xx))

What is [HWhat is [H33OO++] if pH = 8.6?] if pH = 8.6?

pH: Quantitative Measure of Acidity

Acidity is related to concentration of H+ (or H3O+)

pH = -log[H3O+]

[H3O+]=10-pH=log-1(-pH)