Scientific Inquiry and Practical Skills
Core ideas
Scientific inquiry begins with a testable question and a hypothesis linked to chemical theory. Identify independent, dependent and controlled variables; include a control group where appropriate; use random assignment or representative sampling; and repeat measurements to estimate reliability. Practical competence includes safe handling, risk assessment, correct use of glassware, calibration, preparation of standard solutions and titrations. Distinguish accuracy (closeness to true value) from precision (closeness of repeats), and random from systematic error. Validity depends on whether the method measures the intended quantity; reliability depends on consistency. Report measurements with units, appropriate significant figures and an uncertainty, and display data with labelled axes and suitable scales.
Traps
Questions often blur endpoint and equivalence point, treat repeated readings as replicates when the same aliquot is reused, or claim a result is accurate because it is precise. Do not ignore parallax, meniscus reading, or the volume delivered by a burette (final minus initial). A systematic offset cannot be removed by averaging. Changing two variables at once destroys a cause-and-effect claim. Remember that a more sensitive balance does not necessarily improve validity.
Worked example
A burette reads 0.50 mL initially and 24.80 mL at the endpoint, so the titre is 24.30 mL. If the accepted value is 24.00 mL, percentage error = (24.30 − 24.00)/24.00 × 100 = 1.25%. Rule of thumb: record raw readings, calculate the difference, then compare with the accepted value only after checking units and significant figures; quote uncertainty as ± half the smallest scale division or the manufacturer’s tolerance, whichever is larger.