问题 问答题

现有铜与另一种金属的混合物粉末,另一种金属可能是镁、铁、锌中的一种,现欲测定其组成.取该混合物粉末10g放入烧杯中,将200g 19.6%的稀硫酸分四次加入该烧杯中,充分反应后,测得剩余固体质量数据记录如下:

次数1234
加入稀硫酸的质量/g50505050
剩余固体的质量/g7.65.22.82.4
求:(1)该混合物粉末中铜的质量分数为______

(2)该混合物粉末中另一金属为______

(3)第三次加入硫酸充分反应后,所得溶液中溶质的质量分数是多少?

答案

(1)因铜与酸不反应,反应后剩余固体质量2.4g即为其质量.

2.4g
10g
×100%=24%

故答案为:24%

(2)每50g稀硫酸可与2.4g这种金属恰好完全反应.设该金属为R,其相对原子质量为r

R+H2SO4═RSO4+H2

r   98

2.4g  50g×19.6%

r
2.4g
=
98
50g×19.6%

解得:r=24

相对原子质量为24的元素是镁元素.

故答案为:Mg

(3)第三次加入硫酸充分反应后,所用硫酸的质量为150g,反应的金属的质量为10g-2.8g=7.2g.反应后生成的溶质为MgSO4.

设生成MgSO4的质量为x,生成H2的质量为y

Mg+H2SO4═MgSO4+H2

98    120    2

150g×19.6%    x     y

98
150g×19.6%
=
120
x
=
2
y

解得:x=36g   y=0.6g

C%=

36g
10g-2.8g+150g-0.6g
×100%=23.0%

答:所得溶液中溶质的质量分数为23.0%

阅读理解

Everything that humans hear is in the form of waves (波).Just as the eye sees light wares in the form of colors, the ear and the eye Curs these different waves into signals that the brain (大脑) can make sense of.

The ears and brain have an Amazing amities to recognize(识别)particular sounds. For example, a mother often can tell when her baby is crying even if there are other crying babies in the same room. This is because the sound of her baby’s cry has special meaning to her and the brain has recorded is importance.

The ability to recognize sounds improves with experiences. As the brain receives information about sounds from day to day, it stores the information in its memory. When the brain hears new sounds, it gives meaning to them based on the information already in the memory. This is why certain words or songs can make a person happy. Often it is not the words or songs themselves that cause this feeling. The sounds are connected to happy memories for that person.

After hearing process controlled by the brain is to decide where a sound is coming from. One ear is usually closer to the source (来源) of a sound than the other ear is. Sound waves are stronger when they reach the ear that is closer. They also reach the closer ear first. The brain recognizes these differences and uses them to decide the location of the source of the sound.

小题1:Which of the following shows the normal hearing process of a mother hearing her baby crying?

a. The ears receive the sound waves.

b. The mother recognizes her baby’s cry.

c. The ears turn the sound waves into signals.

d. The baby’s cry ravels in the form of sound waves

e. The brain connects the signals to the information in me memory.

A.d-a-c-b-e

B.d-a-c-e-b

C.a-d-c-b-e

D.a-d-c-e-b小题2: Certain words or songs can change tarpon’s moods mainly because of his         .

A.lifestyle

B.personality

C.experiences

D.hobbies小题3:According to the last paragraph, It will be the most difficult for a person who has lost the hearing in one ear to tell         .

A.where the source of a sound is

B.how loud a sound is

C.when a sound starts to appear

D.what makes a sound小题4:What is the best title for this passage?

A.Human Brain’s Amazing Facts

B.Human Hearing Characteristics

C.How to improve Hearing

D.How Do Humans Hear

问答题 简答题