Chemical Analysis of Household Oxygen-Based Powdered Bleach: An Engaging Approach to Teaching Sampling of Heterogeneous Materials and Addressing Statistics

Abstract

Crucial steps of a chemical analysis, such as sampling, determination, and statistical analysis of data, are addressed in a well-tested and stimulating laboratory activity that convincingly unveils the stratification of ingredients in a heterogeneous household product for laundry: a powdered oxygen bleach. Three different samples of bleach were taken from a single jar: one from the top, one from the bottom, and a more representative mixture collected by driving a core sampler (a graduated cylinder was found to be appropriate) throughout the full depth of the jar content. The resulting frequency distribution curves (histograms) of the H 2 O 2 titrations with MnO 4 − presented widely separated maxima for the three samples, while no statistically significant difference was found for the titration of CO 3 2− with HCl. These results intrigue the students, leading them to reflect until they understand that this is due to the presence of a single compound acting as a source of H 2 O 2 (sodium percarbonate), while two ingredients in the formulation of the stratified bleach powder provide CO 3 2− after dissolution. Large and light percarbonate grains are more frequent in the upper layer of the bleach jar, while smaller and denser Na 2 CO 3 particles are richer at the bottom.

Hypothesis Tests and Exploratory Analysis Using R Commander and Factoshiny

“…Spreadsheet 4 contains 20–18 carbonate percentages and percarbonate percentages in three samples (MIX, BOT, and TOP) …”

“…Case Study 4: Comparing More Than Two Groups. Santos et al 91 determined sodium carbonate (Na 2 CO 3 ) and sodium percarbonate (2Na 2 CO 3 •3H 2 O 2 ) in a household oxygen-based powdered bleach at different depths of the bleach jar. Three fractions were taken from the powdered bleach: a core sample, obtained by pressing a graduated cylinder throughout the full depth of the jar content (MIX), an upper layer fraction (TOP), and a bottom layer (BOT) (spreadsheet 4; Supporting Information).…”

“…90 Spreadsheet 4 contains 20−18 carbonate percentages and percarbonate percentages in three samples (MIX, BOT, and TOP). 91 Spreadsheet 6 has five measurements of water density using a beaker, pipet, and graduated cylinder. Measurements were carried out using a calibrated and miscalibrated balance.…”

Teaching Descriptive Statistics and Hypothesis Tests Measuring Water Density

“…Descriptive statistics and parametric hypothesis tests ( t test and one-way ANOVA − ) were taught using spreadsheets. − However, spreadsheets did not provide nonparametric tests, and a visual interpretation of these tests was not a default option. As an alternative, programming software such as MATLAB, − Python, − Octave, − R project .…”

Threshold Concepts in Analytical Chemistry

“…A number of articles explore ways to help students understand various aspects of statistics. − In the laboratory, one possible way to help students cross this threshold is to have them conduct a titration to determine the moles of solute present in a sample under two different situations: one in which the concentration of the titrant is well-characterized (i.e., small uncertainty) and the volume that the solid analyte is dissolved in is poorly characterized, and another using a poorly characterized titrant solution (i.e., large uncertainty) but a well-characterized volume of analyte solution. After conducting the experiments and propagating error to determine the amount of sample present, students could be asked to consider in which situation the number of moles of analyte was more accurately determined.…”