Counting Atoms and Chemical Reactions

Serotonin is a chemical substance that acts as a neurotransmitter. It helps relay messages in the human brain. The formula for one molecule of serotonin is shown below.

C₁₀H₁₂N₂O

How many atoms in all are in a molecule of serotonin?

• 1

• 4

• 25

• 24

Tags

NGSS.MS-PS1-1

Identify the reactants in the chemical equation below.

• NaCl and H₂O

• HCl and NaCl

• NaOH and HCl

• HCl and H₂O

Which of the following chemical equations is balanced?

• 3Na + Cl₂ --> 3NaCl

• CO₂ + H₂O --> C₆H₁₂O₅ + O₂

• 2H₂O + O₂ --> 2H₂O + OH

• 3AgBr + GaPO₄ --> Ag₃PO₄ + GaBr₃

Tags

NGSS.MS-PS1-5

How many copper (Cu) atoms are there in the Cu(NO₃)₂ molecule below?

• 6

• 1

• 5

• 2

Tags

NGSS.MS-PS1-1

Which of the following is the CORRECT number of atoms?

• calcium= 2 atoms

  oxygen = 1 atom

  hydrogen= 1 atom

• calcium = 1 atom

  Oxygen= 2 atoms

  hydrogen = 2 atoms

• copper = 1 atom

  oxygen = 1 atom

  hydrogen= 2 atoms

Tags

NGSS.MS-PS1-1

How many oxygen atoms are in this chemical formula?

• 6 oxygen atoms

• 2 oxygen atoms

• 3 oxygen atoms

• 4 oxygen atoms

Answer explanation

Remember, the coefficient tells you how many molecules there are, and the subscript tells you how many atoms there are per molecule!

Tags

formulas

How many hydrogen atoms are in this chemical formula:

• 4 hydrogen atoms

• 1 hydrogen atom

• 2 hydrogen atoms

• 3 hydrogen atoms

Tags

NGSS.MS-PS1-1

Count the atoms

• 2

• 6

• 15

• 8

• 4

Tags

NGSS.MS-PS1-1

A student mixes two solutions (liquids), planning to produce carbon dioxide. Which of the following is the BEST evidence that a chemical reactions as taken place and carbon dioxide (gas) has been formed.

• Color Change

• Temperature Change

• Formation of bubbles

• formation of a solid

Tags

NGSS.MS-PS1-2

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

• 12

• 4

• 6

• 5

Tags

NGSS.MS-PS1-1