Chapter 15: Problem 124
Consider a solution formed by mixing 50.0 \(\mathrm{mL}\) of 0.100 \(\mathrm{M}\) \(\mathrm{H}_{2} \mathrm{SO}_{4}, 30.0 \mathrm{mL}\) of 0.100 \(\mathrm{M}\) HOCl, 25.0 \(\mathrm{mL}\) of 0.200 \(\mathrm{M}\) \(\mathrm{NaOH}, 25.0 \mathrm{mL}\) of \(0.100 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2},\) and 10.0 \(\mathrm{mL}\) of 0.150 \(M \mathrm{KOH}\) . Calculate the \(\mathrm{pH}\) of this solution.
Short Answer
Step by step solution
Calculation of moles of each reactant
Water as a solvent and total volume
Neutralization reactions
Calculation of final concentrations
Calculation of pH
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Neutralization Reactions
- Strong acids and strong bases: Fully dissociate in water, leading to complete neutralization. For example, \(\ce{H2SO4}\) (sulfuric acid) neutralizes with \(\ce{NaOH}\) or \(\ce{Ba(OH)2}\).
- Weak acids and strong bases: The acid does not completely ionize in solution. With \(\ce{HOCl}\) being a weak acid, it only partially neutralizes until a strong base like \(\ce{KOH}\) completes the reaction.
Acid-Base Chemistry
- Acid: A substance that donates protons (\(\ce{H^+}\)). \(\ce{H2SO4}\) is a strong acid that donates protons easily, making it highly reactive in neutralization reactions.
- Base: Accepts protons. Compounds like \(\ce{NaOH}\) release hydroxide ions (\(\ce{OH^-}\)) in solution. Strong bases dissociate completely in water, facilitating neutralization reactions.
- pH Scale: Ranges from 0 to 14, describing how acidic or basic a solution is:
- pH < 7: Acidic
- pH = 7: Neutral
- pH > 7: Basic
Mole Calculations
- Moles: A mole is a standard unit in chemistry that quantifies the amount of substance. It's equivalent to Avogadro's number, \(6.022 \times 10^{23}\) atoms or molecules.
- Initial Calculations: For the given exercise, we used the formula: \\[molarity (M) = \frac{moles}{volume (L)}\] We calculated moles by multiplying the molarity by the volume in litres of each solution (converted from milliliters). For example, \(50 \text{ mL of } 0.100 \text{ M } \ce{H2SO4}\Rightarrow 5000 \text{ mmol}\).
Aqueous Solution Chemistry
- Solvent properties of water: Water is known as the "universal solvent" due to its ability to dissolve a wide range of substances, particularly ionic compounds and polar molecules.
- Dissociation: When acids or bases dissolve in water, they dissociate into ions. For example, \(\ce{NaOH}\) dissociates into \(\ce{Na^+}\) and \(\ce{OH^-}\) ions, contributing to the basicity of the solution.
- Volume and Concentration Calculations: Given total volume (140 mL in the example), the concentration of ions post-reaction was important for pH calculations. Remaining \(\ce{OH^-}\) ions led to a basic pH, as observed in the final solution of the given problem.