How does a chemist design a fair investigation and judge whether data are trustworthy?
Scientific investigation and experimental design: plan and conduct safe investigations, identify independent, dependent and controlled variables, and distinguish hypothesis, theory and law.
A focused Virginia SOL Chemistry answer on standard CH.1: planning a safe, fair investigation, identifying independent, dependent and controlled variables, the difference between accuracy and precision, and how hypothesis, theory and law differ in science.
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What this topic is asking
Standard CH.1 is the scientific-investigation backbone of the course. Virginia expects you to plan and carry out a safe, fair investigation, to tell the difference between the variable you change, the variable you measure and the variables you hold constant, to judge whether data are accurate and precise, and to use the words hypothesis, theory and law correctly. On the SOL these skills are tested both directly and embedded inside content items, so almost every question on the test leans on CH.1 in some way.
Variables in a fair test
A fair test isolates cause and effect by changing only one thing at a time. If two factors change together, you cannot tell which one caused the result, a problem called a confounded experiment. A control group receives no treatment (or a standard treatment) and gives a baseline to compare the experimental groups against. For example, to test whether a catalyst speeds up a reaction, the control flask has no catalyst while everything else (temperature, concentration, volume) is identical.
Accuracy and precision
These two words are not interchangeable, and the SOL tests the difference directly.
A useful image is a target: precise shots land in a tight group; accurate shots center on the bullseye. Systematic errors (a zeroing error, a mis-calibrated instrument) push every reading the same way and hurt accuracy. Random errors (small, unpredictable variations) scatter readings and hurt precision; taking more trials and averaging reduces their effect.
Hypothesis, theory and law
A common misconception is that a theory becomes a law once it is "proven". They are different kinds of statement: a law describes what happens, a theory explains why. Neither is a guess; both rest on evidence.
Laboratory safety and tools
CH.1 also covers safe practice: wearing goggles and appropriate protection, never tasting chemicals, handling glassware and heat carefully, knowing where safety equipment is, and disposing of materials correctly. Choosing the right tool matters too: a graduated cylinder for volume (read at the bottom of the meniscus, at eye level), a balance for mass, a thermometer for temperature. Recording the correct units is part of a valid measurement.
Try this
Q1. A student tests how light intensity affects the rate of a reaction. Name the dependent variable. [1 point]
- Cue. The reaction rate (or the amount of product formed in a fixed time), because it is measured and responds to the change in light.
Q2. A balance reads g too high for every sample. Does this harm accuracy, precision, or both? [1 point]
- Cue. Accuracy only; every reading is shifted the same amount (a systematic error), so the readings stay close to each other (still precise) but far from the true value.
Exam-style practice questions
Practice questions written in the style of VDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SOL (multiple choice)1 marksA student measures how the temperature of water affects how fast a sugar cube dissolves. Which is the independent variable? (A) the time to dissolve (B) the temperature of the water (C) the mass of the sugar cube (D) the volume of water usedShow worked answer →
The answer is (B) the temperature of the water.
The independent variable is the one the student deliberately changes to test its effect. Here the student sets different water temperatures, so temperature is independent. The time to dissolve (A) is the dependent variable, because it is measured and responds to the change. The mass of sugar (C) and the volume of water (D) are kept the same in every trial, so they are controlled variables.
The trap is choosing the time to dissolve; that is what you measure, not what you set.
SOL (tech-enhanced, fill in blank)2 marksFour students each measure the density of the same metal sample whose true density is g/mL. Student readings are: , , , g/mL. (a) Are the readings accurate, precise, both, or neither? (b) Explain your choice in one sentence.Show worked answer →
A 2-point item on accuracy versus precision.
(a) Both accurate and precise (1 point).
(b) Explanation (1 point): the readings are all very close to one another (precise) and all very close to the true value of g/mL (accurate).
Accuracy is closeness to the accepted value; precision is closeness of repeated measurements to each other. Markers reward naming both and linking precision to the tight spread and accuracy to the true value. A common error is treating the two words as synonyms.
Related dot points
- Measurement, significant figures and dimensional analysis: use SI units, significant figures and scientific notation, convert units by dimensional analysis, and calculate density and percent error.
A focused Virginia SOL Chemistry answer on measurement under CH.1: SI units, the rules for significant figures, scientific notation, converting units by dimensional analysis (factor-label), and calculating density and percent error.
- Structure of the atom: describe protons, neutrons and electrons, atomic number and mass number, and the historical development of the atomic model from Dalton to the modern view.
A focused Virginia SOL Chemistry answer on standard CH.2: the subatomic particles, atomic number and mass number, how they define an element and its ions, and the development of the atomic model from Dalton, Thomson and Rutherford to Bohr and the modern model.
- The periodic table and periodic trends: describe the organization of the periodic table and the trends in atomic radius, ionization energy, electronegativity and reactivity across periods and down groups.
A focused Virginia SOL Chemistry answer on the periodic table under CH.2: how it is organized into groups, periods, metals, nonmetals and metalloids, and the trends in atomic radius, ionization energy, electronegativity and reactivity and why each runs the way it does.
- States of matter and kinetic molecular theory: describe solids, liquids and gases in terms of particle arrangement and motion, and state the assumptions of kinetic molecular theory.
A focused Virginia SOL Chemistry answer on the states of matter under CH.4: how particles are arranged and move in solids, liquids and gases, the link between temperature and average kinetic energy, and the assumptions of kinetic molecular theory.
- Reaction rates and collision theory: explain reaction rate using collision theory, including effective collisions, orientation and the activation energy.
A focused Virginia SOL Chemistry answer on collision theory under CH.6: what reaction rate measures, why particles must collide with enough energy and the correct orientation, the role of activation energy, and the meaning of an effective collision.
Sources & how we know this
- 2018 Science Standards of Learning - Chemistry — Virginia Department of Education (2018)
- Chemistry Curriculum Framework — Virginia Department of Education (2018)