Chapter 1: Experimental Chemistry

SI units for time, temperature, length, mass and volume and their symbols

second s

Kelvin K

metre m

kilogram kg

cubic metres m^3

Two apparatus used to measure time and their accuracy

digital stopwatch +-0.01

analogue stopwatch +-0.1s

Two apparatus used to measure temperature

alcohol thermometer

digital thermometer

A liquid boils at 120°C. Should a mercury thermometer be used to stir the liquid?

no, due care should be taken to ensure that the bulb of the thermometer does not break since mercury is toxic

Apparatus used to measure length

micrometer screw gauge

vernier calipers

metre rule

measuring tape

Apparatus used to measure mass

beam balance and electronic balance

Apparatus used to measure volume and its accuracy

burette +-0.01cm^3

pipette +-0.1cm^3

volumetric flask

measuring cylinder

Two apparatus that measure accurate fixed volumes and the volumes

pipette 10.0cm^3 or 25.0cm^3

volumetric flask 100cm^3 or 250cm^3

Why should eyes be positioned at the meniscus when reading vol. of a liquid?

to avoid parallax error which may affect accuracy of results

4 methods of collecting a gas?

gas syringe

water displacemen

downward delivery

upward delivery

Methods of measuring a gas

gas syringe

Physical properties of a gas are considered when collecting gas

solubility of the gas in water

density of gas compared to air

When using displacement of water, the gas must be __________

insoluble or slightly soluble

Displacement of water cannot be used for ___________

soluble gases

When using downward delivery, the gas must be __________

denser than air

When using upward delivery, the gas must be __________

less dense than air

Three drying agents for drying gas?

concentrated sulfuric acid

quicklime / calcium oxide

fused calcium chloride

Two drying agents that cannot be used for alkaline gases (e.g. ammonia)

concentrated sulfuric acid

fused calcium chloride

Drying agent that cannot be used for acidic gases (e.g. carbon dioxide)

quicklime (calcium oxide)

Gases dried by concentrated sulfuric acid

most gases, chlorine and hydrogen chloride

Gases dried by fused calcium chloride

hydrogen, nitrogen, carbon dioxide

Gases dried by quicklime/calcium oxide

ammonia

Types of mixtures are there

solid-solid

solid-liquid

liquid-liquid

Separation techniques for solid-solid mixtures

magnetic attraction

sieving

using suitable solvents

sublimation

Examples of magnetic materials

iron, cobalt, nickel, alloys

Magnetic attraction method

a magnet separates magnetic solids from non-magnetic solids

Sieving method

a sieve separates solids with different particle sizes

Using suitable solvents method

a suitable solvent seperates solid-solid mixtures where only one of the solids is soluble in the solvent

Sublimation method

sublimation separates a substance that changes from the solid to gaseous state directly

Substances which undergo sublimation

dry ice, iodine, napthalene

Sublimation process (in detail)

separates a mixture of solids where one sublimes on heating while others are stable at sublimation temperatures

solid sublimes into a gas and moves away from the mixture

gas changes back into solid state and deposits on cool surface

pure sublimate is scraped off cool surface

Separation techniques for solid-liquid mixture

filtration

evaporation to dryness

crystallisation

simple distillation

Filtration method

filter funnel and filter paper are used to separate insoluble solids from soluble solids

Explain what is filtrate

liquid that passes through filter paper

Explain what is residue

solid that remains on filter paper

Evaporation to dryness method

separating a dissolved solid from its solvent by heating the mixture until all solvent evaporates

Some substances not be separated by evaporation to dryness because……

some substances are not heat-stable and decompose into simpler substances

Crystallisation method

crystallisation obtains a pure solid from its saturated solution

Definition of a saturated solution

a solution in which no more solute can be dissolved

Process of crystallisation (in detail)

gently heat the solution to evaporate the solution to saturation

cool solution until solid crystals appear in the solution

pass solution through filter paper to collect solid crystals

wash the impure crystals with distilled water

dry crystals between pieces of filter paper

Two advantages of using crystallisation over evaporation to dryness

solid formed from crystallisation is always pure

can be used for substances that are not heat-stable

Simple distillation method

separates pure solvent from solution by relying on its components having different boiling points

Simple distillation process (explain in detail)

mixture is heated until liquid reaches its boiling point and evaporates and enters the condenser

vapour cools in the condenser and condenses back into liquid state

pure solvent collected is called distillate

solution is heated until only solid residue remains in the distillation flask

Reason for bulb of the thermometer to be at mouth of the condenser

to ensure that the vapour entering the condenser is the vapour that will condense to form the distillate to be collected

Reason cold running water enters the water jacket from the bottom of condenser

ensure that the vapour will be fully condensed as much as possible

Reason conical flask is preferred for distillation

narrow neck to prevent loss of distillate via splashing

Boiling chips are used in distillation to ________________

ensure smooth boiling of the solution

Separation techniques for liquid-liquid mixture

separating funnel, chromatography, fractional distillation

Miscible liquids are ______________

liquids which form a homogenous solution when mixed together

Immiscible liquids ________________

liquids which form a heterogenous mixture when mixed together

Separating funnel method

separates immiscible liquids

each component is removed by draining each layer

Chromatography

separates mixtures where each component has different solubilities in a given solvent

Why is the start line marked with pencil instead of pen

pencil lead is insoluble in the solvent and will not travel up the chromatogram and affect accuracy of results

Why should the spots of dyes on the starting line be small?

prevent the spots of dyes from dissolving in the solvent sideways and contaminating the samples

Retention value formula

distance travelled by substance / distance travelled by solvent

Why should Rf values for chromatograms obtained with different solvents not be used for comparison?

given substance may have different levels of solubility in each solvent, affecting the distance travelled by the substance and changing Rf value

Fractional distillation method

separates miscible liquids with different boiling points

Explain the purpose of a fractionating column.

contains glass beads to provide a larger surface area to ensure there is sufficient time for the respective vapour to condense in the condenser and be collected as distillate.

Explain why liquid-liquid mixtures cannot be separated by simple distillation.

difference in boiling points between the two liquids not large enough to be separated by simple distillation

Fractional distillation process

solution is heated and both components rise up the column

component with higher b.p. condenses on the glass beads within column and condensed liquid returns to the flask

component with lower b.p. continues to rise and enter condenser

component cools and condenses into liquid state and is collected as distillate

3 industrial application of fractional distillation

oil refineries separate crude oil into different substances which are further processed into chemicals like petrol, kerosene and lubricating oils

liquefied air is separated into nitrogen, oxygen and argon gas for industrial use

ethanol produced by glucose fermentation is extracted in breweries

Difference in a physical characteristics of pure substances and mixtures.

pure substance has a specific melting and/or boiling point while mixtures melt or boil over a range of temperatures