How to calculate the resultant Ph values when you mix different bases with acids. Give specific examples for the following: weak base with strong acid, weak base with weak acid, strong base with strong acid, strong base with weak acid
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When mixing acids and bases, calculating the resulting pH requires understanding the strength of each component and their relative amounts. The process involves determining the moles of each reactant, identifying the limiting reactant, calculating what remains after the reaction, and determining the final concentrations. The pH calculation method depends on whether you're dealing with excess strong acid or base, a buffer solution, or a salt solution. Let's explore specific examples for different combinations of acids and bases.
Let's examine our first example: mixing a weak base with a strong acid. When we combine 100 milliliters of 0.1 molar ammonia, a weak base, with 50 milliliters of 0.1 molar hydrochloric acid, a strong acid, we first calculate the initial moles of each reactant. We have 0.01 moles of ammonia and 0.005 moles of HCl. The reaction produces ammonium ions and chloride ions. Since HCl is limiting, we'll have 0.005 moles of ammonia remaining and 0.005 moles of ammonium ion formed. In the final volume of 150 milliliters, both ammonia and ammonium ion concentrations are 0.0333 molar. This creates a buffer solution with a pH of 9.26, calculated using the Henderson-Hasselbalch equation.
Our second example involves mixing a weak acid with a weak base. When we combine 100 milliliters of 0.1 molar acetic acid with 100 milliliters of 0.1 molar ammonia, we have equal moles of each reactant. The reaction produces acetate ions and ammonium ions. Since we have equal moles of acid and base, they react completely to form 0.01 moles of each ion. In the final volume of 200 milliliters, both ions have a concentration of 0.05 molar. Both ions undergo hydrolysis in water. The acetate ion acts as a weak base, while the ammonium ion acts as a weak acid. Interestingly, in this case, the acid dissociation constant of ammonium equals the base dissociation constant of acetate. This means the hydrolysis of each ion produces equal amounts of hydrogen and hydroxide ions, resulting in a neutral solution with a pH of 7.0.