问题 问答题 简答题

采用古蔡法进行砷盐限量检查时,加入碘化钾和氯化亚锡的作用是什么?

答案

参考答案:

加入碘化钾和氯化亚锡的主要作用是将供试品中五价砷还原为三价砷;溶液的碘离子与反应中的锌离子能形成配合物,使生成砷化氢的反应不断进行;抑制锑化氢生成;氯化亚锡可与锌粒表面形成锌锡齐,起去极化作用,使锌粒与盐酸作用缓和,产生氢气的速度均匀,有利于砷斑的形成,增加反应的灵敏度和准确度。

单项选择题
阅读理解

Schooling Matters

March 25, 2014  Chengdu  Michelle Obama

You see, the truth is that I grew up like many of you. My mom, my dad, my brother and I, we lived in a tiny apartment in Chicago, which is one of the largest cities in America. My father worked at the local water plant…

While we certainly weren’t rich, my parents had big dreams for me and my brother. They had only a high school education themselves, but they were determined to send us both to universities.

So they poured all of their love and all of their hope into us, and they worked hard. They saved every penny. And I know that wasn’t easy for them, especially for my father. You see, my father had serious illness called multiple sclerosis(多发性硬化症). And as he got sicker, it got harder for him to walk, and it took him longer to get dressed in the morning.

But no matter how tired he felt, no matter how much pain he was in, my father hardly ever missed a day of work, because he was determined to give me and my brother a better life. And every day, like so many of you, I felt the weight of my parents’ sacrifices on my shoulders. Every day, I wanted to make them proud.

So, while most American kids attend public schools near their homes, when it was time for me to attend high school, I took an exam and got into a special public high school where I could get a better education. But the school was very far from my home, so I had to get up early every morning and ride a bus for an hour, sometimes an hour and a half if the weather was bad. And every afternoon, I’d ride that same bus back home and then immediately start my homework, often studying late into the night – and sometimes I would wake up at 4:30 or 5:00 in the morning to study even more.

And it wasn’t easy. But whenever I got tired or discouraged, I would just think about how hard my parents were working for me. And I would remember something my mother always told me – she said, “A good education is something that no one can take away from you.”

小题1:The passage can be sorted as a        

A.self-introduction

B.short story

C.news report

D.speech draft (草稿)小题2:Which of the following is TRUE about Michelle Obama and her family?

A.Her parents were poor but had good educational backgrounds.

B.She attended a public high school near her home.

C.Her father suffered a serious disease and became disabled.

D.She was aware of her parents’ sacrifices and expectations.小题3:Which of the following words best describes Michelle’s father?

A.Optimistic.

B.Humorous.

C.Strong-minded

D.Generous小题4:What does Michelle mainly want to tell readers in this excerpt?

A.We should work hard and get good educations.

B.Our parents always have high expectations for us.

C.She is an ordinary person from an ordinary family.

D.The road to the US First Lady is not easy.