New Hampshire NH SAS Science Grade 8 Practice Questions - New Hampshire Statewide Assessment System Science - Grade 8 Exam

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A student seals 25 g of baking soda and 30 g of vinegar in a sealed plastic bag. After the fizzing stops, the student finds the bag now holds 50 g of liquid and gas. The student is confused because 25 + 30 = 55, not 50. Which conclusion is best supported by this observation?

Some matter appears missing because the bag was sealed but the balance was not precise enough to measure gas pressure. Matter is not conserved in a chemical reaction when gases are produced inside a sealed container. The reaction converted some of the reactants into energy, which is why the mass decreased. The mass was always conserved; the bag leaked gas and the total would still be 55 g if nothing escaped.

Correct Answer:

The mass was always conserved; the bag leaked gas and the total would still be 55 g if nothing escaped.

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