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Hi, I'm Jessica
嗨，我是Jessica
and today I'm gonna be talking about a chemical demonstration I like to call
今天我要讲的化学演示叫作
"mirror, mirror"
"魔镜魔镜"
In this demo, MIT's Dr. John Dolhun will demonstrate Tollens test
MIT的John Dolhun博士将演示Tollens测试
a chemical test created by this man, Bernard Tollens
这是由这个人，十九世纪末德国化学家
a German chemist born in the late 1800's
Bernard Tollens所发明的化学测试
So let's watch Dr. Dolhun perform this demonstration here at MIT
作为MIT剑桥科学节的一部分，来看看Dolhun博士
as part of the Cambridge Science Festival
是如何演示这个的
OK, so I'm gonna be careful
好，我要小心了
and I'm going to pour my first substance into the flask
首先将第一种物质倒入烧瓶
my second substance
然后是第二种物质
down to the last drop
倒完最后一滴
and my third substance
然后是第三种物质
and we're going to do a little shaking
摇一摇
for mixing some things together
让它们能够充分混合
So what did Dr. Dolhun do?
Dolhun博士做了什么呢
Well, he added three solutions to the flask
他往烧瓶中添加了三种溶液
Solution 1 was glucose in water
溶液一是葡萄糖水溶液
Solution 2 was a mixture of silver nitrate and ammonium nitrate
溶液二是硝酸银和硝酸铵的混合溶液
And solution 3 was sodium hydroxide
溶液三是氢氧化钠
which is a base
一种碱
So let's focus on the second two solutions first
我们先来看后两种溶液
When you mix solutions 2 and 3, two things happen
溶液二三混合时，会发生两件事
First, you form Ag20
首先会形成Ag2O
which is insoluble in water
它不溶于水
so it precipitates out as a brown solid
会作为褐色固体沉淀出来
The sodium hydroxide
氢氧化钠
reacts with ammonium, NH4+
会同铵根离子NH反应
to produce ammonia,
NH3 生成氨 NH4
This dissolves the precipitate
这会溶解沉淀物
and you end up with Ag(NH3)2
最终得到Ag(NH3)2
which all has a positive charge
这整个带有一单位正电荷
This is soluble in water and it's called Tollens reagent
它溶于水，叫作Tollens试剂
Now the positive charge is born by the silver
正电荷来自于银离子
So we have in solution is essentially silver ions
溶液中基本上也就是银离子
Now looking at solution 1
再看溶液一
glucose looks like this
葡萄糖是这样的
We don't really care about this whole part of the molecule
分子的这一部分我们并不关心
So we're gonna call it R
可以记作R
for the rest
表示剩余部分
So glucose is basically this
葡萄糖可以写成这样
And this part of the glucose is going to start reacting with the silver ions
葡萄糖的这部分会同银离子反应
Let's watch what happens
看看会发生什么
