Elements & Compounds
Which of the following represents an element?
A. CO₂
B. H₂O
C. O₂
D. NaCl
Answer: C — O₂
Which is a physical change?
A. Iron rusting
B. Wood burning
C. Wax melting
D. Food cooking
Wax Melting
When salt dissolves in water, what is the solvent?
A. Salt
B. Water
C. Saltwater
D. The container
Answer: B — Water
A cyclist travels 66 meters in 6 seconds.
What is the average speed?
A. 9 m/s
B. 10 m/s
C. 11 m/s
D. 12 m/s
Answer: C — 11 m/s
Which measurement represents velocity?
A. 18 meters
B. 18 seconds
C. 18 m/s
D. 18 m/s north
Answer: D
How many total atoms are represented in one molecule of H₂SO₄?
A. 3
B. 6
C. 7
D. 8
Answer: C — 7 atoms
Which observation provides the strongest evidence that a chemical change occurred?
A. An object changes shape.
B. A solid melts.
C. A new substance forms.
D. An object becomes smaller.
Answer C
Two cups contain the same amount of water.
Cup A: 5 g salt
Cup B: 15 g salt
Assuming all the salt dissolves, which solution is more concentrated?
Answer: Cup B
It contains more solute in the same amount of solvent
Two robots travel for exactly 9 seconds.
Robot A: 63 m
Robot B: 81 m
Which robot has the greater average speed, and how can you determine this without calculating?
Answer: Robot B.
Both traveled for the same amount of time, but Robot B traveled a greater distance.
A student walks 14 m east and then 5 m west.
What are the student's distance and displacement?
Answer:
Distance = 19 m
Displacement = 9 m east
A student says:
“CO and Co represent the same substance because capitalization doesn't matter in chemical symbols.”
Which statement best evaluates the claim?
A. Correct; both contain carbon and oxygen.
B. Incorrect; CO contains carbon and oxygen, while Co represents cobalt.
C. Correct; both represent cobalt.
D. Incorrect; CO represents oxygen only.
Answer: B
During a candle demonstration, the wax melts while the wick burns.
Which statement is correct?
A. Both are physical changes.
B. Both are chemical changes.
C. Wax melting is chemical; wick burning is physical.
D. Wax melting is physical; wick burning is chemical.
Answer: D
A student has a concentrated saltwater solution. The student adds 100 mL of water but no additional salt.
What happens to the concentration?
A. Increases
B. Decreases
C. Stays the same
D. Becomes zero
Answer: B — Decreases
Runner A travels 88 m in 11 s.
Runner B travels 81 m in 9 s.
Which runner is faster?
Answer: Runner B
A runner travels 32 m west and then 32 m east, returning to the starting point.
Which statement is correct?
A. Distance = 0 m; displacement = 0 m
B. Distance = 32 m; displacement = 32 m east
C. Distance = 64 m; displacement = 0 m
D. Distance = 64 m; displacement = 64 m
Answer: C
Which statement correctly describes 2(H₂O)?
A. It contains 2 hydrogen atoms and 1 oxygen atom.
B. It contains 2 hydrogen atoms and 2 oxygen atoms.
C. It contains 4 hydrogen atoms and 2 oxygen atoms.
D. It contains 4 hydrogen atoms and 4 oxygen atoms
C
A student says:
“Melting chocolate is a chemical change because heat was added.”
What is wrong with the student's reasoning?
Answer: Adding heat does not automatically make something a chemical change. Melting is a physical change because the substance changes state but no new substance forms.
Four students place identical amounts of sugar into water.
Student A: whole sugar cube + cold water + no stirring
Student B: crushed sugar + cold water + no stirring
Student C: whole sugar cube + hot water + stirring
Student D: crushed sugar + hot water + stirring
Which should dissolve fastest, and identify three factors responsible.
Answer: Student D
Hotter temperature + increased surface area + agitation
A robotic car travels:
What is the car's average speed for the entire trip?
A. 5 m/s
B. 6 m/s
C. 7 m/s
D. 18 m/s
Answer: B — 6 m/s
Car A travels 22 m/s north.
Car B travels 22 m/s south.
A student says:
“The cars have the same velocity because both are traveling 22 m/s.”
Evaluate the claim
Answer: The claim is incorrect. The cars have the same speed but different velocities because velocity includes direction.
A student compares O₂ and CO₂ and says:
“Both substances are compounds because both contain more than one atom.”
Is the student correct? Explain.
Answer: No. O₂ is an element because it contains only oxygen atoms. CO₂ is a compound because it contains two different elements, carbon and oxygen.
During an investigation:
Classify all three changes and justify your answer.
Answer:
A student crushes a sugar cube before placing it into water and says:
“Crushing the sugar increased its solubility, so more sugar can now dissolve.”
Evaluate the student's reasoning.
Answer: The reasoning is correct. Crushing increases the sugar's surface area, which can increase the rate of dissolution.
A robot actually travels 72 meters in 9 seconds.
During the investigation, a student correctly measures the distance but accidentally records the time as 6 seconds.
The student calculates:
72 ÷ 6 = 12 m/s
Explain:
The recorded time is too short, causing the calculated speed to be too high.
Actual:
72 ÷ 9 = 8 m/s
A runner starts at a cone and travels:
Part 1: 36 m east in 4 s
Part 2: 18 m west in 3 s
Part 3: 18 m east in 2 s
Determine:
1. Total distance
2. Displacement
3. Average speed for the entire trip
4. Did the runner's velocity remain constant? Explain.
1. Total distance
36 + 18 + 18 = 72 m
2. Displacement
36 east − 18 west + 18 east = 36 m east
3. Average speed for the entire trip
Total time = 4 + 3 + 2 = 9 s
72 ÷ 9 = 8 m/s
4. Did the runner's velocity remain constant? Explain.
No. The runner changed direction during the trip, so the runner's velocity changed.