Part 1: Engage (Anchoring Phenomenon)

You place a dry log on a campfire. After an hour, all that remains is a small pile of gray ash. The log felt heavy in your hands before you tossed it in, but the ash weighs almost nothing. If matter cannot be created or destroyed, where did the rest of the mass go? What happened to the carbon, hydrogen, and oxygen atoms that made up the wood?

1. Observations and Questions:

• When wood burns, it is actually reacting with oxygen in the air. What products are formed, and where do they end up?
• If atoms are rearranged but never lost during a chemical reaction, how could we measure or prove that every atom from the original log is still present somewhere?
• Generate at least two “need to know” questions about tracking atoms and mass through a chemical reaction.

Part 2: Explore (Simulation Investigation)

Open the Conservation of Mass simulation. You will investigate three chemical reactions — water synthesis, methane combustion, and ammonia synthesis — by balancing equations, setting coefficients, and observing atom counts and mass readouts on a virtual balance scale.

2. Data Collection:

Reaction 1: Water Synthesis (H₂ + O₂ → H₂O)

• Start with the unbalanced equation for water synthesis. Click the coefficient arrows to balance the equation so that the number of hydrogen and oxygen atoms is the same on both sides.
• Record the balanced coefficients and the atom inventory (count of H and O atoms on each side).
• Read the mass readout for reactants and products. Record both values.
• Click “Run Reaction” and observe the balance scale. Did the total mass change?

Reaction 2: Methane Combustion (CH₄ + O₂ → CO₂ + H₂O)

• Select methane combustion from the reaction menu.
• Balance the equation by adjusting coefficients. Verify that the atom inventory shows equal numbers of C, H, and O atoms on both sides.
• Record the balanced coefficients and the total mass of reactants and products.
• Run the reaction. What does the balance scale show?

Reaction 3: Ammonia Synthesis (N₂ + H₂ → NH₃)

• Select ammonia synthesis. Balance the equation using coefficient inputs.
• Check the atom inventory for N and H atoms. Record the balanced coefficients.
• Record the total mass of reactants and products. Run the reaction and note the balance scale reading.

Data Table:

Part 3: Explain (Sensemaking)

3. Analyzing the Data and Connecting to the Phenomenon:

• Look at your data table. For each reaction, compare the total mass of reactants to the total mass of products. What pattern do you observe? Does the balance scale confirm or contradict this pattern?
• The wood log lost mass as it burned, and only ash remained. Based on what you observed in the simulation with methane combustion, where did the atoms from the wood go? Wood is mostly cellulose (C₆H₁₀O₅)ₙ. When it burns with oxygen, similar to methane combustion, what invisible products might carry the missing mass away?

4. Patterns Across Reactions:

• In all three reactions, did the number of each type of atom change from reactants to products? What does this tell you about the relationship between atom counts and mass conservation?
• Compare the balanced equations. In water synthesis, two molecules of H₂ combine with one O₂. In ammonia synthesis, one N₂ combines with three H₂. How does changing the coefficients affect the total number of atoms on each side? What mathematical relationship holds true in every balanced equation?

Part 4: Elaborate/Evaluate (Argumentation & Modeling)

5. Synthesis: Claims, Evidence, and Reasoning (CER)

Construct a complete CER explanation that answers the driving question: If wood burns and turns to ash, where does the rest of the mass go?

Your response must include:

• Claim: A clear statement about whether mass is conserved during combustion and where the “missing” mass actually goes.
• Evidence: Specific data from at least two of the simulation reactions (balanced equations, atom counts, mass readouts, balance scale results). Include calculations showing that total mass of reactants equals total mass of products.
• Reasoning: Explain how the evidence supports your claim, using the concept that atoms are rearranged — not created or destroyed — during chemical reactions. Connect this to the burning wood phenomenon by identifying the invisible products (gases) released during combustion.

Use the following atomic masses for calculations if needed: H = 1 g/mol, C = 12 g/mol, O = 16 g/mol.