MYP · Chemistry MYP Year 4

Acids Bases and Salts

24 min readStandardAssessed through Criterion A (knowledge), B (practical design), C (data processing/evaluation) and D (impacts) tasks — salt preparation practicals and application/evaluation questions are the most heavily tested formats

This topic gets tested less on 'what is an acid' and more on whether you can actually run and justify a preparation — balance the equation, explain why excess solid is used, read a data table of yields, and weigh up environmental or safety consequences. Every worked example below is built from real exam-style questions on copper(II) sulfate preparation and fertiliser chemistry, because that's exactly where marks get dropped.

Overview

Acids, bases and salts is really four ideas stitched together: what makes something acidic or basic (properties), how we measure that (pH and indicators), what happens when acid meets base (neutralisation), and how we turn that reaction into a usable product (salt preparation). Applications and environmental impact sit on top of all of it — fertilisers, antacids, cleaning products — because this is the chemistry topic examiners most often connect to real industry and farming decisions.

An acid produces hydrogen ions ( $H^{+}$ ) when dissolved in water; a base is anything that can neutralise an acid (accepts $H^{+}$ ); an alkali is a base that is soluble in water.
A salt is the ionic compound formed when the $H^{+}$ of an acid is replaced by a metal ion (or ammonium ion) — its name always comes from the acid used (chloride, sulfate, nitrate) plus the metal.
Almost every question on this topic is really asking you to do one of three things: construct/balance an equation, explain a step in a preparation procedure, or evaluate/deduce from given data.

Mind map of Acids Bases and Salts centred on Acids, Bases & Salts.

Command terms that decide your mark

Command term	What it demands	AO	Mark-earning move
State	A brief, factual answer — no working or reasoning needed.	Criterion A	Full marks for the correct fact alone; adding an explanation earns nothing extra and wastes time.
Identify	Name or select the correct substance/observation from given information.	Criterion A	The exact correct name is required — a vague description ('a gas was made') is not accepted.
Describe	Give a detailed account of what happens — observations, not reasons.	Criterion A	Marks reward accurate detail of the process; you don't need to explain why it happens.
Explain	Give reasons — you must connect a cause to its effect using 'because'.	Criterion A/D	Describing without saying why loses the mark even if the description is correct.
Outline	Give a brief summary hitting every key step, in order.	Criterion A	Missing a whole step (e.g. skipping 'filter') loses marks more than being brief on one step.
Construct	Build something — a balanced equation, table or graph — following correct conventions.	Criterion B	Marks are split between correct formulas, correct balancing AND correct state symbols if asked for.
Evaluate	Weigh up strengths and weaknesses of two or more options, then give a justified judgement.	Criterion C	A one-sided answer (only pros, or only cons) caps the mark even if the reasoning given is correct.
Deduce	Use the specific data/evidence given to reach a conclusion not stated outright.	Criterion C	Must reference the actual numbers/data in the question — general knowledge alone earns no credit.

Key point

The salt produced in any reaction is fixed by two things only: which acid you used (HCl → chloride,

H_{2} SO_{4}

→ sulfate,

HNO_{3}

→ nitrate) and which metal/base/carbonate it reacted with. Get that pairing solid before anything else in this topic.

Overview

Acids Bases and Salts

Overview

The shape of the chapter

Command terms that decide your mark