Pharmaceutical Analytical Chemistry 1 PDF

Pharmaceutical Analytical Chemistry 1 Units and measurements (SI units) Uncertainty of measurements Significant figures Mole Dr. Mahmoud A. Tantawy Assoc.Prof. of Analytical Chemistry...

Pharmaceutical Analytical Chemistry 1 Units and measurements (SI units) Uncertainty of measurements Significant figures Mole Dr. Mahmoud A. Tantawy Assoc.Prof. of Analytical Chemistry Faculty of Pharmacy Pharmaceutical Analytical Chemistry 1 Units and measurements (SI units) 1- What is the international system of units (SI units)? What are the SI derived units? International system of units: (SI Units) - It has seven base quantities & base units from which all other quantities can be derived: Quantity Unit Symbol Length Meter m Mass Kilogram kg Time Second s Temperature Kelvin K Amount of substance mole mol Electric current ampere A Luminous intensity candela cd Pharmaceutical Analytical Chemistry 1 Units and measurements (SI units) Derived SI units :- Quantity Symb. Expression SI unit Area A Length2 m2 Volume V Length3 m3 Density D Mass/volume kg.m-3 Velocity v Distance / time m.s-1 Acceleration A Velocity/ time m.s-2 Force F Mass x kg.m.s-2(newton N) acceleration pressure P Force/area kg.m-1.s-2(pascal pa) Energy E Force x kg.m2.s-2(joule J) distance Pharmaceutical Analytical Chemistry 1 Units and measurements (SI units) 2-What are the SI prefixes? Multiple Prefix Symbol 106 mega M 103 kilo k 102 hecto h 101 deka da 10-1 deci d 10-2 centi c 10-3 milli m 10-6 micro µ 10-9 nano n 10-15 femto f Pharmaceutical Analytical Chemistry 1 Units and measurements (SI units) 3-Some common non-SI units: 1- Volume in litre (L) 1mL (cm3) = 10-6 m3 1 L = 1000 mL = 1000 cm3 = 1000 x (10-2m)3= 10-3 m3 2- Temperature in centigrade (oC) ToK = toC + 273 toC = ToK- 273 3- Pressure in atmosphere (atm) 1 atm = 101.325 K.pascal 4- Energy in calories (cal) 1 cal = 4.148 J Pharmaceutical Analytical Chemistry 1 Units and measurements (SI units) 4-Example on Units and Measurement Example 1: A substance has a mass = 250 g and its volume = 1500 mL. Calculate the density in g/cm3 & SI units. Soln D=mass / volume = 250 g / 1500 mL = 0.166 g/mL = 0.166 g/cm3 -In SI units: Mass :250 g = 250 x 10-3 = 0.25 kg Volume 1500 cm3 = 1500 x 10-6 = 0.0015 m3 Therefore D = 0.25 / 0.0015 = 166.66 kg / m3 Pharmaceutical Analytical Chemistry 1 Uncertainty of measurements - No physical quantity can be measured with perfect certainty. - There are always errors (uncertainty) in any measurement. - Each measurement should be reported with some certain digits plus one uncertain digit. 40.51, 40.52, 40.53 Pharmaceutical Analytical Chemistry 1 Uncertainty of measurements Uncertainty depends on accuracy and precision of the measuring device and person using it. Accuracy - It is the measure of exactness of an analytical method or the closeness of agreement between the measured value and the value that is accepted either as a conventional , true value or an accepted reference value. - For example, if you used a balance to find the mass of a known standard 100.00 g mass, and you got a reading of 78.55 g, your measurement would not be accurate. Pharmaceutical Analytical Chemistry 1 Uncertainty of measurements Precision - Precision refers to how close together a group of measurements. - Precision is sometimes referred to as repeatability or reproducibility. Pharmaceutical Analytical Chemistry 1 Uncertainty of measurements N.B. One important distinction between accuracy and precision is that: - Accuracy could be determined from one measurement. - Precision needs multiple measurements. Pharmaceutical Analytical Chemistry 1 Significant figures Significant Figures - The number of significant figures is the number of figures (numbers) 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. Pharmaceutical Analytical Chemistry 1 Significant figures Rules for Significant Digits: 1 All non-zero digits are considered significant. - e.g. 91 has two significant digits (9 and 1), while 123.45 has five significant digits (1, 2, 3, 4 and 5). 2 Zeros; there are three classes of zeros: a. Leading zeros: - Not count as significant figures. - E.g. In the number 0.0034, there are only two significant figures. b. Captive zeros: - Are zeros between nonzero digits. - Count as significant figures. - E.g. 1.007 has 4 significant figures. Pharmaceutical Analytical Chemistry 1 Significant figures c. Trailing zeros: - are zeros at the right end. - They are significant only if the number contains a decimal point. - E.g. The number 100 has only one significant figure. - 1.00 has three significant figures. Pharmaceutical Analytical Chemistry 1 Significant figures Rules for rounding off numbers: (1) If the digit to be dropped is greater than 5, the last retained digit is increased by one. - e.g. 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. - e.g. 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. - e.g. 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. - e.g. For example, 11.5 is rounded to 12, 12.5 is rounded to 12. Pharmaceutical Analytical Chemistry 1 Significant figures Questions 1-How many significant figures are there in each of the following values: Answer a- 6.07 x10-2 a-3 b- 0.003840 b-4 2-Round off each of the following numbers to specified significant figures: Answer a- 0.00034159 to three digits A-0.000342 b-103.351 x 102 to four digits b-103.4 x 102 c-17.9915 to five digits c-17.992 d-3.365 x 105 to three digits d-3.36 x 105 e- 4.348 to two digits e- 4.3 Pharmaceutical Analytical Chemistry 1 The Mole and molar mass The Mole - Is the quantity of a given substance that contains as many molecules or formula units as the number of atoms in exactly 12 g carbon. e.g. number of ethanol molecules in 1 mole ethanol = number of carbon atoms in 12 g carbon (which is called Avogadro's number NA). NA = 6.022 X 1023 - A mole of a substance contains Avogadro's number (6.022 X 1023) of molecules (or formula units). - E.g. a mole of O atoms contains 6.022 X 1023 O atoms. A mole of O2 molecules contains 6.022 X1023 molecules, that is 2 X 6.022 X 1023 O atoms. Pharmaceutical Analytical Chemistry 1 The Mole and molar mass - The molar mass of a substance is the mass of one mole of the substance. - Carbon has molar mass of 12 g / mol. - For all substances, the molar mass (formula weight or molecular weight) in grams (g) is numerically equal to the weight in atomic mass units (amu). - E.g. ethanol has molecular weight of 46.1 amu (or g) and a molar mass of 46.1 g / mol. Pharmaceutical Analytical Chemistry 1 The Mole and molar mass To Calculate the Number of moles (n): - n = N / NA n= number of moles. N= number of molecules, ions or atoms. NA= Avagadro’s number (6.022 x 1023) - Or n = m / M.wt n= number of moles. m= mass in grams. M.wt= molecular weight. Example 1: How many grams of Cu are there in 2.55 mole of Cu? Solution: 1 mole Cu = 63.5 g Cu , so 2.55 mole Cu contains 162 g Cu Pharmaceutical Analytical Chemistry 1 The Mole and molar mass Example 2: What number of moles of aluminum is present in 125 g of Al ? Solution: 1 mole Al = 27.0 g Al ….. Mole = 125 g = 4.63 mole Example 3: How many carbon atoms are there in a 1.0 carat diamond? Diamond is pure carbon and one carat is exactly 0.2 g. Solution: 1 mole C = 12.01 g C …. Mole = 0.2 g 0.01665 mole 1 mole C = 6.022 X 1023 atoms C 0.01665 mole = ……….. Atoms 1.003 X 1022 atoms C