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Chemistry: Compound Composition

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Please discuss how to find the molar mass of a compound, percent composition of the elements of a compound and how to determine the empirical and molecular formulas from percent composition.

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How to find the molar mass. The molar mass is the sum of all the atomic masses of the elements in a compound.
1. Find the atomic mass of each element in the compound by using the periodic table.
2. If there are any subscripts, multiply the atomic mass by the subscript.

Example 1:
Mn= 55 g/mol O= 16 g/mol
(1x55) +(2x16)
55+ 32=87g/mol

Example 2:
Mg=24 g/mol P=31g/mol O=16g/mol
(3x24) +(2x31)+(8x16)=262 g/mol
This is an important concept to understand because you will need it for other calculations in chemistry. One such case is figuring out the % composition of a compound.

Percent Composition:
1. Look up the atomic masses in the periodic ...

Solution Summary

This solution will discuss how to calculate the following: molar mass, percent composition, empirical formula and molecular formula from percent composition. Examples are provided for each concept.

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Chemistry Question Set

Please see the attached file for full problem description.

10a. Determine the number of CH2CH2 monomeric units, n, in one molecule of polyethylene with a molar mass of 40,000 g.

10b. What is the total number of carbon atoms in this polyethylene?

8. Equations 9.1 and 9.2 (listed below) show the polymerization of two ethylene monomers to form a small segment of polyethylene. Use the bond energies of Table 4.1 to calculate the energy change during the reaction in equation 9.1. Is this reaction endothermic or exothermic?

9. How will your result from question 8 differ if, rather than using ethylene as the monomer, tetrafluoroethylene is used as the monomer, forming a small segment of the Teflon polymer, polytetrafluoroehylene? This is the structure of the monomer:

32. Catalysts are used to help control the average molar mass of polyethylene, an important strategy to control polymer chain length. During World War II, low-pressure polyethylene production used varying mixtures of triethyl aluminum, A12(C5H3)
and titanium tetrachloride, TiC14 as a catalyst. Here are some data showing how the
molar ratio of the two components of the catalyst affects the average molar mass of the polymer produced.
a. Prepare a graph to show how the molar mass of the polymer varies with the mole ration of A12 (C5H3 ) /TiC14

b. What conclusion can be drawn about the relationship between the molar mass of the polymer and the mole ratio of A12 (C5H3 ) /TiC14?

8. Some organic compounds exist in isomeric forms that are members of different classes of compounds. For example, in some cases the compound is an alcohol or an ether. For each of these, identify the class of compound represented by the formula as written

Then write the formula of an isomer with the same composition that is a member of a different class of compound. Identify the new class.

12. Ibuprofen is relatively insoluble in water but readily soluble in most organic solvents. Explain this solubility behavior based on its structural formula found at the link below:


15. Compare the physiological effects of aspirin with those of acetaminophen and ibuprofen. Relate differences to the nature of each compound at the molecular and cellular levels.

5. Equation 12.1 (listed below) shows the general case for a nitrogen-containing base reacting with water. Use the structural formula for thymine (link given below) to write an equation showing how thymine could react with water to generate hydroxide ions.

The structural formula for thymine can be found at:


9. Figure 12.6 (link given below) shows the pairing of nucleotide bases in DNA.
Here is the link:
a. What type of intramolecular bonding occurs within each base?
b. What type of intermolecular bonding occurs holds the base pairs together?

34a. The first successful application of gene therapy to a human being was in 1990. What is meant by "gene therapy" and what disease was treated in that landmark case?
b. Has gene therapy been used successfully for treating other diseases as well?
c. Will it work for all diseases?

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