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Chemistry > 1: Experimental Chemistry > Flashcards

1: Experimental Chemistry Flashcards

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1
Q

What is used to measure volume

A

Pipette: measures accurate volumes, eg. 25.0cm3
Volumetric flask: measures accurate fixed volumes that are larger, eg. 100cm3
measuring cylinder: measures a range of volumes to nearest 0.5cm3
burette: measures a range of volumes to nearest 0.05cm3

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2
Q

Gas collection method: Water displacement

A
  • when gas is insoluble/ slightly soluble
  • density does not matter
  • ex: hydrogen, carbon dioxide and oxygen
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3
Q

Gas collection method: Downward delivery of gas

A
  • solubility of gas does not matter
  • when the gas is denser than air
  • dissolves in water to form acidic solution
  • ex: chlorine, hydrogen chloride and sulfur dioxide
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4
Q

Gas collection method: upward delivery of gas

A
  • soluble/insoluble
  • less dense than air
  • dissolves in water to form alkaline solution
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5
Q

Dry gas method: Concentrated sulfuric acid

A
  • for most gases, including chlorine & hydrogen chloride
  • unsuitable for gasses that react with H2SO4 (ammonia for example)
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6
Q

Drying gas method: Quicklime (calcium oxide)

A
  • for ammonia
  • calcium oxide absorbs moisture and CO2 from air, so it must be freshly heated before use
  • cannot be used with gasses that react with calcium oxide, eg. carbon dioxide
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7
Q

Drying gas method: Fused calcium chloride

A
  • for hydrogen, nitrogen, carbon dioxide
  • calcium carbonate readily absorbs moisture from air, hence it must be freshly heated before use
  • cannot be used with gases that react with calcium chloride, eg. ammonia
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8
Q

Separation techniques

A

Solid-solid: magnetic attraction, sieving, using suitable solvents, sublimation
Solid-liquid: filtration, evaporation to dryness, crystallisation, simple distillation.
Liquid-liquid: separating funnel, chromatography and fractional distillation

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9
Q

Magnetic attraction

A
  • used to separate magnetic solids from non-magnetic solids
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10
Q

Sieving

A
  • used to separate solids with different size particles
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11
Q

Using suitable solvents

A
  • a suitable solvent can be used to separate solid-solid mixture in which only one of the solids is soluble in solvent
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12
Q

Sublimation

A
  • used to separate a substance that changes from the solid to the gaseous state directly (most used with iodine & dry ice)
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13
Q

Filtration

A
  • used to separate insoluble solids from liquid
  • liquid that passes through filter paper is filtrate and solid left on filter paper is the residue
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14
Q

Evaporation to dryness

A
  • used to separate a dissolved solid from its solvent by heating the mixture up until all the solvent has vaporised
  • heat solution in an evaporating dish until all the liquid (solvent) evaporates, leaving us with the solid
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15
Q

Crystallisation

A
  • used to obtain a pure solid from a saturated solution
  • a saturated solution is a solution is which no more solute can be dissolved
  1. Heat the filtrate to obtain a saturated solution
  2. Cool the saturated solution for crystals to form
  3. Filter the mixture to obtain crystals
  4. Dry it between few sheets of filter paper
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16
Q

Simple distillation

A
  • used to separate a pure solvent from a solution
  1. solution is heated. boiling chips are added for smooth boiling. at 100ºC, the water boils. the vapour rises and enters the condenser through the exit sidearm of the distillation flask
  2. water vapour cools in condenser and condense back into liquid water. pure water that is collected in conical flask is the distillate
  3. as more water vaporises, the salt solution becomes more concentrated. eventually, a solid residue of salt remains in the distillation flask
17
Q

Separating funnel

A
  • used to separate immiscible liquids which do not dissolve in one another
18
Q

Chromatography

A
  • used to separate a mixture of substances which have different solubility in a given solvent
  • chromatograms show the separated substances on the paper after chromatography
  • more soluble substances will move more rapidly towards solvent front
  • less soluble substance will move at slower rate
  • Rf value = distance travelled by substance/distance travelled by solvent
  • locating agents are used when one or more substances are colourless
19
Q

Application of chromatography

A
  • identify unauthorised substances like pesticides and poisons in foods
  • detect small quantities of banned substances in athlete’s urine or blood sample
  • separate components like DNA fragments for forensic investigations
20
Q

Fractionating distillation

A
  • used to separate miscible liquids with different boiling points
  1. As solution is heated, both ethanol and water rises up column
  2. Water as higher boiling point than ethanol. The water vapour condenses on the cool surfaces within the fractionating column and the liquid water returns to the flask
  3. Ethanol vapour continues to rise. As its boiling point is 78ºc, it exits the column through the sidearm at the top
  4. Hot ethanol vapour cools and condenses into a liquid as it travels through the inner tube of the condenser
  5. The distillate flows into the conical flask
21
Q

How does a fractionating column work?

A
  • it is packed with glass beads/rods 👉 increases surface area for evaporation and condensation
  • when flask is heated, mixture of vapour passes up column. As temp of column is lower, vapour starts to condense
  • vapour w/ higher bp condenses more readily and return to round bottom flask without contaminating distillate
  • liquid that condensed on column is warmed by rising hot vapours and substance with lower bp evaporates more readily
  • continuous evaporation and condensation causes richer and more volatile vapour to move up column
  • vapour with lower bp will be able to reach the top first and be distilled over in receiver
22
Q

Applications of fractional distillation

A
  • oil refineries separate diff substances from crude oil
  • liquified air is separated to produce nitrogen, oxygen and argon gas for industrial applications
  • ethanol produced by glucose fermentation is extracted in breweries
23
Q

Purity of a substance

A
  • a pure substance has a specific melting and boiling point under fixed conditions
  • impure substances have higher boiling point and lower melting points

Chemistry (22 decks)

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