化学专业英语部分原文及翻译

U2

7 The acid-base titration starts with the dissolution of the solid acid sample in deionized water. Add the end-point indicator, which is phenolphthalein, with two drops to each flask containing the acid sample and deionized water.Properly label the flasks. Be consistent in all of the samples when adding the indicator. Swirl the flasks until the solid acid is completely dissolved. Finally, rinse with deionized water three times around, which is critical to ensure that all solid acid has been removed from the flask walls and dissolved in the solution. All solid particles must be dissolved prior to the titration.

7、酸碱滴定伴随着于固体酸溶解于去离子水中发生。在每支装有酸样品和去离子水的试管中加入两滴终点指示剂——酚酞，并在试管上贴好标签。在加指示剂的时候保持所有样品条件一致。震荡试管直到所有固体酸完全溶解。最后，用去离子水冲洗试管壁周围三次，确保试管壁上的固体酸从试管上脱落并溶解于溶液中。所有的固体酸都必须在滴定前完全溶解。

8 The buret needs to be checked for if it is quantitatively clean, both to avoid contamination and to be sure that titrant volumes are accurately read. Make sure the buret stopcock is closed. Fill the buret with water and then drain it to check the buret, making sure that its walls drain cleanly. Before checking for drainage, wait a minute or two after completely draining the buret. Sometimes droplets appear on the inner walls of the buret after some time, indicating that the buret is not quantitatively clean .In this case ,it is necessary to use standard cleaning procedures to clean the buret. If the buret is droplet free, then it is quandtatively clean and can be used for titration.

8.滴定管需要检查，如果它是定量清洁，既避免了污染又能确保滴定剂卷的准确地阅读。确保关闭滴定管活塞。在滴定管内装满水然后排出检查滴定管，确保其壁上的水排干净。在检查排水时，等待一至两分钟后滴定管完全排干。有时滴定管内壁出现小水滴一段时间，表明滴定管不是定量清洁。在这种情况下，必须用标准的清洁程序清洁滴定管。如果滴定管是液滴自由，那么它是定量清洁和可用于滴定。

10 Titrant can then be filled in the well-rinsed buret. Still use a funnel to add titrant to the buret. Carefully lift the funnel for smooth delivery and to avoid overfilling of the titrant. Similar to the cleaning of the buret, an alternative is to remove the buret from the buret holder, and directly pour the titrant from the titrant bottle. Let some titrant run through the buret tip into the waste container and check whether there are any air bubbles in the tip. The bubbles will cause difficulty in obtaining accurate values of volume if they are not removed. The bubbles can be shaken out by opening the stopcock, firmly holding the buret with both hands, and jerking downward a bit. When bubbles are removed, tip off the hanging titrant drop and mount the buret for titration.

10. 然后可以在良好的漂洗滴定管填充滴定剂，可以用漏斗添加滴定液到滴定管中。小心的提起漏斗为了顺利递送，避免滴定液溢出，与清洗滴定管相似，一种代替方法是从试管架上移除滴定管，迅速从滴定剂瓶中倒入滴定剂。让一些滴定剂通过滴定管尖端到废物容器中，检查尖端是否有气泡。如果没有去除气泡会给得到大量精确价值造

成困难，但可以通过打开活塞抖出气泡，用双手稳稳地拿着滴定管，然后迅速的向下一点，当气泡移动悬挂在滴定管下端，安装滴定管进行滴定。

U3

2 Caffeine has the molecular formula C8H10N402 with a molecular weight of 194.19

g/mol. Its chemical name is 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione.

Caffeine belongs to a group of compounds called alkaloids, more specifically, a

member of the methylxanthines. The caffeine molecule ha base characteristics

(alkali-like) and the purine ring system, which is an important framework in living

systems.

3 Caffeine is a chemical with a variety of uses. From medicines to beverages to foods,

caffeine is one of the most popular natural products used today. It is the most widely

used of all the stimulants and acts to stimulate the heart, central nervous system,

and the respiratory system. Its usage can increase blood pressure, contraction force,

and volume output by increasing heart rate. A small dose of this compound at an

amount of 50 to 200 mg increases alertness and reduces drowsiness and fatigue.

Caffeine is the main ingredient of many "stay-awake" pills. It is a smooth muscle

relaxant and a diuretic. Caffeine is also a food additive. It can be found in popular

soft drinks. However, it needs to be pointed out that caffeine has side effects. Large

doses in excess of 200 mg can cause insomnia, restlessness, headaches, and muscle

tremors. In addition, continued, heavy use of this chemical may lead to addictiveness.

Furthermore, some research connects high caffeine consumption in pregnant women

with the malformation of their children.

7 Chemicals possess characteristic physical properties which facilitate their identification. In many cases, a thorough determination of the physical properties of a given substance can be used for its identification. The physical properties of an unknown compound can be compared to properties of known substances that are tabulated in the chemical literature, and identification can be assumed if a match can be made. The physical properties most commonly listed in handbooks of chemical data include color, density, solubility in various solvents, melting point, sublimation characteristics, and so on. The melting point of a compound refers to the temperature at which the solid and liquid states are in equilibrium. A pure substance usually has a quite sharp melting transition and a very narrow range of melting point. Impurities lower the melting point and cause a broadening of the range. The criteria for purity of a solid are the correspondence to the value in the literature and the narrowness of the melting-point range. Thus the purity of caffeine after sublimation can be verified by its melting point. Pure caffeine forms white, hexagonal crystals, which can be ground into soft powder. Its melting point in chemical handbook is 238°C

9 Without tearing the paper, open two tea bags with care. Weigh the contents to the nearest 1 mg and record this weight. Put the tea leaves back into the bags. Then close and securely seal the bags with staples. Place the tea bags in a 150-mL beaker and let the bags lie flat at the bottom. Add 30 mL of distilled water and 2.0 g of anhydrous Na2CO3 into the beaker. Heat the water on a hot plate to a gentle boiling. Cover the beaker with a watch glass and continue heating for approximately 15 minutes. Keep the tea bags under water by occasionally pushing them back down

with a glass rod, making sure that the tea leaves are covered with as much hot water as possible. Watch for loss of water, additional water may be needed.

11 Transfer the cool tea extract from the flask to a 125-mL separatory funnel supported on a ring stand with a ring clamp. Into the funnel, add 5.0 mL of dichloromethane. Stopper the funnel and lift it with two hands. Hold the stopper in place with one hand and invert the funnel to gently mix the contents three to four times. Be sure that the liquid is not in contact with the stopcock. When the funnel is inverted for mixing, open the stopcock to release any pressure built up by the volatile solvent. Always point the opening away from any person.

11. 把茶叶提取液从烧杯中转移到125ml的放置在一个环状坐台上带着一个环状夹子的分液漏斗中。在分液漏斗中加入5.0ml的二氯甲烷。止住漏斗并用双手举起，用一只手把持塞子并倒置漏斗，轻轻地颠倒摇匀3-4次。确保液体没有漏出活塞。当在混合颠倒时，应该打开活塞释放因挥发性溶剂积累而产生多余的压力。同时活塞的口子不能对着任何人。

12 Put the separatory funnel back to the ring clamp. Remove the stopper and let the aqueous layer settle and separate from the dichloromethane layer, resulting in two distinct layers after a few minutes. Carefully manipulate the stopcock and drain the dichloromethane layer at the bottom into a 25-mL Erlenmeyer flask. Try not to transfer any of the aqueous solution along with the organic layer. Add a fresh 5.0 mL of dichloromethane and repeat the extraction. Combine the separated bottom dichloromethane layers. Dry the combined extract by adding 0.5 g of anhydrous

Na2SO4. Swirl the flask for better performance.

12. 把分液漏斗放回环形夹子。移除活塞让水层安定并从二氯甲烷层中分离出来，在几分钟之后导致2层明显的分层。小心的熟练操作活塞，把底层的二氯甲烷从分液漏斗底部释放到25ml的锥形瓶中。尽量不要把任何水层转移到有机层里。加入纯净的5ml 二氯甲烷重复萃取。合并几次分离得到的二氯甲烷层，并向合并后的萃取液中加入0.5g硫酸钠用来干燥。旋转震荡烧杯得到更好地产

U4

1 In pharmaceutical and fine chemicals industries, most processes are developed for batch or semi-continuous operations. In a batch process all the reaction components are combined and held under controlled conditions until the desired process end point has been reached. Reactions are typically slow, taking hours, and the product

is isolated at the end ofthe process cycle. Unit operations, such as fermentation and crystallization, can be carried out on the entire batch with fine control. Because the product output, typically no more than hundreds of kilos, can be readily correlated with input materials, batch operations are suited for cGMP considerations and commonly used in the pharmaceutical and fine chemicals industries.

3 Continuous processing is typically used to prepare commodity chemicals on a tonnage basis. There are two primary types, continuously stirred tank reactors (CSTR) and plug flow reactors (PFR), along with the recently developed microreactors. In CSTR processing, process streams are continuously mixed in reactors and continuously harvested; after a vessel is filled the output streams overflow into another reactor at the same rate as the input streams are added, thus mamtaining a constant volume under steady-state conditions. On a microscopic scale there is a range of residence times for molecules as they enter and leave such a mixed vessel, and as more mixed vessels are added in series the reactor train becomes more characteristic of a batch system. The continuous, controlled movement of the process streams through equipment increases the product throughput on a space-time basis, allowing more material to be made from a smaller plant with smaller capital investment than would be possible under batch conditions. Typically continuous processes are used for fast reactions, requiring minutes or less. For the preparation of high-quality material it is essential that the process be conducted with little variation from optimal conditions; such steady-state conditions should be reached quickly upon start-up of the processing for optimal yields.

4 PFRs are tubes commonly constructed of metal or plastic. As narrow-bore tubes, the high surface area-to-volume ratio allows for rapid heat transfer and control of reaction temperature. Mixing in PFRs occurs radially, not axially, making PFRs useful for minimizing side reactions in which reagents react with the product. PFRs that are

mn at elevated temperatures are sometimes called hot tube reactors, and they have many uses in industry. Other PFRs are static mixers, inexpensive tubes with stationary internal elements that split and sometimes rotate the stream flow, producing intimate mixing. Static mixers are powerful tools, with diverse applications ranging from mixing solutions in low-viscosity solvents to blending peanut butter. Most PFRs are relatively inexpensive, portable, and useful for the laboratory, pilot plant, and manufacturing.

8 The chlorination of the furfuryl alcohol 1 (Fig. 4.1) provides one of the most powerful examples of how continuous processing can be readily applied in the laboratory. The chloride 2 was an intermediate in the preparation of the nitrile 3. When the chlorination was scaled up to more than 100 g in a batch mode, unacceptable yields of 3 were obtained. The poor stability of 2（ t1/2 at room temperature of only 20 min) was the cause of poor yields upon scale-up of the batch process. A CSTR process was set up to convert 2 to 3 soon after 2 had been generated, using two 10-mL round-bottomed flasks with magnetic stirrers. Separate solutions of 1 and SOCl2 were charged to a flask by ganged syringe pumps, and the reaction stream overflowed into a second flask and then into a reactor charged with an excess of NaCN. PTC conditions rapidly converted 2 to 3. Continuous operations for one week produced 10 kg of 3 using化is train of two 10-mL reactors!

9 Safety studies showed that nitration of the pyrimidine 4 (Fig. 4.2) was highly exothermic and generated a large amount of gases upon decomposition at a relatively low temperature. Due to safety considerations this reaction was run on scales no larger than 22 L in a batch mode. The nitration was found to be rapid and was adapted for PFR processing. Using a translucent Teflon tube, at 45 C a solution of 4 in H2SO4 was combined with 90% HN03. Residence time in the reactor was

about 2.5 min, and the use of the open-ended tube decreased concerns of any gas build-up. The reaction was quenched into cold H2O, and the salt 5 was isolated in 86% yield from 45 kg of 4.

Unit1

1.我们很少会遇到纯物质。相反地，很多物质都是由两种或者两种以上不同的化学物质组成。为了从混合物中分离得到纯净物，化学家们研发了一系列通过各组分的物理性质的差异进行分离混合物的方法。其中重结晶就是实验室常用的一种重要分离方法。

2.重结晶用于在实验温度下纯化一个固体物质。它是一种基于固体不同溶解度的基本纯化技术。不能溶解的杂质能够很容易通过过滤去除，然后需要被纯化的固体就溶解，而少量的能够溶解的杂质仍然留在溶液中。升高温度让溶液过饱和能够获得纯溶质的晶体。当缓慢的降低溶液温度至室温，晶体生成并析出，杂质就在溶液中了。有时用两种溶剂很容易进行重结晶，即一种好的溶剂和一种不好的溶剂混合。

5.称取少量固体溶质于试管中，加入1毫升待试溶剂。在室温条件下如果固体溶质很快溶解，那么该测试溶剂不适合作为重结晶溶剂。另取一支干净试管和另一待测溶剂重复上述过程。如果溶质不能溶解，就用热水浴加热试管至溶剂沸点，如果固体溶质仍然不能被溶解，那么此待测溶剂也不适合作为重结晶溶剂。再取其他溶剂重复上述过程，直到固体溶质在室温条件下不溶解，在待测溶剂沸点条件下溶解，才表明此溶剂是一个合适的溶剂。

6.溶解固体在第二步，使被重结晶的固体溶解在热的适合的溶剂中。两个锥形瓶（一个用来装溶剂，另一个用来装晶体）、一块加热板、一支用后可丢弃的移液管和洗耳球、手指操控、和需要一些沸石在一步中。在两个锥形瓶中各放置两颗沸石确保加热过程中不暴沸。一小部分溶剂被加载包含有不纯固体的烧瓶里。然后悬浮于烧瓶中被加热到溶剂沸点直到固体完全溶解。如果固体不溶解，一滴一滴不断地加入更多的溶剂知道固体完全溶解。如果溶液含有可见的固体杂质量超过沸石量则需要热过滤。如果溶液出现颜色，在煮沸的深色溶液中短时间加入活性炭出去带有颜色的杂质，接下来通过热过滤去除活性炭。

11.结晶形成后，现在该是把结晶从溶液中分离出来的时候。真空过滤时常被用于分离和干燥纯化的固体，有时会用冷的溶剂清洗纯化的固体。当清洗产品时用尽可能少的冷溶剂为了避免溶解一些样品。

12.如图1.1所示的仪器，真空过滤器是由真空泵和连着橡胶管的过滤锥形瓶组成的。将一张滤纸放置在真空过滤器调节器在过滤锥形瓶的瓶颈处的漏斗中。用少许重结晶溶剂润湿滤纸后打开真空泵。流出转变后的晶体，溶液置于滤纸中心过滤。将冷溶剂加入锥形瓶中，旋转振摇残留的晶体。

Unit2

1.一定量的体积分析表明，通常所采用的方法是酸碱中和滴定。酸碱中和的基础是中和反应，如果一种溶液时酸性的，则滴定就用使其全部中和的碱性物质。

2.酸碱滴定法能用于大多数酸和碱，包括盐酸，硫酸，醋酸，氢氧化钠，氨等等。尤其是，在一个滴定过程中，它甚至可以确定含不同强度的酸或碱的混合物的构成，例如，碳酸钠和碳酸氢钠。在酸碱滴定中，盐酸和氢氧化钠是两种最常用的试剂。

3.酸碱滴定反应伴随着一个化学计量关系。在酸碱滴定中的化学计量点（反应终点）我们可以通过指示剂在视觉上就可以判定什么时候滴定完成了。可以从视觉上发现反应结束是维持滴定（过程）简单性的重要因素。可视化的指示剂是一种当溶液pH改变时（自身）颜色也发生改变的有机化合物。那些依赖pH发生颜色变化的指示剂是由于指示剂本身和其所在的化学环境发生反应导致H+或OH-的增加（而产生的结果）。用一种经常用到的指示剂酚酞的部分功能为例，在Ph(8.0—9.0)由无色变为粉红色，如图2.1所示。