芒硝测定

null芒硝中Na2so4含量测定 芒硝中Na2so4含量测定 沉淀重量法沉淀重量法一. 沉淀重量法的基本步骤 例：试样溶液沉淀形式 称量形式 null（一） 试样的溶解 1．准备好洁净的烧杯，合适的搅拌棒（长度应高出烧杯5～l0cm）和表面皿 （略大于烧杯口）。烧杯内壁和底不应有划痕。 2．放入试样后，用表面皿凸面向下盖好烧杯。 3．进行溶样。null（二） 沉淀 应根据沉淀性质采取不同的操作。 晶形沉淀应在热的稀溶液中进行沉淀，加沉淀剂速度要慢，并须不断搅拌。操作时，左手拿滴管逐滴加入沉淀剂，滴管口要接近液面，勿使溶液溅出；右手持玻棒不断搅拌，注意勿使玻棒碰到烧杯壁和底。沉淀之后应检查沉淀是否完全，方法是：待沉淀下沉后，在上层清液中滴加少量沉淀剂，观察是否出现混浊，如无混浊，说明沉淀已完全。沉淀完全后，盖上表面皿，放置过夜或在水浴上加热0.5~1小时（勿沸！）左右，使沉淀陈化（aging). null 过滤和洗涤 过滤 “倾注法” 洗涤 “少量多次”原则 过滤和洗涤 过滤 “倾注法” 洗涤 “少量多次”原则 图5-2．滤纸的折褶图 图 5-3．倾注法过滤步骤步骤⑴ Dissolution of sample: Weigh out accurately 0.4g of mirabilite sample, place it into a beaker (250ml), add 50ml of distilled water, stir and dissolve, then add 2ml of HCl (6mal/L), add again distilled water until total volume 100ml, cover the watch glass cleaned, heat until boiling nearly, wash the watch glass and put the liquid into the beaker. (After blowing and washing, the convex of the watch glass should beforward top on the table.) 烧杯蒸馏水芒硝表面皿null⑵ Formation of precipitate: Dropping slowly 20ml of (5%) warm-solution, until precipitate forms completely. (Check: put a few of drops of precipitating regent into the supernatant, if should be continued to drop the precipitating regent). After the precipitate completes, heating and aging it for 20min.null⑶ Filtering of the precipitate: Place calmly and demit, filtrate the supernatant with decantation method (note, at first, the filter should be made by middle speed quantitative paper), leave the precipitate in the beaker, add distilled water according to small batch (total 3-4 times, 10ml/time), stir and wash cleanly.null⑷ Transfer of the precipitate: Stir the precipitate using a little of distilled water, put it into the funnel along with gloss rod (note! Do not lose the precipitate). Wash the precipitate in many times, shift the all precipitate to funnel, finally wash-clean the filter-paper spirally with the wash bottle, allow the precipitate to be gathered in the bottom of the funnel. Whether the precipitate wash-clean or not, put a few drops of (0.1mol/L) into the filtrate liquid, if clean, it should not be turbid.