Nursing Elites

1. How many moles of potassium bromide are in 25 mL of a 4 M KBr solution?

• A. 0.035 mol
• B. 0.1 mol
• C. 0.18 mol
• D. 1.6 mol

Correct answer: B

Rationale: To find the moles of potassium bromide in 25 mL of a 4 M KBr solution, we first need to convert the volume from milliliters to liters. 25 mL is equal to 0.025 L. Then, we use the formula moles = molarity x volume in liters. Substituting the values, moles = 4 M x 0.025 L = 0.1 mol. Therefore, there are 0.1 moles of KBr in 25 mL of a 4 M solution. Choice A, 0.035 mol, is incorrect as it does not properly calculate the moles. Choice C, 0.18 mol, and choice D, 1.6 mol, are also incorrect as they are not the result of the correct calculation based on the given molarity and volume.

2. What are the horizontal rows of the periodic table called?

• A. Periods
• B. Families
• C. Groups
• D. Columns

Correct answer: A

Rationale: The correct answer is A: Periods. Rows in the periodic table are called periods. They are arranged horizontally from left to right and represent the energy levels of the elements. Each period starts a new energy level or shell, indicating the number of electron shells an element has. Choices B, C, and D are incorrect. Families and groups refer to vertical columns in the periodic table that share similar chemical properties, while columns are vertical arrangements of elements known as groups or families.

3. What is the oxidation state of the sulfur atom in sulfuric acid H2SO4?

• A. 4
• B. 6
• C. 8
• D. 10

Correct answer: B

Rationale: In sulfuric acid (H2SO4), sulfur has an oxidation state of +6. The oxidation state is determined by considering the overall charge of the compound and the known oxidation states of other elements. In this case, hydrogen is typically +1, and oxygen is -2. To balance the charges and match the compound's overall charge of 0, sulfur must have an oxidation state of +6. Choice A (4) is incorrect because it doesn't balance the charges in the compound. Choices C (8) and D (10) are also incorrect as they are not valid oxidation states for sulfur in this compound.

4. How many electrons are shared in a single covalent bond?

• A. 1
• B. 2
• C. 3
• D. 4

Correct answer: B

Rationale: The correct answer is B: '2'. In a single covalent bond, two electrons are shared between two atoms. Each atom contributes one electron to form the bond, resulting in the sharing of a total of two electrons. Choice A is incorrect because a single covalent bond involves the sharing of two electrons, not one. Choices C and D are incorrect as they do not represent the correct number of electrons shared in a single covalent bond.

5. How many times more acidic is a substance with a pH of 3 compared to a substance with a pH of 5?

• A. 8
• B. 2
• C. 100
• D. 1,000

Correct answer: D

Rationale: The pH scale is logarithmic, indicating that each pH unit change reflects a 10-fold difference in acidity level. Going from pH 5 to pH 3 involves a difference of 2 units, which translates to a 100-fold increase in acidity level (10^2 = 100 for each unit). Therefore, a substance with a pH of 3 is 1,000 times more acidic than a substance with a pH of 5 (100 * 10 = 1,000). Choice A (8) is incorrect as it does not consider the logarithmic nature of the pH scale. Choice B (2) is incorrect because it represents the difference in pH units, not the increase in acidity level. Choice C (100) is incorrect as it miscalculates the increase in acidity level, which is 1,000 times and not 100 times.

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