experimental chemistry Flashcards
advantages of using a burette compared to a measuring cylinder
burette (measures a range of volumes to the nearest 0.05 cm^3) is more accurate in measurement than the measuring cylinder (measures a range of volumes to the nearest 0.5 cm^3)
what apparatus should you use to measure 600 cm^3 of liquid
volumetric flask. it measures accurate fixed large volumes
how can parallax error be avoided when reading volume from measuring cylinder
position the eye at the level of the liquid, and read the scale at the bottom of the meniscus
meniscus definition
the upward or downward curve at the surface of a liquid/solution in a container
what apparatus should you use to measure 5 cm^3 of gas?
gas syringe
two properties of gas that determines gas collection method
- solubility: how easily the gas dissolves in water
- density: how dense the gas is as compared to the surrounding air
deduce the solubility of a gas that can be collected through the displacement of water
insoluble in water OR slightly soluble in water
explain why a gas with Mr lower than that of air can be collected through upward delivery
the gas is less dense than air and will rise into the gas jar for collection
similarity between gases collected through upward delivery and downward delivery
the gases can be insoluble or soluble
how does the density of gas affect the displacement of water
it does not affect the displacement of water
properties of gases that can be collected through downward delivery
- denser than air
- soluble/insoluble in water
limitation of concentrated sulfuric acid as a drying agent
alkaline gases that react with sulfuric acid cannot be dried with this method (eg. ammonia)
property of gases that enables it to be dried with quicklime
they are alkaline gas (ONLY AMMONIA)
- turn damp red litmus paper blue
why is fused calcium chloride the best way to dry gases
it is neutral –> can dry both alkaline and acidic gases EXCEPT AMMONIA
why must fused calcium chloride be freshly heated before use
it to remove all traces of water –> readily absorbs moisture from surrounding air
how to determine if a substance is pure
if a substance is pure, it will have a fixed melting and boiling point.
if not, it will melt and boil over a range of temperatures
effect on impurities on melting and boiling points
with impurities,
1. a substance melts below its melting point over a range of temperatures
2. a substance boils higher than its melting point over a range of temperatures
solid-solid physical separation techniques
- magnetic attraction –> magnetic properties
- sieving –> particle size
- using suitable solvents –> solubility
- sublimation –> ability to sublime
solid-liquid physical separation techniques
- filtration –> solubility
- crystallisation –> solubility
- evaporation to dryness –> melting/boiling point
- simple distillation –> difference in melting/boiling points
liquid-liquid physical separation techniques
- chromatography –> solubility
- separating funnel –> immiscibility
- fractional distillation –> boiling point
what is ability to sublime mean
the ability to change into a gas directly without melting –> with the presence of heat
steps for a filtration experiment (eg. NaCl, sand)
- add water to dissolve NaCl
- filter out the mixture to remove the excess sand
- evaporate NaCl solution to dryness
- solid NaCl crystals will be formed
steps for a crystallisation experiment (eg. sugar, sand)
- add water to dissolve sugar in the solid-solid mixture of sand and sugar
- filter out the mixture to remove excess insoluble solid sand
- heat the solution gently until saturation
- allow the saturated solution to cool. sugar crystals will form
- filter out crystals
- cool distilled water –> sheets of filter paper
during simple distillation, when does collection of the liquid with lower boiling point stop
when temperature starts to rise above the boiling point of the liquid
