Write the name from the formula or the formula from the name for each hydrated ionic compound. a. cobalt(II) phosphate octahydrate b. BeCl2 # 2H2O c. chromium(III) phosphate trihydrate d. LiNO2 # H2O
The Correct Answer and Explanation is:
Let’s break down each hydrated ionic compound to give the correct formula or name:
a. Cobalt(II) phosphate octahydrate
- Name: Cobalt(II) phosphate octahydrate
- Formula: Co3(PO4)2·8H2O
Explanation:
- Cobalt(II) refers to cobalt with a +2 charge.
- Phosphate is the PO4^3− anion.
- The formula for cobalt(II) phosphate is Co3(PO4)2, because cobalt(II) has a +2 charge, and each phosphate ion has a -3 charge. To balance the charges, three Co2+ ions are needed for every two PO4^3− ions.
- Octahydrate means there are 8 molecules of water (H2O) for every formula unit of the compound. The water molecules are associated with the ionic compound in the crystal structure, so the complete formula is Co3(PO4)2·8H2O.
b. BeCl2 · 2H2O
- Name: Beryllium chloride dihydrate
- Formula: BeCl2·2H2O
Explanation:
- BeCl2 is the formula for beryllium chloride, where Be is beryllium (with a +2 charge) and Cl is chloride (with a -1 charge). To balance the charges, one beryllium ion combines with two chloride ions.
- Dihydrate indicates there are two molecules of water associated with each formula unit of beryllium chloride. Hence, the formula is BeCl2·2H2O.
c. Chromium(III) phosphate trihydrate
- Name: Chromium(III) phosphate trihydrate
- Formula: CrPO4·3H2O
Explanation:
- Chromium(III) refers to chromium with a +3 charge.
- Phosphate is PO4^3−.
- The formula for chromium(III) phosphate is CrPO4, because the charge on the chromium ion (+3) is balanced by the charge on the phosphate ion (−3).
- Trihydrate means three molecules of water are associated with each formula unit of chromium(III) phosphate, so the complete formula is CrPO4·3H2O.
d. LiNO2 · H2O
- Name: Lithium nitrite monohydrate
- Formula: LiNO2·H2O
Explanation:
- LiNO2 is lithium nitrite, where Li is lithium with a +1 charge, and NO2 is the nitrite ion with a -1 charge. The charges balance out with one lithium ion for each nitrite ion.
- Monohydrate means one water molecule is associated with each formula unit of lithium nitrite, so the complete formula is LiNO2·H2O.
These names and formulas are derived based on the conventions for naming hydrated ionic compounds, where the number of water molecules is indicated by prefixes like “mono,” “di,” “tri,” and so on.
