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Chemistry > 21. Experiment Techniques > Flashcards

21. Experiment Techniques Flashcards

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1
Q

Name appropriate apparatus for the
measurement of time, temperature, mass and volume

A
  1. Time: stopwatches
  2. Temperature: Thermometers or temperature probe
  3. Mass: Balance scale
  4. Volume (liquid): Volumetric pipettes, measuring cylinders or buretters
  5. Volume (gas): Gas syringe
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2
Q

State the advantages of temperature probe versus thermometer

A
  1. More precise readings
    2.Can easily take multiple repeat readings
  2. Can be automated to run over longer periods of time
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3
Q

State the disadvantages of temperature probe versus thermometer

A
  1. Probe can be corroded by some reagents
  2. Probes are more expensive to replace
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4
Q

State the advantages of volumetric pipette versus a measuring cylinder

A
  1. Pipette measures very accurately
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5
Q

State the disadvantages of volumetric pipette versus a measuring cylinder

A
  1. Harder to use and only measures one fixed volume
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6
Q

State the advantages of gas syringes verses inverted cylinder for collecting gases

A
  1. Gas syringes are easy to set up and keep the gas dry
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7
Q

State the disadvantages of gas syringes verses inverted cylinder for collecting gases

A
  1. The pistons can stick
  2. Limited volume can be collected
  3. Delicate and expensive
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8
Q

State the advantages of microscale versus normal scale quantities

A
  1. Less wasteful of reagents
  2. Saves energy
  3. Safer
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9
Q

State the disadvantages of microscale versus normal scale quantities

A
  1. Hard to see what’s happening
  2. Lose a lot of material in separating and purifying products
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10
Q

State the definition of Solvent

A

A substance that dissolves in a solute

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11
Q

State the definition of solute

A

A substance that is dissolved in a solvent to form a solution

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12
Q

State the definition of solution

A

A mixture of one or more solutes dissolved in a solvent

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13
Q

State the definition of saturated solution

A

A solution containing the maximum concentration of a solute dissolved in the solvent at a specified temperature

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14
Q

State the definition of residue

A

A substance that remains after evaporation, distillation, filtration or any similar process

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15
Q

State the definition of filtrate

A

A liquid or solution that has passed through a filter

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16
Q

Describe an acid–base titration

A
  • A method of analysing concentration of solution and to prepare salt
  • Materials typically used are:
    1. 50cm³ burette
    2. 25cm³ volumetric pipette
    3. Suitable indicator (to show the end-point of titration) such as methyl orange and phenolphthalein
17
Q

How to know whether a substance is an alkali, acid or neutral using methyl orange and phenolphthalein indicator

A

Methyl orange: Red (Acid), Yellow (alkali), Orange (neutral)

Phenolphthalein: Colourless (Acid), Pink (alkali), Colourless (neutral)

18
Q

Describe how to identify the end-point of a titration using an indicator

A

When theres a slight change in colour indicates the endpoint and a thick full in colour is an overshot and thus should be avoided

19
Q

Describe how paper chromatography is used to separate mixtures of soluble coloured substances, using a suitable solvent

A
  • Used to separate mixtures of soluble coloured substances to provide information to help identify them
    1. Pencil line drawn on paper and sample is placed
    2. Put the paper into solvent container above the line
    3. Solvent travels up the paper
    ◦ Different substances have different solubilities so they’ll travel at different lengths and rates
20
Q

Interpret simple chromatograms to identify:
(a) unknown substances by comparison with known substances
(b) pure and impure substance

A
  • Pure substances: Only one spot
  • Impure substances: More than one spot
  • Two or more substances are the same: Identical chromatograms
  • A mixture: Separate spots to show all differences
21
Q

Describe how a suitable solvent and a locating agent is used
to separate mixtures of soluble colourless substances

A
  • A colourless or “invisible” substance can be identified by using a suitable solvent and a locating agent
  • A locating agent reacts with the sample to produce a visible/coloured spot for the product(s), used after the chromatography run has been carried out
22
Q

State the equation for Rf value

A

Rf = distance travelled by substance ÷ distance travelled by solvent

23
Q

Describe and explain method of filtration

A

Filtration: Separate an undissolved solid from a mixture of the solid and a liquid (e.g. sand and water)
1. Place filter paper in a filter funnel above the beaker
2. The mixture is poured into the filter funnel
3. Only allow small liquid particles will pass through the filter paper (filtrate)
4. Too large solid particles will not pass through the filter paper (residue)

24
Q

Describe and explain method of crystallisation

A

Crystallisation: Separate a dissolved solid from a solution
1. Boil and remove the heat to let the solvent evaporate, leaving a saturated solution behind
2. Dip a clean, dry, cold glass rod to check whether its saturated solution
3. Slowly cool the saturated solution
4. Collect the crystals by filtration and wash it with distilled water
5. Dry

25
Q

Describe and explain method of simple distillation

A
  1. Heat the solution until pure water evaporates
  2. Vapour passes through the condenser → cools and condenses → pure water
  3. Solid solute will be left behind
26
Q

Describe and explain method of fractional distillation

A

Separate two or more miscible liquids
1. Heat the solution to the lowest boiling point of the substance
2. Evaporates and passes through a condenser → cools and condense
3. Condensed liquid is then collected in a beaker
4. Leaves behind the other components of the mixture

27
Q

How to identify substances and assess their purity

A
  • Pure: Melt and boil at specific and sharp temperatures
  • Mixtures: Range of M.P and B.P
  • Unknown pure substance: Experimentally determine its M.P and B.P by comparing them to data tables
    ◦ Use distillation to determine B.P
    ◦ Use M.P apparatus to determine M.P (heats up a small amount of sample)
28
Q

12.5 Identification of ions and gases (CHECK OUT GOOGLE DOCS TO MEMORISE POATATO STIC)

A

Chemistry (5 decks)

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