问题 问答题

某同学用氯化钠固体配制0.04mol/L的NaCl溶液500mL,设计了如下的操作步骤:A:计算;B:称量;C:洗涤转移;D:定容摇匀;E:溶液转移

回答下列问题

(1)实验中需要称量NaCl固体______g;称量时NaCl固体应该放在托盘天平的______盘.

(2)上述操作步骤的正确顺序是(添字母代号)______;

为保证实验的正常进行,所需仪器除了容量瓶(500mL规格)、托盘天平、量筒外,还要需要的实验仪器有:______.

(3)试分析下列操作对所配溶液的浓度有何影响及造成该影响的原因.

①为加速固体溶解,可稍微加热并不断搅拌.在未降至室温时,立即将溶液转移至容量瓶定容.对所配溶液浓度的影响是______(选填“偏低”或“偏高”或“无影响”),原因是______.

②定容后,加盖倒转摇匀后,发现溶液面低于刻度线,又滴加蒸馏水至刻度.对所配溶液浓度的影响是______(选填“偏低”或“偏高”或“无影响”),原因是______.

答案

(1)配制0.04mol/L的NaCl溶液500mL,n(NaCl)=0.04mol/L×0.5L=0.02mol,需要氯化钠的质量为:m(NaCl)=58.5g/mol×0.02mol=1.17g;

根据左物右码原则,称量时NaCl固体应该放在托盘天平的左盘,

故答案为:1.17;左;

(2)配制一定物质的量浓度的溶液步骤为:计算、称量、溶解、转移、洗涤、定容、摇匀等,所以操作步骤的正确顺序是:A、B、E、C、D;使用的仪器为:药匙、托盘天平、烧杯、玻璃棒、500mL容量瓶、胶头滴管,所以还缺少烧杯、玻璃棒、胶头滴管,

故答案为:A、B、E、C、D;烧杯、玻璃棒、胶头滴管;

(3)①在未降至室温时,立即将溶液转移至容量瓶定容,热的溶液体积偏大,冷却后溶液体积偏小,导致配制的溶液浓度偏高,

故答案为:偏大;溶液未冷却,导致定容时加水不足;

②定容后,加盖倒转摇匀后,发现溶液面低于刻度线,属于正常现象,不需要加入蒸馏水,若又滴加蒸馏水至刻度,导致配制的溶液体积偏大,溶液浓度偏小,

故答案为:偏小;倒转摇匀中部分溶液附在容量瓶颈部,故出现溶液液面低于刻度线,若再加水,会使溶液过多.

阅读理解

阅读理解。

     For most  people, the  word  " fashion "  means"clothes". People  may  

say " His  shirt is  in fashion. " or" She  is  wearing  a fashionable  coat. "

But  in  fact, there are fashions in holidays ,in restaurants , in films and

books. There are even fashions in school subjects,jobs, and in languages.

Fashions change as time goes. Ifyou look at pictures of people or things

from the past,you will see that fashions have changed. An English house

of 1750 was different from one of 1650. A fashionable manin 1780

looked very different from his grandson in 1860.Today fashions change

quickly. We hear about things much more quickly than in the past.

Newspapers, radios,telephones, televisions and Internet send

informationfrom one country to another in a few minutes. New fash-ions

mean that people will buy new things, so you see"There is money in

fashion. "

1 . From this passage we know that"fashion" means            .

A. many things

B. clothes

C. newspapers

D. everything

2. Which of the following things is fashionable today?

A. Doing morning exercises at school.

B. Having a family dinner on New Year's Day.

C. Leaming to sing songs on the radio.

D. Surfing on the Internet.

3. Today fashions change very quickly because .

A. people read newspapers every day

B. radios send information from one country to another

C. people can learn what is happening in the world quickly

D. new things that people like are often shown on TV

4. " There is money in fashion. " means .

A. Clothes are expensive

B. Fashions make big money

C. People like new things

D. Money comes from fashion

5. What is the hest title(标题) for the article?

A. Clothes

B. Fashions

C. Fashions in clothes

D. How to make money

单项选择题