Block 5: Acids and Bases Flashcards Preview

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Flashcards in Block 5: Acids and Bases Deck (63)
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1

What is the equation to calculate pH from [H3O+]?

pH = -log[H3O+]

2

What is the equation to calculate [H3O+] from pH?

[H3O+] = 10^-pH

3

What is the definition of an acid?

A substance that can donate a proton to another substance (proton donor)

4

What is the definition of a base?

A substance that can accept a proton from another substance (proton acceptor)

5

What is a conjugate acid?

A species formed after a base has accepted a proton

6

What is a conjugate base?

A species formed after an acid has donated a proton

7

What does 'amphiprotic' mean?

A species which can sometimes be an acid and sometimes a base

8

What affects the position of an equilibrium in a given system?

The ability of an acid/base to accept/donate a proton- related to their strength.

9

Where will eq lie if HA is a better proton donor to B than HB+ is to A-?

It will lie to the right- products favored

10

Where will eq lie if HB+ is a better proton donor to A- than HA is to B?

It will lie to the left- reactants favored

11

What molecule is used to reference the strength of acids?

Water

12

If an acid is strong, will its conjugate base be weak or strong?

Weak (NB this works vice versa)

13

If a base is strong, will its conjugate acid be weak or strong?

Weak (NB this works vice versa)

14

What is the equilibrium constant?

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

15

What does not appear in the eq constant?

Water

16

Why doesn't water appear in the eq constant?

The equation is only a ratio of the real concentrations, and as water is pure water it has a concentration of 1, causing both its value and units to cancel out. Therefore as it is a (l), it doesn't feature. NB this also applies to (s).

17

What is denoted by a larger Ka value?

A stronger acid

18

What is the formula for finding pKa?

pKa = -log(Ka)

19

What does a smaller pKa denote?

A stronger acid

20

Why does pKa = 0 for H3O+ with H2O?

Because the same species are on both sides of the equation
H3O+ + H2O H3O+ + H2O

21

What affects the strength of an acid?

The charge of A in HA
The polarity of the HA bond
The strength of the HA bond

22

How does the charge of A in HA affect acid strength?

If a is positive, it will be stronger as the + charge of H and A repel, making proton donation easier.
If a is negative it will be weaker as the -ve charge of A and + H attract, making proton donation harder

23

How does the polarity of the HA bond affect acid strength?

If the A is more electronegative the delta + charge on H will be higher, making the transfer easier

24

How does the strength of the HA bond affect acid strength?

HA will be stronger if the HA bond is weak (and longer eg. for large elements)

25

Which is more important for determining acid strength between strength and polarity of bond?

Strength

26

What helps to determine acid strength with oxoacids?

Whether Hs are bonded to Os or to less electronegative atoms
The number of atoms bonded to the central atom

27

How does Hs bonded to Os or other atoms affect acid strength of oxoacids?

If there are more Hs on Os, these have a larger delta plus value and so are more easily removed, making the acid stronger.
If there are fewer, they are less positive and harder to remove, making the acid weaker.

28

How does the number of electronegative atoms on the central atoms affect acid strength of oxoacids?

More electronegative atoms on the central atom means that a negative charge formed when the H is removed can be shared between multiple centers, stabilizing the molecule and making it more likely to form. Therefore the acid is stronger. NB this can be extended to the rest of the molecule

29

Are haloacids (CH2Cl COOH) stronger than regular acids and why?

Haloacids are stronger as they have more electronegative centers to share the negative charge with, making them more stable. (The more substituted, the stronger)

30

What is Kw?

Kw= [H3O+][OH-], and is called the autoprotolysis of water. At room temperature it is 1x10-14, but this increases with an increase in temperature.