measurement Flashcards
Gas syringe purpose
collect and measure the volume of gas up to 100cm3
rough calibration
known volume
SI unit for time
second (same as record timing)
si unit for temp
kelvin (K)
record temp to the nearest
0.5 degree celsius
conversion of temp to kelvin
273 + degree celcius
si unit for mass
kilogram
record mass to the nearest
0.1g without plastic cover, 0.01 with
SI unit for volume of gas
m3
record volume of gas depend on
instrument
volume is commonly measured in
cubic centimetre and cubic decimeter
1dm3 is
1000cm3
the methods of gas collection depends on
solubility of gas in water and density of gas to air
downward delivery is for gases that are
denser than air
gases that are denser than air are
carbon dioxide CO2 and chlorine gas Cl2
upward delivery of gas is for gases that are
less denser than air
less dense than air are gases like
ammonia NH3 and hydrogen H2
displacement of water is for gases that are
insoluble or slightly soluble in water
gases that are insoluble or slightly soluble are gases like
hydrogen, nitrogen N2, oxygen O2 and carbon dioxide
why can you not use concentrated sulfuric acid to dry ammonia
ammonia is an alkaline gas and will react with the acid
why can you not use quicklime (calcium oxide) to dry sulfur dioxide and hydrogen chloride
since quicklime will react with acidic gases
fused calcium is a calcium chloride that has been
heated to remove water
fused calcium can dry most gases but cant dry ammonia because
it reacts to form a complex
what is purification
its a process to separate pure substances from mixures or impurities
filtration is used to separate
insoluble solids from a liquid-solid mixture
when to use evaporation to dryness
to obtain a soluble solid from its solvent until the all solvent is boiled off. For the solid that does not decompose during strong heating
1st step for evaporation to dryness
heat the solution until all the water has evaporated
2nd step for evaporation to dryness
ensure the soluble solid must be stable to heat so that it does not decompose on heating and must not contain water of crystallisation. Solid obtained is not always pure, any soluble impurities will be left with the solid
water of crystallisation refers to
water molecules that make up the structure of a salt crystal
when to use crystallisation
to obtain a soluble PURE solid from its concentrated solution is the solid decomposes on strong heating
crystallisation occurs when
a saturated solution (a solution in which no more solid can be dissolved) is cool
1st step to obtain pure crystals
dissolve impure solid in water until no more can be dissolved
crystallisation is based on the principle that the
solubility of compounds increases with temp
2nd step to obtain pure crystals
filter the solution to remove extra undissolved solid and insoluble impurity
3rd step to obtain pure crystals
heat the solution till saturation
4th step to obtain pure crystals
leave the hot saturated solution to cool. crystals will start to form in the solution
5th step to obtain pure crystals
the cooled solution is then filtered to obtain the pure crystals. The crystals are dried by pressing them gently between sheets of filter paper
a crystal is pure because
only the particles of the compound arrange together to form a highly ordered structure. impurities are left behind in the solution
how to check for saturation
dip a clean glass rod into the solution and remove it. if small crystals form on the rod when the solution cools, the solution is saturated. The slower the rate of cooling, the larger the crystals.
when is sublimation used
to separate a mixture of solids, in which one of the solids will become a gas when heated
1st step to sublimation
heat the mixture. the vapour of the sublimed solid is cooled to yield the solid.
solids that sublime on heating include
ammonium chloride, iodine and carbon dioxide
when to use simple distillation
when separating a pure solvent from a solution
1st step to distillation
heat the solution in a distillation flask connected to a condenser
2nd step to distillation
the liquid boils and its vapour enters the cold condenser where condensation takes place
3rd step to distillation
the vapour is converted back to its pure liquid form and collected as the distillate
when to use fractional distillation
to obtain a pure liquid from a solution of two or more miscible liquids with different boiling points
miscible liquids are those that are
completely soluble in one another when mixed
the liquids in fractional distillation are separated according to their
boiling points
for fractional distillation, the liquid with the lowest boiling point will be
distilled first
whats the principle of fractional distillation
the liquid with the lowest boiling point distills off first
when to use a separating funnel
when separating immiscible liquids
immiscible liquids are liquids that
do not mix with one another
a separating funnel has
a stopper covering the top and a tap at the bottom
a mixture of two immiscible liquids will form
two separate layers
the less dense liquid will be on top while the denser liquid will
sink to the bottom of the funnel
paper chromatography is used to
separate and identify of both coloured and colourless mixtures such as drugs and dyes
the solvent comes into contact with the
bottom of the chromatography paper and moves up by capillary action
(chromatography) different substances in the mixture become separated as they
travel at different rates due to the varying solubilities in the solvent
some inks are water soluble and some are not. To separate non soluble water components, use
ethanol
separated substances are identified by
comparing their positions on paper with that of known substances, calculating the retention factor
retention factor is obtained by
dividing the distance travelled by the solute up the paper by the distance travelled by the solvent
for substances that share the same retention factor value, choreography can be performed with
a different solvent to distinguish them
for separating colourless compounds,use
locating agents are used to show the position of these compounds in the chromatogram
locating agents are substances that
react to form coloured products with the colourless compounds
state the 3 drying agents
concentrated sulfuric acid, quicklime (calcium oxide), calcium chloride
pure substances are made of
one single element or compound
state the process of filtration
- pour the mixture into a filter funnel that is lined with filter paper. 2. collect the filtrate that passes through the filter paper in a beaker. 3. wash the residue with some distilled water to remove impurities. 4. dry the residue between pieces of filter paper
during crystallisation, water is
removed when heated
during crystallisation, heating is stopped when
a hot saturated solution is formed
crystallisation procedure
- using a glass rod, stir and dissolve the impurities in water. 2. pour the mixture into filter funnel lined with filter paper, filter to remove any insoluble impurities, and collect filtrate in a beaker. 3. Heat solution till saturated. 4. when solution is saturated, leave it it to cool at room temp, crystals will start to form in the solution. 5. filter to collect the crystals, wash the crystals with cold distilled water to remove impurities. 6. Dry the crystals with filter paper
Using a suitable solvent when a mixture of two solids in which
only one is soluble in the solvent
a substance that sublimes has the same
melting and boiling point
examples of solids that sublimes
iodine, ammonium chloride, carbon dioxide, and naphthalene
during sublimation, the surface must be
lower temp than the mp and bp of the solid
describe an advantage of chromatography over other physical methods of separation
chromatography only requires filter paper and a solvent, it is not as costly as other physical methods
explain why test tubes are enclosed with a cork during chromatography
to make the atmosphere in the container become saturated with solvent vapour, so that it can prevent the solvent from evaporating as it rises up the paper
Mixture in chromatography is when there are ____ spots
more than 1
caveats for simple distillation (thermometer and condenser)
Thermometer should be placed near the outlet of the flask, ensures the thermometer measures the boiling point of the vapour instead of the heat from the flame. Water should be flowing against the flow of vapour. This ensures the presence of a permenant cold surface in which all vapour condenses into liquid effectively before leaving the condenser.
Volatile liquid is
near room temp
important role of fractionating column
provides large surface area for evaporation and condensation of vapour of different liquids so that the separation of liquids can be more efficient.
eg for physical changes
liquid to gas, solid to liquid
principle of chromatography
different dyes have different solubility in the solvent (water) so they travel from the center of the paper at different speeds. The more soluble the dye, the further it will travel from it
ascending chromatography is faster because
it moves in the same direction as gravity
