Chemistry Practical Notes

Planning Section

Things You Need To Write

  • Aim/Approach (Basically hypothesis)
  • Variables: 1 independent, 1 dependent, and 3 constant
  • Procedure (Should be about 4-5 steps, but not fixed)
  • Result Analysis (Include any needed calculations/formulas)

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Experimental Errors

Human Errors

  • Reaction time, results in inaccuracy (for experiments requiring things like stopwatches)
  • Inconsistent stirring. Solve the problem by using a magnetic stirrer

Experimental Errors

  • Heat loss to surroundings. There are many different ways something could lose heat, so it depends on the context of the question
  • Decomposition of reagents. This error usually only appears if hydrogen peroxide (Decomposes when light and heat is present) is involved. Solve by storing hydrogen peroxide in a cool and dark place.
  • Colour-related experiments (Hard to determine colour). Solve by using pH probe/colour scale (For pH indicator)

Graph Drawing

Important Things To Note:

  • Extrapolating. It’s easy to extrapolate a straight line, but not a curve. Do practices or look through papers you’ve done before.
  • Not all graphs pass through 0-0 (The point where the x and y-axis are at 0).
  • Use appropriate scales. Don’t use odd scales (e.g. 5cm = 3 units).
  • The graph should occupy about ¾ of the paper.
  • LABEL YOUR X-AXIS AND Y-AXIS

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Titration

Normal Titration Techniques

  • When you take down burette readings, they should be at an accuracy of 0.05 cm3 (2 d.p.)
  • Always read the bottom of the meniscus (Unless you’re using potassium manganate)
  • Know what the colour change of the indicator you’re using is (e.g. If you’re using methyl orange, you should be ending when it turns orange)
  • Draw your titration table correctly! Order: Titration number, Final burette reading, Initial burette reading, Volume from the burette used, Best titration results.

Qualitative Analysis

Cations:

Cation

Ammonia (aq.)

NaOH (aq.)

Zinc

White ppt, soluble in excess

White ppt, soluble in excess

Aluminium

White ppt, INSOLUBLE in excess

White ppt, soluble in excess

Lead

White ppt, INSOLUBLE in excess

White ppt, soluble in excess

Calcium

No ppt

White ppt, INSOLUBLE in excess

Copper (II)

Blue ppt, forms deep blue solution in excess NH3

Blue ppt

Iron (II)

Dirty-green ppt

Dirty-green ppt

Iron (III)

Reddish-brown ppt

Reddish-brown ppt

Ammonium

No ppt

No ppt, produces ammonia on heating

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Lead(II) ions can be distinguished from aluminium ions by the insolubility of lead(II) chloride.

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Anions:

Anion

Test

Observation

Carbonate

Add dilute HCl, pass gas through limewater

Effervescence + white ppt forms in limewater

Chloride

Add dilute HNO3, add aq. AgNO3

Insoluble AgCl forms (white ppt)

Iodide

Same as test for chloride

Insoluble yellow ppt forms

Sulfate

Add dilute HNO3, add aq. Ba(NO3)2

Insoluble white ppt forms

Nitrate

Add aqueous sodium hydroxide, then aluminium foil; warm carefully

Ammonia produced

Test For Gases

Gas

Colour and Odour

Test

Observation

Ammonia (NH4)

Colourless, Pungent

Moist red litmus paper near the mouth of the test tube

Red litmus turns blue

Carbon Dioxide (CO2)

Colourless, Odourless

Pass gas through limewater

White ppt forms in limewater

Chlorine (Cl2)

Greenish-yellow, Pungent

Moist blue litmus paper near the mouth of the test tube

Blue litmus turns red, then becomes bleached

Hydrogen (H2)

Colourless, Odourless

Lighted splint near the mouth of the test tube

Lighted splint extinguishes with a ‘pop’ sound

Oxygen (O2)

Colourless, Odourless

Insert glowing splint into the gas

The glowing splint is rekindled (re-lights)

Sulfur Dioxide (SO2)

Colourless, Pungent

Place a piece of filter paper with acidified potassium manganate (VII)

Purple to colourless

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Test For Oxidising/Reducing Agent

Oxidising agent: Use potassium iodide

Reducing agent: Use acidified potassium manganate (VII)

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General Tips

  • Draw out any tables needed for an easier time when collecting results during an experiment.
  • Do your experiments and record down your data first before answering theory questions.
  • Follow the question carefully and read through it. Make sure not to miss anything

Degree Of Accuracy

  • Burette: 0.05 (2 d.p.)
  • Thermometer: 1 d.p.
  • etc.

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Calculations/Formulas

Concentration:

  • Number of moles/Mass divided by volume in dm3 

Number of moles:

  • For volume, take your volume (converted to dm3) divided by 24dm3
  • For mass, take the mass and divide it by the molar mass of the substance

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