8.3.1 Science Review

The graph shows the composition of the air we breathe.

Which of the following statements correctly classifies the air we breathe?

• The air we breathe is an element.

• The air we breathe is a compound.

• The air we breathe is a homogeneous mixture.

• The air we breathe is a heterogeneous mixture.

Answer explanation

homos is the latin word for "the same as." As a prefix it is shortened to homo.

Air looks uniform throughout so it is a homogeneous mixture.

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Salts form when which two substances are combined?

• two acids

• two bases

• an acid and a base

• an acid and a neutral

Answer explanation

Neutral is the middle pH.

When an acid and a base combine they want to be neutral.

The "neutral" is a salt!

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Your table group was shown a globe that contained sand, shells, and water. How should your group classify the given substance?

• Due to it containing several elements, we classified it as a compound.

• Due to it being made up of various compounds, we classified it as a pure substance. 

• Due to it not having  the same uniform appearance or composition, we classified it as a heterogeneous mixture.

• Due to it having the same uniform appearance and composition throughout, we classified it as a homogeneous mixture.

Answer explanation

hetero means "other."

So in science it is used when there are two or more things.

heterogeneous mixture means that we can see more than one thing.

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Which of the following pH values is considered an acid?

• pH 3

• pH 7

• pH 11

• pH 14

Answer explanation

Acids have a pH less than 7

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Which of the following describes rice and beans combined in a bowl?

• compound

• pure substance

• homogenous mixture

• heterogeneous mixture

Answer explanation

hetero means other.

In mixtures, if we can see more than one thing, we call in heterogeneous.

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Which of the following is formed when salt is dissolved in water?

• solution

• compound

• pure substance

• heterogeneous mixture

Answer explanation

A homogeneous mixture in a liquid is called a solution.

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Based on the pH scale, which substance is more acidic than tomato juice?

• Lemon juice has a lower pH therefore it is more acidic than tomato juice.

• Baking soda has a lower pH therefore it is more acidic than tomato juice.

• Black coffee has a greater pH therefore it is more acidic than tomato juice.

• Milk has a pH closest to neutral therefore it is more acidic than tomato juice.

Answer explanation

Lower pH means more acidic.

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The more basic a solution is the better it performs as a cleaning agent. Which of the following would make the best cleaning agent and why?

• Vinegar would be the best cleaner, because it has a pH of 3.

• Toilet Bowl Cleaner would be the best cleaner, because its pH is 1-3.

• Mild Dish Soap would be the best cleaner because it has a pH is closest to neutral.

• Tub & Tile Cleaner would be the best cleaner, because it has a pH of approximately 11-13.

Answer explanation

The higher the pH the more basic a substance is.

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Which of the substances in the chart is considered an acid?

• Lye

• Soda

• Borax

• Water

Answer explanation

pH less than 7 = Acid

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What would the outcome of a solution be, if Gastric Juice and Sodium Hydroxide (as shown in the pH scale above) are mixed in a beaker during a lab?

• a salt solution

• a more basic solution

• a neutral acid solution

• a more acidic solution

Answer explanation

Gastric Juice is a strong acid.

Sodium Hydroxide is a strong base.

Acid + Base = Salt

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