12 Experimental techniques and chemical analysis

Question 1

Variables

Answer 1

A factor that can affect the outcome of a scientific experiment, for example temperature.

Question 2

Si units

Answer 2

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)

Question 3

Alternative units of measurement

Answer 3

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

Question 4

Measuring cylinder

Answer 4

A measuring cylinder is used to prepare liquids for use in an experiment or investigation.

Question 5

Pipette

Answer 5

A volumetric pipette is used to accurately transfer small volumes of liquids from one vessel to another

Question 6

Burette

Answer 6

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

Question 7

Gas syringes

Answer 7

A gas syringe has an inner chamber which has a ground glass surface. The syringe barrel also has a ground glass surface.

Question 8

Solvent

Answer 8

The larger component of a liquid mixture, a substance that dissolves a solute(usually water)

Question 9

Solute

Answer 9

The smaller component of a liquid mixture a substance that is dissolved in a solvent(usually the solid that dissolves)

Question 10

Suspension

Answer 10

A mixture of substances; usually a liquid that may or may not be a solution, and an insoluble solid.

Question 11

Residue

Answer 11

The solution that does not pass through the filter during filtration.

Question 12

Filtrate

Answer 12

The solution which passes through the filter during filtration.

Question 13

Solution

Answer 13

A mixture of one or more dissolved solids(solutes) in liquid(solvent)

Question 14

Saturated solution

Answer 14

A solution containing the maximum concentration of a solute dissolved in the solvent at a specific temperature(cannot dissolve anymore solid)

Question 15

Chromatography

Answer 15

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.

Question 16

Paper chromatography

Answer 16

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)

Question 17

Retardation value

Answer 17

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.

Question 18

Chromatogram

Answer 18

A sheet of chromatography paper, obtained after chromatography has finished, showing separated solutes (coloured substances).

Question 19

Rf value is found by

Answer 19

Rf value = distance travelled by the solute ÷ distance travelled by the solvent

Question 20

Locating agent

Answer 20

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.

Question 21

The characteristics of a pure substance of a chromatogram

Answer 21

Only has one colour or mark/dot

Question 22

Solubility

Answer 22

The ability of a substance to dissolve into a solvent.

Question 23

Crystallisation

Answer 23

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.

Question 24

Distilation

Answer 24

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

Question 25

Filtration

Answer 25

A purification method used to remove an insoluble solid from liquids by pouring through a filter, such as filter paper.

Question 26

Desalination

Answer 26

The process of removing the salt from sea water to create fresh water.

Question 27

Fractional distillation

Answer 27

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.

Question 28

Purification with a solvent

Answer 28

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.

Question 29

Apparatus used for distillation

Answer 29

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.

Question 30

Assessing purity

Answer 30

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.

Question 31

Identify gases

Answer 31

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

Question 32

Flame test

Answer 32

Sodium: Yellow flame
Potassium: Lilcac flame
Copper: Blue/green flame
Barium: Light green flame
Calcium: Orange-red flame
Lithium: Red flame

Question 33

Identify cations using the effect of aqueous sodium hydroxide

Answer 33

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

Question 34

Identify cations using the effect of aqueous ammonia

Answer 34

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

Question 35

Identifying anions

Answer 35

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