210951
| Question | Answer |
| Gravimetric Precipitate properties | 1. Have a known formula 2. Have low solubility 3. Remain stable as heated 4. Be the product of one specified reaction (inert) |
| Steps in measuring water content | 1. Weigh the sample 2. Heat the sample in an oven at 110 degrees 3. Allow sample to dry 4. Reweigh (and repeat until mass is constant) |
| Steps in Gravimetric Analysis | 1. Weigh the sample 2. Mix sample in water to dissolve soluble ion 3. Filter to remove impurities 4. Add excess reagent to form a specific precipitate 5. Filter precipitate and wash with water 6. Dry precipitate at 100 degrees 7. Weigh the precipitate (repeat 6 and this step until at constant mass) |
| Errors in Gravimetric | - Loss of some precipitate (under) - Incomplete precipitation (under) - Decomposition of samples during drying to form gases (under) - Incomplete drying (over) - Presence of contaminants (over) - Adsorption of ions in solution on surface of precipitate (over) - Formation of other precipitates (over) |
| Primary Standards and standard solutions | A primary standard is a substance so pure that its amount (mol) can be determined from its mass A standard solution is a solution with a known concentration that is prepared from a primary standard |
| Criteria of primary standards | - It is obtainable in pure form - It has a known formula - Does not react with the atmosphere - It has a high molar mass to minimise weighing errors - cheap and readily available - highly soluble |
| Steps in Volumetric Analysis | 1. A burette is filled with standard solution 2. Our unknown is delivered into a conical flask with a known volume 3. Indicator is added 4. The end point is found |
| Acid-Base titration equivalence points | - Strong acid, Strong base: pH of 7 - Weak acid, Strong base: approx pH of 9 - Strong acid, Weak base: approx pH of 5 - Weak acid, weak base: back titration because of the slow rate of the reaction |
| Back Titration | 1. Find the amount in mol of common solution in secondary (excess) reaction 2. Find the amount in mol of common added initially 3. Find the amount in mol reacting (initial - excess) 4. Consider dilution factors, move back from aliquot to flask (flask/aliquot x mol) 5. Work out calculations as asked |
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