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Novosadov [1.4K]
3 years ago
11

Which of the following are considered pure substances?

Chemistry
2 answers:
Tanzania [10]3 years ago
8 0

Element. Everything is else is a mixture, therefore not pure.

Ganezh [65]3 years ago
3 0

Answer: A. Element and B. Compound

Explanation:

Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Copper Cu

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: water H_2O

Heterogeneous mixture : It is a mixture that has non-uniform composition throughout the solution and the particle size or shapes are also different.There is a physical boundary between the dispersed phase and dispersion medium.

Homogeneous mixture:  It is a mixture that has uniform composition throughout the solution and the particle size or shapes are not different.There is no physical boundary between the dispersed phase and dispersion medium.

Thus element and compound are pure substances.

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1) Chemical equation

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2) Molar ratios:

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number of moles = mass in grams / molar mass

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16 mol Fe / 3 mol S8                 0.0537 mol Fe / 0.009746 mol S8

5.33                                               5.50

So, there is a little bit more Fe than the theoretical needed to react all the S8, which means the S8 is the limiting reactant.

5) Calculate the number of moles of iron (III) produced with 2.5 g (0.009746 moles) of S8

3moles S8 / 8 moles Fe2S3 = 0.009746 moles S8 / x

=> x = 0.009746 * 8 / 3 moles Fe2S3 = 0.026 moles Fe2S3

6) Convert 0.026 moles Fe2S3 into grams

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molar mass of Fe2S3 = 207.9 g/mol

mass = 0.026 mol * 207.9 g/mol = 5.40 g

7) Answer: option D)




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