Saponification

Identify the reactants used in the preparation of soap

Fat / lard / oil //

sodium hydroxide

Identify the solvent used in the preparation of soap

Ethanol

Name the co-product formed when soap is prepared in this way.

Draw the molecular structure of this co-product, including all atoms and bonds

Glycerol

Why was the reaction mixture refluxed?

Speeds up reaction / helps mix reactants / helps reaction reach activation energy

Suggest a suitable heating method for refluxing the reaction mixture and then distilling off the ethanol

Water bath (heated with bunsen burner or hot plate)

Justify the suitability of your suggested heating method

Oil (water) bath: gentle heating possible temperature easily controlled safe (no flame)

Heating mantle: temperature easily controlled / safe (no flame) / convenient / quick / easy to use

Bunsen with wire gauze: gentle heating possible / temperature easily controlled / flask not heated directly

Why is it desirable to remove all the ethanol?

Improves yield / to get more soap / makes soap less soluble in brine / helps precipitate soap / for re-use

Name the co-product of the reaction

Glycerol

Write the systematic IUPAC name for glycerol

1,2,3-propanetriol

What is brine?

Saturated solution of salt in water / salt water

Explain the function of the brine in the procedure

To precipitate soap / to dissolve components other than soap

Describe how the solid soap was separated from the solution in the beaker

Filter (filtration) / decant (pour) off brine (liquid)

Where is the excess NaOH at this stage of the procedure?

In brine / in the filtration flask / some mixed with soap

The diagram represents the arrangement of a number of soap molecules in water.

Explain why one end of a soap molecule is described as water loving (hydrophilic).

One end ionic (polar)

Calculation 2021 Q2

Name the piece of glassware labelled X

Condenser

Identify the two reactants and the solvent initially present in the flask

Reactants: fat // sodium hydroxide

Solvent: ethanol

Name the type of reaction that occurred in stage 1 of the reaction

Saponification

What substance was removed by distillation in Stage 2?

Ethanol

Why was it necessary to wash the soap thoroughly in Stage 4?

To remove sodium hydroxide

How should the student have washed the soap?

Brine / ice-cold water

Calculation 2014 Q2

Suggest, with reference to its structure, how a soap like sodium stearate can dissolve both the non-polar oils and the ionic salts in sweat from the skin

Hydrocarbon part (end) is non-polar (hydrophobic) and dissolves oils (non-polar substances)

Ionic (hydrophilic) part (end) attracted to (dissolves) salts in sweat

Draw a fully labelled diagram of the reflux apparatus used in an experiment from your course where you refluxed a mixture

What happened to the liquid in the flask during reflux?

Hot vapour rose / liquid evaporated //

vapour was condensed / returned to flask

How did refluxing this mixture help bring the reaction to completion?

Allowed enough time / provide the activation energy / heating without loss of reactants

What was the purpose of the ethanol?

Solvent

Describe, with the aid of a labelled diagram, how the ethanol was removed after the reflux stage

Why was a minimum of hot water used to dissolve the residue from the distillation?

To minimize soap remaining dissolved / maximise soap precipitating out

How was the soap isolated from the other substances left in the reaction mixture?

Added to brine

precipitated soap got by filtration

After isolating the soap, how was it purified and dried?

Purified: wash with brine / wash with water

Dried: warm place / oven

Calculation 2010 Q2

What would you observe, upon shaking, if a little of the soap prepared in this experiment is added to

i) a test tube containing deionised water,

ii) a test tube containing mineral water from a limestone region

i) (immediate) lather

ii) scum / no lather / less lather / does not easily form lather

What is the principle chemical difference between vegetable and animal fats?

Animal saturates //

vegetable unsaturated

Have different degree of saturation