CHEM 103 MODULE 1 TO 6 EXAM
Comprehensive -Question Practice Exam with
Verified Answers & Detailed Rationales Portage
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Question 1
Convert 845.3 to exponential form and explain your reasoning.
A) 8.453 × 10¹
B) 8.453 × 10²
C) 0.8453 × 10³
D) 84.53 × 10¹
Correct Answer: B. 8.453 × 10²
Rationale: Since 845.3 is larger than 1, the exponent is positive. Move the decimal
point 2 places to the left to place it after the first digit (8). The exponent equals the
number of places moved (2). Therefore, 845.3 = 8.453 × 10².
Question 2
Convert 3.21 × 10⁻⁵ to ordinary form and explain your reasoning.
A) 0.000321
B) 0.0000321
C) 321000
D) 0.00321
Correct Answer: B. 0.0000321
Rationale: The exponent is negative (-5), indicating a number smaller than 1.
Move the decimal point 5 places to the left, adding zeros as needed. 3.21 × 10⁻⁵ =
0.0000321 (move decimal 5 places left: 3.21 → 0.0000321).
Question 3
Convert 24.6 grams to kilograms. Show all work.
,A) 2460 kg
B) 2.46 kg
C) 0.0246 kg
D) 0.246 kg
Correct Answer: C. 0.0246 kg
Rationale: Use the conversion factor 1 kg = 1000 g. Multiply 24.6 g × (1 kg /
1000 g) = 0.0246 kg. The grams cancel, leaving kilograms. Option A is incorrect
(multiplied instead of divided), Option B is incorrect (divided by 10 instead of
1000).
Question 4
How many significant figures are in 0.00450?
A) 2
B) 3
C) 4
D) 5
Correct Answer: B. 3
Rationale: Leading zeros are not significant. The zeros between the decimal and
the 4 are leading zeros and are not counted. The digits 4, 5, and the trailing zero are
significant. The trailing zero after the decimal is significant because it indicates
precision. Therefore, 0.00450 has 3 significant figures (4, 5, 0).
Question 5
What is the result of 12.34 + 2.1 + 0.045, reported with the correct number of
significant figures?
A) 14.485
B) 14.49
C) 14.5
D) 14
Correct Answer: C. 14.5
,Rationale: When adding or subtracting, the answer should have the same number
of decimal places as the measurement with the fewest decimal places. 12.34 has 2
decimal places, 2.1 has 1 decimal place, and 0.045 has 3 decimal places. The
answer should have 1 decimal place. 12.34 + 2.1 + 0.045 = 14.485 → rounded to 1
decimal place = 14.5.
Question 6
Convert 250.0 mL to liters.
A) 0.2500 L
B) 2.500 L
C) 25.00 L
D) 2500 L
Correct Answer: A. 0.2500 L
Rationale: Use the conversion factor 1 L = 1000 mL. 250.0 mL × (1 L / 1000 mL)
= 0.2500 L. The answer should maintain the same number of significant figures as
the original measurement (4 significant figures).
Question 7
Which of the following is an example of a physical change?
A) Burning wood
B) Rusting iron
C) Melting ice
D) Digesting food
Correct Answer: C. Melting ice
Rationale: A physical change does not alter the chemical composition of a
substance. Melting ice is a phase change from solid to liquid, but the chemical
formula (H₂O) remains the same. Burning wood, rusting iron, and digesting food
are all chemical changes.
Question 8
Which of the following is a chemical property?
, A) Density
B) Boiling point
C) Flammability
D) Melting point
Correct Answer: C. Flammability
Rationale: Flammability is a chemical property because it describes how a
substance reacts with oxygen to produce heat and light. Density, boiling point, and
melting point are physical properties that can be observed without changing the
chemical composition.
Question 9
What is the density of a substance with a mass of 25.0 g and a volume of 10.0 mL?
A) 2.50 g/mL
B) 0.40 g/mL
C) 250 g/mL
D) 15.0 g/mL
Correct Answer: A. 2.50 g/mL
Rationale: Density = mass / volume. 25.0 g ÷ 10.0 mL = 2.50 g/mL. The answer
has 3 significant figures (consistent with the data). Density is an intensive property
that does not depend on the amount of substance.
Question 10
Convert 150°C to Kelvin.
A) 123 K
B) 273 K
C) 423 K
D) 150 K
Correct Answer: C. 423 K
Rationale: To convert Celsius to Kelvin, add 273.15 (or 273). K = °C + 273.15.
150 + 273.15 = 423.15 K → 423 K (rounded). The Kelvin scale is an absolute
temperature scale where 0 K is absolute zero.
Comprehensive -Question Practice Exam with
Verified Answers & Detailed Rationales Portage
Learning | Graded A+ | Latest 2026
Leave your honest rating⭐⭐⭐⭐⭐
Question 1
Convert 845.3 to exponential form and explain your reasoning.
A) 8.453 × 10¹
B) 8.453 × 10²
C) 0.8453 × 10³
D) 84.53 × 10¹
Correct Answer: B. 8.453 × 10²
Rationale: Since 845.3 is larger than 1, the exponent is positive. Move the decimal
point 2 places to the left to place it after the first digit (8). The exponent equals the
number of places moved (2). Therefore, 845.3 = 8.453 × 10².
Question 2
Convert 3.21 × 10⁻⁵ to ordinary form and explain your reasoning.
A) 0.000321
B) 0.0000321
C) 321000
D) 0.00321
Correct Answer: B. 0.0000321
Rationale: The exponent is negative (-5), indicating a number smaller than 1.
Move the decimal point 5 places to the left, adding zeros as needed. 3.21 × 10⁻⁵ =
0.0000321 (move decimal 5 places left: 3.21 → 0.0000321).
Question 3
Convert 24.6 grams to kilograms. Show all work.
,A) 2460 kg
B) 2.46 kg
C) 0.0246 kg
D) 0.246 kg
Correct Answer: C. 0.0246 kg
Rationale: Use the conversion factor 1 kg = 1000 g. Multiply 24.6 g × (1 kg /
1000 g) = 0.0246 kg. The grams cancel, leaving kilograms. Option A is incorrect
(multiplied instead of divided), Option B is incorrect (divided by 10 instead of
1000).
Question 4
How many significant figures are in 0.00450?
A) 2
B) 3
C) 4
D) 5
Correct Answer: B. 3
Rationale: Leading zeros are not significant. The zeros between the decimal and
the 4 are leading zeros and are not counted. The digits 4, 5, and the trailing zero are
significant. The trailing zero after the decimal is significant because it indicates
precision. Therefore, 0.00450 has 3 significant figures (4, 5, 0).
Question 5
What is the result of 12.34 + 2.1 + 0.045, reported with the correct number of
significant figures?
A) 14.485
B) 14.49
C) 14.5
D) 14
Correct Answer: C. 14.5
,Rationale: When adding or subtracting, the answer should have the same number
of decimal places as the measurement with the fewest decimal places. 12.34 has 2
decimal places, 2.1 has 1 decimal place, and 0.045 has 3 decimal places. The
answer should have 1 decimal place. 12.34 + 2.1 + 0.045 = 14.485 → rounded to 1
decimal place = 14.5.
Question 6
Convert 250.0 mL to liters.
A) 0.2500 L
B) 2.500 L
C) 25.00 L
D) 2500 L
Correct Answer: A. 0.2500 L
Rationale: Use the conversion factor 1 L = 1000 mL. 250.0 mL × (1 L / 1000 mL)
= 0.2500 L. The answer should maintain the same number of significant figures as
the original measurement (4 significant figures).
Question 7
Which of the following is an example of a physical change?
A) Burning wood
B) Rusting iron
C) Melting ice
D) Digesting food
Correct Answer: C. Melting ice
Rationale: A physical change does not alter the chemical composition of a
substance. Melting ice is a phase change from solid to liquid, but the chemical
formula (H₂O) remains the same. Burning wood, rusting iron, and digesting food
are all chemical changes.
Question 8
Which of the following is a chemical property?
, A) Density
B) Boiling point
C) Flammability
D) Melting point
Correct Answer: C. Flammability
Rationale: Flammability is a chemical property because it describes how a
substance reacts with oxygen to produce heat and light. Density, boiling point, and
melting point are physical properties that can be observed without changing the
chemical composition.
Question 9
What is the density of a substance with a mass of 25.0 g and a volume of 10.0 mL?
A) 2.50 g/mL
B) 0.40 g/mL
C) 250 g/mL
D) 15.0 g/mL
Correct Answer: A. 2.50 g/mL
Rationale: Density = mass / volume. 25.0 g ÷ 10.0 mL = 2.50 g/mL. The answer
has 3 significant figures (consistent with the data). Density is an intensive property
that does not depend on the amount of substance.
Question 10
Convert 150°C to Kelvin.
A) 123 K
B) 273 K
C) 423 K
D) 150 K
Correct Answer: C. 423 K
Rationale: To convert Celsius to Kelvin, add 273.15 (or 273). K = °C + 273.15.
150 + 273.15 = 423.15 K → 423 K (rounded). The Kelvin scale is an absolute
temperature scale where 0 K is absolute zero.
