Answer to the Practice Problems

1. Name the following ionic compounds:

Cr₂(SeO₄)₃ chromium(III) selenate (Se and S are elements of the same group. Since SO₄^2- is called sulfate, an educated guess is to name the SeO₄^2- selenate.)

Sr(ClO)₂ strontium hypochlorite

MnO₂ manganese(IV) oxide ( 'manganese dioxide' is not a systematic name. The systematic naming method does not use prefixes in naming ionic compounds.)

Na₂O₂ sodium peroxide (sodium dioxide is incorrect because the anion is a peroxide anion, not an oxide anion.)

2. Give the chemical formulas for the following ionic compounds:

cobaltic nitrate Co(NO₃)₃

vanadium(V) oxide V₂O₅

magnesium dihydrogen phosphate Mg(H₂PO₄)₂ dihydrogen phosphate is H₂PO_4^-

ammonium ferrous sulfate hexahydrate (NH₄)₂Fe(SO₄)₂·6H₂O

3. Name the following covalent compounds:

NO₂ nitrogen dioxide

NO nitrogen monoxide; it is commonly called nitric oxide.

N₂O dinitrogen monoxide; it is also called nitrous oxide or laughing gas.

P₄O₁₀ tetraphosphorus decaoxide

4. Give the chemical formulas for the following covalent compounds:

hydrogen sulfide H₂S (It is not called dihydrogen sulfide because it takes two H⁺ to combine with one S^2- to make a electrically neutral molecule. No other combination is possible.)

dinitrogen tetroxide N₂O₄

5. Name the following compounds/ions:

Na₃N sodium nitride

CaCr₂O₇ calcium dichromate

HI(aq) hydroiodic acid

H₂S(aq) hydrosulfuric acid

SeO₃ selenium trioxide

SO₃^2- sulfite ion (it is not sulfur trioxide because it is an anion.)

6. Give the chemical formulas for the following compounds/ions:

potassium superoxide KO₂ (the cation is K⁺ and the anion is O_2^- )

gallium arsenite GaAsO₃

copper(I) sulfate Cu₂SO₄ (It takes two Cu⁺ to go with one SO₄^2- )

radium ion Ra²⁺

ammonium hydrogen phosphate (NH₄)₂HPO₄ (the cation is ammonium = NH₄⁺, the anion is hydrogen phosphate = HPO₄^2-