front 1 Purpose of Experiment 7? | back 1 to illustrate typical techniques used in gravimetric analysis by quantitatively determining the amount of chloride in an unknown |
front 2 What is quantitative analysis? | back 2 aspect of analytical chemistry concerned with determining how much of one or more constituents is present in a sample of material |
front 3 Two common quantitative methods used in analytical chemistry | back 3 Gravimetric analysis Volumetric analysis |
front 4 Gravimetric analysis | back 4 derives name from the fact that the constituent being determined can be in isolated in some weighable form |
front 5 Volumetric Analysis | back 5 derives name from the fact that the method used to determine amount of constituent involves measuring the volume of a reagent |
front 6 What are the steps involved in gravimetric analysis (7)? (These are not steps, they are not are in order) | back 6 1. Dry and weigh samples of material 2. Dissolve the samples 3. Precipitate the constituent (substance you are trying to attain) by adding a suitable reagent 4. Isolate the precipitate by filtration 5. Wash precipitate to free it of contaminants 6. Dry the precipitate (to obtain weighable form) 7. Calculate the percentage of the desired consituent (from masses of the sample and precipitate) |
front 7 Example of precipitation reaction | back 7 a chloride ion may be precipitated by adding the silver ion to make AgCl - AgCl is very insoluble, so adding Ag to Cl precipitates AgCl quantitatively (the precipitate can be collected, dried, and weighed) From the amount of AgCl obtained, amount of Cl can be calculated |
front 8 Stoichiometry | back 8 the determination of the proportions in which elements combine and the mass relations in any chemical reaction |
front 9 gravimetric factor | back 9 - converts gram of a compound into grams of a single element - used repeatedly in analytical chemistry and are tabulated in books |
front 10 Example of Gravimetric Analysis | back 10 |
front 11 Which acid was used in this procedure? Which silver compound was used? | back 11 HNO_{3} - nitric acid AgNO_{3- silver nitrate (.25M instead of .5 M)} |
front 12 How was the filter paper placed into the funnel? | back 12 open the paper so that it has one piece of paper against one side of the funnel and three pieces of paper against the other - wet the paper w/ distilled water to hold it in place |
front 13 Which compound was highly flammable and needed to be kept away from the flames? | back 13 acetone |
front 14 What were the instructions for storing the AgCl precipitate? Why? | back 14 Keep it out of bright light because it is photosensitive and slowly decomposes in the presence of light (hv= symbol for electromagnetic radiation |
front 15 What is the purpose of standard deviation? | back 15 to estimate the precision of your results The smaller the deviation, the more precise the measurements |
front 16 accuracy | back 16 correctness of measurement, closeness to true result |
front 17 precision | back 17 internal consistency among one's own results (reproducibility) |
front 18 error | back 18 difference btwn the true result and the determined result |
front 19 Determinate errors | back 19 errors in method or performance that can be discovered and eliminated *these errors are known and are controllable (e.g.instrumental errors, human errors) |
front 20 Indeterminate errors | back 20 random errors, which are incapable of discovery but which can be treated by statistics *these errors are unknown and beyond analysts' control (e.g. room temperature |
front 21 mean | back 21 arithmetic mean or overage (μ) |
front 22 median | back 22 midpoint of results (if odd number of results) average of two middle results (if even number of results) |
front 23 How is relative deviation calculated? | back 23 by dividing the average deviation from mean by the mean |
front 24 What is the best measure of precision | back 24 standard deviation |
front 25 What is the rule for retaining or discarding a standard deviation figure? | back 25 discard any result that is more than two standard deviations away from the mean |