问题 填空题

用火柴、澄清的石灰水和一只干燥的烧杯,探究干燥的白纸中的元素成分.

(1)通过证明白纸中含有C和H两种元素.

(2)本实验能否证明白纸中含有O元素?为什么?

答案

(1)实验步骤:点燃干燥的白纸,用冷而干燥的烧杯罩在火焰上方,发现烧杯内壁有水珠生成,根据质量守恒定律可知白纸中一定含有氢元素;迅速把烧杯倒过来,向烧杯内加入澄清的石灰水振荡,发现澄清的石灰水变浑浊,根据质量守恒定律可知二氧化碳中的碳元素一定来自白纸,即白纸中一定含有碳元素.

(2)烧杯壁上有水珠生成,说明生成了水,水由氢、氧元素组成,反应物氧气中只含氧元素,根据质量守恒定律可知水中的氢元素一定来自白纸,即白纸中一定含有氢元素;澄清石灰水变浑浊,说明生成了二氧化碳,二氧化碳由碳、氧元素组成,反应物氧气中只含氧元素,根据质量守恒定律可知二氧化碳中的碳元素一定来自白纸,即白纸中一定含有碳元素,无法判断水和二氧化碳中的氧元素是否全部自氧气,因此只能说白纸中可能含有氧元素.

故答案为:(1)点燃干燥的白纸,用冷而干燥的烧杯罩在火焰上方,发现烧杯内壁有水珠生成,根据质量守恒定律可知白纸中一定含有氢元素;迅速把烧杯倒过来,向烧杯内加入澄清的石灰水振荡,发现澄清的石灰水变浑浊,根据质量守恒定律可知二氧化碳中的碳元素一定来自白纸,即白纸中一定含有碳元素;

(2)不能;有氧气参加反应,因此无法判断水和二氧化碳中的氧元素是否全部自氧气,因此只能说白纸中可能含有氧元素.

选择题
单项选择题

Effective communication is essential for all organisations. It links the activities of the various parts of the organisation and ensures that everyone is working towards a Common goal. It is also extremely important for motivating employees. Staff need to know how they are getting on, what they are doing right and in which areas they could improve. Working alone can be extremely difficult and it is much easier if someone takes an interest and provides support. Employees need to understand why their job is important and how it contributes to the overall success of the firm. Personal communication should also include target setting. People usually respond well to goals, provided these are agreed between the manager and subordinate and not imposed.

However, firms often have communications problems that can undermine their performance. In many cases, these problems occur because messages are passed on in an inappropriate way. There are of course, several ways of conveying information to others in the organisation. These include speaking to them directly, e-mailing, telephoning or sending a memo. The most appropriate method depends on what exactly it is you are communicating. For example, anything that is particularly sensitive or confidential, such as an employee’s appraisal, should be done face-to-face.

One of the main problems for senior executives is that they do not have the time or resources needed to communicate effectively. In large companies, for example, it is impossible for senior managers to meet and discuss progress with each employee individually. Obviously this task can be delegated but at the cost of creating a gap between senior management and staff. As a result, managers are often forced to use other methods of communication. Like memos or notes, even if they know these are not necessarily the most suitable means of passing on messages.

The use of technology, such as e-mail, mobile phones and network system, is speeding up communication immensely. However, this does not mean that more investment in technology automatically proves beneficial, systems can become outdated or employees may lack appropriate training. There are many communications tools now available but a firm cannot afford all of them. Even if it could, it does not actually need them all. The potential gains must be weighed up against the costs, and firms should realise that more communication does not necessarily mean better communication.

As the number of people involved in an organisation increase, the use of written communication rises even faster. Instead of a quick conversation to sort something out numerous messages can be passed backwards and forwards. This can lead to a tremendous amount of paperwork and is often less effective than face to face communication. When you are actually talking to someone you can discuss things until you are happy they have understood and feedback is immediate. With written messages, however, you are never quite sure how it will be received. What you think you have said and what the other person thinks you have said can be very different.

The amount of written information generated in large organisations today can lead to communication overload. So much information is gathered that it gets in the-way of making decisions. Take a look at the average manager’s desk and you will see the problem—it is often covered in letters, reports and memos. This overload can lead to inefficiencies. For example, managers may not be able to find the information they want when they need it. Communication is also becoming more difficult with the changes occurring in employment patterns. With more people working part-time and working from home, managing communication is becoming increasingly complex.

According to the article, what is the effect of receiving large amounts of written information()

A. It is counter-productive

B. It causes conflict in a company

C. It leads to changes in work patterns

D. It makes the main points more difficult to identify