Topic 2 Flashcards
Define independent variable and where it situated on a graph (2)
What is changed
always x axis on a graph
Define dependent variable and where it situated on a graph (2)
what is measured
always y axis on a graph
Define control variable
factor(s) which are controlled during the investigation
which apparatus is used to measure time
stopwatch
Which apparatus is used to measure temperature
thermometer
Which apparatus is used to measure mass
mass balance
Define SI units
standardised units for measuring
Name the unit and symbol for electric current (2)
Unit: ampere
symbol: A
1L is also equal to? (2)
1dm^3
1000cm^3
Purpose of measuring cylinder
used to measure out a volume of liquid to be used in a reaction
Purpose of pipette
used to transfer a volume of liquid from one vessel to another
Purpose of burette (3)
used during titration reactions
Allows volume of liquid to be added to another and the addition of the liquid is controlled by a tap
scientist is then able to measure how much liquid was needed in the reaction
Define precise results
a set of results, measurements or values that are close to each other
Define accurate results
results, measurements or values that are close to the atual value
name the different measurement techniques used to seperate mixtures (5)
filtration
fractional distillation
crystallisation
Distillation
Paper chromatography
Explain filtration (4)
used to seperate insoluble solid from a liquid
solid gets stuck in the filter paper while the liquid is able to pass through
solid is known as residue
liquid is known as filtrate
Explain evaporation (2)
used to seperate soluble solid from a liquid
liquid is evaporated off to leave behind the soluble solid
Define pure substance
having only one type of particle
Define impure substance
has more than one type of particle
Relationship between melting/boiling point and purity (2)
pure substance has sharp melting and boiling point
pure substance has a set melting point and boiling point at which the intermolecular forces of attraction breaks
Relationship between melting/boiling point and impurity (2)
graph for melting and boiling point of an impure sustance would show a slope with a gradient between the state changes (seperate componenets melt at different temperature so it cannot be a horzontal line)
impure substances melt over a range of tmperatuers
Impure solids have a lower melting point than the pure solid
True or False
true
A liquid with a solute will have a higher boiling
point than the pure solvent.
True or False
true
where and Why is purity important? (2)
important in food and pharmaceutical industries
any impurities could have potential lethal side effects
Explain crystallisation (3)
allows pure crystals of a solid to be obtained from a solution as it cools
slower the cooling, the larger the growth of crystals
crystals form when the temperature of the solution decreases meaning the solid particles have less space within the liquid. The solid particles are pushed out of the solution and grows as crystals.
What is distillation used to seperate
used to seperate a liquid with a soluble solid
When is distillation used over evaporation
used over evaporation when you want to obtain the liquid vs in evaporation when you want to obtain the solid
Can liquids be used to seperate a mixture of liquids with different boiling points in distillation? EXPLAIN.
can be used to seperate a mixture of liquids with different boiling points. However, liquids must have boiling points that have a significant different in temperature
Explain the process of distillation (5)
original source is heated within the round bottomed flask
The liquid with the lower boiling point boils and changes state to gas
the vapour passes along the condensor, where cold water runs through, acting as a heat exchanger and absorbing the heat from the gas until it turns back into a liquid
liquid is collected in the beaker
The other liquid (which has a higher b.p) is left behind in the rounded flask
When is fractional distillation used (2)
used to seperate more complex liquid mixtures
used when the different in boiling points of the seperate components is rougly 25degrees
Explain process of fractional distillation (5)
mixture of liquids in the rounded bottomed flask is heated
both substances start to vapourise because of their similar b.p
vapour travels past the glass beads which have a cool surface area
Vapour from the liquid with the higher b.p condenses and drops back into the flask
the vapour from the other liquid mvoes through the top of the column and then into the condensor
Use of fractional distillation in industry
used in the oil industry to seperate out crude oil
crude oil is useless but it has many useful components such as petrol, diesel and kerosene. All of the above are seperaeted out using fractional distillation.
When is paper chromatography used
used to seperate out small quantities of substances from a solution
Explain the process of paper chromatography (4)
the ink spots are carried up by the filter paper by the water
the water is the mobile phase while the filter paper is the stationary phase
after a certain time,the filter paper is taken out and a solvent front is marked (later used to calculate the Rf value)
spots travel up the stationary phase at different rates, causing them to seperate out
Which two factors are responsible for ow far the spots travel in paper chromatography (2)
mass
solubility of the spots
Equation for Rf value
Rf value = distance moved by teh spot from the baseline / distance moved by the solvent front from the baseline
Equation for Rf value
Rf value = distance moved by teh spot from the baseline / distance moved by the solvent front from the baseline
purpose of Rf values (2)
substances with Rf values can be referenced to determine unknown compounds
Rf values of known substances can be compared to Rf values of unknown substance. If Rf values are same, substance is same
How to use paper chromatography to test for purity
if substance is impure then there are more spots than would characteristically be expected
