Sodium oxide formula mass

Which of the three terms, atomic mass, molecular mass, or formula mass, is most appropriate for each of the following ammonia, calcium oxide, barium, chlorine, sodium carbonate ... 

A transition metal compound contains a cobalt ion, chloride ions, and water molecules. The H2O molecules are the ligands in the complex ion and the Cl ions are the counterions. A 0.256-g sample of the compound was dissolved in water, and excess silver nitrate was added. The silver chloride was filtered, dried, and weighed, and it had a mass of 0.308 g. A second sample of 0.416 g of the compound was dissolved in water, and an excess of sodium hydroxide was added. The hydroxide salt was filtered and heated in a flame, forming cobalt(lll) oxide. The mass of cobalt(ItI) oxide formed was 0.145 g. What is the oxidation state of cobalt in the complex ion and what is the formula of the compound ... 

The periodic table was invented independently by Mendeleev and Meyer. Both noticed that if the elements were listed in the order of increasing atomic mass, there was a repetition (periodicity) of chemical and physical properties. For example, lithium, sodium, potassium, rubidium, and cesium all form oxides with the formula M2O and chlorides... 

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