Introduction to Chemistry

Which of the following is a chemical reaction?

• New atoms are formed when substances are mixed together

• A solid material melts and becomes a liquid

• Atoms of the reactants rearrange to form a new substance

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NGSS.MS-PS1-5

NGSS.MS-PS1-2

A student dissolves 3 gram of sugar in 10 grams of water. She then determines the mass of the solution. What is the mass of the dissolved sugar and water?

• 13 grams because the substance is a mixture and the molecules are floating next to each other.

• 13 grams because a chemical reaction occurred making a new substance.

• Less then 13 grams because the water absorbed the sugar.

• More than 13 grams because the sugar absorbed the water.

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NGSS.MS-PS1-5

Which of the following is true about the principle of the conservation of mass?

• The mass of the products is never equal to the mass of the reactants.

• The mass of the products is less than the mass of the reactants.

• The mass of the products is equal to the mass of the reactants.

• The mass of the products is greater than the mass of the reactants

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NGSS.MS-PS1-5

NGSS.MS-PS1-2

Jay had two clear liquids in bottles. The mass of one liquid was 10.0 grams and the other was 7.0 grams. When he mixed them, a yellow solid formed and settled to the bottom of the bottle. He predicted that the liquid plus the solid would have more mass, so he put the bottle on a scale. The mass was 17.0 grams.

Why did the mass not change?

• Because it is a mixture and mass doesn't change.

• His scale is broken.

• Do to the Law of conservation of mass, matter cannot be created nor destroyed so the mass is the same as the reactant and the product.

• He forgot to tare his bottle and the scale had the mass of the bottle added in.

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NGSS.MS-PS1-5

Which statement is always true about conservation of matter?

• If a gas forms, the mass of a system decreases.

• The mass of a system does not change during a chemical reaction.

• If a solid forms, the mass of a system increases.

• The mass of a system changes when a substance changes from liquid to gas, but it does not change in a chemical reaction.

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NGSS.MS-PS1-5

In the equation

magnesium + oxygen 🡪 magnesium oxide, Magnesium + oxygen is the reactant?

• true

• false

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NGSS.MS-PS1-1

In the equation

magnesium + oxygen 🡪 magnesium oxide, magnesium oxide is the product?

• true

• fale

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NGSS.MS-PS1-2

Describe three pieces of evidence you could look for to determine whether a chemical reaction occurred.

• Formation of a gas

• Formation of a precipitate

• Temperature change

• Color change

• property change

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NGSS.MS-PS1-2

Explain what happens to water during electrolysis. Is this a chemical reaction or a phase change? Explain your answer.

• This is a chemical reaction because the water is broken apart into Hydrogen and oxygen gas.

• This is a physical change because the water boiled and turned into vapor.

• This is a chemical reaction because there was bubbling.

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NGSS.MS-PS1-5

NGSS.MS-PS1-2

Seth learned in school that iron reacts with oxygen in the air to form iron oxide. The chemical equation is: Fe + O2 🡪 FeO2 Seth wanted to see if this would really happen, so he put 13 grams of tiny iron (Fe) pieces on the window sill outside his house. After two weeks, he saw that the iron no longer looked shiny. He checked the mass of the pieces and saw that it went from 13 to 21 grams. Seth’s friend said this shows that matter is not conserved. Do you agree or disagree with Seth’s friend? Select all the answers to make a CER.

• Seth's friend is wrong because matter is conserved and the iron went up because it is now a new substance.

• The Iron combined with oxygen and added 8 grams of oxygen in the chemical reaction causing the mass to go up.

• This chemical reaction occurred in an open system which is why the mass went up.

• Since, I know matter cannot be created or destroyed I can say that Seth's friend is wrong and that matter is conserved in this chemical reaction.

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NGSS.MS-PS1-5

NGSS.MS-PS1-2