Question Video: Calculating the Number of Atoms in a Single Unit of Aluminum Sulfate | Nagwa Question Video: Calculating the Number of Atoms in a Single Unit of Aluminum Sulfate | Nagwa

Question Video: Calculating the Number of Atoms in a Single Unit of Aluminum Sulfate Science • First Year of Preparatory School

How many atoms are there in a single unit of the compound Al₂(SO₄)₃?

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Video Transcript

How many atoms are there in a single unit of the compound Al2(SO4)3?

First, we need to identify the elements in the compound. Elemental symbols are either formed of a capital letter or a capital letter followed by a lowercase letter. There are three different elements in this compound: Al, aluminum; S, sulfur; and O, oxygen. But we need to know how many atoms there are in a single unit of the compound. We need to use the subscript values, or lack thereof, to calculate this. The subscript two after Al indicates that one unit of the compound contains two aluminum atoms.

Let’s now look at the contents of the brackets. The subscript four after O tells us that there are four oxygen atoms. The absence of a subscript after S tells us that there is only one sulfur atom. But the entire bracket has the subscript three. Therefore, there’s actually a total of three sulfur atoms and 12 oxygen atoms. These numbers can actually be calculated by multiplying the subscripts for each atom within the brackets with the subscript on the outside of the brackets.

So there are two aluminum atoms, three sulfur atoms, and 12 oxygen atoms in a single unit of the compound Al2(SO4)3. This sums to 17. Therefore, there are 17 atoms in a single unit of the compound Al2(SO4)3.

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