Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions.
Understanding
- I can explain the difference between a substance made of separate molecules, such as H₂O, and one described by a formula unit, such as NaCl. (Guide: “What a pure substance is made of”, Figure 1; Practice Q7)
- I can state the law of definite proportions in my own words and explain why it follows from a fixed formula. (Guide: “The law of definite proportions”)
- I can define an empirical formula and reduce a molecular formula to one. (Guide: “The empirical formula”; Practice Q1)
- I can explain why two different compounds can have the same percentage composition. (Guide: “The empirical formula”; Practice Q7)
Calculation
- I can calculate the percentage by mass of each element from a formula, counting every atom. (Guide: “Percentage by mass from a formula”; Practice Q3)
- I can use a fixed composition to predict the mass of an element in a sample of any size. (Practice Q2)
- I can find an empirical formula from percentage composition by assuming a 100 g sample. (Guide: Worked example 1; Practice Q4)
- I can find an empirical formula from measured masses, finding the second element’s mass by subtraction. (Guide: Worked example 2; Practice Q5)
- I can turn a ratio such as 1 : 1.50 or 1 : 1.33 into whole numbers by multiplying, not rounding. (Guide: “Turning a ratio into whole numbers”; Practice Q4)
- I can check an empirical formula by working its percentage composition back out. (Guide: Worked examples 1 and 2)
Reasoning
- I can use the law of definite proportions to decide whether a sample could be a stated pure compound. (Practice Q6)
- I can write a testable scientific question based on composition data. (Guide: “Asking a testable question”; Practice Q6)
All ticked? Move on to Topic 1.4, Composition of Mixtures, or return to the course roadmap.