Reading Comprehension TOEFL Exams 134

TOEFL Exams: Reading Comprehension - Lesson 134 (Đọc hiểu - TOEFL - Bài 134) 

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Distillation, the process of separating the elements of a solution, is widely used in industry today. The two most common methods of distillation are fractional distillation, used in the preparation of alcoholic beverages, and flash distillation, used for the conversion 5 of ocean water to fresh water. In fractional distillation a mixtureis separated into its various component parts by boiling. This method makes use of the fact that different elements boil at varying temperatures. For example, alcohol has a considerably lower boiling temperature than water: the boiling temperature of water is 212 degrees and the 10 boiling temperature of alcohol is 172 degrees. Thus, when a mixture of alcohol and water is heated, the alcohol vaporizes more quickly than the water. The distillate is collected and the process is repeated until the desired purity has been achieved. Flash distillation does not require high temperatures but instead is based on pressure. In 15 this process, a liquid that is to be separated is forced from a compartment kept under high pressure into a compartment kept at a lower pressure. When a liquid moves into the low-pressure chamber, it suddenly vaporizes, and the vapor is then condensed into distillate.

1. According to the passage, what makes fractional distillation occur?
(A) Time
(B) Pressure
(C) Heat
(D) Water
2. According to the passage, fractional distillation can occur only if
(A) one element is at a higher pressure than the other
(B) the elements of the solution have different boiling temperatures
(C) the solution is forced from a compartment at one temperature into a compartment at another temperature
(D) the solution to be distilled is completely pure
3. Which of the following statements about boiling temperatures is true?
(A) All elements have the same boiling temperature.
(B) Water boils at a lower temperature than alcohol.
(C) Any solution containing water boils at 212 degrees.
(D) Water does not boil at as low a temperature as alcohol.
4. According to the passage, in the flash distillation process, what causes the liquid to vaporize?
(A) The pressure on the liquid is suddenly changed.
(B) The liquid changes compartments.
(C) The addition of sea water to a solution causes a chemical change to occur.
(D) There is a rapid increase in the pressure on the liquid.
5. Which of the following processes would probably involve distillation?
(A) Adding a new substance to a mixture
(B) Dividing a pure element into smaller quantities
(C) Mixing two elements together to form a new solution
(D) Removing impurities from a solution
6. The main purpose of this passage is to
(A) explain how salt water can be turned into fresh water
(B) give an example of fractional distillation
(C) describe a scientific process
(D) discuss the boiling temperatures of various liquids