Flashcards in Chemistry: Acids & Bases Deck (59)

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1

## Strong Acids

###
Strongest: HCl, H2SO4, HNO

HBr, HI, HClO4 (HPO4?), HClO3

Strong acid Formula

Perchloric acid HClO4

Hydroiodic acid HI

Hydrobromic acid HBr

Sulfuric acid H2SO4

Hydrochloric acid HCl

Nitric acid HNO3

Hydronium ion H3O+ or H+

2

## Strong Bases

###
Strong bases Formula

Lithium hydroxide LiOH

Sodium hydroxide NaOH

Potassium hydroxide KOH

Rubidium hydroxide RbOH

Cesium hydroxide CsOH

Calcium Hydroxide Ca(OH)2

Strontium hydroxide Sr(OH)2

Barium hydroxide Ba(OH)2

3

## What is the ionization constant of H2S?

###
much less than 1

WEAK ACID!

4

## -SH vs. -OH

###
Because of charge density (charge per volume):

-SH: weak

-OH: strong

Share ~same charge but S has larger volume it has lower charge density... means more stable and therefore less reactive

charge density= charge/volume

5

## pH

### -log[H+]

6

##
Assuming 25 degrees Celsius:

pH + pOH =

### 14

7

##
What is the relationship between the variables on the L and R sides of the equations?

pH=-log[H+]

pOH=-log[OH]

pKa = -log[Ka]

pKb = -log[Kb]

###
inverse:

ie: if pH goes down, [H+] goes up

8

##
a) What is pH if [H+] = 1.0 x 10^-1?

b) What is pOH if 1.0 x 10^8

(@25 degrees C)

###
a) 1

b) -8

9

##
Steps to convert concentrations of H+ and OH- into pH and pOH (@25 degrees C)

Examples

A) H+: 6.4 x 10^-3

B) OH-: 2.1 x 10^-8

###
A) H+: 6.4 x 10^-3

1) For ones value of answer (pH from [H+]): Lock in on the power of 10. Flip the sign and subtract 1.

(10^-3) --> -3 --> +2

2) For decimal of answer: Subtract the digits (before the power of 10) from 10.

(6.4 ~ 6) --> 10-6 = 4

3) Put it together: 2.4 = pH

_______________

B) OH-: 2.1 x 10^-8

pOH=7.8

10

##
(In 3 steps)

Convert pH into [H+]

a) pH: 13.3

b) pH: 1.8

(also works for pOH-->OH, pKa-->Ka, pKb--Kb, @25 degrees C)

###
A)pH: 13.3

1) 13 --> 10^-14

2) .3 -->10-3 = 7

3) 7 x 10^-14 = [H+]

A)pH: 1.8

1) 1 --> 10^-2

2) .8 -->10-8 = 2

3) 2 x 10^-2 = [H+]

11

##
Based on the pKa, which of the following species is the strongest base?

pKa of ammonium ion for:

*NH3: 9.26

*(CH3CH2)2NH: 10.64

*(Ch3CH2)2NH: 10.98

*(CH3CH2)3N: 10.76

###
Answer: (CH3CH2)2NH:

pKa --> pKb of ammonium ion: (14-pKa=pKb)

So,

*NH3: 9.26 (pKb: 4.74)

*(CH3CH2)2NH: 10.64 (pKb: 3.36)

*(CH3CH2)2NH: 10.98 (pKb: 3.02)

*(CH3CH2)3N: 10.76 (pKb) 3.24

Smallest Kb: 4.74

***Largest Kb: 3.02**

Largest pKa = Smallest pKb = Largest Kb = strongest base

12

## The bigger the pKa, the ____ the base?

###
Bigger the pKa -->

Smaller the Ka

Smaller the Ka -->

Bigger the Kb

Bigger the Kb -->

Stronger the base

13

## Reacting equivalents

###
make stoich corrections for how many mol acid/base are produced per mol of reacting source

Ex:

HCl --> H+ + Cl-

(1 mol HCl --> 1 eq acid)

H2SO4 --> 2H+ + SO4^2-

(1 mol HsSO4 --> 2 eq acid)

Ca(OH)2 --> Ca^2+ + 2OH-

(1mol Ca(OH)2 --> 2 eq base)

----------------------

(MCAT limits to Acid-Bases... but it applies elsewhere)

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##
Gram-Equivalent Weight

Ex: NaOH and Na2CO3

###
Stoich correction of molecular weight

g/eq = g/mol X mol/eq

NaOH (1mol:1eq ratio)

40 g/mol x 1 mol/1eq= 40 g/eq

Na2CO3 (1mol:2eq ratio)

106 g/mol x 1 mol/2 eq = 53 g/eq

15

##
Normality (N)

Ex: H2SO4

###
stoich corrections for molality--needed for world of equivalents in world of eq points (as opposed to world of mols)

eq/L = mol/L x eq/mol

1O^-1 mol/L x 2 eq/mol = 2 x 10^-1 eq/L

16

## Titration Curves

###
Strong Acid-Strong Base: steeper

Weak Acid-Strong Base: less steep

17

## Titrant

### solution of known concentration

18

## Equivalence Point Formula

###
WHEN you are at the equivalence point:

Eq acid = Eq base

*Use this formular to find the M? or vol? or grams?

*Does not care about pH if asking for volume of base added!!!

*If everything is monoprotic/monobasic, you can interchange M and N... but be read JIC

19

## Eq Pt Formula: Both aq

###
(Normality of Acids)(Volume of Acid) = (Normality of Base)(Volume of Base)

(eq/L)(L) = (eq/L)(L)

20

## Eq Pt Formula: aq/solid

### (Normality of Acids)(Volume of Acid) = mass base/gram eq wt = mass/mw x eq/mol

21

##
Titration Question Types

(pH question families)

###
1) What is the pH at X point in the curve?

2) What is the volume/grams/moles of the solution ?

22

## Eq Pt Formula: if using both solids

### mass of acid/gram eq wt = mass of base/ gram eq wt

23

##
Set up the formula to find:

How many mg of NaOH (s) is required to neutralize 408 mg of KHP (s), a monoprotic weak acid with a mw of 204 amu?

###
Monoprotic means Gram Eq Wt (GEW)= mw

Mass of acid/ GEW = mass of base / GEW

408/204 = x/40

2=x/40

x=80

24

##
Set up the formula to find:

How many mg of NaOH (s) is required to neutralize 40 mL of a 10^-1 M HCl solution?

###
(N of acid) * (V of acid) = mass/GEW

(10^-1)(40) = x/40

x=160

25

##
In Weak Acid-Strong Base (or SA-WB--same)Titrations, how are the following affected?

*pH initial

*pH Halfway

*pH at eq pt

e.g.

HA + NaOH --> H2O + A-Cl+

###
Buffer solution: weak acid with its weak CB in solution at the same time (Henderson-Hasselbach time)

Simulation:

-Initial: HCl=30eq, NaCl=0eq

-Halfway: HCl=15eq, NaCl=15eq

-Eq Pt: HCl=0eq, A-Cl+=30eq

*pH initial: must use Ka expression to solve

*pH Halfway: buffer soln (must use H-H eqn to solve)

*pH at eq pt: HA neutralized, A- = wk base, pH > 7

25

##
In Weak Acid-Strong Base (or SA-WB--same)Titrations, how are the following affected?

*pH initial

*pH Halfway

*pH at eq pt

e.g.

HA + NaOH --> H2O + A-Cl+

###
Buffer solution: weak acid with its weak CB in solution at the same time (Henderson-Hasselbach time)

Simulation:

-Initial: HCl=30eq, NaCl=0eq

-Halfway: HCl=15eq, NaCl=15eq

-Eq Pt: HCl=0eq, A-Cl+=30eq

*pH initial: must use Ka expression to solve

*pH Halfway: buffer soln (must use H-H eqn to solve)

*pH at eq pt: HA neutralized, A- = wk base, pH > 7

26

##
In Strong Acid-Strong Base Titrations, how are the following affected?

*pH initial

*pH Halfway

*pH at eq pt

e.g.

HCl + NaOH --> H2O + NaCl

###
*Assume 100% disassociation.

Simulation:

-Initial: HCl=30eq, NaCl=0eq

-Halfway: HCl=15eq, NaCl=15eq

-Eq Pt: HCl=0eq, NaCl=30eq

*pH initial: easy to solve bc [HCl]initial = [H+]

*pH Halfway: NaCl is inert, so [HCl]halfway = [H+]

*pH at eq pt (look at the products): HCl neutralized, NaCl inert, pH = 7

Aside: how do we know NaCl is inert? it is a conjugate of strong species. That is HCl is strong so produces inert Cl. NaOH is strong so produces inert Na.

26

##
In Strong Acid-Strong Base Titrations, how are the following affected?

*pH initial

*pH Halfway

*pH at eq pt

e.g.

HCl + NaOH --> H2O + NaCl

###
*Assume 100% disassociation.

Simulation:

-Initial: HCl=30eq, NaCl=0eq

-Halfway: HCl=15eq, NaCl=15eq

-Eq Pt: HCl=0eq, NaCl=30eq

*pH initial: easy to solve bc [HCl]initial = [H+]

*pH Halfway: NaCl is inert, so [HCl]halfway = [H+]

*pH at eq pt (look at the products): HCl neutralized, NaCl inert, pH = 7

Aside: how do we know NaCl is inert? it is a conjugate of strong species. That is HCl is strong so produces inert Cl. NaOH is strong so produces inert Na.

27

## What is the pH of a 10^-3 HCl soln (pKa = -8)

###
Strong acid soln: 100% disassociation

[HCl]initial --> [H3O+]

[H+] = 10^-3

pH = 3

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