单选题
发布日期:2020-12-11
Cu2+
Ag+
CaCO3
MnO2
高锰酸钾(Potassium permanganate)是一种强氧化剂,化学式为KMnO4,为黑紫色结晶,带蓝色的金属光泽,无臭,与某些有机物或易氧化物接触,易发生爆炸,溶于水、碱液,微溶于甲醇、丙酮、硫酸。在化学品生产中,广泛用作氧化剂。
返滴定法(剩余量滴定,俗称回滴) 当反应较慢或反应物是固体时,加入符合计量关系的滴定剂,反应常常不能立即完成。此时可以先加入一定量过量的滴定剂,使反应加速。等反应完成后,再用另一种标准溶液滴定剩余的滴定剂。这种滴定方式称为返滴定法。
测定是获得某一物质的物理或化学特征数据信息的方法,或这种方法的执行过程。在分析化学中,一般是通过实验来确定待测对象诸如质量、时间、温度、体积、电流强度、浓度等物理量或其他变化,进而确定物质或材料中某些化学组分的含量或结构等情况。在测量学里,测定是指使用测量仪器和工具,通过测量和计算,得到一系列测量数据,或把地球表面的地形缩绘成地形图。
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Questions 1 to 5 are based on the following passage. A call home can cost £1.37 a min BRITISH tourists are still ripped off by mobile phone firms charging over the odds for “roaming” services, the European Commission has found. Calls made or received on mobiles while abroad cost up to £1.37 a minute—or 19 times as much as domestic calls, a study revealed. Users have to pay roaming charges when using a foreign network, under an agreement with their own operator. Mobiles automatically switch to a local network when outside the UK. Companies such as Vodafone and T-Mobile are accused of abusing their dominant position by charging high fees and passing them on to customers. British operator Vodafone and T-Mobile’s parent company Deutsche Telekom are guilty of anti-competitive practices in Germany, the EC claims. If found guilty, both could be fined millions of pounds for abusing their monopoly. Vodafone is appealing against earlier EC allegations that its British roaming rates are “unfair and excessive”. Jonathan Morris, of What Mobile? magazine, said: “If people use their phone when away, they can rack up hundreds of pounds quickly. Making quick calls won’t help as calls are charged by the minute, not the second.” Questions: 1.Mobile phone firms cheat British tourists by making them pay too much money for ______________. 2.Which mobile phone company is cheapest to call UK from Australia? 3.If found guilty, which two mobile phone firms could be fined millions of pounds for abusing their monopoly? 4.What are the European Commission’s allegations about Vodafone? 5.How will people be charged if they use their phone when away?
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