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1.(NH4)2SO4 and Ca3(PO4)2 are compounds with both ionic and covalent bonds.

2. B. MgCl Mg2+ 2Cl– 

Ionic bonding has both a cation and an anion which MgCl has. CCl FeCl both splits into anions.

3. C. A sample of NaNO3 contains an Na+ ion and an NO3– polyatomic ion, which are held together with ionic bonds. The atoms in the NO3– ion are held together by covalent bonds. All of the bonds in the other choices are covalent bonds.

4. -8.37 x 10-19 J

E= (2.31 x 10-19 J nm) ( Q1Q2/r)

(2.31 x 10-19 J nm) [(+1)(-1)/ 0.276 nm] = -8.37 x 10-19 J

5. A. The numerical ion charges.

6. –183 kJ

Bonds broken – Bonds formed

(432 kJ/mol + 239kJ/mol) – (427 kJ/mol x 2mol) = -183kJ

7. –109 kJ

Bonds broken – Bonds formed

[3mol (432kJ/mol) + 941kJ/mol] – 6mol (391kJ/mol) = -109kJ

8. B. –808 kJ

Bonds broken – Bonds formed

[4mol (413 kJ/mol) + 2mol (495kJ.mol)] – [2mol (799kJ/mol) +4mol(463kJ/mol)] = -808kJ

9. B. The energy required to separate an ionic compound into gaseous ions is called the lattice energy. The most important factor in determining the lattice energy is the strength of the changes on the two ions. In MgO, the Mg ion is +2 and the O ion is –2. All of the other choices listed contain +1 or the –1 ions, so their lattice energies will not be as large.

10. C. H20

H20 is the only one that is polar. CH4 and CO2 both have charges that cancel out. 11. A. To the right because it goes from positive to negative.                                                                                      Back to Problems

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