Midterm Exam Practice

Given the equation representing a reaction: 3Mg(s) + N₂(g) → Mg₃N₂(s) What is the mass of Mg₃N₂ that is produced when 14.58 grams of magnesium completely reacts with 5.60 grams of nitrogen?

• 8.98 g

• 10.46 g

• 20.18 g

• 49.34 g

Answer explanation

To find the mass of Mg₃N₂ produced, first determine the limiting reactant. 3 moles of Mg react with 1 mole of N₂. From 14.58 g Mg (0.605 mol) and 5.60 g N₂ (0.200 mol), N₂ is limiting. Thus, 10.46 g of Mg₃N₂ is produced.

Tags

NGSS.HS-PS1-7

At room temperature, a student determines the density of a sample of nickel to be 9.79 g/cm³. Based on Table S, what is the student's percent error for the density of nickel?

• 0.091%

• 0.10%

• 9.1%

• 10%

Answer explanation

To find the percent error, use the formula: |(experimental value - theoretical value)| / theoretical value x 100. The theoretical density of nickel is 8.90 g/cm³. The calculation gives a percent error of 0.10%, which is the correct choice.

Given the diagram representing a classification of matter, which types of matter are represented by X and Z in the diagram?

• X is mixture, and Z is substance.

• X is substance, and Z is mixture.

• X is element, and Z is compound.

• X is compound, and Z is element.

Answer explanation

In the classification of matter, mixtures are combinations of two or more substances, while substances can be elements or compounds. Therefore, X represents a mixture and Z represents a substance.

Which two particle diagrams represent two different phases of the same compound, only?

• A and B

• A and C

• B and C

• B and D

Answer explanation

Diagrams A and C represent different phases of the same compound, showing variations in particle arrangement or energy states. Diagrams B and D do not correspond to the same compound, making A and C the correct choice.

A sample of KCl(s) is dissolved in water to form KCl(aq). When the water in the KCl(aq) is completely evaporated, KCl(s) remains. Which statement describes a property of the KCl(s) after the water evaporated?

• The KCl(s) becomes a molecular compound.

• The molar mass of the KCl(s) decreases.

• The melting point of the KCl(s) is unchanged.

• The KCl(s) conducts an electric current.

Answer explanation

The melting point of KCl(s) remains unchanged after the water evaporates, as the physical state of the compound does not affect its intrinsic properties. The other options are incorrect regarding the nature of KCl.

Which statement describes ice and liquid water in a stoppered flask at 0°C at equilibrium?

• The rate of melting must equal the rate of freezing.

• The rate of freezing must be greater than the rate of melting.

• The mass of the ice must equal the mass of the liquid water.

• The mass of the ice must be greater than the mass of the liquid water.

Answer explanation

At equilibrium, the rate of melting equals the rate of freezing, meaning the amount of ice and liquid water remains constant. This is why the correct statement is that the rate of melting must equal the rate of freezing.

Tags

NGSS.HS-PS3-4

Atoms of which element in Group 15 have the greatest electronegativity?

• As

• Bi

• N

• P

Answer explanation

In Group 15, nitrogen (N) has the greatest electronegativity due to its small atomic size and high effective nuclear charge, allowing it to attract electrons more strongly than arsenic (As), phosphorus (P), or bismuth (Bi).

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

All matter can be classified as

• an element

• a compound

• a mixture or an element

• a mixture or a substance

Answer explanation

All matter is classified as either a mixture or a substance. A substance can be an element or a compound, while mixtures consist of two or more substances. Therefore, the correct choice is 'a mixture or a substance'.

Which sample of argon gas has the same number of atoms as a 100-milliliter sample of helium gas at 1.0 atm and 300.K?

• 50 mL at 1.0 atm and 300.K

• 50 mL at 0.5 atm and 300.K

• 100 mL at 0.5 atm and 300.K

• 100 mL at 1.0 atm and 300.K

Answer explanation

According to the ideal gas law, at the same temperature and pressure, equal volumes of gases contain the same number of molecules. Therefore, a 100 mL sample of argon at 1.0 atm and 300 K has the same number of atoms as the helium sample.

Which element is a nonmetal and solid at STP?

• lead

• nitrogen

• sodium

• sulfur

Answer explanation

Sulfur is a nonmetal that exists as a solid at standard temperature and pressure (STP). In contrast, lead and sodium are metals, while nitrogen is a gas at STP. Therefore, sulfur is the correct choice.