题干

同学们,你们爱吃巧克力吗?你们可知道,在巧克力中含有一种常见的化学物质﹣﹣草酸(化学式为C2H2O4). 草酸通常以晶体(C2H2O4•2H2O)的形式存在,在常温下为固体.以下是某化学兴趣小组提取了草酸晶体之后对其进行研究的过程.

【提出问题】草酸晶体受热分解产生了什么?

【猜想与假设】根据质量守恒定律,草酸晶体分解的产物中可能含水、CO或CO2

【实验论证】研究小组设计了以下实验装置(图1)对上述猜想进行了探究.

信息提示:装置B为干燥管,其中的无水硫酸铜与水反应会变成蓝色

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    Sixteen is a special age in the United States. There's often a special celebration for a girl's 16th birthday---a big party called Sweet-16. It is like a wedding reception(结婚晚宴) in the number of guests and gifts handed out.

    About a month before the party, the girl's family sends out invitations to the guests. They must buy a special present for the birthday girl and the girl guests find good dresses to wear. A sweet-16 present usually costs $40 to $60. This is about $20 more than the usual-cost of a birthday present.

    The party itself is not held at someone's house. The hostess rents(租赁) a reception hall for the event. Food, cake and a DJ are provided. Around 6'clock, guests arrive and meet the birthday girl. Then the girl and her father have a special father-daughter dance. After that, guests dance for about 30 to 45 minutes.

    Then there is the most important part of the Sweet-16 party, the candle-lighting ceremony.

    The sweet-16 hostess stands behind 16 unlit(未点燃的) candles and dedicates(献给) each candle to her friends, family, and anything that she feels is important to her. A lot of crying and hugging goes on at this time.

    Afterwards, people sit and eat. Most guests begin leaving around 11 o'clock.

    This school year, I have been to two Sweet-16s. I am one of the youngest students in my grade (My birthday is in December). I'll have to wait another year before I can have my own special Sweet-16 party. I can't wait for it!