[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.09,0:00:03.51,Default,,0000,0000,0000,,我们上集遇到了弱酸
Dialogue: 0,0:00:03.56,0:00:05.82,Default,,0000,0000,0000,,今天我们来试个弱碱的例子
Dialogue: 0,0:00:05.86,0:00:09.02,Default,,0000,0000,0000,,我们以氨为例吧
Dialogue: 0,0:00:09.07,0:00:10.75,Default,,0000,0000,0000,,氨(NH3)
Dialogue: 0,0:00:10.79,0:00:12.96,Default,,0000,0000,0000,,就是1个氮(N) 和3个氢(H)
Dialogue: 0,0:00:12.99,0:00:14.31,Default,,0000,0000,0000,,它是个弱碱
Dialogue: 0,0:00:14.35,0:00:17.67,Default,,0000,0000,0000,,因为它喜欢从水那儿获得氢
Dialogue: 0,0:00:17.70,0:00:19.43,Default,,0000,0000,0000,,让水只剩下一个氢氧根
Dialogue: 0,0:00:19.45,0:00:21.90,Default,,0000,0000,0000,,所以它增加了氢氧根的浓度
Dialogue: 0,0:00:21.94,0:00:25.13,Default,,0000,0000,0000,,所以如果溶液里有些氨分子
Dialogue: 0,0:00:25.17,0:00:26.62,Default,,0000,0000,0000,,加上水分子
Dialogue: 0,0:00:26.66,0:00:29.60,Default,,0000,0000,0000,,我准备倒点水进去
Dialogue: 0,0:00:29.65,0:00:35.35,Default,,0000,0000,0000,,往溶液里加水
Dialogue: 0,0:00:35.39,0:00:37.51,Default,,0000,0000,0000,,因为这是个弱碱
Dialogue: 0,0:00:37.55,0:00:40.92,Default,,0000,0000,0000,,所以反应不会只往一个方向进行
Dialogue: 0,0:00:40.97,0:00:46.25,Default,,0000,0000,0000,,这反应是个可逆平衡反应
Dialogue: 0,0:00:46.29,0:00:48.16,Default,,0000,0000,0000,,又因为这是个弱碱 它…
Dialogue: 0,0:00:48.20,0:00:52.05,Default,,0000,0000,0000,,这个时候布伦斯特定义
Dialogue: 0,0:00:52.09,0:00:53.62,Default,,0000,0000,0000,,就派上用场了
Dialogue: 0,0:00:53.66,0:00:56.60,Default,,0000,0000,0000,,它是个质子的受体而不是供体
Dialogue: 0,0:00:56.65,0:01:00.71,Default,,0000,0000,0000,,所以它变成了铵根
Dialogue: 0,0:01:00.75,0:01:04.51,Default,,0000,0000,0000,,或者铵阳离子
Dialogue: 0,0:01:04.55,0:01:07.01,Default,,0000,0000,0000,,因为铵根比氨多了一个氢
Dialogue: 0,0:01:07.06,0:01:09.56,Default,,0000,0000,0000,,所以现在它多了一个质子
Dialogue: 0,0:01:09.61,0:01:11.39,Default,,0000,0000,0000,,所以是正电
Dialogue: 0,0:01:11.41,0:01:12.87,Default,,0000,0000,0000,,同时它在溶液里
Dialogue: 0,0:01:12.91,0:01:14.67,Default,,0000,0000,0000,,又因为它从水里拿走了氢
Dialogue: 0,0:01:14.71,0:01:20.39,Default,,0000,0000,0000,,所以再加上溶液中的OH-
Dialogue: 0,0:01:20.43,0:01:21.22,Default,,0000,0000,0000,,记住
Dialogue: 0,0:01:21.26,0:01:22.96,Default,,0000,0000,0000,,根据质子酸碱理论
Dialogue: 0,0:01:23.00,0:01:25.00,Default,,0000,0000,0000,,因为它是个质子的受体
Dialogue: 0,0:01:25.04,0:01:26.89,Default,,0000,0000,0000,,所以它被看成碱
Dialogue: 0,0:01:26.93,0:01:28.40,Default,,0000,0000,0000,,或者如果根据阿伦尼乌斯的定义
Dialogue: 0,0:01:28.44,0:01:32.18,Default,,0000,0000,0000,,因为溶液中OH-的浓度增加了
Dialogue: 0,0:01:32.22,0:01:34.05,Default,,0000,0000,0000,,所以它也是阿仑尼乌斯碱
Dialogue: 0,0:01:34.09,0:01:35.94,Default,,0000,0000,0000,,好 已知…
Dialogue: 0,0:01:35.98,0:01:38.26,Default,,0000,0000,0000,,随机取个数吧
Dialogue: 0,0:01:38.30,0:01:48.15,Default,,0000,0000,0000,,假设是0.2mol/L的NH3
Dialogue: 0,0:01:48.20,0:01:52.58,Default,,0000,0000,0000,,那么它pH会是多少呢？
Dialogue: 0,0:01:52.62,0:01:55.75,Default,,0000,0000,0000,,那么pH是多少咧
Dialogue: 0,0:01:55.79,0:01:58.46,Default,,0000,0000,0000,,0.2mol/L的氨的pH
Dialogue: 0,0:01:58.50,0:01:59.56,Default,,0000,0000,0000,,那么第一步就是
Dialogue: 0,0:01:59.61,0:02:00.76,Default,,0000,0000,0000,,要找出
Dialogue: 0,0:02:00.80,0:02:03.64,Default,,0000,0000,0000,,这个碱反应的平衡常数
Dialogue: 0,0:02:03.68,0:02:09.27,Default,,0000,0000,0000,,我刚刚去维基百科了一下
Dialogue: 0,0:02:09.31,0:02:11.10,Default,,0000,0000,0000,,我差点说成液体百科
Dialogue: 0,0:02:11.15,0:02:12.85,Default,,0000,0000,0000,,因为我老在讲液体
Dialogue: 0,0:02:12.89,0:02:15.12,Default,,0000,0000,0000,,还有平衡 平衡百科
Dialogue: 0,0:02:15.16,0:02:17.78,Default,,0000,0000,0000,,不过我去的是维基百科啦
Dialogue: 0,0:02:17.82,0:02:19.23,Default,,0000,0000,0000,,那里有一个小图表
Dialogue: 0,0:02:19.27,0:02:20.92,Default,,0000,0000,0000,,几乎包含所有你要查的化合物
Dialogue: 0,0:02:20.95,0:02:23.18,Default,,0000,0000,0000,,还有它们的pKb
Dialogue: 0,0:02:23.23,0:02:26.67,Default,,0000,0000,0000,,pKb
Dialogue: 0,0:02:26.71,0:02:28.28,Default,,0000,0000,0000,,你看 这有个p
Dialogue: 0,0:02:28.31,0:02:29.01,Default,,0000,0000,0000,,那就说明
Dialogue: 0,0:02:29.07,0:02:39.19,Default,,0000,0000,0000,,它是平衡常数的负常用对数
Dialogue: 0,0:02:39.23,0:02:43.32,Default,,0000,0000,0000,,查表可知 它的pKb是4.75
Dialogue: 0,0:02:43.36,0:02:44.95,Default,,0000,0000,0000,,我们现在做一点小运算
Dialogue: 0,0:02:44.98,0:02:47.40,Default,,0000,0000,0000,,来解平衡常数
Dialogue: 0,0:02:47.44,0:02:48.15,Default,,0000,0000,0000,,我们来看看吧
Dialogue: 0,0:02:48.19,0:02:50.42,Default,,0000,0000,0000,,如果我们两边加个负号
Dialogue: 0,0:02:50.46,0:02:53.94,Default,,0000,0000,0000,,就得到以弱碱水解的
Dialogue: 0,0:02:53.98,0:02:57.80,Default,,0000,0000,0000,,平衡常数的常用对数
Dialogue: 0,0:02:57.84,0:02:58.96,Default,,0000,0000,0000,,这里的b就表示碱
Dialogue: 0,0:02:59.00,0:03:02.25,Default,,0000,0000,0000,,等于-4.75
Dialogue: 0,0:03:02.29,0:03:06.37,Default,,0000,0000,0000,,或者说10的-4.75次方就是Kb
Dialogue: 0,0:03:06.41,0:03:11.71,Default,,0000,0000,0000,,Kb=10^(-4.75)
Dialogue: 0,0:03:11.75,0:03:14.41,Default,,0000,0000,0000,,这个指数不是口算就能算出来的
Dialogue: 0,0:03:14.45,0:03:16.17,Default,,0000,0000,0000,,所以我要拿出计算器来算
Dialogue: 0,0:03:16.21,0:03:26.22,Default,,0000,0000,0000,,所以如果是10的-4.75次方 等于
Dialogue: 0,0:03:26.26,0:03:31.03,Default,,0000,0000,0000,,近似取1.8×10^(-5)
Dialogue: 0,0:03:31.07,0:03:37.74,Default,,0000,0000,0000,,这个平衡常数就等于1.8×10^(-5)
Dialogue: 0,0:03:37.78,0:03:39.48,Default,,0000,0000,0000,,那现在我们就可以利用这些数
Dialogue: 0,0:03:39.52,0:03:41.87,Default,,0000,0000,0000,,来做一个运算
Dialogue: 0,0:03:41.91,0:03:43.99,Default,,0000,0000,0000,,和上集的那个非常相似
Dialogue: 0,0:03:44.02,0:03:46.48,Default,,0000,0000,0000,,在这儿很难直接算出
Dialogue: 0,0:03:46.52,0:03:48.22,Default,,0000,0000,0000,,氢离子浓度 对吗？
Dialogue: 0,0:03:48.25,0:03:50.32,Default,,0000,0000,0000,,因为我们的平衡反应只有氢氧根
Dialogue: 0,0:03:50.36,0:03:53.36,Default,,0000,0000,0000,,但如果知道了氢氧根的浓度
Dialogue: 0,0:03:53.40,0:03:55.76,Default,,0000,0000,0000,,然后我就能倒回去算氢浓度
Dialogue: 0,0:03:55.80,0:03:58.85,Default,,0000,0000,0000,,因为氢氧根浓度 乘氢离子浓度
Dialogue: 0,0:03:58.90,0:04:02.75,Default,,0000,0000,0000,,一定得等于10的负14次
Dialogue: 0,0:04:02.80,0:04:07.17,Default,,0000,0000,0000,,或者算出pOH以后 再加上pH就是14
Dialogue: 0,0:04:07.21,0:04:09.34,Default,,0000,0000,0000,,我们在好几个视频之前就讲过这个了
Dialogue: 0,0:04:09.38,0:04:13.29,Default,,0000,0000,0000,,所以这个平衡常数
Dialogue: 0,0:04:13.32,0:04:15.39,Default,,0000,0000,0000,,或者它的表达式就会是这个
Dialogue: 0,0:04:15.43,0:04:24.07,Default,,0000,0000,0000,,1.8×10^(-5)等于
Dialogue: 0,0:04:24.11,0:04:26.06,Default,,0000,0000,0000,,分母是
Dialogue: 0,0:04:26.10,0:04:28.93,Default,,0000,0000,0000,,反应物的浓度
Dialogue: 0,0:04:28.96,0:04:30.73,Default,,0000,0000,0000,,记住啊 不用管溶剂
Dialogue: 0,0:04:30.78,0:04:32.55,Default,,0000,0000,0000,,所以只要写NH3就行
Dialogue: 0,0:04:32.59,0:04:35.06,Default,,0000,0000,0000,,我们放了0.2mol/L进去
Dialogue: 0,0:04:35.10,0:04:36.74,Default,,0000,0000,0000,,不过一部分 设为x吧
Dialogue: 0,0:04:36.78,0:04:37.94,Default,,0000,0000,0000,,会变成
Dialogue: 0,0:04:37.98,0:04:40.29,Default,,0000,0000,0000,,右边这些离子
Dialogue: 0,0:04:40.33,0:04:43.72,Default,,0000,0000,0000,,那么分母中 我们要用0.2减去
Dialogue: 0,0:04:43.76,0:04:46.22,Default,,0000,0000,0000,,x 就是转化成右边的量
Dialogue: 0,0:04:46.26,0:04:47.45,Default,,0000,0000,0000,,所以在右边
Dialogue: 0,0:04:47.49,0:04:52.97,Default,,0000,0000,0000,,会有浓度为x的NH4+ 和OH-
Dialogue: 0,0:04:53.02,0:04:57.98,Default,,0000,0000,0000,,这是氨的浓度
Dialogue: 0,0:04:58.03,0:05:00.91,Default,,0000,0000,0000,,然后是x乘以x
Dialogue: 0,0:05:00.95,0:05:07.98,Default,,0000,0000,0000,,这是NH4+的浓度 这是4
Dialogue: 0,0:05:08.02,0:05:10.69,Default,,0000,0000,0000,,然后这个浓度
Dialogue: 0,0:05:10.73,0:05:16.15,Default,,0000,0000,0000,,这儿就是OH-的浓度 对吧？
Dialogue: 0,0:05:16.19,0:05:17.77,Default,,0000,0000,0000,,我们只要解出x
Dialogue: 0,0:05:17.81,0:05:21.29,Default,,0000,0000,0000,,我们来算一下吧 解x
Dialogue: 0,0:05:21.33,0:05:23.83,Default,,0000,0000,0000,,一旦有了x的值 就得到了OH-的浓度
Dialogue: 0,0:05:23.87,0:05:25.30,Default,,0000,0000,0000,,我们就可以算出pOH
Dialogue: 0,0:05:25.35,0:05:28.05,Default,,0000,0000,0000,,接着就能算出pH
Dialogue: 0,0:05:28.09,0:05:32.01,Default,,0000,0000,0000,,好了 等式两边同时乘以(2-x)
Dialogue: 0,0:05:32.07,0:05:35.32,Default,,0000,0000,0000,,接下来你懂的 这步近似化简
Dialogue: 0,0:05:35.36,0:05:36.72,Default,,0000,0000,0000,,和上集那个是一样的
Dialogue: 0,0:05:36.76,0:05:39.70,Default,,0000,0000,0000,,当它比这里这个数
Dialogue: 0,0:05:39.75,0:05:42.41,Default,,0000,0000,0000,,小几个数量级
Dialogue: 0,0:05:42.45,0:05:49.43,Default,,0000,0000,0000,,我想说…
Dialogue: 0,0:05:49.47,0:05:50.64,Default,,0000,0000,0000,,提示就是
Dialogue: 0,0:05:50.68,0:05:52.13,Default,,0000,0000,0000,,经验法则有时还是挺好用的
Dialogue: 0,0:05:52.15,0:05:53.78,Default,,0000,0000,0000,,我们来解这个二次方程吧
Dialogue: 0,0:05:53.81,0:05:54.88,Default,,0000,0000,0000,,不过你可以稍微想想
Dialogue: 0,0:05:54.92,0:05:57.54,Default,,0000,0000,0000,,有时可以忽略中间这项
Dialogue: 0,0:05:57.58,0:05:58.89,Default,,0000,0000,0000,,不过我们先乘上它吧
Dialogue: 0,0:05:58.93,0:06:02.96,Default,,0000,0000,0000,,0.2乘以1.8等于0.36
Dialogue: 0,0:06:03.01,0:06:08.35,Default,,0000,0000,0000,,0.36×10^(-5) 对吧？
Dialogue: 0,0:06:08.39,0:06:11.66,Default,,0000,0000,0000,,2乘1.8是3.6 这个就是0.36
Dialogue: 0,0:06:11.69,0:06:20.65,Default,,0000,0000,0000,,-1.8乘10^(-5)乘x 对吧？
Dialogue: 0,0:06:20.69,0:06:25.10,Default,,0000,0000,0000,,等于x2
Dialogue: 0,0:06:25.14,0:06:27.87,Default,,0000,0000,0000,,咱们把东西全部搬到同一侧
Dialogue: 0,0:06:27.92,0:06:31.45,Default,,0000,0000,0000,,我要把它们都放到右边
Dialogue: 0,0:06:31.49,0:06:35.17,Default,,0000,0000,0000,,就得到0等于x2…
Dialogue: 0,0:06:35.22,0:06:38.48,Default,,0000,0000,0000,,方程两边同时加上这个
Dialogue: 0,0:06:38.52,0:06:43.46,Default,,0000,0000,0000,,加上1.8×10^(-5)x
Dialogue: 0,0:06:43.50,0:06:49.33,Default,,0000,0000,0000,,1.8×10^(-5)
Dialogue: 0,0:06:49.37,0:06:50.09,Default,,0000,0000,0000,,这样你就可以
Dialogue: 0,0:06:50.13,0:06:52.98,Default,,0000,0000,0000,,把系数和x清楚分开
Dialogue: 0,0:06:53.02,0:07:00.35,Default,,0000,0000,0000,,减去0.36×10^(-5)
Dialogue: 0,0:07:00.39,0:07:01.51,Default,,0000,0000,0000,,解这个方程
Dialogue: 0,0:07:01.55,0:07:03.45,Default,,0000,0000,0000,,再说一次 如果想简单点
Dialogue: 0,0:07:03.48,0:07:05.71,Default,,0000,0000,0000,,你可以忽略这一项
Dialogue: 0,0:07:05.75,0:07:08.02,Default,,0000,0000,0000,,然后直接用平方根算
Dialogue: 0,0:07:08.07,0:07:08.79,Default,,0000,0000,0000,,不过我们不用这样
Dialogue: 0,0:07:08.84,0:07:10.32,Default,,0000,0000,0000,,我们用一般的二次方程的解法
Dialogue: 0,0:07:10.35,0:07:12.30,Default,,0000,0000,0000,,那么a是1
Dialogue: 0,0:07:12.34,0:07:13.85,Default,,0000,0000,0000,,b在这
Dialogue: 0,0:07:13.88,0:07:14.97,Default,,0000,0000,0000,,那就是b
Dialogue: 0,0:07:14.99,0:07:15.97,Default,,0000,0000,0000,,而这个是c
Dialogue: 0,0:07:16.01,0:07:17.87,Default,,0000,0000,0000,,你只要把它们放进解的公式里面\N【译者注：一元二次方程的一般形式为ax2+bx+c=0】
Dialogue: 0,0:07:17.89,0:07:20.66,Default,,0000,0000,0000,,先写-b
Dialogue: 0,0:07:20.70,0:07:26.70,Default,,0000,0000,0000,,也就是 -1.8×10^(-5)
Dialogue: 0,0:07:26.75,0:07:27.49,Default,,0000,0000,0000,,加减
Dialogue: 0,0:07:27.53,0:07:29.52,Default,,0000,0000,0000,,我们只要加的 因为如果用了减
Dialogue: 0,0:07:29.56,0:07:30.79,Default,,0000,0000,0000,,就会得到一个负的浓度
Dialogue: 0,0:07:30.84,0:07:33.22,Default,,0000,0000,0000,,所以加上 这个平方根
Dialogue: 0,0:07:33.27,0:07:35.49,Default,,0000,0000,0000,,这里好难算
Dialogue: 0,0:07:35.53,0:07:37.46,Default,,0000,0000,0000,,先是b2
Dialogue: 0,0:07:37.50,0:07:39.71,Default,,0000,0000,0000,,b等于1.8×10^(-5)
Dialogue: 0,0:07:39.75,0:07:42.16,Default,,0000,0000,0000,,这是1.8
Dialogue: 0,0:07:42.20,0:07:45.76,Default,,0000,0000,0000,,它的平方是3.24
Dialogue: 0,0:07:45.80,0:07:48.88,Default,,0000,0000,0000,,所以是3.24乘以
Dialogue: 0,0:07:48.92,0:07:50.36,Default,,0000,0000,0000,,10^(-5)的平方就是
Dialogue: 0,0:07:50.40,0:07:53.86,Default,,0000,0000,0000,,10^(-10)
Dialogue: 0,0:07:53.90,0:07:58.10,Default,,0000,0000,0000,,减去4乘a a是1
Dialogue: 0,0:07:58.14,0:07:59.90,Default,,0000,0000,0000,,乘以c c是负的
Dialogue: 0,0:07:59.95,0:08:02.50,Default,,0000,0000,0000,,所以就是4乘… 负负得正
Dialogue: 0,0:08:02.54,0:08:08.74,Default,,0000,0000,0000,,乘以0.36×10^(-5)
Dialogue: 0,0:08:08.78,0:08:20.62,Default,,0000,0000,0000,,4乘以0.36等于1.44
Dialogue: 0,0:08:20.66,0:08:22.27,Default,,0000,0000,0000,,我应该可以口算的
Dialogue: 0,0:08:22.31,0:08:26.05,Default,,0000,0000,0000,,结果就是1.44e(-5)
Dialogue: 0,0:08:26.08,0:08:28.80,Default,,0000,0000,0000,,就是乘10^(-5) 我写下来吧
Dialogue: 0,0:08:28.83,0:08:32.77,Default,,0000,0000,0000,,这是1.44
Dialogue: 0,0:08:32.82,0:08:36.75,Default,,0000,0000,0000,,当然 这些还得除以2a 也就是2
Dialogue: 0,0:08:36.80,0:08:37.71,Default,,0000,0000,0000,,嗯…
Dialogue: 0,0:08:37.72,0:08:39.32,Default,,0000,0000,0000,,这就是x的值
Dialogue: 0,0:08:39.37,0:08:41.20,Default,,0000,0000,0000,,我的OH-的浓度
Dialogue: 0,0:08:41.25,0:08:42.93,Default,,0000,0000,0000,,我算算
Dialogue: 0,0:08:42.97,0:08:51.65,Default,,0000,0000,0000,,3.24×10^(-10)
Dialogue: 0,0:08:51.69,0:08:52.83,Default,,0000,0000,0000,,就是这个
Dialogue: 0,0:08:52.88,0:09:04.42,Default,,0000,0000,0000,,加上1.44×10^(-5)等于这个数
Dialogue: 0,0:09:04.46,0:09:06.06,Default,,0000,0000,0000,,那么根号下就等于这个
Dialogue: 0,0:09:06.10,0:09:07.71,Default,,0000,0000,0000,,然后取它的平方根
Dialogue: 0,0:09:07.78,0:09:13.28,Default,,0000,0000,0000,,也就是0.5次方
Dialogue: 0,0:09:13.32,0:09:16.18,Default,,0000,0000,0000,,就是0.00379
Dialogue: 0,0:09:16.25,0:09:19.02,Default,,0000,0000,0000,,我再个颜色
Dialogue: 0,0:09:19.07,0:09:26.00,Default,,0000,0000,0000,,算出来x就等于-1.8×10^(-5)
Dialogue: 0,0:09:26.04,0:09:33.83,Default,,0000,0000,0000,,加上0.003794
Dialogue: 0,0:09:33.88,0:09:35.69,Default,,0000,0000,0000,,再除以2
Dialogue: 0,0:09:35.73,0:09:36.95,Default,,0000,0000,0000,,算一下
Dialogue: 0,0:09:36.99,0:09:43.30,Default,,0000,0000,0000,,我要减去这儿负的这项
Dialogue: 0,0:09:43.33,0:09:44.18,Default,,0000,0000,0000,,我得到这个值
Dialogue: 0,0:09:44.22,0:09:45.46,Default,,0000,0000,0000,,我只要减去这个
Dialogue: 0,0:09:45.48,0:09:53.87,Default,,0000,0000,0000,,减去1.8e(-5) 等于这个
Dialogue: 0,0:09:53.91,0:09:55.23,Default,,0000,0000,0000,,这是分子的值
Dialogue: 0,0:09:55.24,0:09:57.36,Default,,0000,0000,0000,,现在我只要把它除以2就行
Dialogue: 0,0:09:57.41,0:10:04.25,Default,,0000,0000,0000,,除以2以后 就等于0.001……
Dialogue: 0,0:10:04.27,0:10:05.17,Default,,0000,0000,0000,,我来写一下
Dialogue: 0,0:10:05.21,0:10:06.46,Default,,0000,0000,0000,,x就出来了
Dialogue: 0,0:10:06.47,0:10:08.43,Default,,0000,0000,0000,,我再随便换个颜色
Dialogue: 0,0:10:08.47,0:10:17.78,Default,,0000,0000,0000,,x等于0.001888
Dialogue: 0,0:10:17.82,0:10:20.14,Default,,0000,0000,0000,,呐 后面还有3等等
Dialogue: 0,0:10:20.18,0:10:21.98,Default,,0000,0000,0000,,不过如果你还记得一开始那个等式
Dialogue: 0,0:10:22.02,0:10:23.03,Default,,0000,0000,0000,,x是什么呢？
Dialogue: 0,0:10:23.07,0:10:26.63,Default,,0000,0000,0000,,它既是铵根的浓度
Dialogue: 0,0:10:26.67,0:10:28.67,Default,,0000,0000,0000,,也是氢氧根的浓度
Dialogue: 0,0:10:28.71,0:10:31.12,Default,,0000,0000,0000,,但我们只关心氢氧根的浓度
Dialogue: 0,0:10:31.16,0:10:35.39,Default,,0000,0000,0000,,所以x就等于氢氧根浓度
Dialogue: 0,0:10:35.43,0:10:38.53,Default,,0000,0000,0000,,现在如果我想算出pOH
Dialogue: 0,0:10:38.57,0:10:42.36,Default,,0000,0000,0000,,我只要对这个数取负对数
Dialogue: 0,0:10:42.38,0:10:44.63,Default,,0000,0000,0000,,就是等于
Dialogue: 0,0:10:44.67,0:10:46.46,Default,,0000,0000,0000,,我们先取个对数吧
Dialogue: 0,0:10:46.50,0:10:49.61,Default,,0000,0000,0000,,它的对数就是这个 然后加个负号
Dialogue: 0,0:10:49.63,0:10:54.93,Default,,0000,0000,0000,,结果就是2.72
Dialogue: 0,0:10:54.97,0:10:57.78,Default,,0000,0000,0000,,现在如果我们想算出pH
Dialogue: 0,0:10:57.83,0:11:01.99,Default,,0000,0000,0000,,氢离子的浓度
Dialogue: 0,0:11:02.04,0:11:04.75,Default,,0000,0000,0000,,要记住 一个25°C下的
Dialogue: 0,0:11:04.77,0:11:07.39,Default,,0000,0000,0000,,水溶液里
Dialogue: 0,0:11:07.43,0:11:15.08,Default,,0000,0000,0000,,水的pK等于pOH+pH
Dialogue: 0,0:11:15.12,0:11:19.08,Default,,0000,0000,0000,,25°C下的pK是14
Dialogue: 0,0:11:19.12,0:11:23.68,Default,,0000,0000,0000,,因为浓度是10^(-14)mol/L
Dialogue: 0,0:11:23.72,0:11:25.08,Default,,0000,0000,0000,,嗯… 不再深入了
Dialogue: 0,0:11:25.13,0:11:26.91,Default,,0000,0000,0000,,只要知道它们分别是10^(-7)就行
Dialogue: 0,0:11:26.95,0:11:28.67,Default,,0000,0000,0000,,总之 这就是水解离的
Dialogue: 0,0:11:28.71,0:11:30.52,Default,,0000,0000,0000,,平衡常数
Dialogue: 0,0:11:30.57,0:11:34.77,Default,,0000,0000,0000,,而pOH 水是中性时 它就是7
Dialogue: 0,0:11:34.81,0:11:38.71,Default,,0000,0000,0000,,也就是说 OH-的浓度是10^(-7)
Dialogue: 0,0:11:38.76,0:11:40.15,Default,,0000,0000,0000,,取负对数以后就是7
Dialogue: 0,0:11:40.19,0:11:44.42,Default,,0000,0000,0000,,不过现在呢 咱们知道OH-的浓度高了很多
Dialogue: 0,0:11:44.46,0:11:45.64,Default,,0000,0000,0000,,pOH是2.72
Dialogue: 0,0:11:45.69,0:11:47.63,Default,,0000,0000,0000,,记住 负对数很容易看错的
Dialogue: 0,0:11:47.67,0:11:52.62,Default,,0000,0000,0000,,应该是pOH越低 OH-浓度就越高
Dialogue: 0,0:11:52.66,0:11:53.65,Default,,0000,0000,0000,,对吧？
Dialogue: 0,0:11:53.70,0:11:57.61,Default,,0000,0000,0000,,pOH越低呢 就是这个数低了 嗯？
Dialogue: 0,0:11:57.64,0:11:59.07,Default,,0000,0000,0000,,pOH越低
Dialogue: 0,0:11:59.12,0:12:01.10,Default,,0000,0000,0000,,pH就越高
Dialogue: 0,0:12:01.14,0:12:03.97,Default,,0000,0000,0000,,我不想把你弄太糊涂
Dialogue: 0,0:12:04.01,0:12:05.18,Default,,0000,0000,0000,,究竟pH是多少呢？
Dialogue: 0,0:12:05.22,0:12:14.91,Default,,0000,0000,0000,,这儿pH就等于 14减去2.72
Dialogue: 0,0:12:14.95,0:12:20.53,Default,,0000,0000,0000,,我算算 这个减去14就等于…
Dialogue: 0,0:12:20.57,0:12:24.05,Default,,0000,0000,0000,,就取11.3吧
Dialogue: 0,0:12:24.07,0:12:26.78,Default,,0000,0000,0000,,pH等于11.3
Dialogue: 0,0:12:26.82,0:12:28.15,Default,,0000,0000,0000,,这个数很合理
Dialogue: 0,0:12:28.19,0:12:30.84,Default,,0000,0000,0000,,因为咱们说过它是弱碱嘛
Dialogue: 0,0:12:30.89,0:12:33.79,Default,,0000,0000,0000,,氨 是一个弱碱
Dialogue: 0,0:12:33.83,0:12:35.40,Default,,0000,0000,0000,,所以它是碱性的
Dialogue: 0,0:12:35.44,0:12:39.48,Default,,0000,0000,0000,,所以它会使pH大于中性的7
Dialogue: 0,0:12:39.53,0:12:41.93,Default,,0000,0000,0000,,所以pH就应该大于7
Dialogue: 0,0:12:41.97,0:12:44.55,Default,,0000,0000,0000,,不过你可以和强碱比较一下
Dialogue: 0,0:12:44.59,0:12:47.53,Default,,0000,0000,0000,,它们浓度为1mol/L时 pH就是14
Dialogue: 0,0:12:47.56,0:12:49.25,Default,,0000,0000,0000,,这让我们的pH…
Dialogue: 0,0:12:49.29,0:12:54.07,Default,,0000,0000,0000,,虽然我们的浓度只有0.2mol/L
Dialogue: 0,0:12:54.11,0:12:57.01,Default,,0000,0000,0000,,总之 比起化学 这更像数学题
Dialogue: 0,0:12:57.05,0:12:59.80,Default,,0000,0000,0000,,最后希望这集讲明白了一些东西