Third Example

In this third example, you are not expected to know the names of these things; but we have silver sulfate (Ag₂SO₄) reacting with calcium chloride (CaCl₂) to become silver chloride (AgCl) and calcium sulfate (CaSO₄).

Later in this course you will become more familiar with polyatomic ions (or clusters of atoms) like this SO₄. Notice that we have an SO₄ on the left and an SO₄ on the right. We don't have to add up the sulfurs separately and the oxygens separately. We can do that but it is usually easier to treat them as groups.

First, a quick inventory. Silver: we have two silvers on the left and one on the right. Sulfur: one sulfur on the left and one on the right. Oxygen: four oxygens on the left and four on the right. Calcium: one calcium on the left and one on the right. Chlorine: two chlorines on the left and one on the right. So the only things that are really out of whack at the moment are the silver and the chlorine.

Ag₂SO₄ + CaCl₂ AgCl + CaSO₄
2 Ag, 1 S, 4 O, 1 Ca, 2 Cl	1 Ag, 1 S, 4 O, 1 Ca, 1 Cl

We start with Ag₂ on the left so we need to have two silvers on the right. If you put a two in front of the AgCl, that gives us two silvers on each side. That also gives us two chlorines on the right, which is what is already shown on the left. We didn't have to change the coefficients for the sulfur or oxygen or calcium, just the silver and the chlorine. Let’s double check to make sure everything is balanced. We have Ag₂ on the left and 2 Ag on the right; that's the same number. We have an SO₄ on the left and an SO₄ on the right; that's the same. We have one Ca on the left and one Ca on the right. Finally, we have Cl₂ on the left and 2 AgCl gives us two chlorines on the right, so everything is the same. The balanced equation is Ag₂SO₄ + CaCl₂

2 AgCl + CaSO₄.

Ag₂SO₄ + CaCl₂ 2 AgCl + CaSO₄
2 Ag, 1 S, 4 O, 1 Ca, 2 Cl	2 Ag, 1 S, 4 O, 1 Ca, 2 Cl

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E-mail instructor: Eden Francis

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