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chem 102 > chapter 15 (midterm 2) > Flashcards

chapter 15 (midterm 2) Flashcards

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1
Q

what are the properties of acids?

A 
sour taste 
react with active metals (Al, Zn,Fe)
corrosive 
react with carbonates (make co2)
change color of vegetable dyes 
react with bases to form ionic salts
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2
Q

what metals do not react with acids?

examples of carbonates?

A

Cu, Ag, Au

marble, baking soda, chalk, limestone

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3
Q

how are acids structured?

A

Binary acids have acidic hydrogens attached to a nonmetal atom - HCl, HBr, HI, HF

Oxy acids have acid hydrogens attached to an oxygen atom - H2SO4, HNO3

Carboxylic acids have COOH group
HC2H3O2, H3C6H5O7

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4
Q

properties of bases?

A

bitter
alkaloids- plant product
slippery
change color of vegetable dyes (different than acids)
react with acids - neutralization- ionic salts produced

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5
Q

how are bases structured?

A

Most ionic bases contain OH− ions
NaOH, Ca(OH)2

Some contain CO32− ions
CaCO3 NaHCO3

Molecular bases contain structures that react with H+
mostly amine groups

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6
Q

Arrhenius theory for bases

A

Bases dissociate in water to produce OH− ions and cations
ionic substances dissociate in water
makes OH
NaOH(aq) → Na+(aq) + OH−(aq)

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7
Q

arrhenius theory for acids

A

Acids ionize in water to produce H+ ions and anions
because molecular acids are not made of ions, they cannot dissociate
makes H+
they must be pulled apart, or ionized, by the water
HCl(aq) → H+(aq) + Cl−(aq)
in formula, ionizable H written in front
HC2H3O2(aq) → H+(aq) + C2H3O2−(aq)

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8
Q

what is the hydronium ion?

A

The H+ ions produced by the acid are so reactive they cannot exist in water
H+ ions are bare protons!!
Instead, they react with water molecules to produce complex ions, mainly hydronium ion, H3O+
H+ + H2O  H3O+
there are also minor amounts of H+ with multiple water molecules, H(H2O)n+

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9
Q

arrhenius theory for acid base reactions

A

The H+ from the acid combines with the OH− from the base to make a molecule of H2O
it is often helpful to think of H2O as H-OH

The cation from the base combines with the anion from the acid to make a salt
acid + base → salt + water
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

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10
Q

what are the problems with arrhenius theory?

A

Does not explain why molecular substances, such as NH3, dissolve in water to form basic solutions – even though they do not contain OH– ions
Does not explain how some ionic compounds, such as Na2CO3 or Na2O, dissolve in water to form basic solutions – even though they do not contain OH– ions
Does not explain why molecular substances, such as CO2, dissolve in water to form acidic solutions – even though they do not contain H+ ions
Does not explain acid–base reactions that take place outside aqueous solution

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11
Q

what is bronsted lowry theory?

A

Brønsted and Lowry redefined acids and bases based on what happens in a reaction.
Any reaction that involves H+ being transferred from one molecule to another is an acid–base reaction
regardless of whether it occurs in aqueous solution, or if there is OH− present
All reactions that fit the Arrhenius definition also fit the Brønsted-Lowry definition, but many more do as well

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12
Q

which is the H donor? acceptor?

A

The acid is an H donor

The base is an H acceptor
base structure must contain an atom with an unshared pair of electrons

In a Brønsted-Lowry acid-base reaction, the acid molecule gives an H+ to the base molecule

H–A + :B :A– + H–B+

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13
Q

describe bronsted lowry bases

A

Brønsted-Lowry bases are H+ acceptors
any material that has atoms with lone pairs can potentially be a Brønsted-Lowry base
because of the molecular structure, often one atom in the molecule is more willing to accept H+ transfer than others
When NH3 dissolves in water, the NH3(aq) is the base because NH3 accepts an H+ from H2O, forming OH–(aq)
water acts as acid, donating H+

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14
Q

lone pairs on base structures?

A

Because chemists know common bonding patterns, we often do not draw lone pair electrons on our structures. You need to be able to recognize when an atom in a molecule has lone pair electrons and when it doesn’t!

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15
Q

what are amphoteric substances?

A

Amphoteric substances can act as either an acid or a base
because they have both a transferable H and an atom with lone pair electrons

Water acts as base, accepting H+ from HCl
HCl(aq) + H2O(l) → Cl–(aq) + H3O+(aq)

Water acts as acid, donating H+ to NH3
NH3(aq) + H2O(l) NH4+(aq) + OH–(aq)

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16
Q

are reactions reversible in bronsted lowry theory? explain

A

One of the advantages of Brønsted-Lowry theory is that it allows reactions to be reversible
H–A + :B :A– + H–B+
The original base has an extra H+ after the reaction, so it will act as an acid in the reverse process
And the original acid has a lone pair of electrons after the reaction – so it will act as a base in the reverse process
:A– + H–B+ H–A + :B

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17
Q

what are conjugate pairs?

A

In a Brønsted-Lowry acid–base reaction, the original base becomes an acid in the reverse reaction, and the original acid becomes a base in the reverse process

Each reactant and the product it becomes is called a conjugate pair

The original base becomes its conjugate acid; and the original acid becomes its conjugate base

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18
Q

describe strong acids

A

A strong acid is a strong electrolyte

practically all the acid molecules ionize, →

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19
Q

describe strong bases

A

A strong base is a strong electrolyte

practically all the base molecules form OH– ions, either through dissociation or reaction with water, →

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20
Q

describe weak acids

A

A weak acid is a weak electrolyte

only a small percentage of the molecules ionize, arrows go both ways

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21
Q

describe weak bases

A

A weak base is a weak electrolyte
only a small percentage of the base molecules form OH– ions, either through dissociation or reaction with water, arrows go both water

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22
Q

what happens with stronger acids?

A

The stronger the acid, the more willing it is to donate H
water is the standard base accepting H
Strong acids donate practically all their H’s
100% ionized in water
strong electrolyte
[H3O+] = [strong acid]
[X] means the molarity of X

23
Q

what happens with weak acids?

A

Weak acids donate small fraction of H’s
most of the weak acid molecules do not donate H to water
«5% ionized in water
[H3O+] &laquo_space;[weak acid]

24
Q

list some strong acids

A 
HCL 
HBR
HI
HNO3
HCIO3
H2SO4
25
Q

list some weak acids

A 
HF
HC2H3O2
HCHO2
H2SO3
H2CO3
H3PO4
26
Q

how are acid and base strengths measured?

A

Commonly, acid or base strength is measured by determining the equilibrium constant of a substance’s reaction with water
HA + H2O A− + H3O+
A− + H2O HA + OH−
The farther the equilibrium position lies toward the products, the stronger the acid or base
The position of equilibrium depends on the strength of attraction between the base form and the H+
stronger attraction means stronger base or weaker acid

27
Q

how is acid strength measured?

A

Acid strength measured by the size of the equilibrium constant when reacts with H2O
HA(aq) + H2O(l) A−(aq) + H3O+(aq)

The equilibrium constant for this reaction is called the acid ionization constant, Ka
larger Ka = stronger acid

28
Q

what is the autoionization of water?

A

Water is actually an extremely weak electrolyte
therefore there must be a few ions present
About 2 out of every 1 billion water molecules form ions through a process called autoionization
H2O H+ + OH–
H2O + H2O H3O+ + OH–
All aqueous solutions contain both H3O+ and OH–
the concentration of H3O+ and OH– are equal in water
[H3O+] = [OH–] = 10−7M @ 25 °C

29
Q

describe kw and the relationship between h3o and oh-

A

The product of the H3O+ and OH– concentrations is always the same number
The number is called the Ion Product of Water and has the symbol Kw
aka the Dissociation Constant of Water
[H3O+] x [OH–] = Kw = 1.00 x 10−14 @ 25 °C
if you measure one of the concentrations, you can calculate the other
As [H3O+] increases the [OH–] must decrease so the product stays constant
inversely proportional

30
Q

what do all aqueous solutions contain?

A

All aqueous solutions contain both H3O+ and OH– ions

31
Q

neutral solutions (H3O and OH)

A

Neutral solutions have equal [H3O+] and [OH–]

[H3O+] = [OH–] = 1.00 x 10−7

32
Q

acidic solutions (H3O and OH)

A

Acidic solutions have a larger [H3O+] than [OH–]

[H3O+] > 1.00 x 10−7; [OH–] < 1.00 x 10−7

33
Q

basic solutions (H3O and OH)

A

Basic solutions have a larger [OH–] than [H3O+]

[H3O+] < 1.00 x 10−7; [OH–] > 1.00 x 10−7

34
Q

how is pH measured

A

The acidity or basicity of a solution is often expressed as pH
pH = −log[H3O+]
exponent on 10 with a positive sign
pHwater = −log[10−7] = 7
need to know the [H3O+] concentration to find pH
pH < 7 is acidic; pH > 7 is basic, pH = 7 is neutral
[H3O+] = 10−pH

35
Q

review slide 28

A

ok

36
Q

sig figs and log

A

Because the part of the scientific notation number that determines the significant figures is the decimal part, the sig figs are the digits after the decimal point in the log
log(2.0 x 106) = 6.30

37
Q

how do we find POH

A

Another way of expressing the acidity/basicity of a solution is pOH
pOH = −log[OH], [OH] = 10−pOH
pOHwater = −log[10−7] = 7
need to know the [OH] concentration to find pOH
pOH < 7 is basic; pOH > 7 is acidic, pOH = 7 is neutral
pH + pOH = 14.0

38
Q

what is PK?

A

A way of expressing the strength of an acid or base is pK

39
Q

describe pKa

A

pKa = −log(Ka), Ka = 10−pKa
The stronger the acid, the smaller the pKa
larger Ka = smaller pKa
because it is the –log

40
Q

describe pKb

A

pKb = −log(Kb), Kb = 10−pKb
The stronger the base, the smaller the pKb
larger Kb = smaller pKb

41
Q

sources of H3O and OH

A

There are two sources of H3O+ in an aqueous solution of a strong acid – the acid and the water
There are two sources of OH− in an aqueous solution of a strong acid – the base and the water

42
Q

describe Kw and how it shifts

A

For a strong acid or base, the contribution of the water to the total [H3O+] or [OH−] is negligible
the [H3O+]acid shifts the Kw equilibrium so far that [H3O+]water is too small to be significant
except in very dilute solutions, generally < 1 x 10−4 M

43
Q

how do we find pH of a weak acid? what is the equation?

A

finding the [H3O+] is complicated by the fact that the acid only undergoes partial ionization
Calculating the [H3O+] requires solving an equilibrium problem for the reaction that defines the acidity of the acid
HA + H2O = A - + H3O+

44
Q

how is percent ionization found?

A

Another way to measure the strength of an acid is to determine the percentage of acid molecules that ionize when dissolved in water – this is called the percent ionization
the higher the percent ionization, the stronger the acid
% ionization= molarity of ionized acid/initial molarity of acid X 100%
so
[H3O]equil/[HA] init X 100%

45
Q

why doesn’t the increase in H3O keep up with the increase in HA?

A

The reaction for ionization of a weak acid is
HA(aq) + H2O(l) A−(aq) + H3O+(aq)
According to Le Châtelier’s Principle, if we reduce the concentrations of all the (aq) components, the equilibrium should shift to the right to increase the total number of dissolved particles
we can reduce the (aq) concentrations by using a more dilute initial acid concentration
The result will be a larger [H3O+] in the dilute solution compared to the initial acid concentration
This will result in a larger percent ionization

46
Q

describe how strong bases act. equation?

A

The stronger the base, the more willing it is to accept H
use water as the standard acid
For ionic bases, practically all units are dissociated into OH– or accept H’s
strong electrolyte
multi-OH strong bases completely dissociated
[HO–] = [strong base] x (# OH)

NaOH = Na+ + OH-

47
Q

describe how weak bases act. equations?

A

In weak bases, only a small fraction of molecules accept H’s
weak electrolyte
most of the weak base molecules do not take H from water
much less than 1% ionization in water
[HO–] &laquo_space;[weak base]
Finding the pH of a weak base solution is similar to finding the pH of a weak acid

NH3 + H2O = NH4+ + OH-

48
Q

describe Kb

A

Base strength measured by the size of the equilibrium constant when react with H2O
:A− + H2O OH− + HA
The equilibrium constant is called the base ionization constant, Kb
larger Kb = stronger base

Kb= [OH-] [H:BASE+]
/
[:BASE]

49
Q

look at slide 48

A

ok

50
Q

what are the properties of salt

A

Salts are water-soluble ionic compounds
Salts that contain the cation of a strong base and an anion that is the conjugate base of a weak acid are basic
NaHCO3 solutions are basic
Na+ is the cation of the strong base NaOH
HCO3− is the conjugate base of the weak acid H2CO3
Salts that contain cations that are the conjugate acid of a weak base and an anion of a strong acid are acidic
NH4Cl solutions are acidic
NH4+ is the conjugate acid of the weak base NH3
Cl− is the anion of the strong acid HCl

51
Q

how do anions work?

A

Every anion can be thought of as the conjugate base of an acid
Therefore, every anion can potentially be a base
A−(aq) + H2O(l) = HA(aq) + OH−(aq)
The stronger the acid is, the weaker the conjugate base is
An anion that is the conjugate base of a strong acid is pH neutral
Cl−(aq) + H2O(l) = HCl(aq) + OH−(aq)
An anion that is the conjugate base of a weak acid is basic
F−(aq) + H2O(l) = HF(aq) + OH−(aq)

52
Q

kb vs Ka

A

Ka x Kb= [H3O][OH-]=KW

Ka= [A-] [H3O+] / [HA]

Kb= [HA][H3O+] / [A-]

53
Q

how do metal cations act as weak acids?

A

Cations of small, highly charged metals are weakly acidic
alkali metal cations and alkali earth metal cations are pH neutral
cations are hydrated

chem 102 (6 decks)

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