Nursing Elites

1. Which compound contains a polar covalent bond?

• A. O
• B. F
• C. Br
• D. H₂O

Correct answer: D

Rationale: The compound 'H₂O' (water) contains a polar covalent bond. In a water molecule, the oxygen atom is more electronegative than the hydrogen atoms. As a result, the electrons in the O-H bonds are unevenly shared, leading to a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. This unequal sharing of electrons creates a polar covalent bond in water. Choices A, B, and C are incorrect because they represent individual elements, not compounds, and do not involve the concept of polar covalent bonds.

2. In what type of covalent compounds are dispersion forces typically found?

• A. Polar
• B. Non-polar
• C. Ionic
• D. Hydrogen

Correct answer: B

Rationale: Dispersion forces, also known as London dispersion forces, are the weakest intermolecular forces that occur in non-polar covalent compounds. These forces result from temporary shifts in electron density within molecules, creating temporary dipoles. As a result, non-polar molecules, which lack a permanent dipole moment, can experience these dispersion forces. Polar compounds exhibit stronger intermolecular forces such as dipole-dipole interactions or hydrogen bonding, while ionic compounds involve electrostatic interactions between ions. Therefore, the correct answer is non-polar (choice B). Choices A, C, and D are incorrect because dispersion forces are typically found in non-polar covalent compounds, not polar, ionic, or hydrogen-bonded compounds.

3. What type of bond is present in sodium chloride?

• A. Covalent
• B. Ionic
• C. Metallic
• D. Hydrogen

Correct answer: B

Rationale: Ionic bonds are found in sodium chloride. In an ionic bond, one atom donates an electron to another atom, resulting in the formation of positively and negatively charged ions that are held together by electrostatic forces of attraction. Sodium chloride is a classic example of an ionic compound, where sodium (Na) donates an electron to chlorine (Cl), forming Na+ and Cl- ions that are attracted to each other, creating a crystal lattice structure. Covalent bonds involve the sharing of electron pairs between atoms, which is not the case in sodium chloride. Metallic bonds occur in metals where electrons are delocalized and shared across a lattice, unlike the specific transfer seen in ionic bonds. Hydrogen bonds are a type of intermolecular force, not the primary bond type present in sodium chloride.

4. 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.

5. How can the reaction rate of a chemical reaction be increased?

• A. Increase the temperature
• B. Increase the surface area
• C. Increase the concentration of reactants
• D. Add a catalyst

Correct answer: A

Rationale: To increase the reaction rate of a chemical reaction, one effective method is to increase the temperature. Raising the temperature provides more energy to the reacting particles, enabling them to collide more frequently and with higher energy, leading to an increase in the reaction rate. While increasing the surface area, concentration of reactants, and adding a catalyst are strategies that can also enhance the reaction rate, raising the temperature has the most direct and immediate impact. Increasing the surface area allows for more contact between reactants, increasing the concentration provides more reactant particles to collide, and adding a catalyst lowers the activation energy required for the reaction to occur. However, these methods may not have as immediate and significant an effect as increasing the temperature.

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