03. Chemical scenarios

ATL

• Critical-thinking skills: Interpret data; revise understanding based on new information and evidence.

• Transfer skills: Apply knowledge and skills to unfamiliar situations; make connections between subject groups and disciplines; change the context of an inquiry to gain different perspectives.

To complete this activity you will need to use the information in the solubility table from lesson 01. A systematic approach

Matter persists in the environment because it cannot be created or destroyed, but when its atoms form new compounds, their electrons may be gained or lost. Compared to their atoms, all ions are much more soluble in water. As the case studies suggest, environmental water, streams, rivers and oceans (and sometimes rain) can disperse matter in he form of ions to unexpected locations.

Dissolved in water, ions are mobile, which means they can also react together.

In pairs, consider these scenarios and produce responses for each one.

1 Imagine a truck carrying chemicals being involved in an accident, and spilling its load into a river.

a Identify which of the following compounds would be insoluble based on information in the table: CuSO₄, PbS, Ag₂SO₄, Cd(OH)₂, Ca(NO₃)₂, Cr₂(SO₄)₃, FeCl₃, ZnBr₂ and MgI₂.

b Could an insoluble precipitate of an ionic compound pose a danger to the environment? Explain your reasoning.

2 Calcium nitrate is a fertiliser. Suggest an example of an ionic compound (aq) that will react with calcium nitrate to produce a precipitate.

3 Imagine the labels had peeled off from three old jars of stock chemicals. Your teacher knows the jars contain solid sodium carbonate, sodium chloride and sodium sulfate, but hopes that you are able to suggest a strategy for determining the compound in each jar. Outline how you could solve this problem in a safe manner.

4 Arsenic poisoning is a favourite method for commiting murder in Victorian crime novels. Arsenic is a semi- metal, found below phosphorus in the periodic table. Arsenate (AsO₄^3-) has similar properties to phosphate, but it can also form the cation As³⁺. Imagine a scene featuring a victim lying face down in his shaving basin, a jug of clear 'water' and an empty glass at his side.

a Suggest how to determine that drowning had not been the cause of death.

b The solution in the jug is transparent. Suggest examples of arsenic compounds that may be dissolved in the water.¹

^{Hints to help with addressing the chemical scenarios are attached below.}

Assessment opportunities

• In this activity you have practiced skills that are assessed using Criterion A: Knowing and understanding.

Citation:

¹Termaat, Annie. “Chapter 5.” Chemistry for the IB MYP 4 & 5, Hodder Education, London, 2016, pp. 102.

²MailOnline, Richard Gray for. “The People Who Can Eat ARSENIC: Remote Village in Andes Found to Have Developed Tolerance to Toxic Chemical.” Daily Mail Online, Associated Newspapers, 4 Mar. 2015, www.dailymail.co.uk/sciencetech/article-2979234/The-people-eat-ARSENIC-Remote-village-Andes-developed-tolerance-toxic-chemical.html.