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Commercial Brass is an alloy composed of Zinc and Copper. If this brass is reacted with hydrochloric acid the zinc will dissolve but the copper wil not react. When 0.5065g of brass alloy is reacted with excess hydrochloric acid, 0.0985g of zinc chloride is eventually isolated.a. Write a balanced equation for the... 顯示更多 Commercial Brass is an alloy composed of Zinc and Copper. If this brass is reacted with hydrochloric acid the zinc will dissolve but the copper wil not react. When 0.5065g of brass alloy is reacted with excess hydrochloric acid, 0.0985g of zinc chloride is eventually isolated. a. Write a balanced equation for the reaction of zinc with the acid b. What is the percent composition of the brass by mass? c. How could this result be checked without changing the above procedure?

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最佳解答:

a. Zn(s) + 2HCl(aq) -----> ZnCl2(aq) + H2(g) b. no. of mole of ZnCl2 = 0.0985g / (65.4 + 35.5 x 2)gmol-1 = 7.22 x 10-4 mol weight of Zn in brass = 7.22x10-4 mol x 65.4gmol-1 = 0.0472g % composition of Zn in brass = 0.0472g / 0.5065g x 100% =9.324% hence % composition of Cu in brass = (100 - 9.324)% = 90.676% c. calculate the no.of mole of Hydrogen gas (see answer (a) above) in the reaction by measuring the volume of hydrogen gas collected: no. of mole of H2 = vol. of H2 (dm^3) / molar volume (24 dm3/mol) no. of mole of H2 = no. of mole of Zn in brass, the weight of Zn hence be calculated and checked. ** atomic mass of Zn = 65.4gmol-1 atomic mass of Cl = 35.5gmol-1

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