Homework 12

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Q 4.86

Question: List these elements in order of decreasing first ionization energy: In, F, Se, Br.

Strategy:

A. Determine the location of the elements on the periodic table

B. Remember the increasing trend of ionization energy in KJ/mol (exception in case of Boron) from left to right on the periodic table

C.Remember the decreasing trend of ionization energies (Kj/mol) from top to bottom (Cs is the exception in the first group)

periodic table.jpg

Solution

F, Br, Se, In

For more information: http://chemwiki.ucdavis.edu/Physical...ization_Energy

Q 5.106

Question: For several compounds both the molar mass and and empirical formulas are listed. What is the molecular formula for each compound.

C₂OH₄, 88 g/mol

C₂H₈N, 46 g/mol

NH₂, 32 g/mol

Strategy:

A. Find the empirical formula mass of the compound

B. Determine the ratio between the empirical formula mass and the molar mass of the compound

C.Multiply the empirical formula by the factor found in part B.

Solution:

C₂OH₄, 88 g/mol

Carbon: 2(12.0g/mol)

Oxygen: 1(16.0g/mol)

Hydrogen: 4(1.0g/mol)

=44.0 g/mol

\[\frac{88.0g/mol}{44.0g/mol}=2\]

2(C₂OH₄)= C₄O₂H₈

C₂H₈N, 46 g/mol

Carbon: 2(12.0g/mol)

Hydrogen: 8(1.0g/mol)

Nitrogen: 1(14.0g/mol)

=46.0 g/mol

\[\frac{46.0g/mol}{46.0g/mol}=1.0\]

1(C₂H₈N)=C₂H₈N

NH₂

Nitrogen: 1(14.0g/mol)

Hydrogen: 2(1.0g/mol)

=16.0g/mol

\[\frac{32.0g/mol}{16.0g/mol}=2\]

2(NH₂)=N₂H₄