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Volumetric analysis new

General volumetric analysis

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Volumetric analysis new

  1. 1. U.A. Deokate Copyright © by U. A. Deokate, all rights reserved.
  2. 2. ♥ It is a general term for a method in quantitative chemical analysis in which the amount of a substance is determined by the measurement of the volume that the substance occupies. ♥ It is commonly used to determine the unknown concentration of a known reactant. ♥Volumetric analysis is often referred to as titration, a laboratory technique in which one substance of known concentration and volume is used to react with another substance of unknown concentration. 9/9/2018 2Deokate UA
  3. 3. Volumetric Analysis  Involves the preparations, storage, and measurement of volume of chemicals for analysis VolumetricTitrimetry  Quantitative chemical analysis which determines volume of a solution of accurately known concentration required to react quantitatively with the analyte (whose concentration to be determined).  The volume of titrant required to just completely react with the analyte is theTITRE. 9/9/2018 3Deokate UA
  4. 4. Titration  A process in which a standard reagent is added to a solution of analyte until the reaction between the two is judged complete Primary Standard A reagent solution of accurately known concentration is called a standard solution. Standardization  A process to determine the concentration of a solution of known concentration by titrating with a primary standard 9/9/2018 4Deokate UA
  5. 5. End point  The point at which the reaction is observed to be completed is the end point  The end point in volumetric method of analysis is the signal that tells the analyst to stop adding reagent and make the final reading on the burette.  Endpoint is observed with the help of indicator Equivalent point  The point at which an equivalent or stoichiometric amount of titrant is added to the analyte based on the stoichiometric equation 9/9/2018 5Deokate UA
  6. 6.  Volumetric analysis involves a few pieces of equipment: Pipette – for measuring accurate and precise volumes of solutions Burette – for pouring measured volumes of solutions Conical flask – for mixing two solutions Wash bottles – these contain distilled water for cleaning equipment Funnel – for transfer of liquids without spilling Volumetric flasks – a flask used to make up accurate volumes for solutions of known concentration 9/9/2018 6Deokate UA
  7. 7.  Reaction must be stoichiometric, well defined reaction between titrant and analyte.  Reaction should be rapid.  Reaction should have no side reaction, no interference from other foreign substances.  Must have some indication of end of reaction, such as color change, sudden increase in pH, zero conductivity, etc.  Known relationship between endpoint and equivalence point. 9/9/2018 7Deokate UA
  8. 8.  Concentration: is a general term expressing the amount of solute contained in a given material. Expressed by different ways  Molarity(M):The number of moles of solute divided by the number of liters of solution containing the solute. (is gram molecular weight dissolved in one liter of solution)  Molarity = moles of solute / volume in liters  Milli moles of solute / volume in milliliters.  Moles = weight (gms) / MW or  Millimoles = weight(mg) / MW 9/9/2018 8Deokate UA
  9. 9.  Defined as no of equivalents of solute divided by the number of liters of solution containing the solute. ( gm equivalent weight dissolved in one liter of solution)  Normality = equivalents of solute / volume in liters  Milli eq. of solute / volume in milliliters.  Equivalents = weight (gms) / EW or  Milliequivalent = weight(mg) / EW 9/9/2018 9Deokate UA
  10. 10.  Molarity = weight / MW xVolume  MW =Weight / Molarity x volume similarly  Normality = weight / EW xVolume  EW =Weight / normality x volume  EW = MW / h  Where h reacting unit.  For acid H+ is reacting unit and for base OH-  For Oxdn redn e- is reacting unit  For Ionic species valences 9/9/2018 10Deokate UA
  11. 11.  Is defined as part by wt of substance which is chemically equivalent to one part by wt of hydrogen or 8 part by wt of oxygen or 35.5 part by wt of chlorine.  Thus in finding out equlent. wt we find out how many grams of that sub are directly or indirectly eq to one gm of hydrogen  It depends on reaction in which it takes place 9/9/2018 11Deokate UA
  12. 12.  Weight percent (w/w) = weight of analyte x 100 weight of sample  Volume percent (v/v) = volume of analyte x 100 volume of sample  Weight percent (w/v) = weight of analyte x 100 volume of sample 9/9/2018 12Deokate UA
  13. 13.  Ppm = weight analyte x 10 6 weight of sample Or ie 1 gm / 10 liters Or 1mg / Liter Or microgram / ml  Molal Solution: Gram molecular wt dissolved in 1000gm of solution  Formal solution: gram formula wt dissolved in 1000ml of solution. 9/9/2018 13Deokate UA
  14. 14.  Commercial acid and basis are available in % by wt, and by further dilutions solution are prepared.  Density = wt / unit volume at sp temp (20OC) unit gm / ml or gram / cm3  Sp. Gravity = mass / mass of eq volume of water at 20OC or  At 4OC density of water is 1.00000gm/ml 9/9/2018 14Deokate UA
  15. 15.  The branch of chemistry which deals with weight relation between reactant and product is called stoichiometry.  HCl react with NaOH according to eq  HCl + NaOH  H2O + NaCl  36.5 40 18 58.5 gm  Ie 36.5 gm of HCl = 1000ml of 1M NaOH  0.0365 gm of HCl = 1 ml of 1M NaOH and  0.00365 gm of HCl = 1 ml of 0.1 M NaOH 9/9/2018 15Deokate UA
  16. 16.  A solution whose con is accurately known  Prepared by dissolving an accurately wt quantity of highly pure material called primary std. and diluted to an accurately volume in volumetric flask.  Otherwise a solution of approximately desired con is titrated against the primary standard solution and concentration is determine, this is called standardization 9/9/2018 16Deokate UA
  17. 17.  Measurements are made with reference to standards  The accuracy of a result is only as good as the quality and accuracy of the standards used  A standard is a reference material whose purity and composition are well known and well defined  Primary Standards – Used as titrants or used to standardize titrants  Eg. Acid base titration Na2CO3, KHP, Succinic acid, Benzoic acid, Oxalic acid.  Eg for redox titration: K2Cr2O7, Potassium bromate, KIO3, Sodium Oxilate, arsionus trioxide  Eg for PPT titrations: NaCl, KCl, KBr, Silver nitrate  Eg for Complometric titration: Pure matels like Zn,Mg, Mn and its salts9/9/2018 17Deokate UA
  18. 18.  It should be 100% pure or with known purity  Should be stable to drying temp.  Usually solid to make it easier to weigh  Easy to obtain, purify and store, and easy to dry  Inert in the atmosphere  High formula weight so that it can be weighed with high precision  It should not absorb moisture, or should not react with oxygen or CO2  Reaction with analyte should be single, rapid complete and stoichiometric 9/9/2018 18Deokate UA
  19. 19.  True or correct or actual value are known only when the count object or when a quantity is assigned a particular value such as atomic weight. Otherwise the true value of a quantity is never known.  Standard value is observed value given by the expert using a suitable method and good quality apparatus and chemicals  Observed value is the result obtained  Error:The difference between true value or standard value is called error 9/9/2018 19Deokate UA
  20. 20.  The Accuracy of an analytical procedure expresses the closeness of agreement between the value, which is accepted either as a conventional true value or an accepted reference value and the value observed (individual observation or mean of measurements).  The Precision (VARIABILITY) of an analytical procedure is nearness between several measurements of the same quantity usually expressed as the standard deviation (S), variance (S2), or coefficient of variation (= relative standard deviation, R.S.D.) of a series of measurements 9/9/2018 20Deokate UA
  21. 21. Inaccurate & imprecise Inaccurate but precise Accurate but imprecise Accurate and precisePrecise Accurate Inaccurate and imprecise 9/9/2018 21Deokate UA
  22. 22. Two analysis (I & II) of substance whose true value is 100% is given below; Analysis I 100.00, 99.60, 99.70, 99.10 Average value is 99.60% Error is (100.00-99.60) = 0.4% The precision is poor but accuracy is good Analysis II 98.80, 98.82, 98.84, 98.82 Average value is 98.82% Error is (100.00-98.82) = 1.18% The accuracy is poor but precision is better 9/9/2018 22Deokate UA
  23. 23.  Since analytical chemistry is the science of making quantitative measurements, it is important that raw data is manipulated and reported correctly to give a realistic estimate of the uncertainty in a result.  Simple data manipulations may only require keeping track of significant figures. More complicated calculations require propagation- of-error methods.  The uncertainity in a result can be categorized into random error and systematic error. 9/9/2018 23Deokate UA
  24. 24.  The term error is used to show the difference between measured and true value.  Since the true value are never known one has to make use standard value.  The standard value can be obtained by  Absolute Method: sample is synthesized using know quantities to obtain a primary standard.  Comparative method: standard data is obtained. 9/9/2018 24Deokate UA
  25. 25.  DETERMINATE OR SYSTEATIC ERRORS  Personal error  Instrumental or reagent error  Method errors  Additive error  Proportional error  INDTERMINATE OR RANDOM ERRORS  The cause of a random error may not be known 9/9/2018 25Deokate UA
  26. 26.  Propositional error: the magnitude of error depends upon sample size  Additive error:The value of error is constant is independent of amount of sample taken for analysis  Endpoint error 9/9/2018 26Deokate UA
  27. 27.  Proper calibration of apparatus  Running a blank determination  Carrying out a control determination (use of standard and reference)  Use of independent method. (results of two different methods are compared)  Reparative determination and statistical evaluation 9/9/2018 27Deokate UA
  28. 28.  Average is measure of central tendency  It is the arithmetic mean of different values obtained by measuring the same quantity several time.  Arithmetic mean = sum of different value Number of times determination is made 9/9/2018 28Deokate UA
  29. 29.  Deviation (d): difference between the measured value and average value d =(x1-x-)  Average or mean deviation (d-) is arithmetic mean of different deviation observed d- = d1+d2+dn n  Relative Mean deviation is = Mean deviation x 100 Mean The positve or negative sing of individual deviation is ignored 9/9/2018 29Deokate UA
  30. 30.  The standard deviation is square root of the sum of the squared individual deviation divided by (n-1) s = √ d1 2 + d2 2 + d3 2 + dn 2 (n-1)  The square of standard deviation is called Variance and coefficient of variation (C.V) (also known as relative Std dev.) is defined as C.V. = s x 100 X- 9/9/2018 30Deokate UA
  31. 31.  The number of significant figures in a result is simply the number of figures that are known with some degree of reliability.The number 13.2 is said to have 3 significant figures.The number 13.20 is said to have 4 significant figures 9/9/2018 31Deokate UA
  32. 32.  All measurements are approximations--no measuring device can give perfect measurements without experimental uncertainty. By convention, a mass measured to 13.2 g is said to have an absolute uncertainty of 0.1 g and is said to have been measured to the nearest 0.1 g.  In other words, we are somewhat uncertain about that last digit —it could be a "2"; then again, it could be a "1" or a "3". A mass of 13.20 g indicates an absolute uncertainty of 0.01 g 9/9/2018 32Deokate UA
  33. 33. 1. All nonzero digits are significant: 1.234 g has 4 significant figures, 1.2 g has 2 significant figures. 2. Zeroes between nonzero digits are significant: 1002 kg has 4 significant figures, 3.07 mL has 3 significant figures. 3. Leading zeros to the left of the first nonzero digits are not significant; such zeroes merely indicate the position of the decimal point: 0.001 oC has only 1 significant figure, 0.012 g has 2 significant figures. 4. Trailing zeroes that are also to the right of a decimal point in a number are significant: 0.0230 mL has 3 significant figures, 0.20 g has 2 significant figures.9/9/2018 33Deokate UA
  34. 34. 5. When a number ends in zeroes that are not to the right of a decimal point, the zeroes are not necessarily significant: 190 miles may be 2 or 3 significant figures, 50,600 calories may be 3, 4, or 5 significant figures. The potential ambiguity in the last rule can be avoided by the use of standard exponential, or "scientific," notation. For example, depending on whether the number of significant figures is 3, 4, or 5, we would write 50,600 calories as: 5.06 × 104 calories (3 significant figures) 5.060 × 104 calories (4 significant figures), or 5.0600 × 104 calories (5 significant figures). 9/9/2018 34Deokate UA
  35. 35. In carrying out calculations, the general rule is that the accuracy of a calculated result is limited by the least accurate measurement involved in the calculation. 1. In addition and subtraction, the result is rounded off to the last common digit occurring furthest to the right in all components. Another way to state this rules, it that, in addition and subtraction, the result is rounded off so that it has the same number of decimal places as the measurement having the fewest decimal places. For example, 100 (assume 3 significant figures) + 23.643 (5 significant figures) = 123.643, which should be rounded to 124 (3 significant figures). 2. In multiplication and division, the result should be rounded off so as to have the same number of significant figures as in the component with the least number of significant figures. For example, 3.0 (2 significant figures ) × 12.60 (4 significant figures) = 37.8000 which should be rounded off to 38 (2 significant figures) 9/9/2018 35Deokate UA
  36. 36. 1. If the digit to be dropped is greater than 5, the last retained digit is increased by one. For example, 12.6 is rounded to 13. 2. If the digit to be dropped is less than 5, the last remaining digit is left as it is. For example, 12.4 is rounded to 12. 3. If the digit to be dropped is 5, and if any digit following it is not zero, the last remaining digit is increased by one. For example, 12.51 is rounded to 13. 4. If the digit to be dropped is 5 and is followed only by zeroes, the last remaining digit is increased by one if it is odd, but left as it is if even. For example, 11.5 is rounded to 12, 12.5 is rounded to 12. This rule means that if the digit to be dropped is 5 followed only by zeroes, the result is always rounded to the even digit.The rationale is to avoid bias in rounding: half of the time we round up, half the time we round down. 9/9/2018 36Deokate UA
  37. 37. 1. 37.76 + 3.907 + 226.4 = 2. 319.15 - 32.614 = 3. 104.630 + 27.08362 + 0.61 = 4. 125 - 0.23 + 4.109 = 5. 2.02 × 2.5 = 6. 600.0 / 5.2302 = 7. 0.0032 × 273 = 8. (5.5)3 = 9. 0.556 × (40 - 32.5) = 10. 45 × 3.00 = 11. 3.00 x 105 - 1.5 x 102 = (Give the exact numerical result, then express it the correct number of significant figures). 12. What is the average of 0.1707, 0.1713, 0.1720, 0.1704, and 0.1715? 13. Calculate the sum of the squares of the deviations from the mean for the five numbers gives in Question 12 above, in two different ways: 9/9/2018 37Deokate UA
  38. 38. 1. 37.76 + 3.907 + 226.4 = 268.1 2. 319.15 - 32.614 = 286.54 3. 104.630 + 27.08362 + 0.61 = 132.32 4. 125 - 0.23 + 4.109 = 129 5. 2.02 × 2.5 = 5.0 6. 600.0 / 5.2302 = 114.7 7. 0.0032 × 273 = 0.87 8. (5.5)3 = 1.7 x 102 9. 0.556 × (40 - 32.5) = 4 10. 45 × 3.00 = 1.4 x 102 11. 3.00 x 105 - 1.5 x 102 = (Give the exact numerical result, then express it the correct number of significant figures). 12. What is the average of 0.1707, 0.1713, 0.1720, 0.1704, and 0.1715? Answer = 0.1712 13. Calculate the sum of the squares of the deviations from the mean for the five numbers given in Question 12 above, in two different ways: (a) carrying all digits through all the calculations; (b) Round all intermediate result to 2 figures 9/9/2018 38Deokate UA

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