Question

question #6
a student mixes two substances and observes a rise in temperature and small, white particles that fall to the bottom of the test - tube. what conclusion can be drawn?
a a physical reaction occurred because of the temperature change.
b a chemical reaction occurred because a new substance was formed.
c a physical reaction occurred because it can be separated by filtering out the particles.
d a chemical reaction occurred because two substances were mixed.
question #7
select the two ways you could tell that the physical properties of a mixture had changed during a chemical reaction.
a melting
b gas bubbles appear
c evaporating
d freezing
e changes in temperature
question #8
a white granular substance is dissolved into a clear liquid. the mixture becomes cloudy. some granules remain undissolved at the bottom of the cup, and the mixture becomes cold. which observation shows that a chemical reaction took place?
*granules - crystal like substance example: sugar
a a substance dissolves.
b the mixture becomes cloudy and a precipitate forms.
c some granules do not dissolve.
d the mixture becomes evenly mixed.

Explanation:

• Question #6: A chemical reaction is indicated by the formation of a new substance (the white particles, a precipitate). A temperature change alone doesn't define a physical or chemical reaction, and just mixing substances isn't conclusive. Filtering out particles doesn't determine the type of reaction.
• Question #7: Gas bubbles appearing and changes in temperature are signs of a chemical - reaction that can also change physical properties of a mixture. Melting, evaporating, and freezing are physical changes on their own and not specific to chemical reactions changing physical properties.
• Question #8: The formation of a precipitate (the mixture becoming cloudy) is a sign of a chemical reaction. A substance dissolving or some granules not dissolving are physical - change related, and the mixture becoming evenly mixed is also a physical - change aspect.

Answer:

• Question #6: B. A chemical reaction occurred because a new substance was formed.
• Question #7: B. gas bubbles appear, E. changes in temperature
• Question #8: B. The mixture becomes cloudy and a precipitate forms.