, CHEM 121 | Module 4 | Original General Chemistry Practice
CHEM 121 Module Exam 4 Portage General
Chemistry w/Lab 100% Correct
1. What does one mole represent?
A) 6.022 x 10^23 representative particles
B) The mass of one proton
C) 22.4 particles
D) 1.00 x 10^3 particles
Correct Answer: 6.022 x 10^23 representative particles
Rationale: A mole is an amount of substance containing Avogadro's number, 6.022 x 10^23, of specified entities such
as atoms, molecules, ions, or formula units.
2. What is formula mass?
A) The mass of one electron
B) The charge on an ion
C) The number of moles in one liter
D) The sum of the atomic masses of all atoms represented in a chemical formula
Correct Answer: The sum of the atomic masses of all atoms represented in a chemical formula
Rationale: Formula or molar mass is obtained by adding the atomic masses for every atom in the formula.
Numerically it is expressed in g/mol for a mole of the substance.
3. What does percent composition describe?
A) The mass percent contributed by each element in a compound
B) The volume percent of gases only
C) The reaction rate
D) The charge of each atom
Correct Answer: The mass percent contributed by each element in a compound
Rationale: Percent composition is calculated as the mass contribution of an element divided by the molar mass of the
compound, multiplied by 100.
4. What does an empirical formula show?
A) Only the ionic charge
B) The exact number of atoms in every molecule
C) The 3-D molecular shape
D) The simplest whole-number ratio of atoms in a compound
Correct Answer: The simplest whole-number ratio of atoms in a compound
Rationale: An empirical formula reduces subscripts to the lowest whole-number ratio. A molecular formula can be an
integer multiple of the empirical formula.
5. What does a molecular formula show?
A) The oxidation state of each atom
Page 2
, CHEM 121 | Module 4 | Original General Chemistry Practice
B) Only the simplest ratio
C) The actual number of each type of atom in a molecule
D) Only the molar mass
Correct Answer: The actual number of each type of atom in a molecule
Rationale: A molecular formula gives the actual atom counts. Its subscripts are an integer multiple of those in the
empirical formula.
6. What is molarity?
A) Liters of solute per mole of solvent
B) Moles of solvent per gram of solution
C) Moles of solute per liter of solution
D) Grams of solute per liter of solvent
Correct Answer: Moles of solute per liter of solution
Rationale: Molarity M = moles of solute / liters of solution. The denominator is total solution volume, not solvent
volume.
7. Which equation is used for a simple dilution when the solute amount is conserved?
A) M1V1 = M2V2
B) q = mcDeltaT
C) E = mc^2
D) PV = nRT
Correct Answer: M1V1 = M2V2
Rationale: For dilution of the same solute, moles before and after dilution are conserved, so M1V1 = M2V2.
8. Why must a chemical equation be balanced?
A) To make all coefficients equal to 1
B) To obey conservation of atoms and mass
C) To force every reaction to completion
D) To change the identities of reactants
Correct Answer: To obey conservation of atoms and mass
Rationale: Balancing changes coefficients so each element has the same atom count on both sides, reflecting
conservation of matter.
9. Which change is allowed when balancing a chemical equation?
A) Changing subscripts inside formulas
B) Changing coefficients
C) Changing element symbols
D) Changing ionic charges
Correct Answer: Changing coefficients
Rationale: Coefficients may be adjusted. Subscripts are part of a substance's identity and must not be altered to
balance an equation.
10. What characterizes a precipitation reaction?
Page 3
CHEM 121 Module Exam 4 Portage General
Chemistry w/Lab 100% Correct
1. What does one mole represent?
A) 6.022 x 10^23 representative particles
B) The mass of one proton
C) 22.4 particles
D) 1.00 x 10^3 particles
Correct Answer: 6.022 x 10^23 representative particles
Rationale: A mole is an amount of substance containing Avogadro's number, 6.022 x 10^23, of specified entities such
as atoms, molecules, ions, or formula units.
2. What is formula mass?
A) The mass of one electron
B) The charge on an ion
C) The number of moles in one liter
D) The sum of the atomic masses of all atoms represented in a chemical formula
Correct Answer: The sum of the atomic masses of all atoms represented in a chemical formula
Rationale: Formula or molar mass is obtained by adding the atomic masses for every atom in the formula.
Numerically it is expressed in g/mol for a mole of the substance.
3. What does percent composition describe?
A) The mass percent contributed by each element in a compound
B) The volume percent of gases only
C) The reaction rate
D) The charge of each atom
Correct Answer: The mass percent contributed by each element in a compound
Rationale: Percent composition is calculated as the mass contribution of an element divided by the molar mass of the
compound, multiplied by 100.
4. What does an empirical formula show?
A) Only the ionic charge
B) The exact number of atoms in every molecule
C) The 3-D molecular shape
D) The simplest whole-number ratio of atoms in a compound
Correct Answer: The simplest whole-number ratio of atoms in a compound
Rationale: An empirical formula reduces subscripts to the lowest whole-number ratio. A molecular formula can be an
integer multiple of the empirical formula.
5. What does a molecular formula show?
A) The oxidation state of each atom
Page 2
, CHEM 121 | Module 4 | Original General Chemistry Practice
B) Only the simplest ratio
C) The actual number of each type of atom in a molecule
D) Only the molar mass
Correct Answer: The actual number of each type of atom in a molecule
Rationale: A molecular formula gives the actual atom counts. Its subscripts are an integer multiple of those in the
empirical formula.
6. What is molarity?
A) Liters of solute per mole of solvent
B) Moles of solvent per gram of solution
C) Moles of solute per liter of solution
D) Grams of solute per liter of solvent
Correct Answer: Moles of solute per liter of solution
Rationale: Molarity M = moles of solute / liters of solution. The denominator is total solution volume, not solvent
volume.
7. Which equation is used for a simple dilution when the solute amount is conserved?
A) M1V1 = M2V2
B) q = mcDeltaT
C) E = mc^2
D) PV = nRT
Correct Answer: M1V1 = M2V2
Rationale: For dilution of the same solute, moles before and after dilution are conserved, so M1V1 = M2V2.
8. Why must a chemical equation be balanced?
A) To make all coefficients equal to 1
B) To obey conservation of atoms and mass
C) To force every reaction to completion
D) To change the identities of reactants
Correct Answer: To obey conservation of atoms and mass
Rationale: Balancing changes coefficients so each element has the same atom count on both sides, reflecting
conservation of matter.
9. Which change is allowed when balancing a chemical equation?
A) Changing subscripts inside formulas
B) Changing coefficients
C) Changing element symbols
D) Changing ionic charges
Correct Answer: Changing coefficients
Rationale: Coefficients may be adjusted. Subscripts are part of a substance's identity and must not be altered to
balance an equation.
10. What characterizes a precipitation reaction?
Page 3
