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 is the alkaline hydrolysis of triglycerides.

Soap, represented by compound C, has a dual nature: a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. When soap is added to a mixture of oil and water, the hydrophobic tails of the soap molecules attach to the oil particles while the hydrophilic heads remain in the water. This allows the oil to be emulsified, forming micelles that can be easily rinsed away, effectively cleaning the surface.

Emulsifiers are made from edible oils through a process that involves reacting the oils with glycerol or other substances such as alcohols. This reaction leads to the formation of molecules that have both hydrophilic and hydrophobic properties, allowing them to stabilize mixtures of oil and water.

A pure covalent bond is characterized by an equal sharing of bonding electrons between two atoms. This occurs when both atoms have similar electronegativity values, resulting in no partial charges within the bond.

An excess of sodium hydroxide is used to ensure that all chlorine is reacted fully, preventing the release of chlorine gas and ensuring that the reaction proceeds to completion.

By adding an acid to the bleach cleaner, the equilibrium can be shifted to the right as per Le Chatelier's principle. The addition of H+ ions from the acid will react with OCl− ions, thus reducing their concentration. This drives the equilibrium forward, promoting the release of chlorine gas as the bleach decomposes to form Cl2 and H2O.

The ion-electron equation for the reduction reaction is:

$OCl^{-} + 2H^+ + 2e^{-} → Cl_2 + H_2O$

To calculate the concentration of sodium hypochlorite, we start by finding the moles of iodine produced:

1. Moles of thiosulfate used in titration:

   $C_1V_1 = C_2V_2$

   $0.098 imes 0.009 = n_{thiosulfate}$

   $n_{thiosulfate} = 0.000882$

2. From the stoichiometry of the reaction, since 1 mole of I2 reacts with 2 moles of thiosulfate:

   n_{I2} = rac{n_{thiosulfate}}{2} = rac{0.000882}{2} = 0.000441

3. Since this amount comes from 25cm³ of bleach:

   ext{Concentration of sodium hypochlorite} = rac{0.000441}{0.025} = 0.01764 ext{ mol dm}^{-3}