Chapter 1: Experimental Chemistry (copy)

List the SI unit for time, temperature, length, mass and volume and its symbol in brackets.

second (s), Kelvin (K), metre (m), kilogram (kg), cubic metres (m^3)

List the two apparatus used to measure time and its accuracy in brackets.

digital stopwatch (+-0.01s), analogue stopwatch (+-0.1s)

List the 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.

List the apparatus used to measure length

Micrometer screw gauge, vernier calipers, metre rule, measuring tape

List the apparatus used to measure mass

Beam balance and electronic balance

List the apparatus used to measure volume and its accuracy where applicable.

burette (+-0.01cm^3), pipette (+-0.1cm^3), volumetric flask, measuring cylinder

List the two apparatus that measure accurate fixed volumes and the volumes in brackets.

pipette (10.0cm^3, 25.0cm^3), volumetric flask (100cm^3, 250cm^3)

Why should our eyes be positioned at the meniscus when reading the volume of a liquid?

To avoid parallax error which may affect the accuracy of the results.

List the 4 method of collecting a gas.

Gas syringe, water displacement, downward delivery, upward delivery

List the methods of measuring a gas

Gas syringe

What physical properties of a gas are considered when collecting the gas?

1. Solubility of the gas in water

2. 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 ___________

insoluble gases

\n When using downward delivery, the gas must be __________

denser than air

When using upward delivery, the gas must be __________

less dense than air

List the three method for drying gas.

Concentrated sulfuric acid, quicklime (calcium oxide), Fused calcium chloride

Which two drying agents cannot be used for alkaline gases (e.g. ammonia)?

Cncentrated sulfuric acid and fused calcium chloride

Why drying agent cannot be used for acidic gases (e.g. carbon dioxide)?

Quicklime (calcium oxide)

What gases can be dried by concentrated sulfuric acid?

Most gases, chlorine and hydrogen chloride

What types of mixtures are there?

Solid-Solid mixture, Solid-Liquid mixture, Liquid-Liquid mixture

Separation techniques for solid-solid mixture

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**__

Examples of substances which undergo sublimation

Dry ice, iodine, napthalene

Sublimation process (in detail)

Sublimation separates a mixture of solids where __**one sublimes on heating**__ while __**others are stable**__ at the sublimation temperatures. Firstly, the solid sublimes into a __**gas**__ and moves away from the mixture. Then, the gas will __**change back into solid state**__ and deposit on a cool surface. Lastly, the pure __**sublimate**__ is scraped off the cool surface.

Separation techniques for solid-liquid mixture

Filtration, evaporation to dryness, crystallisation, simple distillation

Filtration method

A filter funnel and filter paper are used to separate __**insoluble**__ solids from __**soluble**__ solids.

Explain what is filtrate.

The liquid that passes through the filter paper

Explain what is residue

The solid that remains on the filter paper

Evaporation to dryness method

Separating a dissolved solid from its solvent by heating the mixture until __**all the solvent**__ has __**vaporised.**__

Explain why evaporation to dryness may not be able to separate some substances.

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

Crystallisation method

Crystallisation obtains a pure solid from its saturated solution

Explain the definition of a saturated solution.

A solution in which no more solute can be dissolved

Explain the process of crystallisation (in detail)

1. Gently heat the solution to evaporate the solution to saturation

2. Cool the solution until solid crystals appear in the solution

3. Pass the solution through filter paper to collect the solid crystals

4. Wash the impure crystals with distilled water

5. __Dry the crystal__s between pieces of filter paper

State two advantages of using crystallisation over evaporation to dryness

1. The solid formed from crystallisation is always pure, while the substance obtained from evaporation may not be pure

2. Crystallization can be used

   for substances that are not heat-stable and decompose into simpler substances under high heat

Simple distillation method

Simple distillation separates a pure solvent from a solution by relying on its components having __**different boiling points.**__

Simple distillation process (explain in detail)

1. The mixture is heated until the liquid reaches its boiling point and evaporates, entering the condenser

2. The vapour cools in the condenser and condenses back into liquid state

3. The pure solvent collected is called distillate

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

Explain why the bulb of the thermometer must be at the 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.

Explain why cold running water enters the water jacket from the bottom of condenser

To ensure that the vapour will be f__**ully condensed**__ as much as possible to ensure __**accuracy of results.**__

Explain why a conical flask is preferred for distillation

A conical flask has a narrow neck to __**prevent loss of distillate**__ via splashing to ensure accuracy of results

Explain why boiling chips are used for distillation

To ensure smooth boiling of the solution

Separation techniques for liquid-liquid mixture

Separating funnel, chromatography, fractional distillation

Explain what are miscible liquids

Liquids which form a __**homogenous solution**__ when mixed together

Explain what are immiscible liquids

Liquids which form a __**heterogenous mixture**__ when mixed together. Immiscible liquids will separate into layers known as __**phases**__ when left undisturbed, with the densest liquid being at the bottom.

Separating funnel method

A separating funnel separates __**immiscible liquids.**__ Each component is removes by draining each layer.

Chromatography

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

Why is the start line marked with pencil?

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

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

To prevent the spots of dyes from dissolving in the solvent sideways and __**contaminating**__ the samples, hence reducing the __**accuracy of the results**__

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?

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

Fractional distillation method

Fractional distillation separates __**miscible liquids**__ with __different boiling points__

Explain the purpose of a fractionating column.

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.

The difference in boiling points between the two liquids __**may not be as large**__ to be separated by simple distillation

Fractional distillation process

1. The solution is heated and both components rise up the column

2. The component with the higher bp condenses on the glass beads within the column and the condensed liquid returns to the flask

3. The component with the lower bp continues to rise and enters the condenser

4. The component cools and condenses into liquid state and is collected as distillate.

List and explain 3 industrial application of fractional distillation

1. Oil refineries separate crude oil into different substances which are further processed into chemicals such as petrol, kerosene and lubricating oils

2. Liquefied air is separated into nitrogen, oxygen and argon gas for industrial use

3. Ethanol produced by glucose fermentation is extracted in breweries

Explain the difference in a physical characteristic of pure substances and mixtures.

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

What gases can be dried by quicklime (calcium oxide)?

ammonia

What gases can be dried by fused calcium chloride?

hydrogen, nitrogen, carbon dioxide