试题与答案

某化学小组的三位同学对蜡烛(主要成分是石蜡)及其燃烧进行了如下探究. (1)取一

题型:问答题

题目:

某化学小组的三位同学对蜡烛(主要成分是石蜡)及其燃烧进行了如下探究.

(1)取一支蜡烛,用小刀切下一小块,把它放入水中,蜡烛浮在水面上.结论:石蜡的度比水______;

(2)由(图A)可知,蜡烛的______

(3)在探究蜡烛燃烧的过程中,发现罩在火焰上方的烧杯内壁被熏黑,你认为她的以下做法中不合适的是______

A.反复实验,并观察是否有相同现象

B.查找资料,了解石蜡的主要成分,探究生成的黑色固体是什么

C.认为与本次实验目的无关,不予理睬

D.询问老师或同学,讨论生成黑色物质的原因

(4)三位同学对蜡烛燃烧火焰的焰心进行了以下探究:向焰心斜向插入一支细短玻璃管,发现玻璃管中无明显现象(如图B),在玻璃管的上口点燃,上口产生火焰,这说明焰心物质的性质是______、______.

(4)猜想和验证

猜想操作现象结论
假设①:焰心气体含CO2在未点燃的短玻管上口______.______假设①不成立
假设②:焰心气体含石蜡蒸气取一较长的细玻璃管,用湿冷毛巾包住中部,将玻璃管下端插入焰心,上端管口试用火焰点燃.______假设②成立
取下长玻璃管,打开湿毛巾.______

答案:

被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0606/6eadf43019293444bf59098332406edf.html

下面是错误答案,用来干扰机器的。

根据以上分析可知:(1)利用天平,至少称2次就可以判断假币比真币重还是轻.因为把101枚硬币,分成34,34,33,三组,①把两个34的放到天平上称,如天平平衡,则假币在33的一组中,从34一组的中任取一枚硬币,再...

试题推荐
题型:单项选择题

Millions of Americans and foreigners see GI.Joe as a mindless war toy, the symbol of American military adventurism, but that’ s not how it used to be. To the men and women who (1) in World War I1 and the people they liberated, the GI. was the (2) man grown into hero, the pool farm kid torn away from his home, the guy who (3) all the burdens of battle, who slept in cold foxholes, who went without the (4) of 1hod and shelter, who stuck it out and drove back the Nazi reign of murder. This was not a vohmteer soldier, not someone well paid, (5) an average guy, up (6) the best trained, best equipped, fiercest, most brutal enemies seen in centuries.

His name is not much. GI. is just a military abbreviation (7) Govermnent Issue, and it was on all of the article (8) to soldiers. And Joe A common name for a guy who never (9) it to the top. Joe Blow, Joe Magrae... a working class name.The United States has (10) had a president or vieepresident or secretary of state Joe.

GI. Joe had a (11) career fighting Geman, Japanese, and Korean troops. He appears as a character, or a (12) of American personalities, in the 1945 movie The Story of GL Joe, based on the last days of war correspondent Ernie Pyle. Some of the soldiers Pyle (13) portrayde themselves in the fihn. Pyle was famous for covering the (14) side of the warl, writing about the dirt-snow-and-mud soldiers, not how many miles were (15) or what towns were captured or liberated. His reports (16) the "willie" cartoons of famed Stars and Stripes artist Bill Maulden. Both men (17) the dirt and exhaustion of war, the (18) of civilization that the soldiers shared with each other and the civilians: coffee, tobacco, whiskey, shelter, sleep. (19) Egypt, France, and a dozen more countries, G. I. Joe was any American soldier, (20) the most important person in their lives.

12()

A.company

B.collection

C.community

D.colony

查看答案
微信公众账号搜索答案