10. Acids and Bases

Question 1

What is the difference between an Arrhenius acid and an Arrhenius base?

Answer 1

Arrhenius Acids dissociate to produce an excess of hydrogen ions in solution.

Arrhenius bases dissociate to produce an excess of hydroxide ions in solution

Question 2

What’s the difference between a Bronsted Lowry acid and a Bronsted Lowry Base?

Answer 2

Bronsted Lowry Acids species that can donate hydrogen ions. Bronsted Lowry Bases are species than can accept hydrogen ions.

H+ acceptor and and donor

Question 3

What’s the definition of a lewis acid and base?

Answer 3

Acid: Electron pair acceptor
Base: Electron Pair donor

Question 4

What’s the main difference between Bronsted Lowry and Arrhenius definitions of acids and bases?

Answer 4

There’s not
The only difference would be a water molecule.

Question 5

What common molecule is amphoteric?

Answer 5

Water

Question 6

The K_w, a constant is generally the same.

What can change the equilibrium constant?

Answer 6

Temperature

Question 7

How do you figure out the pH when you have a decimal with number?

i.e. What is the pH of a solution with a concentration of hydrogen atoms of 3 x 10^-4?

Answer 7

pH=m-log(n)

pH= n x 10^m

p[OH or H]= m-0.n

pH= 4-0.3= 3.7

Question 8

What’s the difference between a strong acid/base and a weak acid/base?

Answer 8

Strong Acid/base= completely dissociates in solution

Weak Acid/Base= do not completely dissociate in solution

Question 9

What is a salt or neutralization reaction?

Answer 9

When the reaction forms a salt and sometimes water.

Question 10

What is an amphoteric species?

Answer 10

An amphoteric species can act as an acid or a base.

Question 11

If a compound has a Ka value&raquo_space; water, what does it mean about its behavior in solution? How does this compare with a solution that has only a slightly higher Ka than water

Answer 11

High K_a indicates a strong acid, which will dissociate completely in solution. Having a K_a slightly greater than water means the acid is a weak acid with minimal dissociation.

Question 12

Complete the following table

Answer 12

p[OH or H]= m-0.n

n x 10 ^-m

Answer 13

a. K_a x K_b = K_w

Question 14

Determine the concentration of hydrogen ions and pH of a solution of 0.2 M acetic acid (K_a= 1.8 X 10^-5)

Answer 14

K_a= ([x][x])/.2

x= 1.9 x 10^-3

pH= 2.8

Question 15

What does polyvalent acids or bases mean?

Answer 15

Polyvalent acids and bases are those that can donate or accept multiple electrons

Question 16

What is the difference between a titrant and a titrand?

Answer 16

titrant has a known concentration and is added slowly to the titrand to reach the equivalence point.

titrand has an unknown concentration but a known volume.

Question 17

What is the half-equivalence point?

Answer 17

The half-equivalence point is the midpoint of the buffering region, in which half of the titrant has been protonated (or deprotonated); thus, [HA]= [A-] and a buffer is formed.

Question 18

How do you know where the equivalence point when evaluating acids/bases is when provided information on a graph

Answer 18

It is at the steepest part of the graph.

Question 19

What two ways do you use to calculate the equivalence point of acids and bases?

Answer 19

1. Graph it with amount of acid/base added vs pH
2. You can use an indictor

Question 20

Why are buffers useful in general?

Answer 20

They resist changes in pH when small amounts of acid or base is added

Question 21

(Equation) What is the Henderson-Hasselbalch Equation and what it is its purpose?

Answer 21

It us used to estimate the pH or pOH of a buffer solution

[A-]= concentration of the conjugate base
[HA]= concentration of the weak acid

Question 22

Describe each of the following parts of a titration curve:
Buffering Region
Half-equivalence point
Equivalence point
End point

Answer 22

Buffering Region: occurs when [HA] = [A-] and is the flattest portion of the titration curve (resistant to changes in the pH)

Half-Equivalence Point: center of the buffering region, where [HA]=[A-]

Equivalence Point: Is the steepest point on the titration curve, and occurs when equivalents of acid present equal the equivalents of base added (or vice-versa).

Endpoint: the pH at which an indicator turns its final color

Question 23

In which part of the pH range (acidic, basic, or neutral) will the equivalence points fall for each of the following titrations?

Strong acid + weak base=

Strong base + weak acid=

Strong Acid + strong base=

Weak acid + weak base=

Answer 23

Strong acid + weak base= acidic range

Strong base + weak acid= basic range

Strong Acid + strong base= 7

Weak acid + weak base=can be anywhere, depending on the equivalence point and the relative strengths of the acids and bases.

Question 24

What are the pH and pOH of a solution containing 5ml of 5M benzoic acid (Ka= 6.3 x 10 -5) and 100 mL of 0.005 M benzoate solution?

Answer 24

*** I do not understand this one

Need to use the Henderson Hasselbach Equation

ph= 2.57
pOH= 11.43