8th Grade Science Q1 Review

The diagram above is a model of a molecule of methane. What is the formula for methane?

• CH₈
• C₈H₄
• CH₄
• C₈H₈

2Mg + O₂ → 2MgO
In the equation above, how many atoms are in the oxygen molecule?

• 2
• 0
• 1
• 3

The formula below represents the most common carbohydrate known as Glucose. Glucose is synthesized by Chlorophyll in plants as they use carbon dioxide from the air and sunlight as an energy source during the process of photosynthesis.
C₆H₁₂O_{6
What information can be determined from the chemical formula?}

• The structural arrangement of the atoms in a glucose molecule.
• The color of a glucose molecule.
• The size of a glucose molecule.
• The number of atoms of each element in a glucose molecule.

Which of the following formulas contain the same number of oxygen atoms?
1. Mg(NO)₂
2. NH₄NO₂
3. Ca(ClO₂)₂
4. Co(NO₃)₂

• Formulas 1 and 2
• Formulas 2 and 4
• Formulas 1, 2, and 3
• Formulas 1, 2, and 4

How many atoms are in one molecule of baking soda, NaHCO₃?

• 4
• 5
• 3
• 6

A student placed 2 grams of baking soda in a balloon, and 100 mL of vinegar in a Erlyenmeyer flask. After stretching the balloon across the neck of the flask, the student raised it to drop the baking soda into the flask. He immediately observed foaming bubbles in the flask and the balloon began to expand. The student concluded that -

• Only a physical change was occuring
• The baking soda and vinegar were products of a chemical reaction
• The gas was oxygen
• The bubbles indicated that a chemical change was occuring

During an investigation, students dropped a tarnished penny into a solution a acetic acid and sodium chloride. Tiny bubbles formed around the penny, and the penny was less tarnished after two minutes of soaking in the acetic acid and sodium chloride solution. The student inferred that a chemical reaction occured. What evidence supports the students' inference?

• The penny experienced a color change, and a gas was produced.
• The penny experienced a color change, and a precipitate was formed.
• The penny experienced a color change and is in a new state of matter.
• The penny experienced a color change and produced light.

Students in a science lab conducted an investigation. Students recored the following observations.
Substance 1 produced light when burned.
Substance 2 dissolved in water.
Substance 3 melted at 100⁰ C.
Substance 4 formed a precipitate.
Which substances produced a chemical change?

• Substances 1 and 2
• Substances 1 and 3
• Substances 1 and 4
• Substances 2 and 3

Which of the following equations follows the law of conservation of mass?

• 3H₂O → 3H₂ + 3O₂
• C₂H₄ + 3O₂ → 2CO₂ + 2H₂O
• C + 4H₂ → CH₄
• 2Na + Cl → NaCl

How can a student determine that a chemical reaction demonstrates the law of conservation of mass?

• Students can compare the products and reactants to determine if the same molecules are present before and after the reaction.
• Students can compare the products and reactants to determine if the same number of atoms of each element are present before and after the reaction.
• Students can compare the products and reactants to determine if the same number of molecules are present before and after the reaction.
• Students can compare the products and reactants to determine if the same elements are present before and after the reaction.