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.

Soaps, like compound C, have a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. The hydrophilic end interacts with water, while the hydrophobic tail binds to grease and oil. This dual action allows soap to surround and emulsify dirt and grease, which can then be washed away with water. The ionic nature of the soap's head group further enhances its ability to stabilize these emulsions by reducing surface tension.

Emulsifiers are made from edible oils through a process called esterification, where edible oils react with glycerol or other alcohols to form emulsifiers.

A pure covalent bond occurs when two atoms share electrons equally, resulting in no charge separation within the bond. This happens when the atoms have the same electronegativity, producing a non-polar molecule.

An excess of sodium hydroxide is used to ensure that all of the chlorine is reacted, preventing any leftover chlorine gas which can be hazardous.

Adding an acid introduces H+ ions, which will react with the hypochlorite ions (OCl–) and shift the equilibrium to the right according to Le Chatelier's principle. This reaction would produce more chlorine gas (Cl2), resulting in increased release of chlorine gas from the bleach.

The ion-electron equation for the reduction reaction is:

OCl– + 2H+ + 2e– → Cl– + H2O.

The concentration of sodium hypochlorite can be calculated using the titration data. First, calculate the moles of thiosulfate:

Moles of Na2S2O3 = Concentration × Volume = 0.098 mol/dm³ × 0.009 dm³ = 0.000882 mol.

Since 1 mole of I2 reacts with 2 moles of Na2S2O3, moles of I2 = 0.000882 mol / 2 = 0.000441 mol.

From the reaction with OCl–, the moles of OCl– will also be 0.000441 mol. Therefore, for the diluted bleach:

Concentration of NaOCl = Moles / Volume = 0.000441 mol / 0.025 dm³ = 0.01764 mol/dm³.