Chromatography Lab 色谱法实验

Chromatography Lab 色谱法实验

1

Purpose 目标

Determine the specific heat by measuring the amount of thermal energy transferred in a chemical reaction.

通过测量化学反应中转移的热能来计算出一个物质的比热容。

2

Materials 材料

3 beakers

12 chromatography paper strips

3 wooden sticks

4 pens (3 knows/ collected from students and 1 unknowns/ left at crime scene)

3个烧杯

12 张色谱法的纸条

3根木头棍

4只钢笔(3根已知钢笔/ 从学生那里收集到的和1根未知钢笔/ 在犯罪现场被遗留下来的)

Diagram 图表

Chemicals 化学品

3

Procedure 过程

4

Observation and Data collection

观察与数据分析

Observation----Each strip of chromatography paper with four different inks is a set of strips of chromatography paper pasted on wooden sticks, and then placed in three different solvents (Mixture, Ethanol, Methanol). As time goes by, Solvent climbs up the chromatography paper at different speeds. In the end, Methanol climbs the highest, Mixture climbs second, and Ethanol climbs the shortest. The dye of Ink 1 and 2 in Methanol separate to transparent， gray, purple. The dye of Ink 2 and 4 in Methanol separate to blue, light purple, dark purple, light pink. The dyes of Ink 1 and 2 in Ethanol separate to transparent and purple. The dyes of Ink 3 and 4 in Ethanol separate to blue, pink, purple. The dye of Ink 1 and 2 in Mixture separate to transparent, black, purple. The dye of Ink 2 and 4 in the Mixture is separate to blue, purple, pink.

观察----每条层析纸条和四种不同的墨水被称为一组层析纸条，并且每组都会粘在一根木棍上，然后放进三个不同的溶剂里面。(混合物, 乙醇, 甲醇). 随着时间的流动，溶剂会以不同的速度 “爬上”层析纸。到最后，甲醇爬得最高，混合物排第二，乙醇爬得距离最短。墨水1和2里的染料在甲醇中分离为透明，灰色，和紫色。墨水2和4里的染料在乙醇中分离为蓝色，淡紫色，和深紫色。墨水1和2里的染料在乙醇中分离为透明和紫色。墨水3和4里的染料在乙醇中分离为蓝色，粉色，和紫色。墨水1和2里的染料在混合物中中分离为透明，黑色，和紫色。墨水2和4里的染料在混合物中中分离为蓝色，紫色，和粉色。

Changes within 0 mins ~ 5 mins

1-5分钟之间的改变

Changes within 5mins ~ 10mins

5-10分钟之间的改变

Changes within 10mins ~ 15mins

10-15分钟之间的改变

Data Collection 数据收集

5

Data Analysis 数据分析

To compare the position of the band in the sample with the standard position to determine which the band is the same as the unknown pen we have to calculate the Rf value by this equation:

通过比较样本条带上的位置与标准位置来确定哪个条带和未知笔相同，我们要用以下公式来求出Rf值：

Result: Compare the Rf values of three pens tothe  unknowns pen, the pen 3 has most similar Rf values with unknowns pen, therefore pen 3 is the are the items left by the murderer.

结果: 比较三根钢笔的Rf值和未知钢笔的Rf值，3号钢笔与未知钢笔有最接近的Rf值，所以谋杀者在现场掉落的是三号钢笔。

6

Discussion 讨论

Chromatography paper separates substances on the basis of their differences in solubility in a solvent to achieve the purpose of identifying substances. As the solvent climbs up because of the capillary action, it would also carry the ink up the chromatography paper. Then chromatography paper would appear various pigments based on different chemicals have a different solubility. Different solvents would climb different heights and speeds only affected by the strength attraction to the paper, but the climbing speed and heights of pigments are affected by the strength of their attraction to the paper and the solvent.

色谱纸根据物质在溶剂中溶解度的差异来分离物质，来达到鉴别物质的目的。在溶剂通过毛细管作用向上爬的时候，会同时带动到墨水。然后层析纸会通过化学物质不同的溶解度来呈现出不同的颜色。不同的溶剂会爬升不同的高度和速度，因为会受到对纸和溶剂的吸引力的影响。

In order to understand the principle of Chromatography, we need to start from the reason why the solvent will climb to the paper. As Capillary action occurs at the time that adhesion between the solvent and the object is overcome and cohesion within the solvent, the solvent would ignore the gravity and climb up the paper. According to the concept of polar attract to polar, nonpolar attract to nonpolar, and attraction increase as the IMFs increase, we can infer the Chromatography paper was polar based on all three solvents( Mixture, Ethanol, Methanol) were polar. It is the fundamental requirement for capillary action to occur. All of the three solvents have LDF、hydrogen bonding、dipole dipole, which means chromatography paper must also have hydrogen bonding, dipole dipole, and strongest LDFs to break up the cohesion force between in ethanol molecule, and then form adhesion force with it.

为了能明白色谱法的原理，我们要从为什么溶剂会往上爬升这个点入手。由于毛细管作用发生在溶剂与物体之间的粘附和溶剂里的内聚力被克服掉了，溶剂会忽略地心引力并往上爬升。根据极性吸引极性，非极性吸引非极性，和吸引力随着分子间作用力增加而增加的这些个概念，我们可以通过三种溶剂（混合物，乙醇，和甲醇）的极性来推理出层析纸也是极性的。这个是毛细血管作用发生的最基础的要求。所有三个溶剂都有伦敦色散力，氢键，和取向力，这就代表着层析纸也要有氢键，取向力，和伦敦色散力来拆散乙醇分子间的内聚力和粘附力。

Based on the observation and the data collection, the ranking list for solvents to climb from high to low is Methanol, Mixture, and Ethanol. Under the situation of all of the three solvents having LDF、hydrogen bonding and dipole-dipole, the difference only shows up by the LDF. According to the bigger electrons cloud the stronger LDFs to order strength of LDFs from strong to weak would be Ethanol, Mixture, Methanol. We can infer that the height of solvent increases as the attraction between solvent and paper decreases. The science concept behind it is that as the attraction increases the strength of the intermolecular bonding would be stronger which required more force to separate the molecule so which caused a different climbing height of the solvents.

根据观察和数据收集，溶剂爬升的排名从高到低是甲醇，混合物，和乙醇。在三个溶剂都有氢键，取向力，和伦敦色散力的情况下，差异仅有伦敦色散力显示。根据越大的电子可以聚更强的伦敦色散力，拥有从强到弱的伦敦色散力排名是乙醇，混合物，和甲醇。我们可以推理出溶剂爬升的距离增加随着溶剂与纸的吸引力减少。背后的科学理念是吸引力会将分子间键合增强，导致需要更多的力才能分离分子。

Generally, the stronger the intermolecular forces between solute(in this case, the chemicals in the ink) and solvent, the more soluble the solute is in the solvent. Because when the solutes are dissolved in the solvent, if solvent and solute have stronger intermolecular forces, it means that they will have more abilities capable of capturing each other and thus combine with each other more quickly and easily. But it doesn't mean the solute will climb higher. In the Chromatography Lab, we cannot ignore a general factor, which is the intermolecular force between Chromatography paper and solute. As we identify the kinds of IMFs that Chromatography paper has in before, it has stronger LDFs than all solvents, as the polarity of the solute increases which means there will be stronger LDFs. Under the same conditions of IMFs, larger LFDs will have more attraction to each other. Therefore, the greater the polarity of Solute, the more attracted to Chromatography paper. In other words, larger molecules which have lower polarity and it would travel longer distances and faster. This is the basic concept supported chromatography can use to separate the different chemicals in a mixture.

通常来说，溶剂和溶质（墨水里的化学物质）之间的分子间作用力越强，溶质在溶剂中的溶解度越大。因为当溶质在溶剂里溶解的时候，如果溶质溶剂的分子间作用力更强的话，就代表在它们有更大的能力来互相吸引，从而更快速，更容易地互相结合。但是这不代表溶质会爬升的更高。在这个实验里，我们不能忽略一个因素，也就是溶质与层析纸之间的分子间作用力。我们之前已经推理出层析纸里面都有什么不同的分子间作用力了：它有着比所有溶剂都要强的伦敦色散力，随着溶质极性的增加，伦敦色散力也会增加。在一样的分子间作用力的情况下，较大的伦敦色散力将相互吸引更多。因此，溶质的极性越大，就越会被层析纸吸引。换句话来说，具有较低极性的较大分子，会爬升的更高且更快。这个是色谱法能证明的一个最基础的概念，能用来分离一个混合物中不同化学物质。

After understanding the concept, people can perfectly use Chromatography in many fields. For example, it is used for solving crimes, checking the substances contained in pigments on fruits to infer health, extracting pigments from plants, etc. In conclusion, concentration chromatography is a very effective scientific method to separate organic and inorganic compounds for analysis and research.

在理解了概念之后，人们可以在许多领域完美地使用色谱法。比如说，它可以用来破案，检查水果色素所含的物质来推断新鲜/健康程度，从植物中提取色素，等等。综上所述，色谱法是一个能有效地分离有机和无机化合物的科学方法。

7

Error Analysis 错误分析

The data used to calculate the error percentage Rf value of purple of Ink 3 and Ink 4.

用来计算误差百分比的墨水3和4的的Rf值：

Error 1: The length of the ink 3 strip was longer than ink 4 strip when they both fixed on the stick led to pink in ink3 has longer distance.

误差 1: 当两条都粘在木棍上的时候，墨水3条的长度比墨水4条的要长，导致墨水3条中的粉色距离更长。

Propagation: Because the length of the ink 3 strip was longer than ink 4 strip led to ink3 strip has more time for the chromatography paper to absorb the solvent so the solutes in ink3 would separate more properly than the solute in ink4, therefore the distance of pink in ink3 is further than ink4, which affected the Rf value of pink in ink3 is bigger than the actual Rf value. In order to fix it, after attaching the strips to the wooden sticks, measure their length with a ruler, and repeat the construction with scissors until the length is completely consistent before putting it into the solvent.

分析: 因为墨水3号条的长度比墨水4号条的要长，这导致了墨水3号条有更多的时间来让层析纸条吸收溶剂，所以墨水3号条里的溶质比4号条里的分离得更好，这就是为什么墨水3号里面粉色的距离要比墨水4号的要长，这也就同样影响到了墨水3号里粉色的Rf值:比原本的数值更大。为了弥补这个错误，在把纸条粘在木棍上之后，用一个尺子来量它们的长度，并用剪子来修整长度直到所有纸条都一样长，然后再放到溶剂里面。

误差 2: 因为火苗太小所以会消失得很快，导致在我们反应过来之前温度已经下降了，导致真实温度比我们收集到的温度会高一点。

Error 2: Because the flame on the Cheeto is too small so it extinguishes too quickly, the temperature has begun to drop before we are aware of it, causing the actual temperature to be a little higher than what we collected.

分析: 没有在层析纸条干后立马收集数据，导致随着乙醇随时间蒸发，很难看到乙醇停止攀升的位置, 这有可能会导致墨水3和4里面的粉色距离不是很准确然后墨水3中粉色的Rf值被低效了。为了避免这个错误，做实验的时候可以选一个不那么有挥发性的化学物质来作为溶剂。

Propagation: Did not collect data in time after chromatography paper dried led to hard to see where the ethanol stops climbing as the ethanol evaporates over time, which cause finally data of distance of pink in ink 3,4 been unreliable and the Rf value of pink in ink3 is offset. In order to avoid it, people can choose a chemical that is slightly less volatile as the solvent.

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