12 Experimental techniques and chemical analysis Flashcards
Variables
A factor that can affect the outcome of a scientific experiment, for example temperature.
Si units
time, second , s, stopwatch
temperature , degree Celsius, °C, thermometer
mass, kilogram, kg, mass balance
volume, cubic metres , m3, (burettes, volumetric pipettes, measuring cylinders and gas syringes)
Alternative units of measurement
Variable Unit Symbol Conversion
time minute min 1 min = 60 s
time hour h 1 h = 3600 s
time day d 1 d = 86 400 s
temp kelvin K 0 K = −273.15 °C
mass gram g 1000 g = 1 kg
mass tonne t 1 t = 1000 kg
volume litre l 1000 l = 1 m3
volume cubic decimetres dm3 1000 dm3 = 1 m3
volume cubic centimetres cm3 1 000 000 cm3 = 1 m3
Measuring cylinder
A measuring cylinder is used to prepare liquids for use in an experiment or investigation.
Pipette
A volumetric pipette is used to accurately transfer small volumes of liquids from one vessel to another
Burette
A burette is a long tube, usually with the capacity to store 50 cm3 of liquid, with a tap at the base that allows either a continuous flow of fluid or a drip feed
Gas syringes
A gas syringe has an inner chamber which has a ground glass surface. The syringe barrel also has a ground glass surface.
Solvent
The larger component of a liquid mixture, a substance that dissolves a solute(usually water)
Solute
The smaller component of a liquid mixture a substance that is dissolved in a solvent(usually the solid that dissolves)
Suspension
A mixture of substances; usually a liquid that may or may not be a solution, and an insoluble solid.
Residue
The solution that does not pass through the filter during filtration.
Filtrate
The solution which passes through the filter during filtration.
Solution
A mixture of one or more dissolved solids(solutes) in liquid(solvent)
Saturated solution
A solution containing the maximum concentration of a solute dissolved in the solvent at a specific temperature(cannot dissolve anymore solid)
Chromatography
A method used to separate and identify substances by dissolving them in a solvent and allowing them to be carried by the solvent through a sheet of filter paper. The dissolved solutes are deposited along the sheet of paper according to their solubility and mass.
Paper chromatography
is used to separate mixtures of soluble coloured substances, using a suitable solvent
is used to separate mixtures of soluble colourless substances, using a suitable solvent and a locating agent (Knowledge of specific locating agents is not required)
Retardation value
In paper chromatography, it is the value calculated by dividing the distance moved by a solute along the chromatography paper by the overall distance moved by the solvent.
Chromatogram
A sheet of chromatography paper, obtained after chromatography has finished, showing separated solutes (coloured substances).
Rf value is found by
Rf value = distance travelled by the solute ÷ distance travelled by the solvent
Locating agent
A chemical substance that will react with the solute(s) separated in chromatography to produce a coloured substance. Locating agents are used to identify colourless compounds separated by chromatography.
The characteristics of a pure substance of a chromatogram
Only has one colour or mark/dot
Solubility
The ability of a substance to dissolve into a solvent.
Crystallisation
A purification method used to obtain solid dissolved in a solution. As the liquid part of the solution cools and becomes denser, there is less space for the solid particles to occupy. These particles are excluded from the liquid and form crystal arrangements on the side of the vessel containing them. The way this is done by heating the solution evapourating the solvent leaving saturated solution then cooling off making bonds creating crystals.
Distilation
A purification method is used to separate a mixture of liquids by boiling and condensing with different boiling points. The Unwanted element will be left in the flask and the wanted will end up in the condenser from gas to liquid and trickle into the beaker to collect
Filtration
A purification method used to remove an insoluble solid from liquids by pouring through a filter, such as filter paper.
Desalination
The process of removing the salt from sea water to create fresh water.
Fractional distillation
A chemical process that describes heating and separating substances by distillation into more useful products (or fractions) based on their boiling points. It is used in the refining of crude oil.
The Unwanted element will be left in the flask and the wanted will boil and evaporate into the fractionating column and soon end up in the condenser from gas to liquid and trickle into the beaker to collect.
Purification with a solvent
As solvents are not universal, they can be used to separate solids based on solubility. For example, sodium chloride is very soluble in water but insoluble in ethanol. Mixtures of solid substances are separated using solvents to create a suspension that can be filtered.
Apparatus used for distillation
Condenser: The vapour passes along the condenser. Cold water running through the condenser acts as a heat exchanger, absorbing heat energy from the gas, which in turn cools the gas back into a liquid.
Fractional column: The beads provide a cool surface over which the vapour from the liquid with the highest boiling point will condense and then drop back into the flask.
Assessing purity
Pure substances have experimentally defined melting points and boiling points known as fixed points.
Fixed points: Temperature fixed points are precise values of temperature that have been obtained experimentally and recorded for an element, for example boiling point and melting point. The fixed points of almost every pure substance are known.
Identify gases
Ammonia(NH3) damp red litmus paper turns blue
Carbon dioxide(CO2, limewater turns milky
Chlorine(Cl 2), using damp litmus paper bleaches
Hydrogen(H2) lighted splint ignites with gas, (pops)
Oxygen(O2), glowing splint relights
Sulfur dioxide(SO2), turns acidified aqueous
potassium manganate(VII) from purple to colourless
Flame test
Sodium: Yellow flame
Potassium: Lilcac flame
Copper: Blue/green flame
Barium: Light green flame
Calcium: Orange-red flame
Lithium: Red flame
Identify cations using the effect of aqueous sodium hydroxide
Aluminium(Al3+)
white precipitate, soluble in excess – gives a colourless solution
Ammonium(NH4+)
ammonia gas produced on heating. Turn red litmus blue.
Calcium(Ca2+)
white precipitate, insoluble in excess
Chromium(III)(Cr3+)
green precipitate, soluble in excess – gives a green solution
Copper(II)(Cu2+)
light blue precipitate, insoluble in excess
Iron(II)(Fe2+)
green precipitate, insoluble in excess
Iron(III)(Fe3+)
red/brown precipitate, insoluble in excess
Zinc(II)(Zn2+)
white precipitate, soluble in excess – gives a colourless solution
Identify cations using the effect of aqueous ammonia
Aluminium(Al3+)
white precipitate, insoluble in excess
Ammonium(NH4+)
Calcium(Ca2+)
no precipitate, or very slightly white precipitate
Chromium(III)(Cr3+)
grey-green precipitate, soluble to some extent in excess – gives blue solution
Copper(II)(Cu2+)
light blue precipitate, soluble in excess – gives a dark blue solution
Iron(II)(Fe2+)
green precipitate, insoluble in excess
Iron(III)(Fe3+)
red-brown precipitate, insoluble in excess
Zinc(II)(Zn2+)
white precipitate, soluble in excess – gives a colourless solution
Identifying anions
Carbonate(CO3 2–), by reaction with dilute acid
and then testing for carbon dioxide gas
Result: effervescence, carbon dioxide produced
Chloride(Cl–) by acidifying with dilute nitric acid then adding aqueous silver nitrate
Result: white ppt
Bromide(Br–) by acidifying with dilute nitric acid then adding aqueous silver nitrate
Result: cream ppt
Iodide, (I –) by acidifying with dilute nitric acid then adding aqueous silver nitrate
Result: yellow ppt
Nitrate(NO3–) add aluminium foil
and aqueous sodium hydroxide and then
testing for ammonia gas by using damp litmus paper
Result: ammonia produced
Sulfate(SO4 2–) by acidifying with dilute nitric
acid and then adding aqueous barium nitrate
Result: white ppt
Sulfite(SO3 2–) by reaction with acidified
aqueous potassium manganate(VII)
Result: Sulfur dioxide produced will turn acidified aqueous potassium manganate(VII) from purple to colourless
