example problems\n1. a student mixes vinegar with baking powder, and bubbles quickly appear.\nwhich…

example problems\n1. a student mixes vinegar with baking powder, and bubbles quickly appear.\nwhich statement best explains what happened?\na the substances only mixed physically.\nb a new substance formed because a gas was released.\nc the vinegar turned into a solid substance.\nd only the temperature changed, so it was physical.\n2. a student stirs sugar into iced tea. which two statements describe this change?\na the sugar dissolves but remains the same substance.\nb a new substance forms because the tea changes flavor.\nc this is a physical change since the sugar could be recovered.\nd a gas forms, showing a chemical change.\ne the sugar completely disappears, showing it became new matter.\n3. which evidence best supports that a chemical change occurred?\na the mixture became cloudy but stayed the same temperature.\nb heat was given off during the reaction.\nc the mixture was hard to stir.\nd the substance could be filtered back out.\n4. the table shows results from an investigation.\ntrial materials combined observations\n1 oil + water oil floated on top\n2 yeast + sugar water bubbles formed and odor appeared\n3 sand + salt both settled at the bottom\nwhich trial most likely produced a new substance?\na trial 1\nb trial 2\nc trial 3\nd all three

example problems\n1. a student mixes vinegar with baking powder, and bubbles quickly appear.\nwhich statement best explains what happened?\na the substances only mixed physically.\nb a new substance formed because a gas was released.\nc the vinegar turned into a solid substance.\nd only the temperature changed, so it was physical.\n2. a student stirs sugar into iced tea. which two statements describe this change?\na the sugar dissolves but remains the same substance.\nb a new substance forms because the tea changes flavor.\nc this is a physical change since the sugar could be recovered.\nd a gas forms, showing a chemical change.\ne the sugar completely disappears, showing it became new matter.\n3. which evidence best supports that a chemical change occurred?\na the mixture became cloudy but stayed the same temperature.\nb heat was given off during the reaction.\nc the mixture was hard to stir.\nd the substance could be filtered back out.\n4. the table shows results from an investigation.\ntrial materials combined observations\n1 oil + water oil floated on top\n2 yeast + sugar water bubbles formed and odor appeared\n3 sand + salt both settled at the bottom\nwhich trial most likely produced a new substance?\na trial 1\nb trial 2\nc trial 3\nd all three

Answer

Brief Explanations:

  1. When vinegar reacts with baking - powder, a chemical reaction occurs producing carbon - dioxide gas, which indicates the formation of a new substance. Option B is correct as gas evolution is a sign of a chemical change.
  2. When sugar is stirred into iced tea, it dissolves. Dissolving is a physical change as the sugar remains sugar and can be recovered. Options A and C are correct.
  3. Heat being given off during a reaction is a strong indicator of a chemical change. Chemical reactions often involve energy changes. Option B is correct.
  4. In trial 2, yeast reacting with sugar in water causes bubbles (gas formation) and an odor, which are signs of a chemical reaction and the production of a new substance. Option B is correct.

Answer:

  1. B. A new substance formed because a gas was released
  2. A. The sugar dissolves but remains the same substance; C. This is a physical change since the sugar could be recovered
  3. B. Heat was given off during the reaction
  4. B. Trial 2