The label from a bottle of pine fresh bleach cleaner is shown - Scottish Highers Chemistry - Question 12 - 2019

The reaction used to make soaps from fats and oils is called saponification, which involves the alkaline hydrolysis of esters.

Soap molecules, like compound C, have a hydrophilic head that interacts with water and a hydrophobic tail that attaches to grease and oil.

When soap is mixed with water and oil, the hydrophobic tails bind with the oil while the hydrophilic heads remain in water, helping to encapsulate the oil in micelles. This allows oil to be suspended in water and subsequently washed away. Diagrams can illustrate this process by showing micelle formation.

Emulsifiers are made from edible oils through a process of reacting these oils with glycerol or polyols, which creates a structure that can stabilize emulsions by reducing surface tension between different liquid phases.

A pure covalent bond is one where the electrons are shared equally between two atoms, resulting in no partial charges, as seen in diatomic molecules of the same element.

Chlorine gas is formed when the hypochlorite ion in bleach reacts with acids, allowing chlorine to be released as a byproduct of this reaction.

Mixing the bleach with an acid drives the reaction to produce more chlorine gas, as the added acid increases the concentration of protons (H⁺), which shifts the equilibrium according to Le Chatelier's principle, promoting the formation of products including chlorine gas.

The ion-electron equation for the reduction reaction in Step 1 is:

$ext{OCl}^- + 2 ext{e}^- + 2 ext{H}^+ → ext{Cl}_2 + ext{H}_2 ext{O}$

To find the concentration of sodium hypochlorite, first calculate the moles of sodium thiosulfate used:

$ext{Moles of Na}_2 ext{S}_2 ext{O}_3 = ext{Concentration} imes ext{Volume} = 0.098 ext{ mol/dm}^3 imes 0.009 ext{ dm}^3 = 0.000882 ext{ mol}$

Using the stoichiometry from Step 1, 1 mole of OCl⁻ reacts with 2 moles of Na₂S₂O₃, so:

ext{Moles of OCl}^- = rac{0.000882}{2} = 0.000441 ext{ mol}

Finally, calculate the concentration in the 25 cm³ sample:

ext{Concentration of OCl}^- = rac{0.000441 ext{ mol}}{0.025 ext{ dm}^3} = 0.01764 ext{ mol/dm}^3