What is the formula of Aluminium Sulphate?

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Multiple Choice

What is the formula of Aluminium Sulphate?

Explanation:
Ionic compounds must be electrically neutral, so we balance the charges between the metal ion and the polyatomic ion. Aluminum forms Al3+, while the sulfate ion is SO4 with a 2− charge. To get total charge of zero, you need two Al3+ ions (2 × +3 = +6) and three SO4^2− ions (3 × −2 = −6). That gives +6 and −6, which cancel out, leaving a neutral compound. This is why the formula is Al2(SO4)3—the two aluminum ions with three sulfate groups. Other options don’t balance to zero. AlSO4 would not balance the charges (Al3+ with SO4^2− leaves a net positive charge). Al2SO4 has two aluminums but only one sulfate, giving a net positive charge. Al2(SO4)2 has two aluminums and two sulfates, totaling +6 from aluminum and −4 from sulfate, which also isn’t neutral.

Ionic compounds must be electrically neutral, so we balance the charges between the metal ion and the polyatomic ion. Aluminum forms Al3+, while the sulfate ion is SO4 with a 2− charge. To get total charge of zero, you need two Al3+ ions (2 × +3 = +6) and three SO4^2− ions (3 × −2 = −6). That gives +6 and −6, which cancel out, leaving a neutral compound. This is why the formula is Al2(SO4)3—the two aluminum ions with three sulfate groups.

Other options don’t balance to zero. AlSO4 would not balance the charges (Al3+ with SO4^2− leaves a net positive charge). Al2SO4 has two aluminums but only one sulfate, giving a net positive charge. Al2(SO4)2 has two aluminums and two sulfates, totaling +6 from aluminum and −4 from sulfate, which also isn’t neutral.

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