che 211 analytical chemistry, Cheat Sheet of Chemistry

Download che 211 analytical chemistry and more Cheat Sheet Chemistry in PDF only on Docsity! ANALYTICAL CHEMISTRY • Analytical chemists assess the chemical structure and nature of substances. • Samples are analysed using a range of techniques. • Analytical work demands patience, determination, creativity, flexibility and decisiveness. CHEMICAL ANALYSIS •Steps in chemical analysis •Why is Sampling Necessary in any given Analysis? •Sample composition •Measurement of the desired analyte •Uncertainties: significant figures •Prefixes for SI Units | 10 meters ———_-} 20 meters ——————————_ Segregated heterogeneous material SAMPLE COMPOSITION • Analyte constitute small or large portion of the sample ➢>1% major constituent ➢0.01-1.00% minor constituent ➢<0.001 trace constituent • Matrix – all other components in sample except the analyte QUANTITATIVE ANALYSIS MASS ANALYSIS >1g Macro 10-100mg Semi micro 1-10mg Micro microgram Ultra micro Rules on significant figures • Zeros surrounded by other digits are significant e.g 0.3005(4sig.fig) • Zeros that locate the decimal place are not significant e.g 0.0005(1 sig.fig) • Terminal zeros are generally significant e.g 0.5000(4sig.fig) • Rules of significant figures depend on Addition&Subtration or Multiplication&Division • Addition&Subtration ➢Use smallest no of decimal places e.g 3.4+0.020+7.31=10.7 (1 decimal place) • Multiplication&Division ➢Answer rounded so that contains same number of sig.fig as data(original) with the smallest nummber of sig.fig e.g Calculate density of an objectbof weight 1.78g(3sf) and volume 1.2 cm3 (2sf) 1.78/1.2=1.5g/cm3 CASE A: In rounding off numbers, the last figure kept should beunchanged if the first figure dropped is less than 5. For example, if only one decimal is to be kept, then 6.422 becomes 6.4. CASE B: In rounding off numbers, the last figure kept should beincreased by 1 if the first figure dropped is greater than 5. For example, if only two decimals are to be kept, then 6.4872 becomes 6.49. Similarly, 6.997 becomes 7.00. CASE C: In rounding off numbers, if the first figure dropped is 5, and all the figures following the five are zero or if there are no figures after the 5, then the last figure kept should be unchanged if that last figure is even. For example, if only one decimal is to be kept, then 6.6500 becomes 6.6. For example, if only two decimals are to be kept, then 7.485 becomes 7.48. CASE D: In rounding off numbers, if the first figure dropped is 5, and all the figures following the five are zero or if there are no figures after the 5, then the last figure kept should be increased by 1 if that last figure is odd. For example, if only two decimals are to be kept, then 6.755000 becomes 6.76. For example, if only two decimals are to be kept, 8.995 becomes 9.00. CASE E: In rounding off numbers, if the first figure dropped is 5, and there are any figures following the five that are not zero, then the last figure kept should be increased by 1. For example, if only one decimal is to be kept, then 6.6501 becomes 6.7. For example, if only two decimals are to be kept, then 7.4852007 becomes 7.49.