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Lecture 4

CHEM 123L Lecture 4: Introduction

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Department
Chemistry
Course
CHEM 123L
Professor
Sue Stathopulos
Semester
Winter

Description
Introduction: This experiment was conducted to use pH for titration of acids and bases and to understand buffers. PH is a unit to measure the acidity of a solution, it can be defined by the + + equation pH= log (H ), where H is the concentration measured in molL. We use a pH meter to measure the electromotive force using the solution as an electrolyte. An acid in terms of BronstedLowry definition means the ability of an acid to give up protons, strong acid give up protons easily while weak acid do not. An acid base pair are inversely proportional which means the stronger the conjugate base the stronger the acid, and the other way around. The equilibrium constant for a weak acid in water is K . A buffer solution resists changes in the pH, the buffer a creates a system that shifts the equilibrium between conjugate acidbase pair. When we + theoretically apply buffers we use two equations K = [H ] [a ] [HA], the K stands for tae + equilibrium constant, the [H ] [A ] are concentrations of the product over the reactants [HA]. The second equation is pH= pK +log[Aa] [HA], pK stands forathe measure of strength of acid, and [A ] [HA] stands for the buffer ratio (concentration ratio). The pH of a buffer ratio is directly dependent of the logarithm of the buffer ratio, it is directly related so when it increases as the ratio increases and the other way around. When considering bases we also use the equation pOH=log[OH ] , also we use the equations pH+pOH= 14, 14 is a standard constant. The 14 equation K K a Kb=110w, K is the equiaibrium constant for an acid while K is the b 14 equilibrium constant for a base, which is equal to the constant K =110 . Twe process of titrations happen by neutralizing an unknown acid or base with a specific measured quantity of acid or base. The purpose of this experiment is the discover the concentration of the unknown acid or base, and to use diluted and undiluted buffers to minimize the change in pH when acid or base is added to the solution.
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