Edexcel C3 Topic 3- Chemical Detection

Edexcel 360science Extension Chemistry

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Analysing Substances

Qualitative-Tells you what is present, detects poison etc

Quantitative-Tells you how much is present, used in alcohol test

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Qualitative-Can test mysterious substances, such as Ionic substances, so it helps to find out the different substances because of the Ions.

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Tests for Postive Ions

Flame Test:

  • Sodium Na+- ORANGE
  • Potassium K+-LILAC
  • Calcium Ca2+-RED
  • Copper Cu2+-Blue/Green

Metal Test-

Calcium + Sodium Hydroxide = White Precipitate

Copper(II) + Sodium Hydroxide = Blue Precipitate

Iron(II) + Sodium Hydroxide = Green Precipitate

Iron(III) + Sodium Hydroxide= Reddish Brown Precipitate

Aluminium + Sodium Hydroxide = White at first then colourless

Ammonium + Sodium Hydroxide = None, pungent smell given off

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Tests for Negative Ions

Negative Ion test:

Carbonate + Hydrochloric Acid= Carbon Dioxide and Water, the Carbon Dioxide can be tested by using limewater, which turns milky when CO2 is present.

Sulphites + Hydrochloric Acid= Sulphur Dioxide and Water, SO2 can be tested by using damp Potassium Dichromate(VI) Paper, which turns orange to green when SO2 is present.

Sulphate Test

Barium Chloride + Sulphate= Barium Sulphate Which is White, HCL is added before the test to remove any Sulphite or carbonate Ions.

Halides Test: Nitric Acid + Halide + Silver Nitrate

Chloride= White Precipitate Silver Chloride

Bromide= Cream Silver Bromide Iodide= Yellow Silver Iodide

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Acid & Alkalis

Litmus: Blue turns Red when H+ is present (ACID)

Red turns Blue when OH- is present (ALKALI)

Phenolphthalein: Pink In Alkali, Colourless in Acid

Methyl Orange: Yellow in Alkali, Red in Acid

Universal Indicator- Used to estimate pH

Acid + Metal= Hydrogen Gas- Squeaky pop is used to detect Hydrogen which tells us that Acid is present

Ammonium Salt+ Hydroxides= Ammonia Gas which is smelly and can be tested by using universal indicator, which turns Purple

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Moles= 6.023 x 10^23 ( Power 23)

One mole of any atom or molecule= mass in grams of the relative formula mass such as Carbon which has 12 relative mass, so 1 mole is 12g

Number of moles= Mass in g/ relative formula mass

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Avogadros Law

One mole of any gas always takes 24 dm3 or 24 00cm3 at room temperature and pressure or 25C and 1 Atmosphere.

Volume of gas= Mass of gas/ relative formula mass x 24

To calculate the volume when you know the mass you do:

Find the reacting mass then convert the mass into a volume

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Quantitative chemistry and solution

To find out how much something is dissolved by evaporating water:

Weigh a clean dry evaporating basin then put 10cm3 of the solution in the basin

Gently heat the basin

Weigh the the basin again then reheat and reweigh until the solution is finished

Mass Concentration= Mass (g)/ Volume (dm3)

Mole Concentration= Number of Moles/ Volume (dm3)

You can convert Mass concentration into Mole concentration by:

Mass Concentration (g/dm3)= Mole concentration (mol/dm3) x formula mass

Concentration of a solution doesn't always work because sometimes the solution evaporates with the water so Titration is used.

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Titration allows you to find how much acid is needed to neutralise an alkali solution or vice versa.

You use a pipette and filter, then add some alkali to a conical flask with some indicator.

Next fill the burette with acid, has to be done below eye level. Then with the burette add some acid to alkali a bit at a time. Also give the conical flask a regular swirl.

When the indicator changes colour completely it means the alkali has been neutralised. Record the volume of acid used. Repeat it.

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Water has to be from poisonous salts for drinking, it is filtered and chemicals are added to it to kill microbes. Also filtered to remove nasty tastes and smell.

Water is monitored constantly to ensure water is safe to drink.

Water is used as a solvent for most ionic compounds. It attracts the ions and the solid structure falls apart. Many covalent compounds don't dissolve in water.

It is essential for life. Used for many different things

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extremely useful thank you


yeah very useful!!! i need to find some for the other topic, and i really dont get the topic "explaining ion tests with equations"

oh and looool sabrin =p

Sonam Dubb

Hey could you do some notes on the formulas for calculating volumes and concentration. Also could you expand on how to work out Avagadros Law because I am sat lookin at my text book and revision guide but neither makes sense.

Also could you do some notes on the next topic aswell because your revision notes are really helping me. I wasnt sure how to revise biology and chemistry until i found the way you did it using revision cards.


Matt Clarke

That was great thanks! :)


hey can u please upload topic 4


Aziza Mohamed

Thanks, really helpful, do you have any topic 4 resources

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