年級

問題的種類

自然科學 大學

為什麼[A(org)]=n[An(org)]成立 (第三張圖equation 7.9) 感謝

Experiment 7 Experiment 7 The partition of Organic acid between Water and Organic solvent Objectives Understand the partition of a solute between two immiscible solvents. Introduction A chemical analysis that is performed primarily with the aid of volumetric glassware (e.g., pipets, burets, volumetric flasks) is called a volumetric analysis. For a volumetric analysis procedure, a known quantity or a carefully measured amount of one substance reacts with a to-be-determined amount of another substance with the reaction occurring in aqueous solution. The volumes of all solutions are carefully measured with volumetric glassware. The known amount of the substance for an analysis is generally measured and available in two ways: 1. As a primary standard: An accurate mass (and thus, moles) of a solid substance is measured on a balance, dissolved in water, and then reacted with the substance being analyzed. 2. As a standard solution: A measured number of moles of substance is present in a measured volume of solution - a solution of known concentration, generally expressed as the molar concentration (or molarity) of the substance. A measured volume of the standard solution then reacts with the substance being analyzed. The reaction of the known substance with the substance to be analyzed, occurring in aqueous solution, is generally conducted by a titration procedure. The titration procedure required a buret to dispense a liquid, called the titrant, into a flask containing the analyte. A reaction is complete when stoichiometric amounts of the reacting substances are combined. In a titration this is the stoichiometric point. In this experiment the stoichiometric point for the acid-base titration is detected using a phenolphthalein indicator. Phenolphthalein is colorless in an acidic solution but pink in a basic solution. The point in the titration at which the phenolphthalein changes color is called the endpoint of the indicator. Indicators are selected so that the stoichiometric point in the titration coincides (at approximately the same pH) with the endpoint of the indicator.

待回答 回答數: 0
英文 大學

哪一個段落沒有主題句? 我覺得是第一個,對嗎? 要怎麼替這個段落寫出主題句呢?

2 Despite different home cultures and countries, international students' main overall motivation is the desire get out on their own, to carve out a new direction in their lives. "Foreign students" do not casually abandon the comforts of family and cultural ties; they have done their homework on Canadian schools. All their preparation, though, cannot prepare them for the loneliness and ongoing difficul- ties they face, from cold winters to financial issues related to the higher tuition fees they must pay. Some students, though, emigrate to escape those same tight- knit families and bonds that others find so painful to leave behind. A Macleans "On Campus" report notes that family expectations may be opposed to students' visions for themselves and lead them to reject accepted values and career paths in their hometowns and countries. Csilla, a web-design student at Waterloo admits, "I was always supposed to enter my family's restaurant business in Budapest, but I felt suf- focated even working part-time as a server. Web design is my passion, and I wanted 12: CAUSE OR EFFECT [- a completely fresh start, something that is completely my own ("International Stu- dents"). Finding independent paths to their own dreams is the key here, whether students choose those paths as a result of personal ideals or as a reaction to pre-set future plans.

待回答 回答數: 0
英文 高中

求詳解,感恩

OW dyainst factories that cause pollution. 閱讀測驗3 But the universal of our climate message of crisis wareness hing a fever pitch across the with increasing urgency, a pparent every day. For the Vandana Shiva will never forget a lesson she learned at the age of 13. Her parents insisted that she should wear clothing made only of homespun cotton. One day, Vandana, having returned from a boarding school to her home, demanded a nylon dress, the fashion followed by her rich friends. Her mother agreed. “If that is what you want, of course you shall have it,” she said. “But remember, your nylon dress will help a rich man buy a bigger car. And the cotton that you wear will buy a poor family at least one meal.” Did she buy the nylon dress? Of course not! Maybe this experience led to her resolution to fight for social justice in her later years. Now 60, ever visiting Taiwan in 2010, Vandana's main concern these days is how to preserve Indian traditional crops. This is severely attacked by many global companies. They encourage farmers to grow so-called high-yielding crops; many farmers, therefore, turn to high-tech methods and depend on bioengineered seeds, chemical fertilizers and pesticides. As a result, hundreds of traditional crops are disappearing. Contrary to expectation, high-tech agriculture can not rescue Indians from starvation. Bioengineered seeds are expensive and cannot adapt to local conditions. Hundreds of Indian farmers have committed suicide during the past five he world ironment. ns in 1970. years because of failed harvests. But there is hope. Many farmers are returning to traditional methods promoted by Navdanya, an organization based in New Delhi that Vandana helped found 20 years ago. Navdanya encourages farmers to produce native varieties of crops that can be grown with natural fertilizer and no artificial chemicals. It also helps local farmers form their own self-supporting organization and seed bank. nean? +明一 生能但奇 63

待回答 回答數: 0
1/3