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Chemistry > Chapter 1: Experimental Chemistry > Flashcards

Chapter 1: Experimental Chemistry Flashcards

1
Q

What is an element?

A
  • The simplest substance that cannot be broken down into sny other substances
  • Made up of one atom only
  • Diatomic elements are covalent molecules
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2
Q

What is a compound?

A
  • 2 or more elements chemically combined together
  • Has their own set of physical properties
  • Has a fixed ratio
  • Can be separated chemically
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3
Q

What is a mixture?

A
  • Elements and compounds with no fixed ratio
  • Does not have its own physical properties
  • Properties are same as its constituents
  • M.p. and b.p. are not fixed
  • Are formed and separated by physical methods
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4
Q

What are the SI units for mass, time, temperature, length, and volume of gas/liquid?

A

kg, s, K, m^3

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5
Q

How many kgs and gs is 1 tonne?

A

1000kg, 1 x 10^6g

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6
Q

How many l and cm^3 is 1 dm^3?

A

1l, 1000cm^3

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7
Q

What is the tool for the measurement of mass and how is it rounded off?

A

Electronic balance, nearest 0.1g

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8
Q

What is the tool for the measurement of time and how is it rounded off?

A

Stopwarch, nearest s

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9
Q

What is the tool for the measurement of temperature and how is it rounded off?

A

Thermometer, nearest 0.5°C

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10
Q

What are the tools for the measurement of volume of liquid in increasing accuracy? Include what they are rounded to.

A
  • Beaker
  • Measuring cylinder (1 d.p.)
  • Pipette
  • Volumetric flask
  • Burette (2 d.p.)
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11
Q

What is the tool for the measurement of gas?

A

Gas syringe

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12
Q

What type of gas does the method downward displacement of water collect?

A

Gases that are insoluble or slightly soluble in water. (H2, O2, CO2)

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13
Q

What type of gas does the method downward delivery collect?

A

Gases denser than air. (Cl2, HCl)

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14
Q

What type of gas does the method upward delivery collect?

A

Gases less dense than air. (Ammonia/NH3)

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15
Q

What are the separation techniques used to separate solid-solid mixtures?

A
  • Magnetic attraction
  • Sieving
  • Using suitable solvents (e.g. water and salt)
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16
Q

What are the separation techniques used to separate solid-liquid mixtures?

A
  • Filtration
  • Evaporation to dryness
  • Crystallisation
  • Simple distillation
17
Q

What are the separation techniques used to separate liquid-liquid mixtures?

A
  • Chromatography
  • Fractional distillation
18
Q

What are the two ways to obtain a soluble solid dissolved in water and how to determine which one is suitable to use?

A

If stable to heat/does not have water of crystallisation (sodium & potassium salts):
Evaporation to dryness
If not stable to heat (decomposes upon heating e.g. sugar)/has water of crystallisation:
Crystallisation

19
Q

Describe the process of crystallisation.

A
  1. Dissolve the impure solid in water/solvent
  2. Evaporate the excess water/solvent until a saturated solution is obtained
  3. Cool the hot solution until solid appears as pure crystals
  4. Wash the crystals with cold water
  5. Dry the crystals by pressing between sheets of filter paper
20
Q

What is the separation technique used to obtain a pure sample of liquid from a solution?

A

Simple distillation

21
Q

Why are boiling stones put in the flask when heating during simple distillation?

A

To ensure smooth boiling

22
Q

Why is the thermometer placed at the mouth of the condenser during simple distillation?

A

To ensure purity of the liquid (pure: b.p. is fixed)

23
Q

What is the technique fractional distillation used to separate?

A

Miscible liquid-liquid mixtures with close boiling points.

24
Q

How does fractional distillation work?

A

Repeated condensation and evaporation takes place at the fractionating column and separates liquids with close b.p. effectively. The liquid with the lowest b.p. will be collected first, change the receiver when the temperature on the thermometer increases to the b.p. of another solvent.

25
Q

Why does water flow in from the bottom of the condenser and flows out from the top of the condenser?

A

This ensures a cold surface in the condenser to condense the vapour effectively.

26
Q

How to make fractional distillation more effective?

A

Increase the height of the fractionating column

27
Q

What method is used to separate two or more components that dissolve in the same solvent?

A

Chromatography

28
Q

What is chromatography used for?

A
  • Separation and identification of components
  • Determine the purity of solutions
29
Q

Describe the proces of chromatography.

A
  1. Use pencil to draw starting line and place. small sample spot on the line
  2. Dip the paper into the solvent, ensuring that the solvent level is below the line
  3. Allow to sit. Solvent moves up, different solutes are soluble to different extents, chromatogram forms
30
Q

Why do some solutes in a chromatogram travel faster and further up?

A

The more soluble they are, the faster and further they will travel.

31
Q

What will show on a chromatogram when the same dyes are present?

A

Identical dyes travel up the sane distance and produce the same colour when the same solvent is used.

32
Q

Why is the startin line of a chromatogram drawn in pencil?

A

Pencil lead made of carbon is insoluble in the solvent an hence will not interfere with the chromatogram

33
Q

Why is the solvent level below the starting line?

A

So that components to separate will not dissolve in the solvent otherwise no chromatogram will be developed

34
Q

Why is the sample spot in a chromatogram small?

A

To ensur spots do not overlap and smudge, otherwise identification of components will be difficult

35
Q

What are the characteristics of pure substances?

A
  • They are made up of only one type of subtance
  • Melt and boil at fixed temperatures
  • Have one spot on the chromatogram
36
Q

What are the characteristics of impure subtances?

A
  • Melt below its melting point over a range of temperatures (impurities disrupt solid’s regular structure, making it easier to turn into a liquid)
  • Boils higher than its boiling point over a range of temperatures ( impurities interfere with the cohesive liquid forces, making it difficult for liquid molecules to escape into gas phase)

Chemistry (8 decks)

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