Practice Chemistry EOG

Which is a compound?

• sodium

• sugar

• nitrogen

• air

Answer explanation

Chemistry:

A pure substance composed of two or more elements whose composition (ratio) is constant.

Sugar's formula is C₁₂H₂₂O₁₁ which is an exact ratio.

Nitrogen and Sodium are single elements.

Air is a random mixture with no exact ratio.

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NGSS.MS-PS1-1

This table provides information about some group 1 elements.

Which is the best estimate of the melting point of Rubidium (Rb)?

• 25°C

• 40°C

• 75°C

• 184°C

Answer explanation

Looking from top to bottom on the table, the melting point o each element gets lower.

When you also look at the atomic mass of each element from top to bottom, they increase.

Rb's atomic mass is between potassium and cesium.

This means the melting point of rubidium is between 63^o C and 29^o C.

The BEST answer is 40^oC.

Two different liquids are poured together in an open container. Bubbles begin to form. After the bubbling stops, it is determined that the total weight of the two liquids is less than before they were poured together. Which best describes this observation?

• Some of the atoms during the reaction escaped into the air.

• Some of the atoms during the reaction were destroyed.

• Some of the atoms during the reaction became heavier.

• Some of the atoms during the reaction changed to a different kind of atom.

Answer explanation

If you performed this chemical reaction is a sealed container (like a beaker with a tight lid), all of the atoms before the chemical reaction would still be there after the reaction because none can escape.

Therefore, the weight of the chemicals before is the same as after.

If you performed this chemical reaction is an open container (like a beaker without a lid), all of the atoms before the chemical reaction would not be there after the reaction because some can escape as a gas.

Therefore, the weight of the chemicals before is not the same as after because some atoms (weight) escape as a gas.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

This is a chemical reaction for the decomposition of carbonic acid into water and carbon dioxide.

H₂CO₃ → H₂O + CO₂

How does the reaction support the Law of Conservation of Mass?

• Several molecules of water are produced.

• The mass of carbon atoms is reduced during the reaction.

• The mass of the atoms in the reactant equals the mass of the atoms in the products.

• The mass of hydrogen atoms is the only thing that remains the same before and after the reaction.

Answer explanation

In the chemical reaction:

H₂CO₃ → H₂O + CO₂

Count the number of atoms of each element on

the REACTION side and then number of atoms of each element on the PRODUCT.

If they equal each other, then the Law of Conservation of Mass is proven.

Tags

NGSS.MS-PS1-5

Which is classified as an element?

• carbon dioxide

• iron

• vinegar

• water

Answer explanation

Carbon Dioxide has a formula of CO₂ (an exact ratio).

Iron is an element and has a symbol of Fe.

Vinegar has a chemical formula of CH ₃ COOH (an exact ratio).

Water has a chemical formula of H₂O (an exact ratio).

Which best describes the sequence of the elements in Period 5 of the periodic table?

• highly reactive gases, relatively nonreactive metals, metalloids, very nonreactive gases, nonreactive nonmetals

• highly reactive metals, relatively nonreactive metals, metalloids, reactive nonmetals, nonreactive gases

• nonreactive gases, metalloids, nonreactive metals, highly reactive metals, highly reactive gases

• nonreactive gases, nonreactive metals, highly reactive metals, metalloids, reactive nonmetals, reactive gases

Answer explanation

This question is asking about the reactivity increasing or decreasing between different elements in Period 5.

Look at the Periodic Table (attached image).

This chart tells you the reactivity changes across the Periodic Table.

The chart tells us the correct answer is:

highly reactive metals, relatively nonreactive metals, metalloids, reactive nonmetals, nonreactive gases

Tags

NGSS.MS-PS1-2

Which statement is true about a chemical reaction?

• The physical states of the atoms in the reactants determine the products.

• Some of the atoms in the reactants will be a part of the products.

• The number of atoms in the reactants determines the products.

• All of the atoms in the reactants will be equal to the atoms of the products.

Answer explanation

Matter cannot be created or destroyed.

In a chemical reaction the atoms change form but are still present on earth.

Tags

NGSS.MS-PS1-5

Chlorine has 7 valence electrons.

What group of elements will chlorine most readily bond?

• group 1

• group 2

• group 16

• group 18

Answer explanation

Chlorine has 7 valence electrons.

Look at it on the Periodic Table. Chlorine is in Group 17.

This means it only needs one more electron to be stable (Rule of 8).

Tags

NGSS.MS-PS1-1

NGSS.MS-PS1-2

Which is the best example of a chemical change?

• butter melting

• fireworks explode

• paper tearing

• water evaporating

Answer explanation

When butter melts it can be put back into a refridgerator and become a solid again - physical change

When fireworks explode they are no longer fireworks. It changed from a firework into light & sound energy and bits of ash. You cannot change it back into a firework - chemical change

Paper tearing, it is still paper but smaller pieces.

Water evaporating, it is still water but it is a gas now (like a cloud) physical change.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

Which chemical equation best represents the Law of Conservation of Mass?

• H + O → H₂O

• H₂ + O₂ → H₂O

• 2H₂ + O₂ → 2H₂O

• H₂ + O₂ → 2H₂O₂

Answer explanation

To solve this questions we must count atoms on each side of the arrow. The one that equals on each side is the correct answer.

H + O → H₂O

2 → 3 wrong answer

H₂ + O₂ → H₂O

4 → 3 wrong answer

2H₂ + O₂ → 2H₂O

6 → 6 correct answer

H₂ + O₂ → 2H₂O₂

4 → 8 wrong answer

Tags

NGSS.MS-PS1-5