问题 填空题

(1)某同学按如图装置对质量守恒定律进行实验探究,反应前天平平衡,然后将稀盐酸倒入烧杯中与碳酸钠充分反应后,再称量,观察到反应后天平不平衡,天平指针向______偏转(填“左”或“右”).该反应______质量守恒定律(填“遵守”或“不遵守”).反应后天平不平衡的原因是______.

(2)由质量守恒定律可知,化学反应前后,一定不变的是______;(填序号)

①原子种类;②原子数目;③分子种类;④分子数目;⑤元素种类;⑥物质种类.

答案

(1)盐酸与碳酸钠反应生成氯化钠、水、二氧化碳,而烧杯是敞开的,所以生成的二氧化碳逸散到空气中使质量减小,故指针偏右,但这并不意味着该反应不遵循质量守恒定律;

(2)化学反应的实质是分子破裂成原子,原子再重新组合成新的分子,所以反应前后原子的种类没有改变,原子的数目没有增减,原子的质量没有变化,元素的种类、元素的质量、物质的总质量都不变.

故答案为:(1)右;遵守;产生的二氧化碳气体逸到空气中去了

(2)①②⑤

阅读理解

Have you ever seen a horse with toes(脚趾)?Millions of years ago, horses had many toes. They had four toes on each front foot. They had three toes on each back foot. The horses were no bigger than the cats.These small horses lived in the forest. The toes helped the horses run on the soft, wet ground.

At first, it was very hot in the forest. But the weather changed. It became very cold. Many trees could not live in cold weather. The trees died and fell. Open fields took the place of forests. The sun made the ground dry and hard.

Horsed began to change, too. They began to get bigger. This took a long time. On the dry, hard land, horses needed only their middle toes for running. Their middle toes became hard. After a long time, horses had only one hard toe on each foot. Now we call this hard toe a hoof.

小题1:How many toes did a horse have millions of years ago?

A.14

B.12

C.16

D.13小题2:What does the underlined word “hoof” mean in Chinese?

A.尾巴

B.马鬃

C.腿

D.蹄子小题3:What was the weather like in the forest at first?

A.Very warm

B.Very hot

C.Very cold

D.Very cool小题4:Which is WRONG according to the passage?

A.The horses were much bigger than the cats millions of years ago.

B.The trees died and feel because the weather changed.

C.On the dry, hard land, horses needed only their middle toes for running.

D.The horses have fewer toes than before.小题5:The main idea of the passage is that_______________.

A.horses had three toes on each back foot.

B.horses lived in the hot forest

C.horses changed a lot over the years

D.horses didn’t like the cold weather

单项选择题