15. สารละลายแอมโมเนีย \( \left(\mathrm{NH}_{3}\right) 40 \) กรัม ละลายในน้ำจนได้ปริมาตรรวม 500 มิลลิลิตร จงคำนวณความ เข้มข้นในหน่วยรรอยละโดยมวล \( (\% \mathrm{~W} / \mathrm{W}) \) และร้อยละโดยมวลต่อปริมาตร \( (\% \mathrm{~W} / \mathrm{V}) \)

57. Rappresenta le equazioni delle seguenti reazioni specificando il nome dei prodotti. \( \begin{array}{ll}\text { a) ossidazione dell'esano } & \text { c) dibromurazione dell'esano } \\ \text { b) monoclorurazione del butano } & \text { d) ossidazione del propano }\end{array} \)

During a reaction, the enthalpy of formation of an intermediate is -286 \( \mathrm{~kJ} / \mathrm{mol} \). During the reaction, 2 moles of the intermediate are produced. What is the enthalpy value for this step of the reaction? A. -572 kJ B. 572 kJ C. 286 kJ D. -286 kJ

Explain,why we cannot call any fresh vegetable or fruit a pure substance?

5 What is meant by the term hygroscopic when referring to brake fluid?

Which of these scholars laid the toundations tor modern chemistry?