A technician measures the concentration of a known 10.0 mg/L standard solution three times and obtains 9.6, 9.7, and 9.6 mg/L. How should these measurements be characterized?
AHigh accuracy, high precision
BHigh accuracy, low precision
CLow accuracy, high precision
DLow accuracy, low precision
The three measurements cluster tightly together (9.6–9.7), indicating high precision (low random error). However, they are all consistently below the true value of 10.0 mg/L, indicating low accuracy due to a systematic error (bias) in the method. High precision does not imply high accuracy — a well-calibrated instrument can be systematically biased.
Question 2 True / False
Qualitative analysis determines how much of a substance is present in a sample.
TTrue
FFalse
Answer: False
Qualitative analysis answers 'what is present?' — it identifies the substances in a sample. Quantitative analysis answers 'how much is present?' — it measures the amount or concentration. Both are core branches of analytical chemistry, and many analyses require both steps: first identify, then quantify.
Question 3 Short Answer
List the five stages of a complete analytical process in order.
Think about your answer, then reveal below.
Model answer: Sampling, sample preparation, measurement, data analysis, and interpretation.
Analytical chemistry is a complete workflow, not just the measurement step. Sampling ensures the specimen represents the bulk material. Sample preparation converts it into a form the instrument can measure. Measurement generates raw data. Data analysis extracts quantitative results (e.g., concentration from a calibration curve). Interpretation places results in context and communicates conclusions. Errors can enter at any stage, making the entire chain important.