Giáo trình tiếng anh trong kỹ thuật hóa học phần 1

PGS.TS BÙI THỊ LỆ THỦY PGS.TS BÙI THỊ LỆ THỦY PGS.TS BÙI THỊ LỆ THỦY GIÁO TRÌNH GIÁO TRÌNH GIÁO TRÌNH TIẾNG ANH TRONG KỸ THUẬT HĨA HỌC TRONG KỸ THUẬT HÓA HỌC ISBN: 978-604-76-1983-2 32 Giá: 50.000 đ TRONG KỸ THUẬT HÓA HỌC PGS.TS BÙI THỊ LỆ THỦY GIÁO TRÌNH TIẾNG ANH TRONG KỸ THUẬT HĨA HỌC NHÀ XUẤT BẢN GIAO THÔNG VẬN TẢI HÀ NỘI - 2019 CONTENTS LỜI NÓI ĐẦU PART THE BASIC UNITS I.1 TYPICAL UNITS UNIT SOME CONCEPTS IN CHEMISTRY UNIT HYDROCARBONS 10 UNIT CHEMICAL KINETIC AND CATALYSIS 14 UNIT ANALYTICAL CHEMISTRY 16 UNIT CHEMICAL THERMODYNAMICS 19 UNIT EMULSIONS 23 UNIT PLASTICS IN THE CHEMICAL AGE 27 UNIT ENZYMES 31 I.2 ADDITIONAL UNITS 34 UNIT PROPERTIES OF GELS 34 UNIT 10 SOLVENT PROPERTIES OF SURFACTANT SOLUTIONS EMULTION POLYMERIZATION 37 UNIT 11 THE NATURE OF RUBBER - LIKE ELASTICITY 39 UNIT 12 THERMOPLASTIC ELASTOMERS THERMOSETTING AND THERMOPLASTIC MATERIAL 42 UNIT 13 THERMOPLASTIC ELASTOMERS 45 UNIT 14 ABS PLASTIC 49 UNIT 15 HAFNIUM 52 REFERENCES 56 PART THE CHEMICAL ENGINEERING UNITS 57 UNIT 16 TYPES OF REACTORS 58 UNIT 17 HEAT TRANSFER AND ITS APPLICATIONS 62 UNIT 18 EXTRACTION WITH SOLVENTS 67 UNIT 19 INTRODUCTION TO DISTILLATION AND ATMOSPHERIC DISTILATION 72 UNIT 20 VACUUM DISTILLATION 77 UNIT 21 STEAM DISTILLATION 81 UNIT 22 CRYSTALLIZATION 86 UNIT 23 ADSORPTION 90 UNIT 24 EVAPORATION 93 UNIT 25 CHROMATOGRAPHY 97 UNIT 26 LIQUIS-SOLID CHROMATOGHRAPHY 100 REFERENCES 104 PART THE PETROCHEMICAL INDUSTRY AND REFINERY UNITS 105 III.1 TYPICAL UNITS 106 UNIT 27 ON OIL AND GAS INDUSTRY 106 UNIT 28 COMPOSITION OF PETROLEUM 108 UNIT 29 BASIC PHYSICO-CHEMICAL PROPERTIES OF PETROLEUM AND PETROLEUM PRODUCTS 112 UNIT 30 BASIC PHYSICO-CHEMICAL PROPERTIES OF PETROLEUM AND PETROLEUM PRODUCTS (CONTINUED) 117 UNIT 31 DISTILLATION OF PETROLEUM 121 UNIT 32 THERMAL PROCESSES IN REFINERY 126 THERMAL CRACKING 126 UNIT 33 CATALYTIC PROCESSES IN REFINERY 131 III.2 ADDITIONAL UNITS 136 UNIT 34 CATALYTIC CRACKING OF PETROLEUM 136 UNIT 35 CATALYTIC REFORMING OF PETROLEUM 142 REFERENCES 147 PART ACADEMIC WRITING 148 UNIT 36 INTRODUCTION TO ACADEMIC WRITING 149 UNIT 37 TYPES AND STRUCTURE OF ACADEMIC WRITING 153 UNIT 38 HOW TO WRITE A SUCCESSFUL 157 SCIENTIFIC MANUSCRIPT 157 REFERENCES 161 LỜI NÓI ĐẦU Giáo trình biên soạn cho sinh viên năm cuối ngành Kỹ thuật Hố học Giáo trình nhằm bổ sung cho sinh viên từ vựng, tổ hợp từ, thuật ngữ, cấu trúc ngữ pháp hay gặp tài liệu khoa học kỹ thuật, giúp sinh viên làm quen với việc dịch Anh-Việt ngược lại, viết văn khoa học tiếng Anh Nội dung giáo trình gồm phần Các học phần biên soạn tăng dần theo mức độ chuyên sâu lĩnh vực hoá học Trong phần tác giả chọn khoá liên quan đến kiến thức Hoá học, chuyên đề Hoá học Mỗi khoá xếp theo trật tự logic từ đọc hiểu, tập để sinh viên ơn luyện, từ giúp sinh viên làm quen với từ, tổ hợp từ tập trung vào kỹ đọc hiểu, dịch từ tiếng Anh sang tiếng Việt ngược lại Phần hai gồm khoá liên quan đến lĩnh vực Kỹ thuật Hố học lị phản ứng, kỹ thuật tách chất phổ biến thông dụng Cấu trúc khoá phần tương tự phần Các tập kèm làm cho khoá thêm sinh động đưa vào cấu trúc ngữ pháp hay gặp khoa học Phần ba khoá tập trung vào lĩnh vực Hoá dầu Nội dung gắn với chuyên môn sâu sinh viên Sau có tập để sinh viên rèn luyện khả đọc, dịch viết tiếng Anh Trong phần cuối tác giả biên soạn ba kỹ thuật viết văn khoa học lĩnh vực Kỹ thuật Hoá học, giúp sinh viên nắm bước sườn thảo báo khoa học Tác giả xin trân trọng cảm ơn đồng nghiệp đóng góp ý kiến để hồn thành sách Xin chân thành cảm ơn quan tâm độc giả mong nhận ý kiến góp độc giả bạn đồng nghiệp để sách ngày hoàn thiện Tác giả PART THE BASIC UNITS I.1 TYPICAL UNITS UNIT SOME CONCEPTS IN CHEMISTRY Structure of Atoms According to Dalton’s atomic theory, a chemical element is material composed of only one type of atom Atoms are very small particles that cannot be separated into simpler substances and that singly or in combination constitute all matter All atoms are constructed from the three particles: the electron, proton, and neutron Both neutrons and protons occupy the nucleus, which is in the center of the atom The electrons orbit around the nucleus Each atom contains equal number of electrons and protons, therefore, atoms are neutral An atom of one element is distinguished from an atom of another element by its number of protons The number of proton in the atomic nucleus is called the atomic number Z of an element For instance, carbon atoms contain six protons and six electrons; therefore, the atomic number of carbon is The total mass of an atom is almost entirely by the number of protons and neutrons because the mass of electrons is so much smaller The atoms of almost element have the same proton number but different neutron number; therefore they have different mass number These atoms are called isotopes For example, helium exists as helium-3 or He-3 (its nucleus contains protons but only neutron) or as helium-4 or He-4 (2 protons and neutrons) These two examples are called isotopes of helium The elements are arranged in the periodic table, the invention of which is generally attributed to the 19th century Russian chemist Dimini Mendeleev In the standard periodic table, the elements are listed in order of increasing atomic number (the number of protons in the nucleus of an atom) A new row (period) is started when a new electron shell has its first electron Elements containing the same number of electron layers are arranged in the same period while elements with the same number of electrons in a particular subshell fall into the same columns Molecules, substances, and chemical compounds Molecules are composed of the atoms of one or more elements Nitrogen exists as nitrogen molecules in atmosphere, each molecule contains two nitrogen atoms Its symbolic representation is N2 Water molecule contains one oxygen atom and two hydrogen atoms Compounds are composed of the atoms of one or more elements N2 is an elementary substance and water is a compound but both of them are called substances Exercises 1.1 Read and translate into Vietnamese Concept, structure, atom, atomic, theory, element, material, compose, substance, particle, combination, constitute, matter, electron, proton, neutron, neutral, nucleus, orbit, distinguish, atomic number, mass number, helium, arrange, periodic table, attribute, electron shell, subshell, molecule, substance, elementary substance, compound 1.2 Answer the following questions What is an element? What is an atom? How many kinds of particles are there in every atom? What are they? What is the atomic number of an element? How can we determine the mass of an atom? What is a molecule? Please distinguish an elementary substance and a compound 1.3 Translate into Vietnamese paying attention to the words in bold type The name ABS, based on the first letters of each of the monomeric components has been adopted for this family By introducing acrylonitrile monomer into a similar system, a significant improvement in all these properties is obtained, as well as outstanding toughness and resistance Various combinations of properties are possible, thus making these polymers most attractive for a larger number of current and newly developed applications ABS plastics are extremely useful and versatile, since ease of processing and forming allows them to be used for a great number of applications The strength of a fabricated item produced from ABS plastic is dependent on a number of variables 1.4 Translate into English Nguyên tử phần tử nhỏ vật chất tồn độc lập Nguyên tử cấu tạo từ proton, electron nơtron Electron tích điện âm, ptoton tích điện dương cịn nơtron không mang điện Trong nguyên tử, số proton với số electron nên ngun tử ln trung hịa điện Vì khối lượng eletron nhỏ so với khối lượng nơtron proton nên khối lượng nguyên tử tính xấp xỉ tổng khối lượng proton nơtron Phân tử chứa nguyên tử nhiều nguyên tố Các hợp chất bao gồm nguyên tử hai hay nhiều nguyên tố Các hạt proton neutron nằm trung tâm tạo hạt nhân electron chuyển động xung quanh hạt nhân tạo lớp electron Đồng vị nguyên tử nguyên tố có số nơtron khác Các nguyên tố chu kỳ có số lớp electron 10 Các nguyên tố nhóm có số electron lớp ngồi cùng, đó, chúng có tính chất tương tự 11 Các nguyên tố hóa học xếp vào bảng hệ thơng tuần hồn dựa vào cấu hình electron chúng 1.5 Write a short summary of the text 19.4 Describe a simple distillation process using the figure below Figure Simple distillation process 19.5 Describe a fractional distillation process using the figure below Figure Fractional distillation process 75 19.6 Translate the following sentences into Vietnamese, paying attention to the words in bold type A great number of experiment concerning the nature and extent of filler- rubber adhesion have been conducted The thermoplastic industry was first concerned with rigid polymers, which displaced traditional ones Artificial ageing tests concerned are an extremely important part of rubber testing The development of that part of the rubber industry concerned with the fabrication of rubber articles has been primarily concerned with two processes 19.7 Translate the following sentences into Vietnamese, paying attention to the words in bold type Though thermoplastic elastomers have some rubbery characters, they not compare with conventional vulcanizates as regards rapid retraction with low set from high elongation, resilience, or as regards versatility and aesthetic appeal in many applications Petroleum and its distillates cannot be regarded as a source of raw elemental sulfur The problems regarding the use of pigments in latex are similar to those in other types of coatings and finishes Gerlach developed an interesting table with regard to the boiling points of glycerol solutions 19.8 Write a short summary of the text 76 UNIT 20 VACUUM DISTILLATION Since the boiling temperature of a liquid is decreased by diminishing the pressure on its surface, you can distill at a lower temperature by using an apparatus that is connected to a vacuum pump that maintains a lower inside pressure This procedure is useful for purifying liquids (or low-melting solids) that decompose at elevated temperatures For example, glycerol boils with some decomposition at 290°C under 760 mmHg pressure, but it may be distilled without decomposition under 12-mm pressure, where its boiling point is 180°C A possible disadvantage of fractional distillation under reduced pressure is the reduction in separation effìciency of most fractionating columns In planning a vacuum distillation, three aspects must be considered: the pressure needed to achieve the desired boiling point, the type of vacuum pump needed to lower the pressure to the required level, and finally, the associated glassware, pressure measuring devices, and heat sources Effect of pressure on boiling temperature Estimation of boilling point One useful relationship between pressure and boiling point is given in equation (1), where P is the pressure over the liquid and T is the boiling point at this pressure In this equation, both boiling temperatures are expressed in degrees Kelvin (K = °C + 273) Equation (1) is fairly precise for most organic liquids, but is in error for substances possessing unusually large attractions between molecules (water, alcohols, acids) More precise relationships have been developed, but the extra work required to use them is not justified for preparative organic chemistry 𝒍𝒐𝒈𝟏𝟎 𝟕𝟔𝟎 𝑷 = 𝟓 𝟒𝟔 𝒏𝒐𝒓𝒎𝒂𝒍 𝒃𝒐𝒊𝒍𝒊𝒏𝒈 𝒑𝒐𝒊𝒏𝒕 𝑻 -1 (1) The use of equation (2) is outlined here for nitrobenzene - Normal boiling point of nitrobenzene = 211°C = 484°K - If the desired boiling point is 100°C = 373°K, the equation becomes 𝒍𝒐𝒈𝟏𝟎 𝟕𝟔𝟎 𝑷 𝟒𝟖𝟒 = 𝟓 𝟒𝟔 𝟑𝟕𝟑 − 𝟏 = 𝟏 𝟔𝟐 (1) - The expression is solved for P Ppredicted = 18.0 mm Hg - At a pressure of 18.0 mm Hg, it is observed that nitrobenzene boils at 98°C instead of the desired 100°C That is about as good agreement as you could hope for 77 Another approach to estimating the boiling points at reduced pressure is to use a nomograph, such as the one shown in Figure To estimate the boiling point at some reduced pressure of a hydrocarbon for which boiling point at 760 mm is known, place a straightedge (preferably transparent) on the nomograph connecting the known boiling point on scale B and the reduced pressure on line C for hydrocarbons The boiling point of the compound at the reduced pressure is read from the intersection of the straightedge and the left-hand A scale If the compound contains a carboxylic acid functional group, line C for carboxylic acids is used instead The boiling points of polar molecules and less strongly hydrogen bonded molecules can be estimated as the average of the boiling points obtained by using both the hydrocarbons and carboxylic acid lines Note that for compounds boiling near 100°C both lines give about the same result; it is only for high boiling liquids that different predicted boiling points are obtained Figure Nomograph for boiling points at reduced pressure 78 Exercises 20.1 Read and translate into Vietnamese Diminishing, vacuum, pump, maintain, decompose, decomposition, efficiency, estimation, alcohol, acid, precise, justify, estimate, approach, straightedge, transparent, intersection, carboxylic acid, predict 20.2 Answer the following questions What is the principle of vacuum distillation? When we use vacuum distillation? What is the advantage of vacuum distillation? What is the disadvantage of vacuum distillation? How can we estimate the boiling point of a given compound at a certain reduced pressure? 20.3 Translate the following sentences paying attention to the Passive Voice The employment of latex is being aimed at reinforcing furs, particularly rabbit skins, which are very soft and weak When a solid is attacked by a liquid reagent the product might be either soluble or insoluble in the liquid Polyvinyl chloride was not thought of as a competitor of rubber until the war Branching may be referred to as changing mainly the shape of the molecule It was assumed that the rate of reaction at high conversion would be governed by the diffusion rate of the monomer Fundamental investigations concerning chemical catalysis were aimed at a quantitative expression of activity Polyethylene is not affected by aggressive mediums such as acids, alkalis and salt solutions Rubber is known to be unaffected by many neutral salts, organic acids, etc Soft vulcanized rubber in the presence of antioxidants was acted upon by the oxygen of the air 10 If the substance being ground is a reactive one, the possibility of chemical alteration of the surface by chemisorption of oxygen or water vapour from the air must be reckoned with 11 Since adhesion is greatly influenced by adsorption of gases and vapours, one would expect the bulk density to depend on the humidity of the air 79 20.4 Translate into Vietnamese paying attention to the Gerund Reheating rubber is always attention by increasing its volume Merret identified the component responsible for producing the sol with the graft copolymer Many surface coatings shrink slowly on having been aged Natural rubber vulcanized with zinc oxide in the absence of free sulfur is known for being resistant to ageing The highly coiled rubber chains permit their being extended up to seven times their original length 20.5 Translate into English Nhiệt độ sôi chất giảm giảm áp suất tác dụng lên bề mặt chất lỏng Chưng cất chân khơng dùng để tinh chế chất có nhiệt độ sôi cao bị phân huỷ nhiệt độ sôi Chưng cất chân không cần thiết bị phức tạp Có thể ước tính áp suất cần thiết để chưng cất chất cho trước nhiệt độ mong muốn ngược lại 20.6 Write a short summary of the text 80 UNIT 21 STEAM DISTILLATION Steam distillation consists of distilling a mixture of water and an insoluble or partly soluble substance The practical advantage of steam distillation is that the mixture usually distills at a temperature below the boiling point of the lower boiling component Consequently, it is possible to steam distill a high boiling organic compound at a temperature much below its boiling point (in fact, below 100°) without resorting to vacuum distillation Steam distillation is useful also in separating mixtures when one component has an appreciable vapor pressure (at least mm) in the vicinity of 100° and the other has a negligible vapor pressure The process of steam distillation is widely employed in the laboratory and in industry; e.g., for the isolation of α-pinene, aniline, nitrobenzene, and many natural essences and flavoring oils Principles of Steam Distillation Mixtures of two insoluble substances behave quite differently from homogeneous solutions, and the description of their behavior requires a different physical law The basis of this law can be grasped, by considering the consequence of increasingly positive deviations from Raoult’s law One symptom of small positive deviations is a skewed boiling point composition diagram, as is found with methanol-water solutions Greater positive deviations, as occur in ethanol-water solutions, lead to maxima in the total vapor pressure curve and to low-boiling azeotropes With still greater positive deviations, the two components can separate into two immisible layers In the limit of very large positive deviations from Raoult’s law, the two components are essentially insoluble and each component vaporizes independently of the other to give a total vapor pressure that is the sum of the individual vapor pressures The physical basis for this independent behavior of the two components is depicted in Figure 10 In this diagram component B is represented as two globules suspended in component A; an incipient bubble in contact with both components is shown in the center of the diagram The vapor pressure of component A inside the bubble is PA° (the vapor pressure of pure A) just as it would be if no B were present In the same fashion the vapor pressure of B inside the bubble is PB° Most water insoluble organic compounds approximate this extreme behavior so that steam distillation calculations are normal based on the simple law: The total vapor pressure equals the sum of the pressures of the two components Distillation Temperature and Composition of Distillate As with ordinary distillations, the boiling point is the temperature at which the total vapor pressure equals the atmospheric pressure If the vapor pressure of the two components are known at several temperatures, the distillation temperature is found readily by plotting the vapor pressure curves of the individual components and making a third curve showing the sum of the vapor pressure at the various temperatures The steam distillation temperssures will be the point where the sum equals the atmospheric pressure Knowing the distillation temperature of the mixture and the vapor pressure of the pure components at that temperature, one can calculate the composition of the distillate by means of Dalton’s law of partial pressures 81 Figure 10 Vapor Pressure inside Bubble During Steam Distillation According to Dalton’s law, the total pressure (P) in any mixture of gases is equal to the sum of the partial pressures of the individual gaseous components (PA, PB, etc) The proportion by volume of the two components in the distilling vapor will consequently be equal to the ratio of the partial pressures at that temperature; the molar proportion of the two components (nA and nB) in steam distillation will be given by the relationship nA/nB = pA/pB, where pA + pB equals the atmospheric pressure The weight proportion of the components is obtained by introducing the molecular weights (MA and MB) 𝒎𝑨 𝑷𝑨 𝒙 𝑴𝑨 = 𝒎𝑩 𝑷𝑩 𝒙 𝑴𝑩 Where mA, mB are mass of A and B Example Consider a specific case, such as the steam distillation of bromobenzene and water Since the sum of the individual vapor pressures attains 760 mm Hg at 95.2°C, the mixture will distill at this temperature At 95.2°C the vapor pressures are bromobenzene, 120 mm Hg and water, 640 mm Hg According to Dalton’s law, the vapor at 95.2°C will be composed of molecules of bromobenzene and of water in the proportion of 120: 640 The proportion by weight of the components can be obtained by introducing their molecular weights 𝒎𝒃𝒓𝒐𝒎𝒐𝒃𝒆𝒏𝒛𝒆𝒏𝒆 𝟏𝟐𝟎 𝒙 𝟏𝟓𝟕 𝟏 𝟔𝟑 = = 𝒎𝒘𝒂𝒕𝒆𝒓 𝟔𝟒𝟎 𝒙 𝟏𝟖 𝟏 The weight composition of the distillate will therefore be 62% bromobenzene and 38% water This calculation gives the minimum amount of water in the distillate In the practice, an excess of water or steam is used in the distilling flash to sweep out the vapor mixture and to compensate for imperfect mixing 82 Calculations of the type illustrated with bromobenzene indicate that there are several requirements for the practical use of steam distillation in the laboratory: the substance to be steam distilled must be insoluble or only sparingly soluble, in water; it must not be decomposed by prolonged contact with boiling water or steam; and it must have an appreciable vapor pressure (preferably, at least mm Hg) in the neighborhood of 100°C That water has a very low molecular weight (18) compared with those of typical organic compounds is a favorable circumstance for steam distillation because this permits a substance to be steam distilled at a practical rate eventhough its vapor pressure is relatively small near 100°C Exercises 21.1 Read and translate into Vietnamese Steam, steam distillation, insoluble, soluble, consequently, resort, vicinity, negligible, α-pinene, aniline, nitrobenzene, grasp, deviation, skew, diagram, independent, depict, globule, suspend, incipient, extreme, sum, plot, curve, partial, proportion, compose 21.2 Answer the following questions What is the principle of steam distillation? When we use steam distillation? What is the advantage of steam distillation? What are the requirements for the practical use of steam distillation in the laboratory? How can we calculate the weight composition of distillate in steam distillation? 21.3 Translate into Vietnamese paying attention to the function of the infinitive The mixture to be separated is introduced at the beginning of the column The electrons have come to be known as valence electrons, because the valence of any given element depends on the number of these electrons Valence is the tendency of the atoms of any given element to donate or accept a strictly definite number of electrons Chlorine requires only one electron to form the stable electron layer of the following inert gas Hydrogen is a combustible gas, burning in air or oxygen to form water The organic compounds to be discussed are of great importance in the study of plastics Carbon has a tendency to combine with oxygen from the air to form gaseous carbon dioxide 83 There is no problem to be associated with exuding, leaching or deterioration with polyethylene plastic The stability of polyethylene plastic in storage is to be associated with the lack of chemical active functional groups in the molecular structure 10 To regard the polyethylene as a substitute for stainless steel is not a proper design procedure 21.4 Translate the following sentences into Vietnamese, paying attention to the words in bold type Vulcanization is a vitally important part of all rubber processing To impart the materials hardness, softness and other desirable properties, the materials can be modified Rigid polymers displaced traditional materials partly because of the economic advantages A number of scientists took part in the research of new elastic materials to be applied in surgery The alkyl of R group parts company from the carbonyl carbon exists for a time as a free radical 21.5 Translate the following sentences into Vietnamese paying attention to the words in bold type Thermoplastic elastomers are available in nib form, and since they need no vulcanization, the mastication and mixing steps required with conventional rubbers are avoided There are still some plastics, more or less rubbery, available in emulsion or dispersion form Vinyl chloride and vinyl copolymer latices are available both untreated and preplasticized There are now available several modified Buna n latices having rather distinctive properties Butadiene, which can be made from readily available acetylene, is one of the raw materials of synthetic rubber 21.6 Translate into English Chưng cất với nước dùng để tinh chế chất không tan tan nước Phương pháp thường dùng để phân lập hợp chất thiên nhiên Áp suất hỗn hợp hai chất không tan vào tổng áp suất tinh khiết chất 84 Khi chưng cất với nước hỗn hợp cất nhiệt độ thấp nhiệt độ sôi chất sôi thấp Chất chưng cất với nước phải khơng tan nước, không phân huỷ nước sôi nước phải có áp suất mm Hg gần 100°C 21.7 Write a short summary of the text 85 UNIT 22 CRYSTALLIZATION Crystallization is used to purify chemicals by dissolving both impurities and a compound in an appropriate solvent, either the desired compound or impurities can be removed from the solution, leaving the other behind In a typical synthesis process, a crystalline solid product separating from the reaction mixture is contaminated with impurities Purification is accomplished by crystallization from an appropriate solvent In outline, the procedure consists of the following steps Dissolving the substance in as small amount of solvent as possible at an elevated temperature Filtering the hot solution to remove insoluble impurities (optional step) Allowing the hot solution to cool and deposit crystals of the substance Filtering the cold solution to separate the crystals from the supernatant solution (quaintly still known as the mother liquor) Washing the crystals to remove adhering mother liquor Drying the crystals to remove the last traces of solvent There are several factors to consider in selecting a suitable solvent for crystallization A good solvent for crystallization is one that will dissolve a moderate quantity of the substance at an elevated temperature (about 10-20 mL/g of compound) but only a small quantity at low temperatures The solvent should dissolve the impurities readily (except for mechanical impurities) even at low temperatures and should be easy to remove from the crystals of the purified substance It is essential that the solvent not react in any way with the substance to be purified Other factors such as flammability and cost should also be taken into consideration In selecting a solvent for the purification of a given substance, one should consider its effectiveness for removal of the particular impurities that are likely to be present The following general categories of impurities may be encountered Mechanical impurities (dust, grit, particles of paper, etc.) are readily removed by filtering the hot solution, since they are insoluble in all of the common solvents Inorganic salts may often be separated in this way by using an organic solvent in which they are insoluble; an alternative method is to wash the crystals before recrystallization with a solvent such as water, in which the inorganic salts are soluble and the organic compound is insoluble Traces of coloring matter and resinous impurities may often be removed by warming the solution with a small amount of decolorizing carbon (about 0.2 g/ 100 mL of solution) or other adsorbent (Norit, Darco, Nuchar, etc.) before filtering the hot solution The action of decolorizing agents varies widely, and effectiveness in removing a particular impurity may differ markedly from one solvent to another An excessive amount of decolorizing agent should be avoided because it will also adsorb the compound that is being purified, thereby reducing the amount of pure compound isolated This is particularly true for large molecules, which tend to be held quite strongly on charcoal 86 Impurities more soluble in the solvent are readily removed by crystallization, since they will be retained in the mother liquor Likewise, impurities having about the same solubility as the substance being purified, when present in moderately small amounts, are readily eliminated in the mother liquor Impurities less soluble in the solvent are very difficult to remove if they are present in considerable amount because the hot solvent will dissolve an appreciable amount of the impurity and, on cooling, the impurity will crystallize out and contaminate the product It is for this reason that one tries to select a solvent that will readily dissolve the impurities, even at room temperature Exercises 22.1 Read and translate into Vietnamese Crystallization, recrystallization, crystalline crystallize, technique, impurity, purify, purification, appropriate, appreciate, precipitate, co-precipitate, contaminate, contamination, elevated, soluble, insoluble, filter, filtrate, filtration, deposit, supernatant, procedure, quaintly, adhering, flammability, effectiveness, categories, encounter, mechanical impurity, grit, trace, resinous, absorbent, decolorize, markedly, excessive, adsorb, reduce, saturate, saturated, drop, retain, moderately 22.2 Answer the following questions What is the purpose of recrystallization technique? What is the principle of recrystallization technique? What is the saturated solution? Why we need to prepare the saturated solution? What is a good solvent? 22.3 Describe the recrystallization of benzoic acid using water as solvent Complete the sentences: In this experiment benzoic acid is… by… The apparatus consists of… Below is the procedure: First, the apparatus is set up as shown Then, the water is … dropwise, Meanwhile the mixture is stirred so that the amount of water is minimum Next, the saturated solution… After that, the solution is… and the crystal … 87 Then, the solution is … again Finally, the pure… Figure11 Recrystalization of benzoic acid 22.4 Translate the following sentences paying attention to the Absolute Participle Construction The drops of rubber are suspended in water, when first obtained from the plant, the system resembling an emulsion Emulsion may “ cream “, i e., separate into layers of aqueous phase with a concentrated layer of oil droplets floating on the top, the rate depending primarily on the viscosity of the aqueous phase, the size of the droplets, etc The emulsifier being a solubilizing agent for the monomer, the rate of polymerization varies with the emulsifier content 88 Most of the accelerators used today are derivatives of carbon disulfide, the commonest one being mercaptobenzothiazole The rate of polymerization varies with the emulsifier content, the emulsifier being a solubilizing agent for the monomer 22.5 Translate into English Kết tinh lại phương pháp tinh chế hợp chất dựa vào khác độ tan chất dung môi khác Để thu tinh thể tinh khiết cần lặp lại trình kết tinh lại vài lần Các tạp chất học thường không tan dung môi thông thường nên chúng loại cách lọc nóng 22.6 Write a short summary of the text 89