问题 选择题

下列离子方程式书写正确的是

A.Ba(OH)2溶液与过量的NaHCO3溶液混合Ba2++2OH+2HCO3BaCO3↓+CO32+H2O

B.次氯酸钙溶液中通入少量SO2气体:Ca2++2ClO+SO2+H2OCaSO3↓+2HClO

C.金属钾与水反应 K +2 H2OK+ +2 OH+ H2

D.醋酸与氢氧化钠溶液的反应 H+ + OHH2O

答案

答案:A

离子方程式的书写涉及了对反应物和产物的物态、溶解性、氧化还原性、电离情况等物理化学性质的理解,考查考生对“双基”的掌握和综合运用化学知识的能力。

选项B中,因为ClO有氧化性,而SO2有还原性,两者要发生氧化还原反应,产物应是CaSO4和Cl-,所以不正确。选项C中,反应等式两边电量不守恒,所以不正确。

选项D中,醋酸是弱电解质不能拆成离子形式,所以也不正确。

单项选择题

Bernard Jackson is a free man today, but he has many bitter memories. Jackson spent five, years in prison after a jury wrongly convicted him of raping two women. At Jackson’s trial, although two witnesses testified that Jackson was with them in another location at the times of the crimes, he was convicted anyway. Why The jury believed the testimony of the two victims, who positively identified Jackson as the man who had attacked them. The court eventually freed Jackson after the police found the man who had really committed the crimes. Jackson was similar in appearance to the guilty man. The two women had made a mistake in identity. As a result, Jackson has lost five years of his life.

The two women in this case were eyewitnesses. They clearly saw the man who attacked them, yet they mistakenly identified an innocent person. Similar incidents have occurred before. Eyewitnesses to other crimes have identified the wrong person in a police lineup or in photographs.

Many factors influence the accuracy of eyewitness testimony. For instance, witnesses sometimes see photographs of several suspects before they try to identify the person they saw in a line-up of people. They can become confused by seeing many photographs or similar faces. The number of people in the line-up, and whether it is a live line-up or a photograph, may also affect a witness’s decision. People sometimes have difficulty identifying people of other races. The questions the police ask witnesses also have an effect on them.

Are some witnesses more reliable than others Many people believe that police officers are more reliable than ordinary people. Psychologists decided to test this idea, and they discovered that it is not true. Two psychologists showed a film of crimes to both police officers and civilians. The psychologists found no difference between the police and the civilians in correctly remembering the details of the crimes.

Despite all the possibilities for inaccuracy, courts cannot exclude eyewitness testimony from a trial. American courts depend almost completely on eyewitness testimony to resolve court cases. Sometimes it is the only evidence to a crime, such as rape. Furthermore, eyewitness testimony is often correct. Although people do sometimes make mistakes, many times they really do identify individuals correctly.

American courts depend on the ability of the 12 jurors, and not the judges, to determine the accuracy of the witness’s testimony. It is their responsibility to decide if a certain witness could actually see, hear, and remember what occurred.

In a few cases, the testimony of eyewitnesses has convicted innocent people. More importantly, it has rightly convicted a larger number of guilty people; consequently, it continues to be of great value in the American judicial system.

According to the passage, () might influence the witness’s identification of suspects.

A.the education of the witness

B.the time of the day the crime occurs

C.the appearances of the suspect

D.the age of the suspect

单项选择题