The method and the results are on the balancing equations lab. Do the analysis yourself first, then check the answers below.
Quick answer: A chemical equation shows reactants turning into products. These answers go with the grade 8 science lab on balancing equations: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
Model answers follow the sample data in the table. Your own values will differ slightly, but the open flask should lose clearly more mass than the sealed flask.
Open: (1.45 + 1.43 + 1.45) ÷ 3 = 4.33 ÷ 3 = 1.44 g lost. Sealed: (0.02 + 0.01 + 0.02) ÷ 3 = 0.017, about 0.02 g lost. So open = −1.44 g, sealed = −0.02 g.
Question 2 Explaining the open flask
The reaction made carbon dioxide gas, which escaped into the air. The atoms of carbon and oxygen are still there, but outside the flask. The gas carried the mass away.
Question 3 Explaining the sealed flask
The balloon trapped the gas, so all products stayed on the balance. The tiny drop is within the balance and buoyancy error. Mass is conserved.
Question 4 Checking the equation
Left: Na 1, C 1 + 2 = 3, H 1 + 4 = 5, O 3 + 2 = 5. Right: Na 1, C 2 + 1 = 3, H 3 + 2 = 5, O 2 + 1 + 2 = 5. All equal: balanced.
Question 5 Expected mass of gas
Mass = 3.0 × 44 ÷ 84 = 1.57 g of CO₂.
Question 6 Percentage escaped
1.44 ÷ 1.57 × 100 = 92 %.
Question 7 Why not 100 %?
Some carbon dioxide dissolves in the liquid, and some gas stays in the flask above the liquid. Also the balance reading may not settle exactly. Dissolved and trapped gas.
Question 8 Improving the lab
Plug the neck with cotton wool to stop liquid spray leaving, wait until fizzing completely stops, and repeat to find a mean. Cotton wool and more repeats.
