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. Which type of change occurs when no change is made to the chemical composition of a substance?

• A. Chemical
• B. Physical
• C. Nuclear
• D. Mechanical

Correct answer: B

Rationale: A physical change refers to alterations in the state of matter without modifying the chemical composition of the substance. Examples of physical changes include changes in state (solid, liquid, gas), shape, size, or phase. In a physical change, the substance may look different or behave differently, but its chemical structure remains the same. On the other hand, chemical changes involve the breaking and forming of chemical bonds, resulting in the creation of entirely new substances with different chemical properties. Nuclear changes involve alterations in the nucleus of an atom, such as radioactive decay. Mechanical changes refer to changes in the position or motion of an object caused by applied forces, like pushing, pulling, or twisting.

3. Which substance causes a drop to rapidly turn litmus dye from blue to red?

• A. Milk
• B. Sea water
• C. Ammonia
• D. Lemon juice

Correct answer: D

Rationale: Lemon juice is the correct answer as it is acidic in nature. Acids like lemon juice release hydrogen ions when dissolved in water, which causes litmus dye to change color from blue to red. Milk (Choice A) is neutral, sea water (Choice B) is slightly alkaline, and ammonia (Choice C) is a base. Therefore, these substances do not cause litmus dye to change from blue to red.

4. What number represents the number of protons an element has?

• A. Atomic mass
• B. Mass number
• C. Atomic number
• D. Neutron number

Correct answer: C

Rationale: The correct answer is C, atomic number. The atomic number corresponds to the number of protons in an element. This number is unique to each element and determines its placement on the periodic table. It is equal to the number of protons found in the nucleus of an atom of that element. Choice A, atomic mass, represents the average mass of an element's isotopes. Choice B, mass number, is the sum of protons and neutrons in an atom. Choice D, neutron number, specifically refers to the count of neutrons in an atom and not protons.

5. Which best defines the molarity of an aqueous sugar solution?

• A. Grams of sugar per milliliter of solution
• B. Moles of sugar per milliliter of solution
• C. Grams of sugar per liter of solution
• D. Moles of sugar per liter of solution

Correct answer: D

Rationale: The molarity of a solution is defined as the number of moles of solute per liter of solvent. In the case of an aqueous sugar solution, the molarity would be expressed as moles of sugar per liter of solution. This is because molarity is a measurement of the concentration of a solute in a solution based on the number of moles present in a given volume of the solution. Therefore, the correct answer is D. Choices A, B, and C are incorrect because the molarity is specifically defined in terms of moles of solute per liter of solution, not in grams per milliliter or grams per liter. Molarity is a unit of concentration that relates the amount of solute to the volume of the solution, not the mass of the solute.

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