Question

clearly mark the letter of the best answer for questions 1 – 15 on the scan sheet. (2 points each) 1. an ion has 8 protons, 9 neutrons, and 10 electrons. the symbol for the ion is ____. a) ⁹o²⁻ b) ⁹o²⁺ c) ¹⁷o²⁻ d) ¹⁷o²⁺ 2. what answer should be reported, with the correct number of significant figures, for the following calculation? (8.02 − 7.50) / 3.002 a) 0.2 b) 0.17 c) 0.173 d) 0.1732 3. a student performs an experiment to determine the density of a sugar solution. she obtains the following results: 1.72 g/ml, 1.73 g/ml, 1.72 g/ml, 1.71 g/ml. if the actual value for the density of the sugar solution is 1.72 g/ml, which statement below best describes the student’s results? a) the results are precise, but are not accurate b) the results are not precise, but are accurate c) the results are both precise and accurate d) the results are neither precise nor accurate 4. the image to the right is a close up of a graduated cylinder. what is the correct volume reading with the correct number of significant figures? a) 5 ml b) 5.3 ml c) 5.32 ml d) 5.320 ml image of graduated cylinder 5. which of the following gives a correct, basic description of the structure of an atom? a) neutrons and electrons in the nucleus with protons orbiting the nucleus b) protons and electrons in the nucleus with protons orbiting the nucleus c) protons and neutrons in nucleus with electrons orbiting the nucleus d) protons in the nucleus with neutrons and electrons orbiting the nucleus 6. isotopes of an element contain the same number of __ but differ in the number of ____ in the nucleus: a) protons, electrons b) neutrons, electrons c) protons, neutrons d) neutrons, protons 7. which of the following statements are true? 1. the fe²⁺ and fe³⁺ have the same number of protons 2. the k⁺ ion forms when a potassium atom gains an electron 3. the cl⁻ and br⁻ ions have the same number of electrons a) 1 only b) 2 only c) 1 and 2 d) 1 and 3

Explanation:

Question 1

Step1: Determine the element and mass number

The number of protons is 8, so the element is oxygen (O). The mass number is protons + neutrons = \(8 + 9 = 17\).

Step2: Determine the charge

The number of electrons is 10, and protons are 8. Charge = protons - electrons = \(8 - 10 = -2\), so the ion is \(O^{2-}\) with mass number 17.

Step1: Perform the subtraction

First, calculate \(8.02 - 7.50 = 0.52\) (the result has two decimal places, so two significant figures in the decimal part, but the subtraction result has two decimal places, so the precision is to the hundredth, and the number of significant figures from subtraction: 8.02 (three sig figs) - 7.50 (three sig figs) = 0.52 (two decimal places, two sig figs in the decimal? Wait, 8.02 - 7.50 = 0.52, which has two significant figures in the non - zero part? Wait, 0.52 has two significant figures.

Step2: Perform the division

Then divide by 3.002: \(\frac{0.52}{3.002}\approx0.173\). But when dividing, the number of significant figures is determined by the least number of significant figures in the values. The subtraction result (0.52) has two significant figures? Wait, no: 8.02 has three significant figures, 7.50 has three significant figures. When subtracting, the number of decimal places is considered. 8.02 has two decimal places, 7.50 has two decimal places, so the result of subtraction (0.52) has two decimal places, and the number of significant figures in 0.52 is two? Wait, no, 0.52 has two significant figures (the 5 and 2). Then 3.002 has four significant figures. When dividing, the result should have two significant figures? Wait, no, maybe I made a mistake. Wait, 8.02 - 7.50 = 0.52 (the difference is 0.52, which has two significant figures? Wait, 8.02 is three sig figs, 7.50 is three sig figs. The rule for subtraction is that the result has the same number of decimal places as the least precise measurement. 8.02 has two decimal places, 7.50 has two decimal places, so 0.52 has two decimal places, and the number of significant figures in 0.52: the leading zero is not significant, so 5 and 2 are significant, so two significant figures. Then when dividing by 3.002 (four significant figures), the result should have two significant figures? But 0.52 / 3.002 ≈ 0.173. Wait, maybe the subtraction result is 0.52 (three significant figures? Wait, 8.02 - 7.50 = 0.52, 0.52 has two significant figures? No, 0.52: the 5 is the first non - zero digit, then 2, so two significant figures. But 8.02 is three, 7.50 is three. Wait, perhaps the correct way is: 8.02 - 7.50 = 0.52 (the precision is to the hundredth, so the number of significant figures in the result of subtraction is determined by the number of decimal places. Since both have two decimal places, the result has two decimal places, and the significant figures: 0.52 has two significant figures). Then dividing by 3.002 (four sig figs), the result should have two significant figures? But 0.52/3.002≈0.173. Wait, maybe I messed up. Let's recalculate: 8.02 - 7.50 = 0.52. 0.52 has two significant figures. 3.002 has four. When dividing, the number of significant figures in the result is equal to the number of significant figures in the least precise measurement (the one with the least number of significant figures). So 0.52 has two, so the result should have two? But 0.52/3.002≈0.173, which is approximately 0.17 (two significant figures) or 0.173 (three)? Wait, maybe the subtraction result is 0.52, which is actually 0.520 (if we consider the precision). Wait, 8.02 is three sig figs, 7.50 is three sig figs. The difference is 0.52, but if we write it as 0.520 (to show the precision), then it has three significant figures. Then 0.520/3.002≈0.173. Ah, that makes sense. Because 8.02 and 7.50 have three significant figures, so their difference (0.52) can be considered as 0.520 (with three significant figures, because the original numbers have three, and the decimal places…

Step1: Define precision and accuracy

Precision refers to how close the measured values are to each other. Accuracy refers to how close the measured values are to the true value.

Step2: Analyze the student's results

The student's results are 1.72 g/mL, 1.73 g/mL, 1.72 g/mL, 1.71 g/mL. These values are close to each other (precise). The true value is 1.72 g/mL, and the measured values are also close to the true value (accurate).

Answer:

c) \(^{17}\text{O}^{2-}\)

Question 2