CHEM 201. Quantitative Analysis CHEM 201. Course Objectives. What do you need? Textbook (bcs.whfreeman.com/qca7e)

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1 CHEM 201 Lecture Laboratory CHEM : T,Th: 11:40 a.m. 12:55 p.m., SH-C136 02: T,Th 8:00 10:50 a.m., PS 824 (Dr. Santillan) 03: T,Th 1:30 4:20 p.m., PS 824 (Dr. Wen) Quantitative Analysis Lecture & Laboratory: Dr. Xin Wen, PS 620 Office hours: TR 4:20 5:10 pm, F 4-5 pm phone (323) ; xwen3@calstatela.edu Laboratory: Dr. Gregorio Santillan, PS 610 Office hours: MW 12-1pm, TR 1:30-2:30 pm, F 12:30-1:30 pm phone: (323) gsantil@calstatela.edu What do you need? Textbook (bcs.whfreeman.com/qca7e) Quantitative Chemical Analysis, 7th Edition, D.C. Harris, W.H. Freeman and Company, New York, 2007, Laboratory Manual Laboratory Notebook Gloves and Safety Glasses Calculator Access to a computer with Excel and a printer Course Objectives The main objective of CHEM 201 is to develop students understanding of the principles of analytical chemistry. More detailed objectives include: Tentative Lecture Schedule Tentative Lecture Schedule 1

2 Point Distributions for Grades STUDENTS WITH PHYSICAL OR LEARNING DISABILITES: Students with Disabilities Act are fully supported. Appropriate accommodation to any student with a disability registered with the Office of Students with Disabilities (OSD) who needs and requests accommodation. The OSD may be contacted to verify the presence of a disability and confirm that accommodation is necessary. Students with special needs are encouraged to inform the instructors as soon as possible to ensure that those needs are met in a timely manner. Analytical Chemistry Analytical chemistry deals with methods for determining the chemical composition of samples of matter. Qualitative analysis Information about the identity of atomic or molecular species or the functional groups in the sample (What). Quantitative analysis - Numerical information as to the relative amount of one or more of these components (How much). Classical Quantitative Analysis gravimetric volumetric (or titrimetric) Instrumental electroanalytical spectroscopic chromatographic Comparison of Different Analytical Methods Analytical Terminology heterogeneous homogeneous Analyte: the sample being analyzed 2

3 Method Classification of Analytical Methods According to Size of Sample Sample Weight (mg) Meso >100 >100 Semimicro Micro 1-10 <50 Sample Volume (µl) Constituents Method Constituents major >1% minor 0.1-1% trace <0.1% Ultramicro <1 Steps in a Chemical Analysis Sampling: representative Sample Preparation Analyzing the Sample Interpreting the Results Analyzing the Sample Step 1. Obtain a representative bulk sample. Step 2. Extract from the bulk sample a smaller, homogeneous laboratory sample. Step 3. Convert the laboratory sample into a form suitable for analysis, a process that usually involves dissolving the sample. Analyzing the Sample Step 4. Remove or mask species that will interfere with the chemical analysis. Step 5. Measure the concentration of the analyte in several aliquots. Step 6. Interpret your results and draw conclusions. Safe, Ethical Handling of Chemicals and Waste The primary safety rule is not to do something that you (or your instructor or supervisor) consider to be dangerous. proper clothing food & drink in lab NO WAY!!!!! disposal of solids and liquids always ask instructor for the proper procedure Calibration Curve/Standard Curve 3

4 Eye Protection at all Times Chemical hazards label (NFPA) LABEL ALL CONTAINERS Lab Notebooks Laboratory data will be recorded directly in the notebook. Entries will be made using a ballpoint pen. Be complete, accurate documents of the experiment and be understandable can be served as a legal document for your work Format refers to the syllabus SI Prefixes especially useful in this course mega M 10 6 kilo k 10 3 centi c 10-2 milli m 10-3 micro 10-6 nano n 10-9 pico p solute Solution Terminology solvent aqueous solution (the solvent is water) Liter atomic weight molecular weight (or formula weight) Molarity: Molality: Concentration Units = = = = 4

5 Useful Algebraic Relationships Wt of A ( g) # of mol A = Fw of A ( g / mol) Or # of mol A = Vol. of A ( L) M of A in the soln. ( mol / L) Preparing Solutions EXAMPLE: Describe the preparation of 1.00 L of M NaOH solution (f.w ) from reagent grade solid. Wt of A ( mg) # of mmol A = Fw of A ( g / mol) Or # of mmol A = Vol.of A ( ml) M of A in the soln.( mmol / ml) EXAMPLE: Describe the preparation of 1.00 L of M NaOH solution (f.w ) from reagent grade solid. (1.00 L soln)(0.100 mol NaOH) # of mol NaOH = (1 L soln) EXAMPLE: Describe the preparation of 1.00 L of M NaOH solution (f.w ) from reagent grade solid. (1.00)(0.100 mol NaOH) # of mol NaOH = (1) EXAMPLE: Describe the preparation of 1.00 L of M NaOH solution (f.w ) from reagent grade solid. (1.00)(0.100 mol)(40.00g NaOH) # g NaOH = (1) (1 mol) EXAMPLE: Describe the preparation of 1.00 L of M NaOH solution (f.w ) from reagent grade solid. (1.00)(0.100)(40.00g NaOH) # g NaOH = (1) (1) 5

6 EXAMPLE: Describe the preparation of 1.00 L of M NaOH solution (f.w ) from reagent grade solid. (1.00)(0.100)(40.00g NaOH) # g NaOH = (1) (1) = 4.00 g NaOH EXAMPLE: Describe the preparation of 1.00 L of M NaOH solution (f.w ) from reagent grade solid. (1.00)(0.100)(40.00g NaOH) # g NaOH = (1) (1) = 4.00 g NaOH Weigh 4.00 g of NaOH, transfer to a 1.00 L volumetric flask, and dilute to the line. Dilutions #moles solute in conc. soln equals #moles solut in dil. soln Examples How can one prepare 500 ml 1.0 M HCl solution from concentrated HCl solution (12M)? therefore M conc V conc = M dil V dil Percent Composition wt of a solute w - w% = wt of solution vol of a solute v - v% = vol of solution wt of a solute w - v% = vol of solution Examples- Converting weight percent into Molarity Calculate the molarity of concentrated sulfuric acid (w-w% = %, Density = 1.84 g/ml)? P g 98 g/mol 100g 1.84 g/ml 10 ml/l = M 6

7 w-w% Acetic Acid, Glacial, 100% 17 M Ammonia, 29% 15 M Hydrochloric Acid, 37%, 12 M Nitric Acid, 70%, 16 M Phosphoric Acid, 85%, 15 M Perchloric Acid, 71%, 11 M Sodium Hydroxide, 50%, 19 M Sulfuric Acid, 96%, 18 M (36 N) Solids: Parts per Million (ppm) Times 10 6 if use same units for solute and solution; mg/kg or g/g Water solution (mg/l or g/ml) : wt of a solute ppm = 10 wt of solution ppm = wt of a solute in mg (or vol. of µ g) water in L (or ml) 6 Since the solute is trivial, can be considered as solution Parts per Billion (ppb) Examples- Converting ppm into Molarity wt of a solute ppb = 10 wt of solution ppb = wt of a solute vol. of 9 in µ g water in L How much 0.01 M EDTA solution need to titrate 100 ppm CaCO 3 containing water (1 liter)? (FW of CaCO 3 =100; EDTA:Ca 2+ =1:1) 100 mg/l 1L g/mol 3-5 x = 10 L = 0.01 ml = 10µ L g/mg = 0.01 mol/l x L Examples- Dilutions using ppm You prepare a Cu stock solution with a concentration of ppm. You need to now prepare a standard solution with a concentration of 7.5 ppm in a 25 ml volumetric flask. How do you prepare the standard? C 1 = ppm V 1 =? C 2 = 7.5 ppm V 2 = 25 ml = = = 7

8 Analytical Balance Analytical Balance Analytical Balance Unknown samples & primary standard materials Tare: the mass of the empty vessel, set to 0 Weighing-by-difference (esp. hygroscopic reagents) Weigh bottle + Reagent (1) Remove necessary amount of reagent (2) Weigh bottle + Remaining reagent (3) Mass of reagent removed = (1) (2) Common Sources of Error Non-leveled balance Improper sample handling including without cooling the sample completely Finger prints Unclosed balance cover Buoyancy-induced errors (inherent) m'(1 - d a /d w ) m = (1 - d a /d) Buoyancy where m => true mass of object being weighed m'=> mass read by balance d a => density of air d w => density of the calibration weight d => density of object being weighed 8

9 Buoyancy Correction Buret reading tips: Burets 1. Allow time for draining. 2. Read the bottom of the concave meniscus. 3. Avoid parallax. 4. Account for the thickness of the marking lines in your readings. Air Bubble in Tip Reading a Buret Volumetric Flasks sizes: 5 ml to 2 L TC 20 o C => to contain at 20 o C TD 20 o C => to deliver at 20 o C 9

10 Volumetric Flasks when to use volumetric flasks to make standard solution where an analytical balance was used to weigh the solid to be dissolved to make quantitative dilutions using volumetric pipets Volumetric Flasks when not to use volumetric flasks to make solutions where an analytical balance is not used for weighing the sample (exception to this would be for a large size sample in a large flask) Volumetric Flasks Proper position of the meniscus Volumetric Flasks At the center of the ellipse formed by the front and back of the calibration mark when viewed from above and below Pipets Transfer & Measuring 10

11 Pipets and Syringes Micropipets Using a Transfer Pipet NEVER PIPET BY MOUTH use a bulb or pipet aid of some description NEVER BLOW OUT LAST DROP designed to retain some liquid in tip Using a Syringe used to deliver a small volume Other Volume Tools graduated cylinder use for less accurate volume measurements beakers or flasks inacurrate graduations (usually + 5%) RULE OF THUMB Filtration use a set of tools for an analysis which will keep a consistent number of significant figures 11

12 Folding Filter Paper Filtration Drying protecting sample while in oven Desiccators Drying Desiccants 12