What this standard actually asks for

How this standard is assessed

• AS91910 is internally assessed over several weeks: you plan, run preliminary trials, modify, run the real titrations, calculate, and write it up.
• Every mark comes from a specific phrase in the achievement criteria. Knowing them before you start is worth more than any amount of extra data.

The criteria, in plain words

Grade	What you must do
Achieved	Develop a workable plan to decide whether the sample or the procedure needs modifying; collect, record and process enough data for a conclusion; determine the concentration; describe how significant variables were controlled
Merit	Use preliminary trial results to develop a valid modification plan; collect quality data enabling a valid conclusion; accurately determine the concentration of the standard solution AND the substance; explain how control of variables improved quality
Excellence	Determine the concentration in the product with correct significant figures and units; justify how the modification improved validity and accuracy; evaluate the outcome in relation to the consumer product

• Read the Merit row again. Two concentrations are named — the standard solution and the substance. Most lost Merits are lost right there.

The four titration types you may use

The standard limits you to these four:

Type	What reacts	Typical context
Acid–base	H+ + OH−	vinegar, household ammonia, antacid tablets
Oxidation–reduction	electron transfer	vitamin C, bleach, iron tablets
Precipitation	ions forming an insoluble solid	chloride in soy sauce or saline
Complexometric	a ligand binding a metal ion	calcium or magnesium in hard water or milk

• Your teacher will normally set the context. What you choose within it — the modification, the concentrations, the indicator — is yours.

The two relationships you must use

Explanatory Note 6 names them explicitly. Both must appear in your calculation:

$$n = \frac{m}{M} \qquad c = \frac{n}{V}$$

• $n$ — amount of substance, in mol

• $m$ — mass, in g

• $M$ — molar mass, in g mol⁻¹

• $c$ — concentration, in mol L⁻¹

• $V$ — volume, in L

• The first is used to make up the standard solution from a weighed solid; the second turns titre volumes into moles. An investigation using only one of them has missed a requirement.

The non-1:1 requirement

• Your investigation must include at least one calculation with a mole ratio that is not 1 : 1.
• This is why contexts like sulfuric acid (2 : 1 with hydroxide), calcium carbonate antacids (1 : 2 with acid), or permanganate titrations (1 : 5 with iron(II)) are chosen so often.
• If you titrate NaOH against HCl, the ratio is 1 : 1 and the requirement is not met. Check your equation before you start.

What a finished report contains

• Purpose — which substance, in which product, and why it matters.
• Preliminary trials — what you tried, what happened, what you learned.
• Modification — what you changed, and why.
• Method — in enough detail to be repeated.
• Results — a table of titres, with the concordant ones identified.
• Processing — every calculation step shown.
• Conclusion — the concentration, with units and sensible significant figures.
• Evaluation — validity, accuracy, and what the answer means for the product.