Chemical Reactions: Evidence of Change and Conservation of Mass

Chemical Reactions: Evidence of Change and Conservation of Mass

Grade 8 · Science · NYSSLS MS-PS1-2 · Worksheet (30–35 min)

NYS-Aligned Standard

MS-PS1-2 — Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred. NYS P-12 Science Learning Standards / NYSSLS (2017)

Three-Dimensional Alignment

Teacher Directions

This worksheet uses an original data table (not from any lab kit or copyrighted curriculum) representing a simulated investigation. Students analyze the data to determine whether a chemical reaction occurred in each scenario. Use after an introductory lesson on signs of chemical reactions (color change, gas production, temperature change, precipitate formation, light production).

Student Directions

Name: ________________________ Date: ____________

A chemical reaction produces new substances with different properties from the original reactants. Use the data tables below to determine if a chemical reaction occurred.

Signs of a Chemical Reaction:

• ☐ Color change
• ☐ Gas produced (bubbles)
• ☐ Temperature change
• ☐ New solid formed (precipitate)
• ☐ Light or energy produced

PART 1 — Data Table Analysis

Scenario A: Water and Salt

Question 1a: Did a chemical reaction occur in Scenario A? (Circle: YES / NO) Question 1b: How do you know? List evidence from the table: _______________________

Scenario B: Baking Soda and Vinegar

Question 2a: Did a chemical reaction occur in Scenario B? (Circle: YES / NO) Question 2b: What is the evidence? List at least 2 signs: ___________________________ Question 2c: What gas was likely produced? ______________________________________

Scenario C: Iron Left in Moist Air (2-week observation)

Question 3a: Did a chemical reaction occur? (Circle: YES / NO) Question 3b: What type of reaction is this? ______________________________________ Question 3c: Why did the mass INCREASE? (Hint: What combined with the iron?) ________

PART 2 — Conservation of Mass

Read: The Law of Conservation of Mass states that in a chemical reaction, matter is neither created nor destroyed — the total mass of reactants equals the total mass of products.

Question 4: A student mixes 10 g of Substance X with 15 g of Substance Y in a closed container. After the reaction, they measure 23 g of product. Is 2 g “missing”? Where did it go? _________________________________

PART 3 — Short Response

“Using evidence from one of the scenarios above, explain how you determined whether a chemical reaction occurred. Include at least 2 signs of reaction and connect to the idea that new substances were formed.”

SDI & Differentiation Block

Supports for MLLs/ELLs

Entering/Emerging (NYSESLAT Levels 1–2):

• Provide a Signs of Chemical Reaction visual card with each sign illustrated
• Allow student to circle signs of reaction directly in the table (no written answer required for Part 1)
• Sentence frame: “A chemical reaction ___ (did / did not) occur because I see ___ (sign) in the data.”
• Bilingual glossary: reaction/reacción, temperature/temperatura, evidence/evidencia, gas/gas

Transitioning/Expanding (NYSESLAT Levels 3–4):

• Academic sentence frame for Part 3: “The data shows that ___ occurred because ___ and ___ were observed. This means new substances were formed.”
• Pre-teach vocabulary: precipitate, reactant, product, dissolve vs. react

Supports for Students with IEPs

SDI Adaptation Dimensions: content, delivery

• Content: Reduce to Scenarios A and B only; skip Part 2 (Conservation of Mass) if prerequisite knowledge is not yet in place
• Delivery: Allow extended time; read data tables aloud; provide a Signs-of-Reaction checklist to physically check off; allow verbal response for Part 3 scribed by teacher

Suggested Placement: ICT, Resource Room

Answer Key

1a: NO (physical change — salt dissolved, not reacted) 1b: No temperature change, no new substance, no color change, no gas — only a physical mixing

2a: YES 2b: Gas produced (bubbles), temperature decreased, new substance (CO₂ gas) formed 2c: Carbon dioxide (CO₂)

3a: YES 3b: Oxidation / rusting (iron + oxygen → iron oxide) 3c: Iron combined with oxygen from the air to form iron oxide — adding mass to the sample

4: No mass is truly “missing” — if 2 g is unaccounted for in an open container, a gas was likely produced that escaped. In a closed container, total mass before = total mass after (Conservation of Mass).

Part 3 model: “I determined a chemical reaction occurred in Scenario B because the data shows two signs: gas was produced (bubbles) and the temperature decreased. These indicate that new substances were formed — specifically carbon dioxide gas and water — which are different from the original baking soda and vinegar.”

Alignment Record