AK SCI Review - Physical Sci 1

What is the chemical symbol for water?

Answer explanation

The chemical symbol for water is H₂O, which indicates it is composed of two hydrogen atoms and one oxygen atom. The other options represent different compounds: CO₂ is carbon dioxide, O₂ is oxygen, and H₂ is hydrogen gas.

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AK.SCI.6-8.MS-PS1-1

Which of the following is a synthetic material?

• Cotton

• Nylon

• Wool

• Silk

Answer explanation

Nylon is a synthetic material made from petrochemicals, while cotton, wool, and silk are natural fibers derived from plants and animals. Therefore, the correct answer is Nylon.

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Which of the following best describes a chemical reaction?

• A change in the state of matter

• A change in the shape of a substance

• A change in the composition of a substance

• A change in the temperature of a substance

Answer explanation

A chemical reaction involves a change in the composition of a substance, resulting in the formation of new substances with different properties. The other options describe physical changes, not chemical reactions.

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AK.SCI.6-8.MS-PS1-2

Describe the atomic composition of a water molecule.

• Two hydrogen atoms and one oxygen atom

• One hydrogen atom and two oxygen atoms

• Two oxygen atoms and one hydrogen atom

• Three hydrogen atoms and one oxygen atom

Answer explanation

A water molecule consists of two hydrogen atoms bonded to one oxygen atom, making the correct answer 'Two hydrogen atoms and one oxygen atom'. This composition is essential for the unique properties of water.

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Which of the following processes is an example of a chemical reaction?

• Melting ice

• Burning wood

• Boiling water

• Freezing water

Answer explanation

Burning wood is a chemical reaction because it involves a transformation of substances, producing new products like ash and gases. In contrast, melting ice, boiling water, and freezing water are physical changes.

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AK.SCI.6-8.MS-PS1-2

Analyze the data: A substance changes color and temperature when mixed with another. What can you infer?

• A physical change occurred

• A chemical reaction occurred

• No change occurred

• Only a temperature change occurred

Answer explanation

The change in color and temperature indicates a chemical reaction, as these are signs of new substances forming. A physical change would not typically involve such changes.

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What happens to the motion of particles when thermal energy is added to a substance?

• Particles move slower

• Particles stop moving

• Particles move faster

• Particles move in a circular motion

Answer explanation

When thermal energy is added to a substance, it increases the kinetic energy of the particles, causing them to move faster. This is why the correct answer is that particles move faster.

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Which of the following best explains the conservation of mass in a chemical reaction?

• Mass is lost during a reaction

• Mass is gained during a reaction

• Mass remains constant during a reaction

• Mass is irrelevant in a reaction

Answer explanation

The conservation of mass states that in a chemical reaction, the total mass of reactants equals the total mass of products. Therefore, mass remains constant during a reaction, making this the correct explanation.

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Predict the change in state that will occur when thermal energy is removed from water vapor.

• Water vapor turns into ice

• Water vapor turns into liquid water

• Water vapor remains unchanged

• Water vapor turns into gas

Answer explanation

When thermal energy is removed from water vapor, it undergoes condensation, changing from gas to liquid water. Therefore, the correct answer is that water vapor turns into liquid water.

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Which of the following is a natural resource used to create synthetic materials?

• Plastic

• Coal

• Glass

• Steel

Answer explanation

Coal is a natural resource that can be processed to create synthetic materials like plastics. Unlike plastic, glass, and steel, which are not derived from natural resources in the same way, coal serves as a key raw material in synthetic production.

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