Experiment+2+-+Preparation+of+Buffers+and+Salt+Solutions

=**Experiment 2 - Preparation of Buffers and Salt Solutions** =


 * ~ Objectives of Experiment ||~ Reading in//Boyer// ||~ Principle of Experiment ||
 * = To properly prepare buffers and salt solutions ||= Chapter 3: pages 55-69 ||= Since only slight changes in pH cause marked alterations in cell physiology, the regulation of hydrogen ion concentration is a vital cell function. The cell's most immediate protection from the effects of excess acid or base is provided by its buffer systems. Use of the Henderson-Hasselbalch equation in the preparation of a buffer of known composition will permit you to check the calculated and observed pH in most cases. Some buffers (such as phosphate buffers) do not obey this equation however. This lab involves the making of a Tris Buffer using a Tris base mixed with HCl. (Wikipedia Link) ||

**Important Things to Remember from this lab:**

 * How to standardize a pH meter:
 * 1) Standardize to two types of buffers, rinsing in between each standardization.
 * 2) Return electrode to storage buffer for use later
 * ===Buffer Calculations===
 * Buffer calculations can be divided into three parts (not all three parts are necessary for every problem, but the exam will most likely contain the most complicated version)
 * A) Buffer Concentration is the sum of the concentration of the weak acid and its conjugate base:
 * B) Henderson-Hasselbalch Equation:
 * C) The calculation of the amount of weak acid or conjugate base needed to make these concentrations is the third step. This step varies depending on how the buffer is to be made
 * **If weighing solids:**


 * **If using a stock solution of known concentration:**


 * **Sample Problem**
 * **//Calculate the weight of Tris (121.1 g/mol) and TrisHCl (157.6 g/mol, pKa=8.30) needed to prepare 2.00L of 0.500M Tris buffer, pH = 8.70//**
 * We know the buffer is made of the weak acid and the conjugate base, so then:
 * Calculate the concentration of the acid and base from Henderson-Hasselbalch:

> 1. Calculate the weight of Tris required: > > > 2. Add this to ~80mL RO water in a 250mL beaker (Why? 80mL is <100mL, so there is room to accurately titrate/pH) > 3. Titrate solution to pH 8.00 by adding 1.00M HCl slowly > 4. Add water until buffer is at 100mL
 * **Now just solve for weight via the equations above**
 * Below is a sample of how to prepare 100. mL of 0.100 M Tris Buffer @pH 8.00