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Version 2012 Updated on 022412 Copyright © All rights reserved Dong-Sun Lee, Prof., Ph.D. Chemistry, Seoul Women’s University Chapter 2 Chemicals and Apparatus.

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Presentation on theme: "Version 2012 Updated on 022412 Copyright © All rights reserved Dong-Sun Lee, Prof., Ph.D. Chemistry, Seoul Women’s University Chapter 2 Chemicals and Apparatus."— Presentation transcript:

1 Version 2012 Updated on Copyright © All rights reserved Dong-Sun Lee, Prof., Ph.D. Chemistry, Seoul Women’s University Chapter 2 Chemicals and Apparatus

2 Classification of commercial chemicals 1) Technical or commercial grade Not use in analytical work, but cleaning solution. 2) USP grade : United States Pharmacopoeia The specifications are designed to limit impurities that are physiological hazards 3) Reagent grade Minimum specifications of the Reagent Chemical Committee of the American Chemical Society 4) Primary standard grade / Reference standards 5) Special purpose reagents Spectroscopic, chromatographic etc.

3 Primary standard ★★★ - Definition by the IUPAC(1978) : a substance of high purity which, by stoichiometric reaction, is used to establish the reacting strength of a titrant, or which itself can be used to prepare a titrant solution of accurately known concentration. - Requirements for a primary standard : 1) High purity (99.9% or better) 4) Ready availability 2) Stability in air 5) Reasonable solubility 3) Absence of hydrate water 6) Reasonable large formula weight - Types of primary standards : 1) Reference material(RM) ; used mainly for the calibration 2) High purity substance = chemical standard 3) Certified reference material (CRM) ; by NIST, etc. - Working or secondary standards

4 Primary standard materials Certified reference materials Reference materials Inorganic Organic Quality of life Biological- clinical labs Industry Physical & technical properties Ferrous Nonferrous RMs, CRMs, primary standard materials and their main application fields

5 Types of analytical standards, and relationships between them and traceability of physical, chemical and analytical standards. Chemical standards( 12 C, N) Analytical standards Primary standards Secondary standards Reference materials Chemical standards (pure substance) CRM Physical standards (kg) International Prototype Kilogram: IPK: Kilogram Standard: Le Gran K: 1 kg

6 Table Selected pure chemical standards used in titrimetric analysis (at least 99.9% purity) ★★★ Type of titration Standard Acid-base Potassium hydrogen phthalate Sulfanilic acid, Benzoic acid Sodium carbonate, Borax Complexometric Calcium carbonate, Magnesium, Zinc, EDTA Precipitation Silver, Silver nitrate, Sodium chloride Redox Potassium iodate, Potassium dichromate, Sodium oxalate, Arsenic oxide

7 Rules for Handling Reagents and Solutions 1.Select the best grade of chemical / pick the smallest bottle 2.Replace the top of every container immediately after removal of the reagent 3.Hold the stoppers of reagent bottles between your fingers; never set a stopper on a desk 4. Never return any excess reagent to a bottle. 5. Never insert spatulas, spoons, or knives into a bottle that contains a solid chemical. Pour out the desired quantity. 6. Keep the reagent shelf and the lab balance clean and neat. 7. Observe local regulations concerning the disposal of surplus reagents and solutions

8 Safe handling of chemicals and waste - Material Safety Data Sheet (MSDS) : - Primary safety rule is not to do something that you consider to be dangerous. - Goggles or safety glasses with side shields are necessary at all times in every laboratory to protect you from flying liquids and glass. - Food is never eaten in the lab. - Organic solvents and conc. acids that produce harmful fumes should be handled only in a fume hood. The purpose of a fume hood is to reduce levels of pollutants. - Solid or liquid spills should be cleaned up immediately to prevent accidental contact by the next person who comes along. - Chemical spills on your skin usually are treated first with water. Rubber gloves are recommended to protect your hands. - Proper chemical storage minimizes fire and explosion hazards and human contact with vapors. - Preservation of a habitable environment on our planet demands that we minimize waste production and responsibly dispose of the waste.

9 Goggle All vessels should have labels that indicate what they contain. Safety equipment and hazardous operations are prominently labeled. (D.C. Harris, Quantitative Chemical Analysis, 4 th ed., Freeman, 1995, p. 20)

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11 Arrangement for the evaporation of a liquid Bumping is sudden, often violent boiling that tends to spatter solution out of its container. Wet ashing is the oxidation of the organic constituents of a sample with oxidizing reagents such as nitric acid, sulfuric acid, hydrogen peroxide, aqueous bromine, or a combination of these reagents in a fume- hood.

12 Analytical Balance Readability: An analytical balance measures masses to within g. Use these balances when you need this high degree of precision. Capacity: 100 ~ 220 g ★★★

13 Types of balances and principles of operation Types of balance Principles of operation Mechanical balance Equal-arm, double pan Symmetric lever, Triple beam dial Pendulum Dial Unequal-arm, single pan Substitution Electronic balance Top loading Load-transfer mechanism, Single pan analytical electromagnetic force Microbalance compensation

14 Chemical Balance Definition of terms Mass : An invariant measure of the quantity of matter in an object. Mass is constant. Weight : The force of attraction exerted between an object and the earth. Weight(w) equals mass(m) times the gravitational attraction (g= cm/s 2 ). w = g m Balance : an instrument for weighing. The word derived from the Latin bilanx =having two pans. “scales” = old English, meaning dishes. Capacity : the largest load on one pan for which the balance can be brought to equilibrium Sensitivity : the smallest increment of mass that can be measured

15 Readability ; Accurate, repeatable deflection at the smallest unit of measurement Precision (standard deviation); Degree of agreement of repeated measurement of the same object. Accuracy ; The agreement between the result of measurement and the true value of the quantity measured. Resolution : number of scale division; n = Max / d Tare ; the mass of the empty vessel Weights, Reference masses ; The international prototype kilogram is a mass of platinum-iridium alloy made in The International Bureau of Weights and Measures (Paris) An ordinary set of analytical weights 100, 50, 30, 20, 10, 5, 3, 2, 1 g , 50-10, 5, 3, 2, 1 mg

16 Role of analytical balance : accuracy of analytical results depends on weight.

17 Table Classification of balances Type Reading to Typical capacity(Max) Ultramicroanalytical 0.1  g 3g Microanalytical 1  g 3g Semimicroanalytical 0.01mg 30g Macroanalytical 0.1 mg 100g~200g Precision  1mg 160g~60kg Rough weighing 0.01 g 350 g 0.1g 3500g 0.1g 6kg

18 Weighing accurately = reading unit 0.1 mg Vernier : A short auxillary scale placed along the main instrument scale to permit accurate fractional reading of the least main division of the main scale, invented by Pierre Vernier about The vernier scale is graduated in one or both directions from the fiducial(index) mark in numbered divisions, which are fractionally shorter than those on the main scale. The position of the fiducial mark( the zero mark of the vernier scale) between divisions on the main scale is indicated by the number of graduation on the vernier scale which lines up exactly with a graduation on the main scale. d m = l/n d v = (l – d m ) / n

19 Vernier caliper (G.S. Coyne, The Laboratory Handbook, Prentice Hall, 1992, p.68-69)

20 Vernier scale each division on the Vernier scale is 0·9mm Coincidence d’ d x 7 x = d – d’ = 7 (1) mm – 7 (0.9) mm = 7 (1-0.9) mm = 0.7 mm Reading : 3.17 cm = 31.7 mm Main scale each division on the main scale is 1 mm Index line

21 0.25 mm Reading: mm = cm

22 inside diameter jaws outside diameter jaws locking screw slide piece with index scale (Vernier scale) main scale depth probe

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24 Vernier scales. Left, Direct (reading 3.6). Right, retrograde (reading 12.7) Source: McGraw-Hill Encyclopedia of Science & Technology, Vol.19, p Vernier scales of chemical balance ( reading weight = g). Vernier scales of dial balance

25 Certified analytical weights Class M analytical weights are high precision standards used as reference standards for analytical work. Gram weights are normally made of brass and plated with gold, platinum or rhodium. Class S weights are precise scientific working standards that are chiefly used for calibration of other weights. Class S-1 weights are routine analytical weights for general use. Class P weights (formerly denoted by S-2 ) are rough weights. Class J weights (up to 50mg) are used on microbalances.

26 Table Tolerances of analytical weights provided by the NIST Tolerance (mg) Weight mass Class M Class S Class S-1 Class P 1 kg g g g g g g mg mg mg mg mg mg mg All class J weights have a tolerance of 0.003mg Cf. Standard specification for laboratory weights and precision standards (1990 Annual Book of ASTM Standards) Classification Types I & II Grades S, O, P, and Q Classes 1, 2, 3, 4, 5, 6

27 표준 분동의 허용 오차 : American Society of Testing & Measurement(ASTM E617)

28 ( 왼쪽 ) 백금 (90%)- 이리듐 (10%) 합금으로 만들어진 국제 킬로그램 원기 (International Prototype Kilogram: IPK: Kilogram Standard: Le Gran K: 1 kg) 세브르 (Sevres) 에 위치한 국제도량형국 (BIPM: Bureau International des Poids et Mesures: International Bureau of Weights and Measures) 에 보관 ( 오른쪽 ) 표준 분동

29 저울의 원리 1) Lever( 지레 ) and pendulum( 진자 ) 2) Newton’s 2 nd law of motion ( 운동의 제 2 법칙 ) 3) Force moment( 힘의 모멘트 ) 4) Hook’s law of elasticity ( 탄성력의 후크의 법칙 ) 4)Piezoeletric effect ( 압전기 효과 ) 5)Electromagnetic force compensator ( 전자기력 평형식 ) W = F = 2  rnBI 6)Load transfer mechanism ( 하중 전달 메커니즘 ): 압력 P 를 힘 F 로 변환

30 l 1 l 2 w 1 w 2 w 1 = gm 1 w 2 = gm 2 w 1 l 1 = w 2 l 2 if l 1 = l 2 w 1 = w 2  m 1 = m 2 Principle of mechanical balance

31 Single-pan mechanical analytical balance. Single-pan mechanical balance. To weigh an object on the pan, we use the knobs on the balance to detach removable weights until the balance beam is restored as near as possible to its original position. Remaining small deflection is read on the optical scale. Sartorius 2842 balance

32 Principles of electronic balance 1) The load transfer mechanism Weighing load on the pan Pressure force (P) Lever linkages ; elastic flexure pivots Translate Measurable single force (F) 2) The electromechanical transducer (= load cell) Electromagnetic force compensator Maintain equilibrium Weighing load Compensation force W = P = F = l BI = n2  rBI Where l = total length of coil wire B = magnetic flux density I = current E = IR 3) The electronic signal processing part Three part structure of an electronic balance.

33 An electronic balance (R.M. Schoonover, Anal. Chem. 1982, 54, 976A) and top loading balance (K.M. Lang, American Lab., 1983, 15(3), 72)

34 Electronic balance. Displacement of the balance pan generate a correction current. The electromagnet then restores the pan to its initial position. N and S are the north and south poles of the permanent magnet.

35 Piezoelectric Effect Crystals which acquire a charge when compressed, twisted or distorted are said to be piezoelectric. This provides a convenient transducer effect between electrical and mechanical oscillations. Quartz demonstrates this property and is extremely stable. Quartz crystals are used for watch crystals and for precise frequency reference crystals for radio transmitters. Rochelle salt produces a comparatively large voltage upon compression and was used in early crystal microphones. Barium titanate, lead zirconate, and lead titanate are ceramic materials which exhibit piezoelectricity and are used in ultrasonic transducers as well as microphones. If and electrical oscillation is applied to such ceramic wafers, they will respond with mechanical vibrations which provide the ultrasonic sound source. The standard piezoelectric material for medical imaging processes has been lead zirconate titanate (PZT). Piezoelectric ceramic materials have found use in producing motions on the order of nanometers in the control of scanning tunneling microscopes. The word piezo is Greek for "push". The effect known as piezoelectricity was discovered by brothers Pierre and Jacques Curie when they were 21 and 24 years old in There is a magnetic analog where ferromagnetic material respond mechanically to magnetic fields. This effect, called magnetostriction, is responsible for the familiar hum of transformers and other AC devices containing iron cores.magnetostriction

36 The diagram below provides an explanation of why the piezoelectric effect exists. The diagram at the left depicts six point charges (ions if you will), red being positive charges and green negative. In a relaxed state with no forces acting on them, they are arranged at the vertices of an hexagon. If the electrical potential (V) at a point along the x axes and distant from these charges one can see the three positive charges will appear to act at the center of the hexagon as will the three negative charges. The positive and negative array of charges will cancel each other out and the potential V, at a the distance along the x axes will be zero. If a compressive force is applied to the hexagon along the Y axes direction, the array is distorted in such a way as to bring two of the positive charges closer together at one end and the negative charges at the other. This forms a dipole where one end of the array is positive and the other negative. A potential, V calculated at a distance along the X axes will now be non-zero. One can easily imagine a crystal structure made up of these hexagonal arrangements of ions, all lined up in an orderly matrix throughout the bulk of the crystal volume. When the crystal is compressed, each hexagon would contribute to a net polarization across the crystal.

37 Electronic chemical balance(left), weights(center), top loading balance(right) and triple beam dial balance. Rear weight is in the notch reading...… 70 g Middle weight is in the notch g Front beam weight reads g The object weighs g

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39 Using an Analytical Balance Turn the balance on by pressing the control bar. The display lights up for several seconds, then resets to Place creased, small weighing paper on the balance pan. Close the sliding glass doors. Wait for the green dot on the left to go out. This is the stability indicator light, indicating that the weight is stable.

40 Press the control bar to cancel out the weight of the container or paper. The display will again read Carefully add the substance to be weighed up to the desired mass. Do not attempt to reach a particular mass exactly. Before recording the mass, close the glass doors and wait until the stability detector lamp goes out. Record mass of solid. Don't pick up tare containers with bare hands since your fingerprints add mass. Use Kimwipes or tongs to prevent this. Don't lean on the bench while weighing. Do record the mass of your container, if you will need it later. Do check the level indicator bubble before weighing. The two rear balance feet serve as leveling screws.

41 Clean-up Use the brush provided to clean spills in the weighing chamber. Discard any disposable tare containers, weighing paper, or Kimwipes in the nearest wastebasket.

42 Using a Top-loading Balance Check if the balance is turned on. If not, press the on/off button and wait until the display reads 0.0 g. Place a container or large, creased weighing paper on the balance pan. Push tare button to zero the balance. Carefully add substance to the container or paper. Record mass. Clean-up Use the brush provided to clean any spills. Discard any disposable tare containers, weighing paper, or Kimwipes in the nearest wastebasket.

43 Quantitative transfer of solid sample. Note the use of tongs to hold the weighing bottle and a paper strip to hold the cap to avoid contact between glass and skin. A, 종이로 말아서 칭량병 (weighing bottle) 옮기기와 B, 칭량접시 (weighing dish).

44 Errors in weighing mass : 1) Changes in moisture or CO 2 content 2) Volatility of sample 3) Electrification 4) Temperature 5) Air buoyancy error : This error is due to the weight of air displaced by the object on the pan and is generally quite small. There will be a buoyancy correction whenever the density of the object is not equal to the density of the standard weights.

45 Buoyancy equation : m = [m’{1  (d a / d w )} / {1  (d a / d )}] where m = true mass, m’ = mass read from a balance, d a = density of air ( g/ml near 1atm and 25 o C ), d w = density of balance weights (typically 8.0 g/ml ) d = density of object being weighed Weighing methods : Weighing by directly Weighing by difference  hygroscopic reagents

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49 Equipment and Manipulations Associated with Weighing Weighing bottles Desiccators and Desiccants Manipulating weighing bottles Weighing by difference Weighing hygroscopic solids Weighing liquids

50 Drying Constant mass: In gravimetric analysis the product is heated and cooled to room temperature in a desiccator until successive weighings are “constant”. It is usually taken as about  0.3mg. Drying oven: to dry (110~200 o C) samples prior to weighing Muffle furnace : to ignite(pyrolysis) samples to high temperature (500~1200 o C) Remember to keep the watch glass as a dust cover on and the weighing bottle top off while drying in the oven or desiccator.

51 (a)Ordinary desiccator. (b) Vacuum desiccator that can be evacuated through the sidearm at the top and then sealed by rotating the joint cintaining the sidearm. Drying is more efficient at low pressure. Allow the weighing bottle (top off) to equilibrate overnight in the desiccator. The following period, place the top back on the weighing bottle and keep it this way while storing in the desiccator.

52 Efficiencies of drying agents Agents FormulaWater left in atmosphere (  g H 2 O/L) AluminaAl 2 O AnhydroneMg(ClO 4 ) H 2 O 1.5 AscariteNaOH on asbestos 93 Barium oxideBaO 2.8 Barium perchlorateBa(ClO 4 ) Calcium chloride (dried at 127 o C)CaCl 2 67 Calcium oxideCaO 656 Calcium sulfate( Drierite )CaSO 4 67 Lithium perchlorate, anhydrousLiClO 4 13 Magnesium oxideMgO 753 Magnesium perchlorate, anhydrousMg(ClO 4 ) Phosphorous pentoxideP 4 O Potassium hydroxideKOH 939 Sodium hydroxideNaOH 513 Sulfuric acid (98 %)H 2 SO 4 3

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54 Intermission Break Thanks. To be continued (Chapter 2).


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