题目

 Once there lived an old man in a mountain village. He was a famous hunter（猎人）. He often went hunting along the mountains. He was not afraid of any wild animals, even a tiger. One night, someone saw a tiger come into the village, and stole two sheep away. The next night the tiger came again. The villagers were frightened. They asked the old hunter to catch it so that they could have a safe life. When the old man heard about the tiger, he thought hard. He wondered why the tiger came at night twice but only stole the sheep. The next night he walked about outside the village. Sudd化学兴趣小组的同学发现实验台上一瓶标签破损的无色溶液（标签如图）．他们提出可能是Na2SO4、NaHCO3、Na2CO3溶液中的一种，于是决定对这瓶溶液进行实验探究．查阅资料：三种物质溶液在常温下的PH如下表 溶液Na2SO4NaHCO3Na2CO3pHpH=7pH＞7pH＞7（1）小新同学认为该溶液 的是 ， 理由是 ．（2）标签破损的原因 ．（3）为确定其成分，小新同学设计如下方案进行探究 实验步骤现象结论取该溶液少许于试管中，滴加过量的BaCl2溶液，振荡．①则该溶液是Na2CO3溶液过滤，向滤渣滴加稀盐酸．②（4）小芳认为可以设计更简单的实验方案，该方案是：（写出实验步骤、现象及结论）．