8th grade benchmark

An atom of calcium-48 and an atom of calcium-47 differ in

• atomic number.

• nuclear charge.

• number of neutrons.

• number of electrons.

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You are hired as a scrap metal dealer. A customer wants to sell you a piece of precious scrap metal. You know it is one of these common metals. You slowly heat the metal and it melts at 962 °C. You also take the density of the metal and find it to be roughly 10.5 g/cm³. What is the MOST LIKELY identity of the metal?

• Copper

• Gold

• Silver

• Zinc

One difference between mixtures and pure substances is that

• mixtures can be physically separated.

• mixtures are made of one type of atom.

• pure substances have no chemical bonds.

• pure substances can be physically separated.

In physical science lab, Ben and Jerry added small pieces of magnesium to hydrochloric acid. They noticed that bubbles formed, the test tube got hot, and the magnesium disappeared. What is a sign that a chemical reaction has taken place in this experiment?

• odor

• gas is produced

• magnesium disappeared

• decrease in temperature

It's Peggy Sue's birthday and she's about to blow out the candles on her cake. Brother Roger stops the party when he shouts: "Look at that! Chemical and physical changes taking places on your birthday cake!"

How would you respond to Roger?

• Roger is incorrect. The melting wax is a physical change but there is no chemical change taking place.

• Roger is correct. Lighting the match is a chemical change and burning the candles is a physical change.

• Roger is correct. The melting wax is a physical change and the burning candle wick is a chemical change.

• Roger is incorrect. Only a chemical change is taking place as evidenced by the light and heat of the burning candles.

The table shows the density and volume of four liquid samples. The four liquids do not mix with each other. What is the order in which the layers will be formed, from top to bottom, if the four liquids are poured into a beaker and allowed to settle?

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• Sample A; Sample B; Sample C; Sample D

• Sample C; Sample A; Sample D; Sample B

• Sample D; Sample C; Sample B; Sample A

• Sample B; Sample D; Sample A; Sample C

If water with the mass of 15.0 grams is heated into water vapor in a closed system such as a closed glass jar, what is the mass of the gas after the water completely vaporizes?

• 13.5 grams

• 15.0 grams

• 16.5 grams

• The mass cannot be determined without knowing the volume.

A __________ has distinct properties and composition that never vary.

• solution

• molecule

• pure substance

• heterogeneous mixture

I. O₂ is chemically bonded together.

II. O₂ is divisible.

III. Oxygen is a nonmetal.

IV. The natural state of oxygen is as a diatomic gas.

Which conclusion can be drawn from these statements about O₂?

• O2 is an atom.

• O2 is a molecule.

• O₂ is an electron.

• O₂ is an element.

When Kay added 30 g of hydrochloric acid (HCl) to 65 g of Zn, bubbles appeared and a white precipitate, zinc chloride (ZnCl2) was produced. She found that the mass of the zinc chloride was 63 g. Since the Law of Conservation of Matter stated that matter can't be created or destroyed, she was puzzled about the difference in mass. What is the best explanation for the missing 2 g?

• 2 g of zinc disappeared.

• 2 g of hydrogen gas were produced.

• Kay didn't correctly mass the precipitate.

• Kay didn't collect all of the precipitate.