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Find the emperical formula of a substance which has the following percentage composition by mass (Na=18.2%, S=12.7%, O=19.1%, water if crystallization=50%



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Answer:

Na₂S₃O₇H₇.

Step-by-step explanation:

To find the empirical formula of a substance based on its percentage composition by mass, you need to determine the ratio of the elements in the compound. Given that the substance contains sodium (Na), sulfur (S), oxygen (O), and water of crystallization, you can follow these steps:

Convert the percentages to grams:

Sodium (Na) = 18.2% of the total mass

Sulfur (S) = 12.7% of the total mass

Oxygen (O) = 19.1% of the total mass

Water of crystallization = 50% of the total mass

Assume you have 100 grams of the substance for simplicity. Then:

Sodium (Na) = 18.2 grams

Sulfur (S) = 12.7 grams

Oxygen (O) = 19.1 grams

Water of crystallization = 50 grams

Determine the moles of each element:

Moles of Na = 18.2 g / 23.0 g/mol (molar mass of Na) = 0.791 moles

Moles of S = 12.7 g / 32.1 g/mol (molar mass of S) = 0.395 moles

Moles of O = 19.1 g / 16.0 g/mol (molar mass of O) = 1.194 moles

Moles of H (from water) = 50 g / 18.0 g/mol (molar mass of H2O) = 2.778 moles

Find the simplest whole number ratio of moles:

Divide each of the moles by the smallest number of moles (which is 0.395 moles in this case):

Na: 0.791 moles / 0.395 moles = 2

S: 0.395 moles / 0.395 moles = 1

O: 1.194 moles / 0.395 moles = 3

H: 2.778 moles / 0.395 moles = 7.02 (approximately 7)

Write the empirical formula using the whole number ratios:

The empirical formula for the substance is Na₂S₃O₇H₇. However, empirical formulas are usually written with the simplest whole-number ratios, so you should simplify it further:

Divide all the subscripts by the greatest common factor, which is 1 in this case:

The simplified empirical formula is Na₂S₃O₇H₇.

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