Elements Compounds and Mixtures Test Review

Which of the following best describes a homogeneous mixture?

• A mixture that contains only one type of element.

• A mixture with a uniform composition throughout.

• A mixture that can be separated by physical means.

• A mixture where the components are easily distinguishable.

During a science experiment, Emma mixed stomach acid and a solution of NaOH in a beaker. What would the outcome of the solution be?

• a salt solution

• a more basic solution

• a neutral acid solution

• a more acidic solution

Answer explanation

Mixing stomach acid (acidic) with NaOH (basic) results in a neutralization reaction, producing water and a salt. Therefore, the outcome is a salt solution.

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NGSS.MS-PS1-2

Scarlett and Aiden are examining different samples in a lab. Which sample represents a pure substance?

• Model 1, because it represents compounds.

• Model 2, because it represents several elements.

• Model 3, because it represents one type of compound.

• Model 4, because it contains both elements and compounds.

Answer explanation

Model 3 represents a pure substance because it consists of only one type of compound, distinguishing it from the other models that include multiple elements or a mix of elements and compounds.

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NGSS.MS-PS1-1

Noah and Priya are in a chemistry lab. They combine two or more different atoms. What do they form?

• a cell

• a mixture

• a new atom

• a compound

Answer explanation

When two or more different atoms combine, they form a compound. A compound is a substance made up of two or more elements that are chemically bonded together, unlike a mixture where the components retain their individual properties.

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NGSS.MS-PS1-1

Anika and Liam are discussing the composition of the air we breathe. Based on the graph below, 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

The air we breathe is a homogeneous mixture because it consists of various gases (like nitrogen and oxygen) that are uniformly distributed and cannot be easily distinguished from one another.

Charlotte is making a fizzy drink by mixing carbon dioxide (CO₂) with distilled water (H₂O). How would you classify the fizzy drink and distilled water?

• The fizzy drink and distilled water are both heterogeneous mixtures.

• The fizzy drink is a homogeneous mixture and distilled water is a pure substance.

• The fizzy drink is a pure substance while distilled water is a homogeneous mixture.

• The fizzy drink and distilled water contain hydrogen and oxygen, therefore they are both pure substances.

Answer explanation

Soda water is a homogeneous mixture because it has a uniform composition throughout, while distilled water is a pure substance as it consists only of H₂O without any impurities or other substances.

During a science experiment, Mia tested various solutions and recorded their pH levels. Which of the above substances is considered the most acidic?

• Lye

• Soda

• Borax

• Water

Answer explanation

Soda has a lower pH compared to lye, borax, and water, indicating it is more acidic. Therefore, among the given substances, soda is considered the most acidic.

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NGSS.MS-PS1-2

Madison's lab group is given a dish that contains sand, shells, and water. How should they classify the substance they have been given?

• compound because it contains several elements

• pure substance because it’s made up of various compounds

• heterogeneous mixture because it does not have the same uniform appearance or composition

• homogeneous mixture because it has the same uniform appearance and composition throughout

Answer explanation

The correct classification is a heterogeneous mixture because the dish contains distinct components (sand, shells, water) that do not blend uniformly, resulting in a non-uniform appearance and composition.

Anika is cleaning her house and has a list of common household cleaners and their pH levels. 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.

• Tile Cleaner would be the best cleaner because it has a pH of 12.

• Soap would be the best cleaner because it has a pH greater than 7.

• Toilet Bowl Cleaner would be the best cleaner because it has a pH of 2.

Answer explanation

Tile Cleaner, with a pH of 12, is the most basic option listed, making it the most effective cleaning agent. Basic solutions are better at breaking down dirt and grease compared to acidic solutions like vinegar or toilet bowl cleaner.

Tags

NGSS.MS-PS1-2

Anika is conducting an experiment in her science class. Based on the pH scale, which substance is more acidic than tomato juice?

• Milk, because it has a greater pH

• Vinegar, because it has a lower pH

• Pure water, because it has a greater pH

• Baking soda, because it has a lower pH

Answer explanation

Vinegar is more acidic than tomato juice because it has a lower pH. Substances with lower pH values are more acidic, while those with higher pH values, like milk and pure water, are less acidic.