物质发生化学变化的前后,总质量是否发生改变?是增加、减小还是不变?小刘、小李按下

题型:实验题

问题:

物质发生化学变化的前后,总质量是否发生改变?是增加、减小还是不变?小刘、小李按下面的步骤进行探究:

(1)提出假设:物质发生化学变化前后总质量不变。

(2)设计并进行实验:小刘设计的实验装置和选用药品如图A所示,小李设计的实验装置和选用药品如图B所示,他们在反应前后都进行了规范的操作、准确的称量和细致的观察。

①这两个实验所发生的化学反应方程式为:(提示:BaCl2与Na2SO4反应生成硫酸钡沉淀和氯化钠;Na2CO3与盐酸反应生成氯化钠、水、二氧化碳)

小刘的实验_________________________;小李的实验:_____________________________。

实验结论:小刘认为:在化学反应中,生成物的总质量与反应物的总质量相等;

小李认为:在化学反应中,生成物的总质量与反应物的总质量不相等。

②你认为____的结论正确,导致另一个实验结论错误的原因是:___________________。

③请从原子的角度分析你认为正确结论的原因:_______________。

④使用上述实验装置,请你选择另外两种药品进行实验达到实验目的,这两种药品可以是_____和____。(填化学式)[注:以上四种药品均不能再用]

考点:验证质量守恒定律
题型:实验题

阅读理解。

     One day a red rose blossomed (开花) in a forest. A pine tree not far away said:"What a beautiful flower.

I wish I could he that lovely.

     The rose said:"I am the most beautiful plant in this forest."

     Then the rose looked at a cactus (仙人掌) and said:" Look at that ugly plant. It is full of thorns (刺)"

     The pine tree said:"Red rose, you have thorns, too." Sometimes, the rose would look at the cactus and

say:"This plant is useless. How sorry I am to be his neighbor."

     Summer came and the plants and animals needed water, but no rain fell. One day the rose saw birds

stick (刺) their beaks (鸟嘴) into the cactus and then fly away. The rose asked what the birds were doing.

The pine tree explained that the birds got water from the cactus. The pine tree told the rose:"You can also

drink from it. The birds can bring water to you if you ask the cactus for help."

     The rose fell ashamed (羞愧的), but asked the cactus for help. The cactus kindly agreed and the birds

filled their beaks with water for the rose's roots (根).

     So the rose learned:never judge (判断) anyone by appearance (外表).

1. At the beginning of the story the rose thought that the cactus was _____.

A. ugly

B. lovely

C. beautiful 

2. Both the rose and the cactus have _____.

A. thorns

B. leaves

C. fruit

3. The underlined word "useless" in this passage means "_____" in Chinese. 

A. 无营养的

B. 不友好的

C. 无用的

4. Which of the following is True according to the story?

A. The birds could get water from the pine tree.

B. The rose got water from the cactus at last.

C. The pine tree wanted to get water from the rose.

5. What's the best title (标题) for the passage?

A. Plants and birds

B. Ways of growing roses

C. Appearance isn't everything.

题型:实验题

甲种商品每件m元,乙种商品的单价是甲种商品的单价的2倍,甲、乙两种商品各买2件,共需付(    )元.

题型:实验题

关于献血者联谊说法不正确的是()。

A.对保留献血者起重要作用

B.让献血者有归属感

C.血站不允许建立这个组织

D.献血者之间可以互相交朋友

E.促进输血事业的发展

题型:实验题

竹子的茎生长到一定程度后就不会继续长粗,下列解释正确的是[ ]

A.因为茎内没有形成层

B.因为茎内的木质部随着生长而退化

C.因为茎内没有木质部

D.因为形成层产生的韧皮部细胞及木质部细胞随着茎的生长而老化

题型:实验题

熏烟中有害成分为()、()。

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