Chapter 13 Question Help

Question

 a) Write and balance the reaction for the complete combustion of heptane, C₇H₁₆. Explain the principle of how you chose the coefficients to balance the reaction.



b) What would be the molarity of a solution in which 1.0 mole of KOH is dissolved in enough water to make 0.25 L of solution. Show your work.

Answer 1

For combustion reactions, take the hydrocarbon and add oxygen (O₂) as the reactants and the products are always carbon dioxide (CO₂) and water (H₂O). So the UNBALANCED equation would be:

C₇H₁₆ + O₂ → CO₂ + H₂O

Balancing the carbons gives:

C₇H₁₆ + O₂ → 7CO₂ + H₂O

Balancing the hydrogens gives:

C₇H₁₆ + O₂ → 7CO₂ + 8H₂O

Then balancing the oxygens gives:

C₇H₁₆ + 11O₂ → 7CO₂ + 8H₂O

which is the BALANCED chemical reaction equation.

For problem 2, molarity is the moles of solute to liters of solvent so 1/0.25 = 4 meaning the molarity of the solution is 4M