Chapter 20 - Acids and Bases

Question 1

What is the 100 rule and how is it used when calculating the ph of solutions with a weak acid?

Answer 1

a. Take your initial concentration, divide it by Ka, if the answer turns out to be greater than 100 you can use the assumption that the amount of acid dissociated is very small compared to the initial moles and so you can remove the amount dissociated from the Ka formula and just use the initial moles.
b. You can make sure of this value “x” dissociated by working it out its value using the assumption and dividing it by the initial moles to see if its less than 0.05 (known as the 5% rule).

Question 2

What is the formula for the pH?

Answer 2

pH=-log [H+]

Question 3

What is the formula for the pOH?

Answer 3

pOH=-log [OH-]

Question 4

What is the relationship between pH and pOH?

Answer 4

pH+pOH=14

Question 5

What is the relationship between Kb and Ka?

Answer 5

Kb x Ka = 1x10^-14 This is only true when you are using the Ka of an acid and the Kb of its conjugate base.

Question 6

What is the conjugate of a strong acid?

Answer 6

The conjugate of a strong acid is a weak base.

Question 7

List of strong acids?

Answer 7

HCl, HBr, HI, HNO3, H2SO4, HClO4

Question 8

What is the Kb of NH3?

Answer 8

1.8x10^-5

Question 9

What is the formula for calculating the [H+]?

Answer 9

[H+] = 10^-pH

Question 10

What is an amphoteric chemical?

Answer 10

A chemical is amphoteric if it can be both an acid and a base.

Question 11

List of strong bases?

Answer 11

LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2.

Question 12

How much would you need to dilute a solution of pH 1 to get to a pH of 4?

Answer 12

a. To dilute a solution from pH 1 to a pH of 4 (3 pH units) would require dilution by 10 x 10 x 10 = 1000 times.
b. Generally, a solution with a pH 1 contains 10^13 times more H+ ions as a solution with pH of 14.
c. Also, a pH of 1 has 10 times the concentration of H+ ions as a solution with pH of 2.

Question 13

What is the relationship between Ka and pKa in terms of acidic strength?

Answer 13

a. The stronger the acid, the larger the Ka value and the smaller the pKa value.
b. The weaker the acid, the smaller the Ka value and the larger the pKa value.

Question 14

What name is given to Kw?

Answer 14

The ionic product of water.

Question 15

What does ionisation mean?

Answer 15

Ionisation is the process by which neutral atoms or molecules are converted to electrically charged atoms or molecules (ions).