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QLDChemistryQuick questions
Unit 3: Equilibrium, acids and redox reactions
Quick questions on Bronsted-Lowry acids and bases (QCE Chemistry Unit 3)
14short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is the Bronsted-Lowry framework?Show answer
$$HA + B \rightleftharpoons A^- + HB^+$$
What is conjugate acid-base pairs?Show answer
Worked example. For HCl dissociating in water:
What is amphiprotic species?Show answer
An amphiprotic species can either donate or accept a proton, depending on the partner.
What is strong vs weak acids and bases?Show answer
The Bronsted-Lowry model frames acid strength as the position of the dissociation equilibrium.
What is strong vs concentrated (an exam trap)?Show answer
Strength (fraction dissociated) and concentration (mol/L) are independent.
What is conjugate strength relationship?Show answer
The conjugate of a strong acid is a very weak base (Cl- has essentially no proton-accepting tendency in water). The conjugate of a weak acid is a measurable base (CH3COO- accepts H+ to a small but real extent in water; CH3COO- solutions are basic).
What is linking back to Le Chatelier and Kc?Show answer
The weak acid equilibrium responds to disturbances per Le Chatelier:
What is strong acids and bases dissociate essentially completely?Show answer
The equilibrium lies overwhelmingly to the right; in QCE Chemistry we typically write a single arrow.
What is weak acids and bases dissociate only partially?Show answer
The equilibrium lies to the left; both molecular and ionic forms are present at significant concentration. Written with a double arrow.
What is calling water "neutral" when it acts as an acid?Show answer
Water is amphiprotic. Whether it acts as acid or base depends on the partner.
What is forgetting to write the conjugate acid of the base?Show answer
Every Bronsted-Lowry equation has two pairs; if you label only one, you have only half the answer.
What is mixing up strength and concentration?Show answer
A 0.001 mol/L solution of HCl is dilute but the acid is still strong (fully ionised). Likewise concentrated ethanoic acid is still weak.
What is using "acidic" for the conjugate of a strong base?Show answer
Cl- is a spectator; its presence does not lower pH. A weak conjugate has measurable pH effect; a vanishingly weak one does not.
What is treating the H3O+ vs H+ notation as a substantive distinction?Show answer
Both refer to the proton in water; QCAA accepts either but H3O+ is preferred in Bronsted-Lowry contexts because it reinforces the proton-transfer mechanism.