8th Grade Science Unit 2 Review

Which of the following is the best description of the results of a chemical reaction?

• A new substance with different properties is formed.

• The substance seems to disappear after dissolving in water.

• The substance changes from liquid to solid at a low temperature.

• The reaction can be reversed to get back the original substance.

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NGSS.MS-PS1-2

Rust forming on a piece of iron is an example of which of the following:

• A physical change because the process can be reversed

• The natural process of decay as metallic ions age

• A chemical change because oxygen atoms from the atmosphere bonded with the iron atoms

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Evidence of a chemical reactions is anything that shows - 

• a new substance has formed
• a solid dissolved in a liquid
• interaction between 2 gases
• a change in the state of matter

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One of the signs of a chemical reaction taking place is:

• Bubbles are produced 
• Reactants are not combining
• Products are not forming
• Color is not changing

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Which of the following describes a precipitate?

• a liquid forms when a block of metal is heated
• a solid forms when one liquid is poured into another
• a gas forms when a solid is placed in a liquid
• bubbles form when an acid is poured on a rock

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Which is NOT an indication of a chemical change?

• temperature change
• formation of a precipitate
• shape change
• production of light

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You know you a chemical reaction has occurred if 

• there is a precipitate.
• there is a color change.
• there is a temperature change.
• All of these answers are evidence.

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Four students performed four different investigations by combining different substances. Which of the observations is most indicative of a chemical reaction?

• investigation 1
• investigation 2
• investigation 3
• investigation 4

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A student places a piece of a potato into a container of hydrogen peroxide. One observation the student makes is that bubbles form around the potato. The presence of bubbles might indicate the formation of a new substance because bubbles - 

• could show that a gas is forming.
• always rise to the top of a liquid. 
• are almost always perfectly spherical.
• usually burst after a few minutes.

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A clear liquid from a flask is poured into another clear liquid in a beaker. Which of the following results of this procedure would indicate a new substance was formed?

• The level of the substance in the beaker is higher after the other liquid is added.
• A yellow solid forms and then settles to the bottom of the beaker.
• Small white crystals are left behind in the flask that held the first liquid.
• The mass of the combined liquids is greater than either original liquid.

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NGSS.MS-PS1-2