Reactions of acids key terms

Acid

A substance that donates hydrogen ions (H+) in aqueous solution. In Reactions of acids with metals, this term helps explain state that acids react with some metals to produce salts and hydrogen for AQA GCSE Chemistry 8462 Unit 4.4.

Salt

A compound formed when an acid reacts with a base, typically consisting of a positive ion from the base and a negative ion from the acid.

hydrochloric acid

A strong, colourless acid with the formula HCl that dissociates completely in water to give H⁺ and Cl⁻ ions.

metal salt

An ionic compound formed when a metal reacts with an acid, consisting of the metal cation and the anion derived from the acid (e.g., Na⁺Cl⁻ from NaCl).

Sulfuric acid

A strong diprotic acid (H₂SO₄) that reacts with metals to produce a metal sulfate salt and hydrogen gas.

Metal sulfate salt

The ionic compound formed when a metal reacts with sulfuric acid, consisting of the metal cation and the sulfate anion (SO₄²⁻).

Nitric acid

A strong acid that reacts with metals to produce salts and hydrogen gas. In Reactions of acids with metals, this term helps explain predict the salt produced when nitric acid reacts with a metal for AQA GCSE Chemistry 8462 Unit 4.4.

Salt

A compound formed when an acid reacts with a metal, base, or carbonate, consisting of a positive ion from the metal and a negative ion from the acid.

Acid

A substance that donates hydrogen ions (H+) in aqueous solution. In Reactions of acids with metals, this term helps explain write word equations for reactions between acids and metals for AQA GCSE Chemistry 8462 Unit 4.4.

Metal

An element that typically forms positive ions and can react with acids to produce salts and hydrogen.

acid-metal reaction

A chemical reaction where an acid reacts with a metal to produce a salt and hydrogen gas.

balanced symbol equation

An equation that shows the reactants and products of a chemical reaction with their correct stoichiometric coefficients.

hydrogen gas test

A method to identify hydrogen gas by bringing a lighted splint near the gas, which produces a 'pop' sound.

lighted splint

A small stick of wood or paper that is ignited and used to test for the presence of hydrogen gas.

reactivity series

A list of metals arranged in order of decreasing reactivity, used to predict how metals will react with acids.

dilute acid

An acid that has been mixed with water, resulting in a lower concentration of hydrogen ions.

neutralisation

The reaction between an acid and a base or alkali to produce salt and water. In Neutralisation of acids and salt production, this term helps explain describe neutralisation as the reaction between an acid and a base or alkali for AQA GCSE Chemistry 8462 Unit 4.4.

alkali

A base that dissolves in water, producing hydroxide ions (OH-). In Neutralisation of acids and salt production, this term helps explain describe neutralisation as the reaction between an acid and a base or alkali for AQA GCSE Chemistry 8462 Unit 4.4.

acid

A substance that donates hydrogen ions (H⁺) in aqueous solution. In Neutralisation of acids and salt production, this term helps explain state that acids react with alkalis to produce salts and water for AQA GCSE Chemistry 8462 Unit 4.4.

alkali

A base that donates hydroxide ions (OH⁻) in aqueous solution. In Neutralisation of acids and salt production, this term helps explain state that acids react with alkalis to produce salts and water for AQA GCSE Chemistry 8462 Unit 4.4.

Neutralisation

The reaction between an acid and a base or alkali to produce salt and water. In Neutralisation of acids and salt production, this term helps explain state that acids react with bases to produce salts and water for AQA GCSE Chemistry 8462 Unit 4.4.

Salt

A compound formed when an acid reacts with a base, consisting of a positive ion from the base and a negative ion from the acid.

Neutralisation

The reaction between an acid and a base or alkali to produce salt and water. In Neutralisation of acids and salt production, this term helps explain state that acids react with carbonates to produce salts, water and carbon dioxide for AQA GCSE Chemistry 8462 Unit 4.4.

Carbonate Reaction

The reaction of an acid with a carbonate that produces salt, water, and carbon dioxide.

Salt

A compound formed when an acid reacts with a base, alkali or carbonate, consisting of the conjugate base of the acid and the cation of the base.

Conjugate Base

The species remaining after an acid has donated a proton (H⁺); it combines with the cation of the reacting base to form the salt.

neutralisation

The reaction between an acid and a base or alkali to produce salt and water. In Neutralisation of acids and salt production, this term helps explain write word equations for acid-base, acid-alkali and acid-carbonate reactions for AQA GCSE Chemistry 8462 Unit 4.4.

word equation

A representation of a chemical reaction using the names of the reactants and products.

neutralisation

The reaction between an acid and a base or alkali to produce salt and water. In Neutralisation of acids and salt production, this term helps explain write balanced symbol equations for neutralisation reactions when formulae are supplied for AQA GCSE Chemistry 8462 Unit 4.4.

balanced symbol equation

A representation of a chemical reaction that shows the correct proportions of reactants and products using chemical symbols.

Limewater

A dilute solution of calcium hydroxide used to test for carbon dioxide. In Neutralisation of acids and salt production, this term helps explain describe the test for carbon dioxide using limewater for AQA GCSE Chemistry 8462 Unit 4.4.

Carbon dioxide test

The process of bubbling carbon dioxide through limewater, which turns milky if carbon dioxide is present.

Soluble salt

A salt that can dissolve in water to give a clear solution. In Soluble salts, this term helps explain describe how to prepare a soluble salt from an acid and an insoluble reactant for AQA GCSE Chemistry 8462 Unit 4.4.

Acid–insoluble reactant

A solid that does not dissolve in water but reacts with an acid to form a soluble salt.

Insoluble solid

A substance that does not dissolve in a solvent, used in excess to ensure complete reaction with an acid.

Excess reactant

A reactant that is present in a greater amount than necessary to completely react with another reactant.

filtration

A separation technique that removes solid particles from a liquid by passing the mixture through a porous medium, allowing the liquid to pass while retaining the solid.

excess insoluble solid

A solid reactant added in a quantity greater than stoichiometrically required, ensuring that the reaction proceeds to completion and the remaining solid can be separated by filtration.

evaporation

The process of turning a liquid into a gas, leaving dissolved solids behind. In Soluble salts, this term helps explain describe how evaporation and crystallisation produce a pure dry salt sample for AQA GCSE Chemistry 8462 Unit 4.4.

crystallisation

The formation of solid crystals from a solution when the solute becomes supersaturated and precipitates out.

soluble salt

A salt that dissolves in water to form a solution. In Soluble salts, this term helps explain identify suitable apparatus for preparing, filtering and crystallising a soluble salt. (AT 2, AT 3, AT 4, AT 6) for AQA GCSE Chemistry 8462 Unit 4.4.

crystallisation

The process of forming solid crystals from a solution. In Soluble salts, this term helps explain identify suitable apparatus for preparing, filtering and crystallising a soluble salt. (AT 2, AT 3, AT 4, AT 6) for AQA GCSE Chemistry 8462 Unit 4.4.

soluble salt

A salt that dissolves in water to form a solution. In Soluble salts, this term helps explain write word equations for soluble salt preparation reactions for AQA GCSE Chemistry 8462 Unit 4.4.

word equation

A representation of a chemical reaction using the names of the reactants and products.

soluble salt

A salt that dissolves in water to form a solution. In Soluble salts, this term helps explain write balanced symbol equations for soluble salt preparation when formulae are supplied for AQA GCSE Chemistry 8462 Unit 4.4.

balanced symbol equation

An equation that shows the reactants and products of a chemical reaction with equal numbers of atoms for each element on both sides.

soluble salt

A salt that dissolves in water to form a solution. In Soluble salts, this term helps explain explain how to obtain a pure dry sample of a named soluble salt in the required practical for AQA GCSE Chemistry 8462 Unit 4.4.

required practical

A hands-on experiment conducted to demonstrate a scientific principle or process.

Acid handling

Safe practices for handling acids, including wearing protective equipment, using fume hoods, and avoiding splashes.

Controlled heating

Gradual, monitored heating of acid solutions to prevent rapid boiling, splattering, and pressure build‑up.

pH scale

A scale used to measure the acidity or alkalinity of a solution, ranging from 0 (acidic) to 14 (alkaline), with 7 being neutral.

neutral solution

A solution that has a pH of 7, indicating it is neither acidic nor alkaline. In The pH scale and neutralisation, this term helps explain use the pH scale to classify solutions as acidic, neutral or alkaline for AQA GCSE Chemistry 8462 Unit 4.4.

universal indicator

A pH indicator that changes color to indicate the acidity or alkalinity of a solution.

pH meter

An electronic device used to measure the pH level of a solution accurately. In The pH scale and neutralisation, this term helps explain describe universal indicator and pH meters as methods for measuring pH for AQA GCSE Chemistry 8462 Unit 4.4.

Hydrogen ion (H+)

A positively charged ion formed when an acid dissociates in aqueous solution. In The pH scale and neutralisation, this term helps explain explain that acids produce hydrogen ions, H+, in aqueous solution for AQA GCSE Chemistry 8462 Unit 4.4.

Aqueous solution

A solution in which water is the solvent, commonly used to describe the state of acids and bases.

alkali

A substance that produces hydroxide ions, OH-, in aqueous solution. In The pH scale and neutralisation, this term helps explain explain that alkalis produce hydroxide ions, OH-, in aqueous solution for AQA GCSE Chemistry 8462 Unit 4.4.

hydroxide ion

A negatively charged ion (OH-) formed when an alkali dissolves in water. In The pH scale and neutralisation, this term helps explain explain that alkalis produce hydroxide ions, OH-, in aqueous solution for AQA GCSE Chemistry 8462 Unit 4.4.

neutralisation

The reaction between an acid and a base or alkali to produce salt and water. In The pH scale and neutralisation, this term helps explain describe neutralisation in terms of hydrogen ions reacting with hydroxide ions to produce water for AQA GCSE Chemistry 8462 Unit 4.4.

hydrogen ion

A positively charged ion (H+) that is produced by acids in aqueous solution. In The pH scale and neutralisation, this term helps explain describe neutralisation in terms of hydrogen ions reacting with hydroxide ions to produce water for AQA GCSE Chemistry 8462 Unit 4.4.

ionic equation

A chemical equation that shows the ions involved in a reaction, particularly in acid-base neutralisation.

neutralisation

The reaction between an acid and a base that produces salt and water. In The pH scale and neutralisation, this term helps explain write the ionic equation H+ + OH- -> H2O for neutralisation for AQA GCSE Chemistry 8462 Unit 4.4.

pH

A measure of the acidity or alkalinity of a solution, on a scale from 0 to 14. In The pH scale and neutralisation, this term helps explain explain why pH increases when an acid is neutralised by an alkali for AQA GCSE Chemistry 8462 Unit 4.4.

neutralisation

The chemical reaction between an acid and a base or alkali, resulting in the formation of salt and water.

pH

A measure of the acidity or alkalinity of a solution, where lower values indicate higher acidity.

neutralisation

The chemical reaction between an acid and a base or alkali, resulting in the formation of water and a salt.

pH scale

A numerical scale used to specify the acidity or alkalinity of a solution, ranging from 0 (acidic) to 14 (alkaline), with 7 being neutral.

acidic solution

A solution with a pH less than 7, indicating a higher concentration of hydrogen ions (H+).

strong acid

An acid that is completely ionised in aqueous solution. In Strong and weak acids (HT only), this term helps explain (HT only) Describe a strong acid as completely ionised in aqueous solution for AQA GCSE Chemistry 8462 Unit 4.4.

aqueous solution

A solution in which water is the solvent. In Strong and weak acids (HT only), this term helps explain (HT only) Describe a strong acid as completely ionised in aqueous solution for AQA GCSE Chemistry 8462 Unit 4.4.

weak acid

An acid that is only partially ionised in aqueous solution. In Strong and weak acids (HT only), this term helps explain (HT only) Describe a weak acid as only partially ionised in aqueous solution for AQA GCSE Chemistry 8462 Unit 4.4.

partial ionisation

The process by which only some molecules of a weak acid dissociate into ions in water.

Ionisation

The process by which an acid dissociates into ions in solution. In Strong and weak acids (HT only), this term helps explain (HT only) Explain that acids of the same concentration can have different pH values because of different degrees of ionisation for AQA GCSE Chemistry 8462 Unit 4.4.

pH value

A measure of the acidity or alkalinity of a solution, determined by the concentration of hydrogen ions.

pH

A measure of the acidity or alkalinity of a solution, where lower values indicate higher hydrogen ion concentration.

hydrogen ion concentration

The amount of hydrogen ions (H+) present in a solution, which determines its acidity and is inversely related to pH.

pH

A measure of the acidity or alkalinity of a solution, where lower values indicate higher hydrogen ion concentration.

hydrogen ion concentration

The amount of hydrogen ions (H+) present in a solution, which determines its acidity.

Acid strength

The extent to which an acid dissociates into hydrogen ions in aqueous solution, independent of its concentration.

Acid concentration

The amount of acid present in a given volume of solution, typically expressed as molarity (mol L⁻¹).

pH

A logarithmic scale that quantifies the hydrogen ion concentration in a solution, where lower values indicate higher acidity.

Dilution

The process of reducing the concentration of a solution by adding solvent, which can alter the pH depending on acid strength.

hydrogen ion concentration

The amount of hydrogen ions (H+) present in a solution, which determines its acidity.

pH scale

A logarithmic scale used to measure the acidity or alkalinity of a solution, ranging from 0 (acidic) to 14 (alkaline).