Consider the unbalanced chemical equation: C_2H_5OH + O_2 → CO_2 + H_2O. What is the total number of oxygen atoms present on the left-hand side of this equation?

• A. 3
• B. 5
• C. 4
• D. 2

Answer: (A)

Verified step by step guidance

1. Identify the chemical species on the left-hand side of the equation: ethanol (C_2H_5OH) and oxygen gas (O_2).
2. Determine the number of oxygen atoms in one molecule of ethanol (C_2H_5OH). Since there is one oxygen atom in the hydroxyl group (-OH), ethanol contains 1 oxygen atom per molecule.
3. Determine the number of oxygen atoms in one molecule of oxygen gas (O_2). Since O_2 is diatomic, it contains 2 oxygen atoms per molecule.
4. Add the oxygen atoms from both reactants on the left-hand side: the oxygen atoms from ethanol plus the oxygen atoms from oxygen gas.
5. Express the total number of oxygen atoms on the left side as the sum: 1 (from C_2H_5OH) + 2 (from O_2) = 3 oxygen atoms.