Mod 6 Using Bronsted Lowry Theory Flashcards
What is the concentration of H+ or H3O+ ions equal to in reference to pH?
10 ^ -pH
What is the pH formula?
−log10[H+]
What is the pOH formula?
−log10[OH-]
What is the mathematical relationship between pH and pOH?
pH + pOH = 14
what is Kw equal to?
10^-14
What does concentration of OH- multiplied by concentration of H+ equal to?
Equal to 10^ -14
What are the steps in finding the pH or pOH of a reaction, in which there is an excess and limiting reagent
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
What is a dissociation equation?
Demonstrates the breaking of acids and bases in water, that is they become ionic
How to calculate pH or pOH when solutions are diluted/mixed
Use the equation c1v1 = c2v2 to assist in finding concentrations
What are the differences between strong, weak, concentrated and dilute acids.
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
What is the conjugate of a strong acid?
Extremely weak conjugate base
Why is the conjugate of a strong acid a weak base?
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-
What is the conjugate of a weak acid
A moderate (but relatively strong) conjugate base
Why is the conjugate of a weak acid a moderate conjugate base?
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)
What is the conjugate of a strong base?
Extremely weak conjugate acid
What is the conjugate of a weak base?
Moderate conjugate acid
What is an amphiprotic substance?
A substance that can act as both an acid and base
What are two examples of amphiprotic substances?
Sodium hydrogen carbonate (NaHCO3)
Potassium dihydrogen phosphate (KH2PO4)
What does a weak acid and strong base mean for the pH of the salt solution?
Salt solution will be basic and therefore, pH > 7
What does a strong acid and strong base mean for the pH of the salt solution?
Salt solution will be extremely weak conjugate acids and bases, thus solution is neutral with pH = 7
What does a weak acid and weak base mean for the pH of the salt solution?
Both will provide us with moderate conjugate acids and bases, thus solution is neutral with pH = 7
What does a Strong acid and weak base mean for the pH of the salt solution?
Weak base gives us a moderate conjugate acid. Strong acid gives us extremely weak base –> solution acidic –> pH < 7
What is the school’s method of classifying a certain salt as either acidic, neutral or basic?
- State what the salt ionises to form
- 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
- 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
- Concluding statement: Excess OH- or H+ in solution makes solution (basic/acidic). Thus pH is greater or less than or equal to 7 (depending)
How would we use the school’s method of proving that NH4Cl is acidic
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
