铁酸钠是污水处理过程中使用的一种新型净水剂，制取铁酸钠(M)的化学方程式如下：
2Fe(NO3)3+16NaOH+3C12==2M+6NaNO3+6NaCl+8H2O则M的化学式为
A．Na2Fe2O8
B．NaFeO4
C．Fe2NaO4
D．Na2FeO4
答案：D
题目分析：由反应的化学方程式2Fe(NO3)3+16NaOH+3C12==2M+6NaNO3+6NaCl+8H2O可知，
反应前 反应后
Fe原子 2 0
N原子 6 6
O原子 34 26
Na原子 16 12
H原子 16 16
C1原子 6 6
根据质量守恒定律，化学变化前后原子的种类、数目不变，可判断生成物2M分子中含有2个Fe原子、4个Na原子和8个O原子，则1个M分子中含有1个Fe原子、2个Na原子和4个O原子，故物质M的化学式为Na2FeO4。故选D
点评：本题考查化学式的推断，利用质量守恒定律中的原子守恒来推断是常用的方法，学生应注意守恒思想在解题中的重要作用。
Robby was 11 years old when his mother (a single mom) sent him to have his first piano lesson. I prefer that students begin at an earlier age, but Robby said that it had always been his mother’s 1 to hear him play the piano. So I 2 him as a student. Although Robby worked very hard, he didn’t have a basic 3 of music. However, he never 4 up and continued. And at the end of each weekly lesson he’d always say: “My mom is going to hear me 5 some day.” But it seemed 6 . He didn’t have a natural talent or ability for music. One day Robby 7 to our lessons very late. He told me that his mom had been 8 and unable to take him to piano lessons, but he was still 9 in class. He asked if he could take part in my concert and I 10 . The night of the concert came. The high school gym(体育馆) was 11 with parents, friends and relatives. The concert was going well. Then, Robby came up on stage. He announced (宣布) that he had chosen Mozart’s Concerto No 21 in C Major. I was not prepared for what I heard next. His 12 danced on the keys… He played so 13 that everyone was on his feet, clapping excitedly. In tears, I ran up on stage, “Oh, Robby! How could you do it?” “Well, Miss Hondorf... remember I told you my mom was sick? Well, actually she had cancer(癌) and 14 away this morning. And well… she was born deaf, so tonight was the first time she ever heard me play at the 15 . I wanted to make it special and show her I could do it! My mother’s dream came true at last.”
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