Nokea
The numbers of protons, neutrons, and electrons in K+ are: A) 20 p, 19 n, 19 e
- A. 20 p, 19 n, 20 e
- B. 19 p, 20 n, 20 e
- C. 19 p, 20 n, 19 e
- D. 19 p, 20 n, 18 e
Correct Answer: C
Rationale: The correct answer is C: 19 p, 20 n, 19 e. K+ has an atomic number of 19, indicating 19 protons. Since it is a potassium ion with a +1 charge, it lost one electron, giving it 19 electrons instead of the usual 20. The number of neutrons is found by subtracting the atomic number from the mass number (39 for potassium) to get 20 neutrons. Option A is incorrect due to the incorrect number of electrons. Option B has the incorrect number of protons. Option D has the incorrect number of electrons.
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Avogadro's hypothesis states that:
- A. Each atom of oxygen is 16 times more massive than an atom of hydrogen.
- B. A given compound always contains exactly the same proportion of elements by mass.
- C. When two elements form a series of compounds, the ratios of masses that combine with 1 gram of the first element can always be reduced to small whole numbers.
- D. At the same temperature and pressure, equal volumes of different gases contain an equal number of particles.
Correct Answer: D
Rationale: Rationale for correct answer D: Avogadro's hypothesis states that equal volumes of different gases at the same temperature and pressure contain an equal number of particles. This is because gases behave similarly under these conditions due to the ideal gas law. Avogadro's hypothesis is crucial in understanding the behavior of gases and is fundamental in the study of chemistry.
Summary of incorrect choices:
A: This statement is about the relative mass of atoms of different elements, not Avogadro's hypothesis.
B: This statement relates to the law of definite proportions, not Avogadro's hypothesis.
C: This statement refers to the law of multiple proportions, not Avogadro's hypothesis.
What is the measure of resistance an object has to a change in its state of motion?
- A. mass
- B. weight
- C. volume
- D. length
Correct Answer: A
Rationale: The correct answer is A: mass. Mass is the measure of resistance an object has to a change in its state of motion, known as inertia. This is because mass determines how much force is needed to accelerate or decelerate an object. Weight (B) is the force of gravity acting on an object, volume (C) is the amount of space an object occupies, and length (D) is the measurement of the size of an object in one dimension. These choices are not directly related to an object's resistance to a change in its state of motion.
The amount of uncertainty in a measured quantity is determined by:
- A. both the skill of the observer and the limitations of the measuring instrument
- B. neither the skill of the observer nor the limitations of the measuring instrument
- C. the limitations of the measuring instrument only
- D. the skill of the observer only
Correct Answer: A
Rationale: The correct answer is A because the amount of uncertainty in a measured quantity is influenced by both the skill of the observer and the limitations of the measuring instrument. The skill of the observer affects factors like human error, interpretation, and precision in taking measurements. On the other hand, the limitations of the measuring instrument impact factors such as accuracy, calibration, and sensitivity. Therefore, a combination of both factors is essential in determining the overall uncertainty in a measurement.
Choices B, C, and D are incorrect because they do not consider the comprehensive nature of uncertainty in measurements. Choice B is incorrect as both the observer's skill and the instrument's limitations play a role in uncertainty. Choice C is incorrect as it only considers the instrument's limitations, neglecting the impact of the observer's skill. Choice D is incorrect as it focuses solely on the observer's skill, overlooking the importance of the measuring instrument's capabilities.
We generally report a measurement by recording all of the certain digits plus uncertain digit(s).
- A. no
- B. one
- C. two
- D. three
Correct Answer: B
Rationale: Step 1: In measurement, certain digits are the numbers that are known for sure.
Step 2: Uncertain digits are the last digit that is estimated or measured.
Step 3: We record all the certain digits and one uncertain digit to indicate the precision of the measurement.
Step 4: Choice A is incorrect because we do include uncertain digit(s) in the measurement.
Step 5: Choice C and D are incorrect as including two or three uncertain digits would provide excessive precision beyond what is known for certain.
The element rhenium (Re) exists as two stable isotopes and 18 unstable isotopes. Rhenium-185 has in its nucleus
- A. 75 protons, 75 neutrons
- B. 75 protons, 130 neutrons
- C. 130 protons, 75 neutrons
- D. 75 protons, 110 neutrons
Correct Answer: A
Rationale: The correct answer A is determined by knowing that the atomic number of rhenium is 75. Since the element is rhenium-185, the sum of protons and neutrons must equal 185. As the atomic number is 75, the number of protons is 75. Therefore, the number of neutrons is 185 - 75 = 110. Thus, rhenium-185 has 75 protons and 110 neutrons. Choices B, C, and D are incorrect as they do not adhere to the correct number of protons and neutrons in the nucleus of rhenium-185.