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VICChemistryQuick questions
Unit 2: How do chemical reactions shape the natural world?
Quick questions on Concentration units, acids and bases, and pH: VCE Chemistry Unit 2
10short 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 concentration units?Show answer
Pick the unit that matches the question's data:
What is dilution?Show answer
Adding more solvent decreases concentration but not the moles of solute. The dilution formula follows from n = cV being constant:
What is the Brønsted-Lowry model?Show answer
A Brønsted-Lowry acid is a proton donor; a Brønsted-Lowry base is a proton acceptor. An acid-base reaction is a proton transfer:
What is strong vs weak; concentrated vs dilute?Show answer
Strong = ionises (or dissociates) completely in water. All HCl molecules become H+ and Cl^-. The position of the ionisation equilibrium lies essentially fully to the right.
What is pH?Show answer
where [H+] is in mol L^-1. For pure water at 25 deg C, [H+] = 10^-7 mol L^-1 and pH = 7.
What is confusing strong with concentrated?Show answer
A strong acid can be dilute. A weak acid can be concentrated. Always say which axis you mean.
What is treating weak acids as fully ionised when calculating pH?Show answer
0.10 mol L^-1 CH3COOH does not have pH = 1.00. Only a small fraction ionises, so pH is higher (~2.9).
What is confusing ppm with %m/m?Show answer
1 % = 10,000 ppm. So 0.001% is 10 ppm.
What is writing H+ as the only acid species?Show answer
Strictly, a proton in water exists as H3O^+ (hydronium). VCE accepts either notation; be consistent within a question.
What is using log instead of -log?Show answer
pH = negative log of [H+]. For [H+] = 1 x 10^-3, pH = 3, not -3.