题目

Romantic novelists rarely fail to include in their writings that special moment when two strangers look into each other's eyes across a crowded room and feel the tingle of desire. Now these writings have now been validated（证实）by science, for experts have discovered that eye-to-eye contact in fact leads to a burst of activity in the reward center of the brain. Neuroscientists at University College London asked eight female and eight male volunteers to look at photos of the faces of 40 different people who were either looking at the camera or gazing to one side. While the volunteers look（12分）为测定某Na2SO3样品（含少量Na2SO4杂质）的纯度，实验室按以下步骤进行；① 称取ag样品，置于烧杯中；②加入适量蒸馏水，使样品溶解，然后配制成250mL溶液；③准确量取25.00mL步骤②中配得的溶液；然后，可采用下列两种方法进行测定： 方法一 方法二 ④将25.00mL溶液置于烧杯中，加入过量的稀盐酸充分搅拌； ⑤加入过量BaCl2溶液，充分搅拌，使沉淀完全； ⑥过滤、洗涤、干燥沉淀、称量得到bg固体。 ④将25.00mL溶液置于锥形瓶中； ⑤用0.1 mol/L的酸性KMnO4溶液进行滴定，达到滴定终点时，消耗10.00mL溶液。     请根据上述实验，回答：（1）上图所示仪器中，本实验步骤①②③中必须用的的仪器是E和      （填字母）；（2）在方法一④中加入过量稀盐酸的目的是                                 ；（3）在方法一测定得到Na2SO3样品的纯度是                     （列出算式，可不化简）；（4）在方法二中，是否需要加入指示剂       （填“是”或“否”），请简述理由         ；（5）在方法二中达到滴定终点读取数据时，俯视液面，则测定结果                        （填“偏高”、“偏低”、“无影响”）。