问题
问答题 论述题
测定SiO2时，（1）灼烧后为什么放在干燥器内冷却才能进行称量？（2）灼烧称量为什么进行恒重？
答案
参考答案：
（1）因为天平不能称量热的东西，故须冷却。放在干燥器内冷却，保证无水SiO2不会从空气中吸收水分而导致误差。
（2）灼烧称量SiO2须进行恒重，以示SiO2的水化物、易挥发性物质分解完全，滤纸灰化干净。
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测定SiO2时，（1）灼烧后为什么放在干燥器内冷却才能进行称量？（2）灼烧称量为什么进行恒重？
参考答案：
（1）因为天平不能称量热的东西，故须冷却。放在干燥器内冷却，保证无水SiO2不会从空气中吸收水分而导致误差。
（2）灼烧称量SiO2须进行恒重，以示SiO2的水化物、易挥发性物质分解完全，滤纸灰化干净。
It amazed me—every time I saw Joe，he was smiling.It didn’t ____ whether he had to stop at a stop light，or if he were the seventh person in ____ at the bank，and the service stopped just before he got there.Joe ___ smiled.It made me wonder why he seemed so ____ every day. Having observed Joe with other people，I ____ something else also.Joe asked people how they were doing，and really seemed to listen to their ____.If someone were hurting，he had __7__ for him and kind words，and offered to ____ in any way he could. It made me think...What if I tried to smile more？A(n) ____ of sorts began when I went to the grocery store.I smiled as I went up and down the aisles...and people I didn’t even ___ smiled back at me.Some even ____！The little kid in the cart(购物车) who was giving his mother a ____ time saw me smile and ____ talking...and，you guessed it.He made a shy little attempt at a smile.The man in the handicapped(残疾的) cart ____ a person to reach something...I could get that for him.The smile even transferred over to him，and he ____me. As I drove home，I was smiling.I ____ what I had just learned，and when someone passed me and gave me a(n) ____，I smiled at him.He looked puzzled. Now I know a smile is a small thing，but what if we were all to try to smile a few more times each day？I couldn’t believe how ___ I felt.Nothing in my life had changed，____ maybe it had.For what I learned was that such a small thing could ____ not only my spirits，but those around me as well.
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