Key term
Edexcel GCSE Chemistry 1CH0
Key Concepts in Chemistry
Topic overviewFormulae, word equations and balanced equationsHazard symbols and assessing riskThe changing model of the atomProtons, neutrons and electronsThe nucleus, mass number and atomic massElements and isotopesCalculating particle numbers and relative atomic massMendeleev's periodic tableHow the modern periodic table is arrangedElectronic configuration and the periodic tableHow ionic bonds formIons in ionic compoundsFormulae of ionic compoundsNaming compounds and the ionic latticeCovalent bonds and moleculesDot and cross diagrams for simple moleculesClassifying substances and the properties of ionic compoundsProperties of simple molecular substances, and forms of carbonGraphite and diamondFullerenes and graphenePolymers and models of bondingThe properties of metalsRelative formula mass and percentage compositionEmpirical and molecular formulaeConservation of mass in closed and open systemsReacting masses from balanced equationsConcentration in grams per cubic decimetre
States of Matter and Mixtures
Topic overviewThe three states of matter and changes of stateEnergy changes during changes of state, and predicting statePure substances and melting point dataChoosing a separation techniqueSeparating a mixture in practicePaper chromatography and interpreting a chromatogramInvestigating inks by distillation and chromatographyMaking water potable
Chemical Changes
Topic overviewAcids, alkalis and the pH scaleIndicators: litmus, methyl orange and phenolphthaleinInvestigating pH change when neutralising an acidBases and alkalisReactions of acids, and testing for hydrogen and carbon dioxideNeutralisation and its ionic equationPreparing soluble salts from insoluble and soluble reactantsPreparing pure, dry copper sulfate crystalsCarrying out an acid-alkali titrationSolubility rulesPredicting precipitates and preparing an insoluble saltElectrolytes and what electrolysis isMovement of ions and predicting the products of molten electrolysisElectrolysis with inert electrodesElectrolysis of copper sulfate solutionInvestigating the electrolysis of copper sulfate
Extracting Metals and Equilibria
Transition Metals, Quantitative Chemistry and Industrial Processes
Topic overviewTransition metals and their propertiesCorrosion and electroplatingPreventing rustingAlloys and alloy steelsHow the uses of metals relate to their propertiesCarrying out an accurate titrationPercentage yieldAtom economyThe Haber processFertilisers and ammonium saltsPreparing ammonium sulfate in the lab and in industryChemical cells and fuel cellsEvaluating fuel cells
Groups in the Periodic Table
Topic overviewThe groups of the periodic table, and the alkali metalsReactions of the alkali metals with waterThe pattern in alkali metal reactivity and why it happensPhysical properties of the halogensThe test for chlorine, and halogens reacting with metalsHydrogen halides, and explaining halogen reactivityDisplacement reactions of the halogensGroup 0: the noble gases
Rates of Reaction and Energy Changes
Fuels and Earth Science
Topic overviewHydrocarbons and crude oilFractional distillation and the fractionsProperties of the fractions and homologous seriesComplete and incomplete combustionCarbon monoxide and sootPollutants and acid rainHydrogen and fossil fuels comparedCracking and why it is necessaryThe Earth's early atmosphereHow the oceans formed and how oxygen appearedThe test for oxygen and the greenhouse gasesToday's atmosphere and evidence for climate change
Chemical Analysis, Organic Chemistry and Materials
Topic overviewWhy an ion test must be unique, and flame testsTests for metal ions and for ammoniaTests for carbonate, sulfate and halide ionsIdentifying the ions in an unknown saltInstrumental methods and flame photometryAlkanes and why they are saturatedAlkenes and why they are unsaturatedReactions of alkenes, and combustionWhat a polymer is, and how poly(ethene) formsOther addition polymers, and monomers from polymersUses of polymers, and natural polymers including DNAProblems with polymers and recyclingAlcohols and the -OH functional groupComparing the energy released by alcohol fuelsMaking ethanol by fermentation and distillationCarboxylic acids and the -COOH functional groupOxidising alcohols to carboxylic acids, and homologous seriesThe size of nanoparticlesUses and risks of nanoparticlesChoosing a material for a use
Chemical Analysis, Organic Chemistry and Materials
Why an ion test must be unique, and flame tests
- 3 things to know
- Paper 2
Overview
Why a test result must be unique to one ion and why known compounds are tested alongside, the flame colours of lithium, sodium, potassium, calcium and copper, and how the test is carried out.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What is meant by saying that the result of an ion test is unique?
Key term
A student claims that a white precipitate with sodium hydroxide solution proves calcium ions are present. Why is that conclusion unsafe?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Why must a chemical test for an ion give a result that no other ion gives?
Model answer
Only a result unique to that ion allows a firm conclusion, because a shared result could have been caused by a different ion.
- 2
What is meant by saying that the result of an ion test is unique?
Model answer
The observation is produced by that one ion and by none of the other ions being looked for.
- 3
A student claims that a white precipitate with sodium hydroxide solution proves calcium ions are present. Why is that conclusion unsafe?
Model answer
Aluminium ions also give a white precipitate with sodium hydroxide solution, so this observation alone does not identify the ion.
- 4
Why is more than one test usually needed before an unknown salt can be named?
Model answer
One test identifies the positive ion and another identifies the negative ion, and neither result on its own names the whole compound.
- 5
Give one reason for testing a known compound alongside an unknown one.
Model answer
The known compound shows exactly what a positive result looks like, so the unknown observation can be compared with it.
- 6
What flame colour is produced by a lithium ion, Li⁺?
Model answer
Red.
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