UST Middle School Science Challenge
Week 5 — Matter & Chemical Changes
Grades 6–8 • Focus: Atoms, elements, compounds, mixtures and chemical reactions
Weekly Format
Atoms, elements, compounds, mixtures and chemical reactions
Part A — 15 Multiple Choice
Part B — 15 Fill in the Blank
Part C — 15 Scientific Reasoning / Open Response
Part D — 5 Challenge Problems
Answers and How to Solve are separated at the end.
Part A — Multiple Choice
Questions 1–5
1. The smallest unit of an element is an? A) atom B) an unrelated process C) none of these D) a different scientific idea
2. Two or more elements chemically bonded form a? A) compound B) an unrelated process C) none of these D) a different scientific idea
3. A physical change? A) does not create a new substance B) an unrelated process C) none of these D) a different scientific idea
4. A sign of a chemical reaction can be? A) gas production B) an unrelated process C) none of these D) a different scientific idea
5. In a closed system, chemical reactions obey conservation of? A) mass B) an unrelated process C) none of these D) a different scientific idea
Part A — Multiple Choice
Questions 6–10
6. The smallest unit of an element is an? A) atom B) an unrelated process C) none of these D) a different scientific idea
7. Two or more elements chemically bonded form a? A) compound B) an unrelated process C) none of these D) a different scientific idea
8. A physical change? A) does not create a new substance B) an unrelated process C) none of these D) a different scientific idea
9. A sign of a chemical reaction can be? A) gas production B) an unrelated process C) none of these D) a different scientific idea
10. In a closed system, chemical reactions obey conservation of? A) mass B) an unrelated process C) none of these D) a different scientific idea
Part A — Multiple Choice
Questions 11–15
11. The smallest unit of an element is an? A) atom B) an unrelated process C) none of these D) a different scientific idea
12. Two or more elements chemically bonded form a? A) compound B) an unrelated process C) none of these D) a different scientific idea
13. A physical change? A) does not create a new substance B) an unrelated process C) none of these D) a different scientific idea
14. A sign of a chemical reaction can be? A) gas production B) an unrelated process C) none of these D) a different scientific idea
15. In a closed system, chemical reactions obey conservation of? A) mass B) an unrelated process C) none of these D) a different scientific idea
Part B — Fill in the Blank
Questions 16–20
16. Complete the statement: A physical change ______.
17. Complete the statement: A sign of a chemical reaction can be ______.
18. Complete the statement: In a closed system, chemical reactions obey conservation of ______.
19. Complete the statement: The smallest unit of an element is an ______.
20. Complete the statement: Two or more elements chemically bonded form a ______.
Part B — Fill in the Blank
Questions 21–25
21. Complete the statement: A physical change ______.
22. Complete the statement: A sign of a chemical reaction can be ______.
23. Complete the statement: In a closed system, chemical reactions obey conservation of ______.
24. Complete the statement: The smallest unit of an element is an ______.
25. Complete the statement: Two or more elements chemically bonded form a ______.
Part B — Fill in the Blank
Questions 26–30
26. Complete the statement: A physical change ______.
27. Complete the statement: A sign of a chemical reaction can be ______.
28. Complete the statement: In a closed system, chemical reactions obey conservation of ______.
29. Complete the statement: The smallest unit of an element is an ______.
30. Complete the statement: Two or more elements chemically bonded form a ______.
Part C — Scientific Reasoning
Questions 31–35
31. A student compares two conditions and records results over five trials. Explain how the idea “compound” is relevant. Use 2–3 complete sentences.
32. A class observes a model and explains how its parts work together. Explain how the idea “does not create a new substance” is relevant. Use 2–3 complete sentences.
33. Students examine a data table and notice a consistent pattern. Explain how the idea “gas production” is relevant. Use 2–3 complete sentences.
34. A team changes one factor and measures the response. Explain how the idea “mass” is relevant. Use 2–3 complete sentences.
35. A scientist compares evidence from two possible explanations. Explain how the idea “atom” is relevant. Use 2–3 complete sentences.
Part C — Scientific Reasoning
Questions 36–40
36. A student compares two conditions and records results over five trials. Explain how the idea “compound” is relevant. Use 2–3 complete sentences.
37. A class observes a model and explains how its parts work together. Explain how the idea “does not create a new substance” is relevant. Use 2–3 complete sentences.
38. Students examine a data table and notice a consistent pattern. Explain how the idea “gas production” is relevant. Use 2–3 complete sentences.
39. A team changes one factor and measures the response. Explain how the idea “mass” is relevant. Use 2–3 complete sentences.
40. A scientist compares evidence from two possible explanations. Explain how the idea “atom” is relevant. Use 2–3 complete sentences.
Part C — Scientific Reasoning
Questions 41–45
41. A student compares two conditions and records results over five trials. Explain how the idea “compound” is relevant. Use 2–3 complete sentences.
42. A class observes a model and explains how its parts work together. Explain how the idea “does not create a new substance” is relevant. Use 2–3 complete sentences.
43. Students examine a data table and notice a consistent pattern. Explain how the idea “gas production” is relevant. Use 2–3 complete sentences.
44. A team changes one factor and measures the response. Explain how the idea “mass” is relevant. Use 2–3 complete sentences.
45. A scientist compares evidence from two possible explanations. Explain how the idea “atom” is relevant. Use 2–3 complete sentences.
Part D — Challenge
Questions 46–50
46. Challenge: Design or describe a short investigation that could demonstrate the concept “atom.” Identify what you would observe or measure.
47. Challenge: Design or describe a short investigation that could demonstrate the concept “compound.” Identify what you would observe or measure.
48. Challenge: Design or describe a short investigation that could demonstrate the concept “does not create a new substance.” Identify what you would observe or measure.
49. Challenge: Design or describe a short investigation that could demonstrate the concept “gas production.” Identify what you would observe or measure.
50. Challenge: Design or describe a short investigation that could demonstrate the concept “mass.” Identify what you would observe or measure.
Answer Key — Questions 1–5
Answer + How to Solve
1. Answer: A
How to solve: Atoms retain the chemical identity of an element.
2. Answer: A
How to solve: Compounds contain chemically joined elements.
3. Answer: A
How to solve: Physical changes alter form, not chemical identity.
4. Answer: A
How to solve: Gas formation can indicate new substances are forming.
5. Answer: A
How to solve: Matter is rearranged, not created or destroyed.
Answer Key — Questions 6–10
Answer + How to Solve
6. Answer: A
How to solve: Atoms retain the chemical identity of an element.
7. Answer: A
How to solve: Compounds contain chemically joined elements.
8. Answer: A
How to solve: Physical changes alter form, not chemical identity.
9. Answer: A
How to solve: Gas formation can indicate new substances are forming.
10. Answer: A
How to solve: Matter is rearranged, not created or destroyed.
Answer Key — Questions 11–15
Answer + How to Solve
11. Answer: A
How to solve: Atoms retain the chemical identity of an element.
12. Answer: A
How to solve: Compounds contain chemically joined elements.
13. Answer: A
How to solve: Physical changes alter form, not chemical identity.
14. Answer: A
How to solve: Gas formation can indicate new substances are forming.
15. Answer: A
How to solve: Matter is rearranged, not created or destroyed.
Answer Key — Questions 16–20
Answer + How to Solve
16. Answer: does not create a new substance
How to solve: Physical changes alter form, not chemical identity.
17. Answer: gas production
How to solve: Gas formation can indicate new substances are forming.
18. Answer: mass
How to solve: Matter is rearranged, not created or destroyed.
19. Answer: atom
How to solve: Atoms retain the chemical identity of an element.
20. Answer: compound
How to solve: Compounds contain chemically joined elements.
Answer Key — Questions 21–25
Answer + How to Solve
21. Answer: does not create a new substance
How to solve: Physical changes alter form, not chemical identity.
22. Answer: gas production
How to solve: Gas formation can indicate new substances are forming.
23. Answer: mass
How to solve: Matter is rearranged, not created or destroyed.
24. Answer: atom
How to solve: Atoms retain the chemical identity of an element.
25. Answer: compound
How to solve: Compounds contain chemically joined elements.
Answer Key — Questions 26–30
Answer + How to Solve
26. Answer: does not create a new substance
How to solve: Physical changes alter form, not chemical identity.
27. Answer: gas production
How to solve: Gas formation can indicate new substances are forming.
28. Answer: mass
How to solve: Matter is rearranged, not created or destroyed.
29. Answer: atom
How to solve: Atoms retain the chemical identity of an element.
30. Answer: compound
How to solve: Compounds contain chemically joined elements.
Answer Key — Questions 31–35
Answer + How to Solve
31. Answer: Response should correctly apply: compound.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Compounds contain chemically joined elements.
32. Answer: Response should correctly apply: does not create a new substance.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Physical changes alter form, not chemical identity.
33. Answer: Response should correctly apply: gas production.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Gas formation can indicate new substances are forming.
34. Answer: Response should correctly apply: mass.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Matter is rearranged, not created or destroyed.
35. Answer: Response should correctly apply: atom.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Atoms retain the chemical identity of an element.
Answer Key — Questions 36–40
Answer + How to Solve
36. Answer: Response should correctly apply: compound.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Compounds contain chemically joined elements.
37. Answer: Response should correctly apply: does not create a new substance.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Physical changes alter form, not chemical identity.
38. Answer: Response should correctly apply: gas production.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Gas formation can indicate new substances are forming.
39. Answer: Response should correctly apply: mass.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Matter is rearranged, not created or destroyed.
40. Answer: Response should correctly apply: atom.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Atoms retain the chemical identity of an element.
Answer Key — Questions 41–45
Answer + How to Solve
41. Answer: Response should correctly apply: compound.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Compounds contain chemically joined elements.
42. Answer: Response should correctly apply: does not create a new substance.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Physical changes alter form, not chemical identity.
43. Answer: Response should correctly apply: gas production.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Gas formation can indicate new substances are forming.
44. Answer: Response should correctly apply: mass.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Matter is rearranged, not created or destroyed.
45. Answer: Response should correctly apply: atom.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Atoms retain the chemical identity of an element.
Answer Key — Questions 46–50
Answer + How to Solve
46. Answer: Answers vary; investigation must correctly demonstrate atom.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.
47. Answer: Answers vary; investigation must correctly demonstrate compound.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.
48. Answer: Answers vary; investigation must correctly demonstrate does not create a new substance.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.
49. Answer: Answers vary; investigation must correctly demonstrate gas production.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.
50. Answer: Answers vary; investigation must correctly demonstrate mass.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.