AP Chemistry Final Exam Review
ESSAY. Write your answer in the space provided or on a separate sheet of paper. 1) Explain the difference between a qualitative and a quantitative measurement. Provide examples to illustrate this difference. Answer: A qualitative measurement is a measurement that gives descriptive, nonnumeric results; a quantitative measurement is a measurement that gives definite, usually numeric results. "The rock is heavy" would be a qualitative measurement. "The rock weighs 110 grams" would be a quantitative measurement. Topic: Scientific Measurement
2) Explain the difference between precision and accuracy. Suppose you made three different mass measurements of a sugar sample you knew to have a mass of 1 g. How would you know whether or not the measurements were accurate? How would you know whether or not they were precise? Could the three measurements be precise, but not accurate? Explain. Answer: Precision is the reproducibility, under the same conditions, of a measurement; accuracy is the closeness of a measurement to the true value of what is being measured. The three measurements would be precise if they were very close to each other in value; they would be accurate if they were close to the actual 1-g value for the mass of the sample. If the measurements are very close to each other, they are precise, regardless of how close they are to the real value. Therefore, the measurements could be precise, but not accurate. Topic: Scientific Measurement
3) Describe the rules that are used to determine the number of significant figures in the results of addition, subtraction, multiplication, and division. Answer: The answer of an addition or subtraction can have no more digits to the right of the decimal point than are contained in the measurement with the least number of digits to the right of the decimal point. The answer of a multiplication or division can have no more significant figures than the measurement having the least number of significant figures. For these two operations, the position of the decimal point has nothing to do with the number of significant figures. Topic: Scientific Measurement
4) Why is the metric system the preferred system of measurement for science? Answer: The primary reason for this is that the metric system is based on units that are multiples of ten, thus simplifying conversions between units. In addition, all necessary units can be derived from the seven basic units of the metric system. Topic: Scientific Measurement
5) Why is the density of a metal greater than the density of water? Answer: The student should infer from the text that this is true either because the metal's atoms are heavier than the water molecules or because the metal atoms are more closely packed than the water molecules, or both. Topic: Scientific Measurement
6) Why do the densities of most substances decrease with temperature? Answer: The student should infer that this is because a substance's atoms or molecules tend to move farther apart with an increase in temperature. Consequently, the volume of the substance increases. There is no change in the mass of the substance, however, and therefore the density (mass/volume) decreases. Topic: Scientific Measurement
7) Explain the difference between specific gravity and density.
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Answer: Density has units and is absolute, depending only on temperature. Specific gravity has no units and is a comparison of the density of a substance to the density of a reference substance, usually at the same temperature. The density of aluminum at 25°C is 2.76 g/cm3. The specific gravity of aluminum at 25°C, using the reference standard of water at 4°C, is simply 2.70. Topic: Scientific Measurement
8) Explain the difference between the Celsius and Kelvin temperature scales. Answer: Both scales use the freezing point and boiling point of water as reference temperature values. The Celsius scale designates the freezing point of water as O°C...
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