Al₂SO₃

Lead II dichromate

In this example, lead has an unusual valence of II instead of the expected valence of IV.  Therefore, you must indicate the change with a roman numeral in the name...

KNO₃

FePO₄

Ni(CN)₂ 

don't forget the ( ) around the "CN"

CuCO₃

Copper II carbonate

(must have a roman numeral in the name)

Chromium III phosphate

(must have a roman numeral in the name)

Ag₂CO₃

Silver carbonate 

or 

Silver I carbonate

(The valence of Silver is always I so you don't need a roman numeral in the name this time...)

CaCO₃

FeCr₂O₄

Ca(NO₃)₂

Mercury II sulfide (a binary compound)

(must have a roman numeral in the name)

Mg(HCO₃)₂

Magnesium bicarbonate

or

Magnesium hydrogen carbonate

Cu(OH)₂

BaSO₄

Mercury I iodide

(you need a roman numeral in the name here)

Ni(CN)₂

(don't forget the paranthesis in this formula!!!)

CoSO₄

Cobalt II sulfate

(you need a roman numeral in the name here)

Na₂SO₃

NiCrO₄

Nickel II chromate

(you need a roman numeral in the name here)

Ca(OH)₂

don't forget the ( ) around the OH

HgHCO₃

Mercury I bicarbonate

or

Mercury I hydrogen carbonate

(the valence of Mercury is I in this example)

_{Manganese II sulfate}

Ni(OH)₃

_{remember you need () around the hydroxide!!!}

NiNO₃

_{Nickel I nitrate}

ammonium chloride

Calcium phosphate

KMnO₄

Potassium permanganate

Sodium bicarbonate  (baking soda)

Magnesium sulfate  (epsom salts)

Ammonium carbonate

HgS₂O₃

Mercury II thiosulfate

Must have the roman numeral in the name since Mercury is a transition element of multi valence.