欲将下列物质中所含杂质除去，所选试剂（适量）正确的是（　　）

    My family and I were on our way to Pennsylvania and it was the middle of a snowstorm. We were almost there when we got stuck in a 1 traffic jam. Cars stretched (延伸)ahead of us and behind us as 2 as we could see. We sat in the same 3 without moving for seven hours. We 4periodically to see if the5 ahead of us were moving, which they had never been6there was a large 18-wheeler truck in front of us, my mom had to 7 the door to see around the 18-wheeler to get a 8 of the traffic jam in front of us. All we could do was sit and 9.At no time did any of us fall asleep or stop10 attention, because we were always checking up on the traffic. We sat for hours and heard11 about the cause of the traffic jam from the12and the only person we talked to was a truck driver13 us, who didn't know anything about it either.14after seven hours, the truck in front of us began moving slowly and we were happy to get moving, but when we15in front of the truck, there were absolutely NO cars to be seen, and NONE behind us16 one 18-wheeler. The only other vehicle besides those was the one of the trucker that had been next to us the 17 time. There were no signs of a traffic jam the entire 18 of our trip. It was as though the cars had all 19To this day we have no 20 as to how this could have happened.

绿矾（FeSO₄•7H₂O）可用于色谱分析剂、净水、照相制版等方面．下面是以铁屑（含少量锡等杂质）生产绿矾的一种方法：

已知：在H₂S饱和溶液中，SnS沉淀完全时溶液的pH为1.6；FeS开始沉淀时溶液的pH为3.0，沉淀完全时的pH为5.5．

（1）操作Ⅱ中用pH试纸测定溶液pH的操作是：____ ．

（2）操作Ⅱ中用硫酸酸化至pH=2的目的是____ ．

（3）操作Ⅲ中需要的玻璃仪器是烧杯、____ ．

（4）通入硫化氢至饱和的目的是：①除去操作I所得溶液中含有的Sn²⁺等杂质离子；②____ ．

（5）操作Ⅳ的顺序依次为：____ 、冷却结晶、____ ．

（6）操作Ⅳ得到的绿矾晶体用少量冰水洗涤，其目的是：①除去晶体表面附着的硫酸等杂质；②____ ．