You are handed a small vial of a white solid with a code on it and no other information. By the end of this task you will have said what kind of substance it is and defended the claim with evidence you produced — and then you will have looked at a substance people actually live with and asked whether it is worth having around.
Two halves. The first is a bench argument. The second is a judgement, and judgements are harder.
The situation
Identification is what chemists were doing for two centuries before there was an instrument that could look inside a molecule. It was done entirely by behaviour: what melts, what dissolves in what, what conducts, what reacts with what. Those tests are still the fastest first pass, and they are all you have here.
Your vial contains one substance from a list I will post. The list is long enough that guessing is hopeless and short enough that good evidence narrows it.
The second half starts from a different place. Every substance on that list is used by somebody for something, and most of them are in a kitchen, a bathroom, a garage, or a prep room near you. Being able to say what a substance is is a different skill from being able to say whether it is a good idea, and this course owes you both.
What you have to decide, and defend
On paper, before you touch anything. You will be told the formula of your unknown but not its name. Calculate the electronegativity difference across its bonds and predict the bond type. Then predict what that bond type implies for melting behaviour, solubility, and conductivity. This is your hypothesis and it is dated before any evidence exists.
At the bench. You design the test sequence. You have the same equipment as in Testing for Bond Type, and the same rules. The questions I will ask about your design:
- Which test did you run first, and why that one? A test that eliminates half the list is worth three that eliminate one each.
- What is your operational definition of each result? “Dissolves” and “conducts” need to mean something specific enough that another group could apply your definition and get your answer.
- Where did you run a control, and what would it have told you if it had come out differently?
- What result would have forced you to abandon your prediction? If no possible result would have, you did not have a prediction.
For the research half. Choose a substance people commonly use — from food, cleaning, personal care, medicine, or a workplace — and evaluate its risks and benefits honestly. Some directions that work well:
- A food additive: a preservative, a raising agent, a colour, a sweetener.
- A household cleaning product component: an oxidising bleach, an alkaline degreaser, an acidic descaler.
- A cosmetic or personal care ingredient.
- An over-the-counter medicine and its active ingredient.
- A substance handled in a workplace, where an occupational exposure limit exists.
You may propose something else. Bring it to me early — some choices come back for a redesign, and that is the system working.
The bench half is checked before you run it
Submit your written test sequence, the equipment list, the hazards you have identified, and what you would do about each, before you are given any reagent.
- Eye protection from the first move to the last of the cleanup. Hair tied back, sleeves secured.
- You will recognise some of these substances, and it changes nothing. Nothing in the lab is food — including something that was food this morning, and including a substance you are certain you have identified. Nothing is tasted, at any stage, for any reason.
- Waft, never sniff. Cup a hand and draw air toward you.
- Hot solid, hot spatula, and hot ceramic look exactly like cold ones. Tongs, and a heat mat, and assume hot.
- The conductivity tester is battery-powered. Nothing plugged into the wall goes near a liquid.
- School reagents only, at the concentrations supplied, and combine only what your approved sequence lists. Substances that are safe apart can produce a toxic gas together and you cannot tell by looking, which is why this rule is absolute.
- Never return unused solid or solution to a stock container.
- Know where the eyewash, shower, extinguisher, blanket, and spill kit are before you start, and report every incident immediately, however small.
Full agreement: Safety in the Lab and Lab Safety and WHMIS.
What to hand in
1. An identification report, two pages at most.
- Your electronegativity prediction, with the calculation, dated before the bench work.
- Your test sequence, with the reason for the order.
- A results table: every test, every result, including negatives and controls.
- Your identification, and the evidence chain that supports it. Not a list of results followed by an answer — an argument in which each piece of evidence rules something out.
- What your evidence does not settle. Which substances on the list you cannot distinguish with the tests you ran, and what test would.
2. A risk and benefit brief, addressed to a named audience.
Who it is for changes what belongs in it, so name them on the first line: a household deciding whether to keep the product under the sink, a school deciding whether to stock it in the prep room, a person choosing between two products in a shop, a small business writing a safety procedure.
The brief needs four things:
- What the substance is and what it is used for, in language your audience can use.
- The benefits, specifically. “It works” is not a benefit; what it does that an alternative does not is a benefit.
- The risks, at the concentrations and in the situations your audience will actually meet. A hazard at industrial concentration is not automatically a hazard in a diluted household product, and saying so is part of being accurate.
- A recommendation with a cost attached. Everything you recommend costs somebody money, time, or convenience. Naming that cost is what makes advice usable rather than pious.
Sources. At least three, of the right kind, properly cited using the format in Writing About Chemistry. The kinds that count:
- A safety data sheet from the manufacturer or supplier.
- A government health or safety agency — Health Canada, or the Canadian Centre for Occupational Health and Safety, or the equivalent in another country if your substance is regulated elsewhere.
- A professional or standards body.
- A peer-reviewed article, if you can get one you can actually read.
Every number in the brief must be traceable to a source somebody else can open. If you cannot find a reliable figure, say so — that sentence costs you nothing and an untraceable number costs you a great deal. See What Counts as Evidence and Reading a Data Table.
How it will be judged
| What I am looking for | Level 3 sounds like | Level 4 sounds like |
|---|---|---|
| The prediction | Predicts a bond type using electronegativity | Predicts bond type and the properties that follow, and names what result would refute it |
| Test design | A sensible sequence that gets an answer | The order is justified by how much each test eliminates, with controls placed deliberately |
| Evidence | Results recorded completely, with units | Each result is used to rule something out, and the argument is followed rather than asserted |
| Honesty about limits | Names something the evidence cannot settle | Names exactly which candidates remain indistinguishable, and the test that would separate them |
| The research | Real risks and benefits from real sources | Risks are placed at the concentration and situation the audience meets, not in general |
| Sources | Three appropriate sources, cited | Sources are the right kind for the claim they support, and their limits are noted |
| The recommendation | Follows from the findings | Fits the audience, names the cost, and does not overclaim |
| Writing | Clear and correctly organised | Pitched at the named audience, and a non-chemist could act on it |
What sinks an otherwise good task
- A prediction written after the bench work. It shows, and it removes the only record of how your thinking moved — which is the thing Mistakes Are Data argues is worth most.
- A results table with no negatives. “It did not conduct” is a result and belongs in the table. Blank cells are not results.
- An identification with no chain. Six observations and then a name is not an argument. Each observation has to eliminate something.
- Risk stated without dose or concentration. Nearly every substance is hazardous at some concentration and harmless at another, so a risk claim with no quantity in it says almost nothing.
- A source that is really an aggregator. A page summarising other pages is not a source; find what it was summarising. If you cannot find it, that is information about the claim.
- Inventing a figure, a study, or an organisation to fill a gap. This is the one thing that cannot be repaired by a rewrite. Write “no reliable figure found” instead, every time.
Curriculum connection
B1.2
evaluate the risks and benefits to human health of some commonly used chemical substances (e.g., chemical additives in foods; pharmaceuticals; cosmetics and perfumes; household cleaning products) [AI, C]
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B2.5
predict the nature of a bond (e.g., non-polar covalent, polar covalent, ionic), using electronegativity values of atoms [AI]
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A1.3
identify and locate a variety of print and electronic sources that enable them to address research topics fully and appropriately
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A1.7
select, organize, and record relevant information on research topics from a variety of appropriate sources, including electronic, print, and/or human sources, using suitable formats and an accepted form of academic documentation
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