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An impure sample of zinc (Zn) is treated with an excess of sulfuric acid $\left(\mathrm{H}_{2} \mathrm{SO}_{4}\right)$ to form zinc sulfate $\left(\mathrm{ZnSO}_{4}\right)$ and molecular hydrogen $\left(\mathrm{H}_{2}\right) .$ (a) Write a balanced equation for the reaction. (b) If 0.0764 g of $\mathrm{H}_{2}$ is obtained from $3.86 \mathrm{g}$ of the sample, calculate the percent purity of the sample. (c) What assumptions must you make in (b)?

a) $\quad Z n(s)+H 2 S O 4(a q)-\quad Z n S O 4(a q)+H 2(g)$b) Find the amount zinc that has reacted\[\begin{array}{l}n(Z n): n(H 2)=1: 1 \\n(Z n)=n(H 2) \\m(2 n) / M(Z n)=m(H 2) / M(H 2) \\m(Z n)=[m(H 2) / M(H 2)]^{*} M(Z n) \\m(Z n)=[0.0764 g / 2 g / m o l] * 65.38 \mathrm{g} / m o l \\m(Z n)=2.49 g\end{array}\]So there is 2.49 g pure zinc in the sampleThe purity of zinc therefore is\[\begin{array}{l}w(Z n, \%)=[2.49 / 3.86] * 100 \%=64.50 \% \\w(Z n, \%)=64.50 \%\end{array}\]c) In part (b) you need to assume that in the sample the impurities (metals) don't react with sulfuric acid to produce hydrogen.

Chemistry 101

Chapter 3

Mass Relationships in Chemical Reactions

Chemical reactions and Stoichiometry

University of Central Florida

Drexel University

University of Maryland - University College

Lectures

04:02

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity. Chemical reactions are usually characterized by a chemical change, and they yield one or more products after the reaction is complete. Chemical reactions are described with chemical equations, which symbolically present the starting materials, end products, and sometimes intermediate products and reaction conditions. Chemical reactions happen at a characteristic reaction rate at a given temperature and chemical concentration. Typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms.

08:02

In chemistry, a combination reaction is a chemical reaction in which two or more reactants combine to form more than one product. In a decomposition reaction, one reactant splits into two or more products.

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An impure sample of zinc (…

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On surfer part, a zinc in solid state plus h 2 s, o 4 in was form inducing sulfate in equals, form plus h, 2 and gaseous state answer for part b find the amount of tin that has reacted. So we have a number of moles of ding ratio. Number of moles of h, 2 is equal to 1 ratio, 1 and n into zinc. Ray is equal to n into h. 2 mass of zinc divided by molar. Mass of zing is equal to mass of zing. Divided by molar mass of h, 2, sorry here, mass of h, 2, divided by molar mass of h, 2 and next we have mass of zinc, is equal to mass of h, 2 divided by molar mass of h. 2 is equal to molar mass of zinc and mass of zinc is equal to mass of h, 20.0764 gram to 2 gram per mole divided by 65.38 gram per mole, is equal to mass of zinc is equal to 2.49 gramaso and there is 2.49 gram piercinin this Empire the purity of zint, therefore, is the weight of 10 percent, is equal to 2 into 49 divide by 3.682, .49 divided by 3.68 into 100 percent is equal to 64.50 percent. The rate of zin percent is equal to 64.50 percent, non se par par part c. In part b, we need to assume that in the sample simple, the impurities, this metals don't react with with sulfuric acid, to produce hydrogen.

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