BRAINCAKEChemical changes
Revision notes for Chemical changes in Edexcel Chemistry (1CH0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- Acids and alkalis: hydrogen and hydroxide ionsWhen an acid dissolves in water it releases hydrogen ions, H+.
- The pH scaleThe pH scale measures how acidic or alkaline a solution is.
- Indicators with acids and alkalisAn indicator is a substance that changes colour depending on whether a solution is acidic or alkaline.
- Ion concentration and pHThe pH of a solution depends on the concentration of ions in it.
- A tenfold change in hydrogen ion concentrationThe pH scale is not a normal straight-line scale.
- Core practical: pH change when a base is added to acidIn this core practical you investigate how the pH of dilute hydrochloric acid changes as you add powdered calcium hydroxide or calcium oxide.
- Dilute and concentrated solutionsA solution forms when a solute dissolves in a solvent, which is usually water.
- Weak and strong acidsAn acid in water produces hydrogen ions, H+.
- BasesA base is any substance that reacts with an acid to form a salt and water only.
- AlkalisAn alkali is a soluble base.
- Reactions of acids to make saltsAqueous solutions of acids react in four general ways to make a salt.
- Tests for hydrogen and carbon dioxideHydrogen is tested for with a lit splint.
- Neutralisation: an acid reacting with a baseA neutralisation reaction is a reaction between an acid and a base.
- Neutralisation in terms of hydrogen and hydroxide ionsAcids in solution are a source of hydrogen ions, H+.
- Making a salt from an acid and an insoluble reactantSome soluble salts are made from an acid and an insoluble reactant, such as copper oxide, zinc oxide or an insoluble carbonate.
- Making a salt from an acid and a soluble reactantAn alkali such as sodium hydroxide or potassium hydroxide dissolves in water, so it is a soluble reactant.
- Core practical: making hydrated copper sulfate crystalsIn this core practical, copper oxide, a black solid, is reacted with dilute sulfuric acid to make copper sulfate: copper oxide + sulfuric acid gives…
- Carrying out an acid-alkali titration to make a pure saltA titration finds the exact volume of acid that neutralises a volume of alkali.
- Solubility rules for common saltsA substance is soluble if it dissolves in water.
- Predicting precipitatesA precipitate is an insoluble solid that forms when two solutions are mixed.
- Making an insoluble saltAn insoluble salt is made by precipitation.
- ElectrolytesAn electrolyte is an ionic compound that is either molten or dissolved in water.
- ElectrolysisElectrolysis is a process that uses electrical energy to decompose an electrolyte.
- Movement of ions in electrolysisIn an electrolyte, whether molten or dissolved, the ions are free to move.
- Electrolysis of copper chloride and sodium chloride solutionsIn electrolysis a direct current passes through an electrolyte.
- Predicting products of electrolysis of molten compoundsA binary ionic compound contains just two elements, a metal and a non-metal, for example lead bromide or potassium iodide.
- Half equations at the anode and cathodeA half equation shows what happens at one electrode only.
- Oxidation and reduction in terms of electronsOxidation is the loss of electrons.
- Oxidation and reduction at the electrodesIn every electrolysis, reduction happens at the cathode and oxidation happens at the anode.
- Electrolysis of copper sulfate with copper electrodes and purifying copperWith inert electrodes copper sulfate solution gives copper at the cathode and oxygen at the anode, and the blue colour fades.
- Core Practical: Electrolysis of copper sulfate solution with inert and copper electrodesIn this practical you electrolyse blue copper sulfate solution twice, first with inert graphite electrodes and then with copper electrodes.