Iodometry is an important experimental method in redox titration. The laboratory attempted to determine the equilibrium constant of the reaction $I_2+I^-=I_3^-$ using iodometry, with the procedure as follows:  

Weigh three portions of $0.5 \mathrm{~g}$ of finely ground iodine into three numbered ground-glass conical flasks labeled 1, 2, and 3. Add $\mathrm{80.0~mL}$ of KI solution with a concentration of $c_{0} (\mathrm{mol} \cdot \mathrm{L}^{-1})$ to flask 1; add $\mathrm{80.0~mL}$ of KI solution with a concentration of $2 c_{0} (\mathrm{mol} \cdot \mathrm{L}^{-1})$ to flask 2; and add $\mathrm{200.0~mL}$ of deionized water to flask 3. Add magnetic stir bars, stopper the flasks tightly, and stir the reaction at room temperature for 30 minutes. After the reaction, take the solutions from the three flasks and centrifuge to obtain the supernatant. Pipette $V_{s} \left(\mathrm{mL}\right)$ of the centrifuged solutions from flasks 1 and 2, dilute each with water to $\mathrm{50~mL}$, and titrate with a standard solution of $\mathrm{Na_{2}S_{2}O_{3}}$ at a concentration of $c \ (\mathrm{mol} \cdot \mathrm{L}^{-1})$. The volumes of $\mathrm{Na_{2}S_{2}O_{3}}$ standard solution consumed are $V_{1} \left(\mathrm{mL}\right)$ and $V_{2} \left(\mathrm{mL}\right)$, respectively. Then, pipette $5 V_{s} \left(\mathrm{mL}\right)$ of the centrifuged solution from flask 3 and titrate it with the same $\mathrm{Na_{2}S_{2}O_{3}}$ standard solution, consuming $V_{0} \left(\mathrm{mL}\right)$ of the standard solution.  

Using the given parameters $c, c_{0}, V_{0}, V_{1}, V_{s}$, the equilibrium constant $K$ of the reaction can be calculated.  

Which of the following operational errors would lead to an overestimation of the equilibrium constant $K$?  
1. The masses of the three portions of iodine are slightly different.  
2. After stirring, the solution in flask 3 becomes clear and transparent.  
3. When pipetting the solution from flask 1, solid settled at the bottom is accidentally drawn into the pipette.  
4. While preparing the KI solution, a small amount of solid KI is accidentally spilled after weighing.  
5. The $\mathrm{Na_{2}S_{2}O_{3}}$ standard solution was left for too long after standardization.
碘量法是氧化还原滴定中重要的实验方法。实验室试用碘量法测定 $I_2+I^-=I_3^-$ 反应的平衡常数，方法如下所示：称取三份 $0 . 5 \mathrm { ~ g}$ 研细的碘于编号为1、2、3的三个磨口锥形瓶中。1号瓶中加入 $\mathrm { 8 0 . 0 ~ m L }$ 浓度为 $c _ { 0 } ( \mathrm { m o l } \cdot \mathrm { L } ^ { - 1 } )$ 的KI溶液；2号瓶中加入 $\mathrm { 8 0 . 0 ~ m L }$ 浓度为 $2 c _ { 0 } ( \mathrm { m o l } { \cdot } \mathrm { L } ^ { - 1 } )$ 的KI溶液；3号瓶中加入 $2 0 0 . 0 \mathrm { ~ m L }$ 去离子水。加入磁力搅拌子，塞紧塞子后室温下搅拌反应30分钟。反应结束后，从三个瓶中取出溶液，离心得到上层清液。各取 $V _ { s } \left( \mathrm { m L } \right)$ 离心后的1号和2号溶液，加水稀释至 $5 0 ~ \mathrm { m L }$ 。用浓度为 $c \ ( \mathrm { m o l } \cdot \mathrm { L } ^ { - 1 } )$ 的 $\mathrm { N a _ { 2 } S _ { 2 } O _ { 3 } }$ 标准溶液滴定，消耗$\mathrm { N a _ { 2 } S _ { 2 } O _ { 3 } }$ 标准溶液的体积分别为 $V _ { 1 } \left( \mathrm { m L } \right)$和 $V _ { 2 } \left( \mathrm { m L } \right)$ 。然后取 $5 V _ { s } \left( \mathrm { m L } \right)$ 离心后的3号溶液，用相同浓度的 $\mathrm { N a _ { 2 } S _ { 2 } O _ { 3 } }$ 标准溶液滴定，消耗 $\mathrm { N a } _ { 2 } \mathrm { S } _ { 2 } \mathrm { O } _ { 3 }$ 标准溶液的体积为 $V _ { 0 } \left( \mathrm { m L } \right)$。

用题中所给的 $c , c _ { 0 } , V _ { 0 } , V _ { 1 } , V _ { s }$ 可以计算题目所给反应的平衡常数$K$。

下列操作失误会使平衡常数$K$的测定结果变大的有哪些？  
1. 三份碘的质量稍有不同。  
2. 搅拌结束后3号瓶澄清透明。  
3. 取1号溶液时不慎将沉在底部的固体吸入移液管。
4. 配置KI溶液时，称量完毕后不慎遗撒少量KI固体。
5. $\mathrm { N a _ { 2 } S _ { 2 } O _ { 3 } }$ 标准溶液标定完后放置过久。
1, 2, 3
3, 5
1, 4
2, 3, 4
2, 3, 5
2, 3
2, 3, 4, 5
3, 4
1, 2, 3
3, 5
1, 4
2, 3, 4
2, 3, 5
2, 3
2, 3, 4, 5
3, 4
The data from Erlenmeyer flasks 1 and 3 can be combined to calculate the equilibrium constant $K$. Flask 3 provides the saturated concentration of $I_2$, and together with the data from flask 1, the equilibrium constant for the reaction $I_2 + I^- = I_3^-$ can be obtained. The derivation yields $K = (5V_1 - V_0) * V_s / [(c_0V_s - 0.5cV_1 + 0.1cV_0) * V_0]$.

Analysis of the impact of operational errors on $K$:

1. Since iodine is in excess in the experiment, its mass has no effect on $K$.

<Checkpoint>[Iodine is in excess, so its mass has no effect on $K$.](1)</Checkpoint>

2. If flask 3 becomes clear and transparent after stirring, it indicates insufficient iodine was added, resulting in a measured saturated iodine concentration that is too low, leading to an overestimated equilibrium constant $K$.

<Checkpoint>[Error 2 causes the measured saturated iodine concentration to be too low, resulting in an overestimated $K$.](1)</Checkpoint>

3. If solid settled at the bottom is accidentally drawn into the pipette when sampling solution from flask 1, the measured $I_3^-$ concentration will be too high, leading to an overestimated equilibrium constant $K$.

<Checkpoint>[Error 3 causes the measured $I_3^-$ concentration to be too high, resulting in an overestimated $K$.](1)</Checkpoint>

4. If a small amount of KI solid is accidentally spilled after weighing during the preparation of the KI solution, the actual KI concentration will be less than $c_0$, meaning the $c_0$ used in calculations is overestimated. Based on the expression for $K$, an overestimated $c_0$ leads to an underestimated $K$.

<Checkpoint>[Error 4 causes $c_0$ to be overestimated, resulting in an underestimated $K$.](1)</Checkpoint>

5. If the standardized $\mathrm{Na_2S_2O_3}$ solution is left standing for too long after calibration, its concentration will decrease, meaning the $c$ used in calculations is overestimated. Based on the expression for $K$, an overestimated $c$ leads to an overestimated $K$.

<Checkpoint>[Error 5 causes $c$ to be overestimated, resulting in an overestimated $K$](1)</Checkpoint>

Therefore, the operations that lead to an overestimated $K$ are 2, 3, and 5.
锥形瓶1和3的数据合起来可以计算平衡常数$K$。锥形瓶3可得饱和$I_2$的浓度，结合锥形瓶1的数据可得反应$I_2+I^-=I_3^-$的平衡常数。推导得$K=(5V_1-V_0)*V_s/[(c_0V_s-0.5cV_1+0.1cV_0)*V_0]$

分析各操作失误对$K$的影响：

1. 实验中碘是过量的，所以碘的质量对$K$没有影响。

<Checkpoint>[碘过量，所以碘的质量对$K$没有影响。](1)</Checkpoint>

2. 搅拌结束后3号瓶澄清透明，说明碘添加量不够，测得的饱和碘浓度偏低，导致平衡常数$K$偏大。

<Checkpoint>[失误2使测得的饱和碘浓度偏低，$K$偏大。](1)</Checkpoint>

3. 取1号溶液时不慎将沉在底部的固体吸入移液管，则测得的$I_3^-$浓度偏大，导致平衡常数$K$偏大。

<Checkpoint>[失误3使测得的$I_3^-$浓度偏大，$K$偏大。](1)</Checkpoint>

4. 配置KI溶液时，称量完毕后不慎遗撒少量KI固体，会导致实际的KI浓度小于$c_0$，即计算中使用的$c_0$偏大，结合$K$的表达式可知$c_0$偏大会导致$K$偏小。

<Checkpoint>[失误4使$c_0$偏大，$K$偏小。](1)</Checkpoint>

5. $\mathrm { N a _ { 2 } S _ { 2 } O _ { 3 } }$ 标准溶液标定完后放置过久浓度会变小，即计算中使用的$c$偏大，结合$K$的表达式可知$c$偏大会导致$K$偏大。

<Checkpoint>[失误5使$c$偏大，$K$偏大](1)</Checkpoint>

所以使$K$偏大的操作有2、3和5。