Question

1) Determine the number of moles of Br2 in a sample consisting of:

8.02×1022 Br2 molecules

2.23×10²⁴ Br atoms

11.0 kg bromine

Determine the mass percent H in the hydrocarbon isopentane, CH3CH(CH3)CH2CH3?

Determine the empirical formula of:

benzo[a]pyrene, a suspected carcinogen found in cigarette smoke, consisting of 95.21% C and 4.79% H, by mass

hexachlorophene, used in germicidal soaps, which consists of 38.37% C, 1.49% H, 52.28% Cl, and 7.86% O by mass.

The element X forms the compound XOCl2containing 59.6% Cl.

What is element X?

Dimethylhydrazine is a carbon-hydrogen-nitrogen compound used in rocket fuels. When burned in an excess of oxygen, a 0.312 g sample yields 0.458 gCO2 and 0.374 g H2O.
The nitrogen content of a 0.486 g sample is converted to 0.226 g N2.

The organic solvent thiophene is a carbon–hydrogen–sulfur compound that yields CO2, H2O, and SO2 on complete combustion. When subjected to combustion analysis, a 1.3020−gsample of thiophene produces 2.7224 g CO2, 0.5575 g H2O, and 0.9915 g SO2.

What is the empirical formula of thiophene?

Answer 1

You have to many questions but I will help you with the first 4 subpart, you can kindly post the others in another question:

A.

1 mole of any molecule contains = Avogadro No of molecules = 6.023*10^23 molecules

Thus, the number of moles of Br2 in a sample consisting of :

a) 8.02x 10^ 22 Br2 molecules = 8.16x 10^ 22 / 6.023*10^23 = 0.1331 moles

b) 2.11x10^24 Br atoms :

1 Br2 molecules is formed from 2 Br atoms. Thus, n of Br2 molecules in 2.23x10^24 Br atoms = 2.11x10^24 / 2 = 1.115x10^24 Br2 molecules

Thus, No of moles of Br2 = 1.115x10^24 / 6.023*10^23 = 1.8512 moles

c) 11.0 kg bromine:

Molecular mass of Br2 = 159.8 g/mol

Thus, moles of Br2 in 11.0 kg of Br2 = 11000 g / 159.8 g/mol = 0.06883 kg/moles

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B. Isopentane: C₅H₁₂

so total mass = (5*12g/mol) + (12*1g/mol) = 72 g/mol

and mass of H= 12 g/mol

so mass percent = 12/72 * 100%

%H = 16.667

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C) Steps for Determining an Empirical Formula

Start with the number of grams of each element, given in the problem.If percentages are given, assume that the total mass is 100 grams so that the mass of each element = the percent given.

-Convert the mass of each element to moles using the molar mass from the periodic table.

-Divide each mole value by the smallest number of moles calculated. Round to the nearest whole number. This is the mole ratio of the elements and is represented by subscripts in the empirical formula. If the number is too far to round (x.1 ~ x.9), then multiply each solution by the same factor to get the lowest whole number multiple.

Once the empirical formula is found, the molecular formula for a compound can be determined if the molar mass of the compound is known. Simply calculate the mass of the empirical formula and divide the molar mass of the compound by the mass of the empirical formula to find the ratio between the molecular formula and the empirical formula. Multiply all the atoms (subscripts) by this ratio to find the molecular formula

For benzo[a]pyrene = C20H12

For hexachlorophene = C13H6Cl6O2

3,4,6-trichloro-2- [(2,3,5-trichloro-6-hydroxy-phenyl) methyl]phenol

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D) Mass% of X = 100 - 59.6 = 40.4%

Let M be the molar mass of X

Since moles = mass/molar mass

Moles of X/moles of Cl = (40.4/M) /(59.6/35.45 g/mol) =

Molar mass of X = M = 24.04 g/mol

Thus X is Mg which has the closest molar mass (24.31 g/mol).

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