Question

practice: write the formulas
calcium carbonate → ca²+ and co₃²- → caco₃
sodium nitrate → na+ and no₃- → nano₃
ammonium sulfate → nh₄+ and so₄²- → (nh₄)₂so₄
k+ no₃-
al²

Explanation:

Step1: Determine the formula for magnesium phosphate

• Magnesium ion is \(Mg^{2 +}\), phosphate ion is \(PO_{4}^{3 -}\).
• Using the criss - cross method (the absolute value of the charge of one ion becomes the subscript of the other ion).
• For \(Mg^{2+}\) and \(PO_{4}^{3 -}\), the formula is \(Mg_{3}(PO_{4})_{2}\) because \(|+ 2|\) for \(Mg\) and \(|-3|\) for \(PO_{4}\).

Step2: Determine the formula for ammonium chloride

• Ammonium ion is \(NH_{4}^{+}\), chloride ion is \(Cl^{-}\).
• Since the charges are \(+1\) and \(-1\) respectively, the formula is \(NH_{4}Cl\) (the subscripts are \(1\) and can be omitted).

Step3: Determine the formula for aluminium sulfate

• Aluminium ion is \(Al^{3+}\), sulfate ion is \(SO_{4}^{2 -}\).
• Using the criss - cross method, the formula is \(Al_{2}(SO_{4})_{3}\) ( \(|+3|\) for \(Al\) and \(|-2|\) for \(SO_{4}\)).

Step4: Determine the formula for calcium hydroxide

• Calcium ion is \(Ca^{2+}\), hydroxide ion is \(OH^{-}\).
• Using the criss - cross method, the formula is \(Ca(OH)_{2}\) ( \(|+2|\) for \(Ca\) and \(|-1|\) for \(OH\)).

Step5: Determine the formula for potassium nitrate

• Potassium ion is \(K^{+}\), nitrate ion is \(NO_{3}^{-}\).
• Since the charges are \(+1\) and \(-1\) respectively, the formula is \(KNO_{3}\) (the subscripts are \(1\) and can be omitted).

Answer:

Cation	\(Mg^{2+}\)	\(NH_{4}^{+}\)	\(Al^{3+}\)	\(Ca^{2+}\)	\(K^{+}\)
Final Formula	\(Mg_{3}(PO_{4})_{2}\)	\(NH_{4}Cl\)	\(Al_{2}(SO_{4})_{3}\)	\(Ca(OH)_{2}\)	\(KNO_{3}\)
Name of Compound	Magnesium phosphate	Ammonium chloride	Aluminium sulfate	Calcium hydroxide	Potassium nitrate