Mod 6 Using Bronsted Lowry Theory

Question 1

What is the concentration of H+ or H3O+ ions equal to in reference to pH?

Answer 1

10 ^ -pH

Question 2

What is the pH formula?

Answer 2

−log10[H+]

Question 3

What is the pOH formula?

Answer 3

−log10[OH-]

Question 4

What is the mathematical relationship between pH and pOH?

Answer 4

pH + pOH = 14

Question 5

what is Kw equal to?

Answer 5

10^-14

Question 6

What does concentration of OH- multiplied by concentration of H+ equal to?

Answer 6

Equal to 10^ -14

Question 7

What are the steps in finding the pH or pOH of a reaction, in which there is an excess and limiting reagent

Answer 7

Find which reactant is the limiting reagent.

Calculate how much excess of the other reagent there is left. (in terms of moles)

Convert to concentration using the combined volume

Write dissociation equation of the excess reagent and then figure out the concentration of either OH- or H+ ions

Figure out pH or pOH, given concentrations

Question 8

What is a dissociation equation?

Answer 8

Demonstrates the breaking of acids and bases in water, that is they become ionic

Question 9

How to calculate pH or pOH when solutions are diluted/mixed

Answer 9

Use the equation c1v1 = c2v2 to assist in finding concentrations

Question 10

What are the differences between strong, weak, concentrated and dilute acids.

Answer 10

Strong: Indicates that there is increased dissociation

Weak: Less dissociation of ions

Concentrated: More moles of acid in solution

Dilute: less moles of acid in solution

Question 11

What is the conjugate of a strong acid?

Answer 11

Extremely weak conjugate base

Question 12

Why is the conjugate of a strong acid a weak base?

Answer 12

It becomes extremely weak because it comes from a strong acid, and its desire to reattatch itself to H+ is very little, thus, it becomes an extremely weak conjugate base. It is an unmotivated proton acceptor

HCl –> H+ + Cl-

Question 13

What is the conjugate of a weak acid

Answer 13

A moderate (but relatively strong) conjugate base

Question 14

Why is the conjugate of a weak acid a moderate conjugate base?

Answer 14

Because the conjugate base comes from a weak acid, and is more motivated to reattach itself to the H+ due to the reversible nature of the reaction

CH3COOH ⇌ H+ (aq) + CH3COO - (aq)

Question 15

What is the conjugate of a strong base?

Answer 15

Extremely weak conjugate acid

Question 16

What is the conjugate of a weak base?

Answer 16

Moderate conjugate acid

Question 17

What is an amphiprotic substance?

Answer 17

A substance that can act as both an acid and base

Question 18

What are two examples of amphiprotic substances?

Answer 18

Sodium hydrogen carbonate (NaHCO3)

Potassium dihydrogen phosphate (KH2PO4)

Question 19

What does a weak acid and strong base mean for the pH of the salt solution?

Answer 19

Salt solution will be basic and therefore, pH > 7

Question 20

What does a strong acid and strong base mean for the pH of the salt solution?

Answer 20

Salt solution will be extremely weak conjugate acids and bases, thus solution is neutral with pH = 7

Question 21

What does a weak acid and weak base mean for the pH of the salt solution?

Answer 21

Both will provide us with moderate conjugate acids and bases, thus solution is neutral with pH = 7

Question 22

What does a Strong acid and weak base mean for the pH of the salt solution?

Answer 22

Weak base gives us a moderate conjugate acid. Strong acid gives us extremely weak base –> solution acidic –> pH < 7

Question 23

What is the school’s method of classifying a certain salt as either acidic, neutral or basic?

Answer 23

1. State what the salt ionises to form
2. State which ion is neutral (which can be determined by which came from a strong acid or base), and state that it cant hydrolyse further
3. State that the other ion (which came from a weak acid or base) comes from a certain weak acid or base, and that it will undergo hydrolysis in water
4. Concluding statement: Excess OH- or H+ in solution makes solution (basic/acidic). Thus pH is greater or less than or equal to 7 (depending)

Question 24

How would we use the school’s method of proving that NH4Cl is acidic

Answer 24

NH4Cl ionises to form NH4+ (aq) and Cl- (aq)

NH4Cl –> NH4 + (aq) + Cl- (aq)

Cl- is neutral, so it doesn’t hydrolyse further.

NH$+ comes from the conjugate weak base NH3+, and will act as a proton donor. It will undergo hydrolysis in water:

NH4+ (aq) +H2O (l) ⇌ NH3 (aq) + H3O+ (aq)

Therefore there will be excess H3O+ ions in solutions, which makes solution more acidic, so pH < 7