Problem 3: Cleaning Solutions

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This resource, from the Royal Society of Chemistry, develops students’ skills and understanding of oxidation numbers and the use of mole calculations in redox reactions.

Students are asked to determine the amount of sodium chlorate (I) in various bleach samples in an advertising campaign for a new bleach. Accuracy is an essential feature of this activity to ensure that their data stands up to the scrutiny of the Advertising Standards Agency.

Using the pre-lab questions, students recognise that the concentration of sodium chlorate (I) (NaOCl) in each bleach can be determined by reacting each of them with an excess of hydrogen peroxide and measuring the volume of oxygen produced. Using this information, students can determine if the new bleach is better value for money compared to other brands.
Students are required to decide upon a suitable scale for their experiments and to carry out reactions for each of the bleaches. Calculations for each bleach include the concentration of NaOCl in g dm–3 and the cost per gram of NaOCl.

Curriculum links: oxidation numbers, redox, halogen, moles, reacting masses

Practical skills: collection of gas, accuracy

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