问题 问答题

重庆市黔江区有一保存比较完好的地质公园,其“小南海”水下公园是古代某一村庄因地震而下沉形成,风景优美,水中暗藏秘密.潜水员潜入深水区进行探测作业时需要携带供氧等设备.供氧设备中有种供氧剂(用R表示,R为纯净物)能与二氧化碳或水接触产生氧气.现将7.8g R投入73.8g 水中,充分反应后得到80g溶液.请回答:

(1) 反应方程式2R+2H2O═4NaOH+O2↑中R的化学式为______;理论上产生氧气的质量为______克.

(2) 计算反应后所得溶液的溶质质量分数(写出计算过程).

答案

(1)根据反应方程式2R+2H2O═4NaOH+O2↑,反应后所有生成物的粒子中共含有Na、H、O三种元素的原子个数分别为4、4、6,而反应物水的2个分子中只含有4个H原子和2个O原子,所以在物质R的2个分子中应含有4个Na原子和4个O原子,物质R的化学式可表示为Na2O2

根据质量守恒定律,理论上产生氧气的质量=73.8g+7.8g-80g=1.6g

故答案为:Na2O2 ;1.6;

(2)设生成氢氧化钠的质量为x

2Na2O2+2H2O═4NaOH+O2

156          160

7.8g          x

156
7.8g
=
160
x
 

解得:x=8g

反应后所得溶液溶质质量分数=

8g
80g
×100%=10%

答:反应后所得溶液的溶质质量分数为10%.(其它计算过程合理也可给分)

填空题
单项选择题

(A)

Around the world more people are taking part in dangerous sports and activities. Now, there are people who look for an immediate excitement from a risky activity which may only last a few minutes or even seconds.

I would consider bungee jumping (蹦极) to be a good example of such an activity. You jump from a high place 200 meters above the ground with an elastic (弹性的) rope tied to your feet. You fall at up to 150 kilometers an hour until the rope stops you from hitting the ground. It is said that about 2 million people around the world have now tried bungee jumping. Other activities which most people would say are as risky as bungee jumping include jumping from tall buildings and diving into the sea from the top of high cliffs.

Why do people take part in such activities as these Some psychologists suggest that it is because life in modem societies has become safe and boring. Not very 10ng ago, people’s lives were constantly in danger. They had to go out and hunt for food, diseases could not easily be cured, and life was a continuous battle for survival.

Nowadays, according to many people, life offers little excitement. They live and work in quite safe conditions: they buy food in shops, and there are doctors and hospitals to look after them if they become ill. The answer for some of these people is to look for danger in activities such as bungee jumping.

Which of the following is true according to the passage()。

A. About 200,000 people in the world have tried bungee jumping.

B. In order to keep one safe, a rope is tied to feet of the jumping.

C. Diving into the sea from the top of the cliffs is much more dangerous than bungee jumping.

D. Many people nowadays feel life dull because they haven’t tried bungee jumping.