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chem > chapter 1 > Flashcards

chapter 1 Flashcards

separation techniques, subs.

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1
Q

what is crystallisation

A

→ obtain pure solid from saturated solution

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2
Q

steps for crystallisation

A

step 1: impure solid dissolved in solvent

step 2: solution is heated to obtain hot saturated solution (no more solute can be dissolved)

step 3. hot saturated solution is allowed to cool, dissolved solid appears as pure crystals

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3
Q

what is simple distillation

A

→ separates a pure liquid from solution (diff boiling points)

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4
Q

what is important in setting up the apparatus in simple distillation

A

** bulb of thermometer should be at the entrance of condenser → measures boiling point of subs

** water in is below water out in condenser

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5
Q

what does boiling chips do

A

ensure smooth boiling

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6
Q

why are conical flasks usually used to collect distillate

A

it has a smaller surface area → slower rate of evaporation

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7
Q

how do you dry gases

A

use drying agents → absorbs moisture

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8
Q

how do you dry ammonia

A

using calcium oxide (solid)

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9
Q

how do you dry acidic gases

A

using concentrated sulfuric acid (liquid) and FUSED calcium chloride (solid)

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10
Q

can you use concentrated sulfuric acid to dry ammonia

A

no they will react with each other because they are acidic and alkaline

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11
Q

what are the acidic gases

A

chlorine, hydrochloric gas, nitrogen dioxide, carbon dioxide, sulfur dioxide

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12
Q

what are the neutral gases

A

carbon monoxide, hydrogen, argon, oxygen, helium, nitrogen monoxide

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13
Q

what is the only alkaline gas

A

ammonia

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14
Q

properties of pure substances

A
  • melts and boils at fixed temp
  • only have one spot on chromatogram
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15
Q

what does chromatography do

A

→ separates a mixture of substances which have diff solubilty in a solvent

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16
Q

steps for chromatography

A

step 1: draw the starting line in pencil and place a small spot of the sample on the line

step 2: dip the paper into the solvent, make sure solvent is below the start line

step 3: diff. solutes are soluble to the diff. extent in the solvent and a chromatogram forms (when solvent moves up paper)

step 4: draw the solvent front in pencil when solvent is near the top of the paper

17
Q

why is the starting line drawn in pencil

A

→pencil lead is made up of carbon which doesn’t dissolve in the solvent and not move up the chromatogram. (dosen’t interfere with chromatogram)

18
Q

why must the solvent be below the starting line

A

→ to ensure that chromatogram to be separated do not dissolve in the solvent (otherwise, no chromatogram will be developed)

19
Q

why must the spot of the sample at the start line be small

A

→to ensure that the spots don’t smudge and overlap as this will make identification of the components in the sample difficult

20
Q

why should the chromatogram be as long as possible

A

→ to ensure a better chromatogram of the components

21
Q

why do we need to cover the beaker with a lid during chromatography

A

→ to slow down evaporation of the solvent and to maintain a saturated vapor mixture within the beaker

22
Q

how to identify colourless substances

A

→ locating agents are used to make colourless substances on chromatogram more visible

23
Q

what is Rf value

A

→ dist. travelled by solute / dist. travelled by solvent
→ accuracy: 2 d.p. (no units)
→ higher Rf value, higher solubility (subst. travelled further)

24
Q

what is fractional distillation and their industrial uses

A

→ to separate miscible liquids w close boiling points
→ industrial use: crude oil, liquid air, fermented alcohol

25
Q

what is the general function of a fractionating column

A

effectively separates 2 or more subs. w similar boiling points
**distillate comes out at the subs. boiling point
similar to simple distil

26
Q

what is the specific function of a fractionating column

A

provide larger surface area for condensation and repeatedly condenses subs. w lower boiling point (drips into flask, evaporates, condenses, repeat) until it reaches the upper part of the column and distills over

27
Q

describe the properties of hydrogen

A

not soluble in water
less dense than air

28
Q

describe the properties of oxygen

A

slightly soluble in water
slightly denser than air

28
Q

describe the properties of sulfur dioxide

A

very soluble in water
denser than air

28
Q

describe the properties of carbon dioxide

A

slightly soluble in water
denser than air

28
Q

describe the properties of chlorine

A

soluble in water
denser than air

28
Q

describe the properties of hydrogen chloride

A

very soluble in water
denser than air

28
Q

describe the properties of ammonia

A

very soluble in water
less dense than air

29
Q

what substances are soluble in water

A

→ all group 1 salts, nitrates, chlorides / iodides / bromides / sulfates are soluble IN WATER

30
Q

what substances are insoluble in water

A

→ ** carbonates / oxides / hydroxides, silver and lead (II) chlorides, calcium sulfate, barium and lead(II) sulfates are INSOLUBLE IN WATER

31
Q

properties of impure substances

A
  • melts below melting point
  • boils higher than boiling point
  • melts and boils over a range of temp

chem (4 decks)

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