CHEM 106/320: Fundamentals of Analytical Chemistry Erika Portero CHEM 400

Goals and Objectives of CHEM 160/320 Data Analysis and Statistics Solution Equilibria Emphasis on acid/base equilibria Electrochemistry Spectroscopy Emphasis on spectrophotometry and fluorescence

Data Analysis and Statistics Accuracy: Relationship between a measured value and the actual value. Precision: Reproducibility of the measurement . Average or Mean: The sum of all the measured values divided by the number of measurements. Range: The difference between the lowest and highest values (in the data set). Mode: Most frequently occurring number found in a data set. Standard Deviation: measurement used to quantify the amount of variation or dispersion of a set of data values

Data Analysis and Statistics Gaussian Distribution It is a two parameter function: µ, the mean and σ, the standard deviation.

Data Analysis and Statistics Confidence interval Ex. 95% confidence interval – “ we are 95% confident that the true mean lies within the confidence interval” T test – tests the difference of two averages P sig – Probability that the difference in the data set is real. If P sig > 0.95 then significantly different P insig – Probability that the difference in two sets is due to random error t = x ± ts , |x 1 – x 2| t calc = √n √s 12/ n 1+ s 2 2 /n 2

Data Analysis and Statistics F test = tests the difference of two standard deviations F calc = If F calc > F table, then the standard deviations are significantly different If F calc < F table, then calculate S pooled and t calc If t calc is > t tab, then the means are significantly different S21 S22

Solutions and Dilutions Making Solutions (Rules ): Graduated cylinders are considerably less accurate and precise than glass transferring pipettes Larger glassware has relative less uncertainty Multiple dilutions introduce more error Glassware is designed to hold a specific volume only at a stated temperature Dilutions C1V1=C2V2

The importance of Ionic Strength Solubility – the amount of solid that dissolves in a solution , expressed in units if mol/L . Ksp – Solubility product constant aA(s)⇌cC(aq)+dD(aq) Ksp=[C]c[D] d Ionic Strength – Measure of the total ion concentration of a solution. It is given the symbol µ and has units of molarity. Activity coefficient, β ,that changes with ionic strength Ksp=βc[C]cβd[D] d

The importance of Ionic Strength

Multiple Equilibria AgCN(s) Ag+ + CN- Ksp = 2.19 X 10 E-16 = [Ag+ ][CN-] As the pH of the solution decreases, then HCN is more abundant. CN- is a base. In a more acidic environment, reacts with H + to form HCN This is an example of competing reactions and the effect pH has on these reactions

Acid/Base Equilibria When pH = pKa , the same amount of both ions co- exist at the same time Example : H2CO3, Carbonic acid

Electrochemistry Galvanic Cell – uses spontaneous chemical reactions to generate electricity Oxidation : Loss of electron and Reduction : Gain of electron Chemistry and Electricity: Electric charge q=n F , F= 9.649 x10E4 C/mol Free energy and electric potential ∆G = -nFE