1: Experimental Chemistry Flashcards
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
2
Q
Gas collection method: Water displacement
A
- when gas is insoluble/ slightly soluble
- density does not matter
- ex: hydrogen, carbon dioxide and oxygen
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
4
Q
Gas collection method: upward delivery of gas
A
- soluble/insoluble
- less dense than air
- dissolves in water to form alkaline solution
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)
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
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
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
9
Q
Magnetic attraction
A
- used to separate magnetic solids from non-magnetic solids
10
Q
Sieving
A
- used to separate solids with different size particles
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
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)
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
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
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
- Heat the filtrate to obtain a saturated solution
- Cool the saturated solution for crystals to form
- Filter the mixture to obtain crystals
- Dry it between few sheets of filter paper
16
Q
Simple distillation
A
- used to separate a pure solvent from a solution
- 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
- water vapour cools in condenser and condense back into liquid water. pure water that is collected in conical flask is the distillate
- 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
- As solution is heated, both ethanol and water rises up column
- 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
- Ethanol vapour continues to rise. As its boiling point is 78ºc, it exits the column through the sidearm at the top
- Hot ethanol vapour cools and condenses into a liquid as it travels through the inner tube of the condenser
- 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
