There are set of rules that are a guide to determine if an inorganic compound is soluble in water. The rules are listed in order of importance and rule 1 will overwrite rule 5.
Rule 1: All salts that include a group 1 element or ammonium are soluble.
Rule 2: All nitrates and acetates are soluble.
Rule 3: All compounds with halogens and a metal except for fluorine are soluble except those with silver, mercury and lead.
Rule 4: All sulphates are soluble except those with barium, strontium, lead, calcium, silver and mercury.
Rule 5: Carbonates, oxides, hydroxides, and phosphates are insoluble.
Is Ca(NO3)2 soluble in water?
Yes. Rule 2 states that all nitrates are soluble.
Is Na2(CO3) soluble in water?
Yes. Even though rule 5 states that carbonates are insoluble, rule 1 is higher and thus this compound is soluble in water.
Is Ca(OH)2 soluble in water?
No. No other rule above 5 applies to this compound and so rule 5 states that hydroxides are insoluble.
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This article was written for you by Jeremie, one of the tutors with Test Prep Academy.