Equivalents: Study with Video Lessons, Practice Problems & Examples

Equivalents measure the amount of charge contributed by ions in solutions, defined as the number of moles of charge per ion. One equivalent equals one mole of charge, and to calculate equivalents, use the formula: $\mathrm{Equivalent}=\mathrm{Ion}\mathrm{Charge}\mathrm{Moles}$. Normality, represented as N, indicates the concentration of equivalents per liter of solution, calculated as $\mathrm{Normality}=\mathrm{Equivalence}/\mathrm{Liters}$.

Equivalents Concept 1

Equivalents are used to measure individual ion amounts present in body fluids and intravenous solutions. Here we're going to say that an equivalent or abbreviated as eq is the number of moles of charge that one ion contributes to a solution. And we're going to say here that an equivalent equals 1 mole of positive or negative charge. One important thing to remember is that an equivalent can only be a positive value though. So, for example, here we have 1 mole of sodium ion. The charge is plus 1, so we'd say we have 1 equivalent. Here we'd say 1 mole of iron(III) ion, the number in the charge is 3, which equates to 3 equivalents of iron(III) ion. We'll see how to calculate that right below. We're going to say to calculate the number of equivalents of an ion, we simply multiply ion charge by the number of moles of ion present. Here we're going to say that a milliequivalent is a common unit used to express equivalence. And remember milli, so one equivalent equals 1,000 milliequivalents. And when it comes to an equivalent, just remember, equivalent=ion charge⋅moles of ions. So if we went up above again, the charge here is 1 and the number of moles is 1 so that's why it was 1 equivalent. Here the mole the ion charge was 3 and it's just 1 mole of iron(III) ion, so that's why the equivalent was 3. So just keep that in mind when asked to calculate the equivalence of any ionic solution.

Equivalents Example 1

Calculate the number of equivalents in each of the following. Just remember, an equivalent equals the ion charge times the moles of ion. So for the first one, (a), ion charge: Calcium has a 2+ charge, so the charge is 2 times the moles of the ion which is just 1 mole. So that means we have 2 equivalents of calcium ion. For (v), the ion charge of the phosphate ion is 3−, so that's 3 times the number of moles is 2 moles, so that's 6 equivalents of the phosphate ion. So those would be your answers for both a and v.

Equivalents Concept 2

That we've looked at equivalence, we can talk about normality. Now, normality is the concentration of ions in an aqueous solution, and we're going to say that normality, which uses the variable capital N, represents the number of equivalents per liter of solution. Right? So just remember we've calculated equivalence before where it's equal to the ion charge times the moles of ions. Now we're going to incorporate that understanding into this idea of normality. Normality equals equivalence over liters of solution.

Equivalents Example 2

Here we need to calculate the normality of 0.35 moles of magnesium ions present in 300 milliliters of blood. Right. So normality equals your equivalence divided by your liters of solution. Here, we know what our liters of solution are. In a sense, we have 300 milliliters of blood. Blood is our solution here. Converting that into liters gives us 0.300 liters. Now we need to figure out the number of equivalents. So remember, your equivalents equals the ion charge times the moles of ions. So here the charge of magnesium is 2+, so that's 2 times 0.35 moles which is equal to 0.7. So we have 0.7 equivalents. So when we do 0.70.3, that's going to give us 2.33 or just 2.3 normality. So this would be the normality of this particular solution.

Calculate mass (grams) needed for the following ion equivalent:1.5 mEq of Na⁺ ions.

• A. 3.4 g
• B. 15.0 g
• C. 0.065 g
• D. 0.034 g

The concentration of Cl^- ion in blood is approximately 105 mEq/L. How many milliliters of blood would be needed to obtain 1.4 g of Cl^- ions?

• A. 110 mL
• B. 380 mL
• C. 75 mL
• D. 240 mL

An intravenous saline solution contains 140 mEq/L of Na⁺. How many mEq of Na⁺ are present in 750 mL of the solution?

• A. 525 mEq
• B. 5.36 mEq
• C. 105 mEq
• D. 187 mEq

Calculate the normality (mEq/L) of potassium ions in a 500 mL Ringer's solution that is 2.0 x 10^-3 M in potassium ions.

• A. 2.0 mEq/L
• B. 0.200 mEq/L
• C. 2.5 mEq/L
• D. 0.250 mEq/L

Here’s what students ask on this topic:

What is an equivalent in chemistry?

An equivalent in chemistry is a measure of the amount of charge contributed by ions in a solution. It is defined as the number of moles of charge per ion. One equivalent equals one mole of positive or negative charge. To calculate the number of equivalents, you use the formula:

$\mathrm{Equivalent}=\mathrm{Ion}\mathrm{Charge}\mathrm{Moles}$

For example, 1 mole of Na⁺ (sodium ion) with a charge of +1 equals 1 equivalent, while 1 mole of Fe³⁺ (iron 3 ion) with a charge of +3 equals 3 equivalents.

How do you calculate the number of equivalents of an ion?

To calculate the number of equivalents of an ion, you multiply the ion's charge by the number of moles of the ion present. The formula is:

$\mathrm{Equivalent}=\mathrm{Ion}\mathrm{Charge}\mathrm{Moles}$

For example, if you have 2 moles of Ca²⁺ (calcium ion), the charge is +2. Therefore, the number of equivalents is:

$22=4$

So, you have 4 equivalents of Ca²⁺.

What is the difference between equivalents and normality?

Equivalents measure the amount of charge contributed by ions in a solution, defined as the number of moles of charge per ion. Normality, represented as N, indicates the concentration of equivalents per liter of solution. The formula for normality is:

$N=\frac{\mathrm{Equivalents}}{\mathrm{Liters}}$

For example, if you have 2 equivalents of an ion in 1 liter of solution, the normality is 2 N. Normality incorporates the concept of equivalents into the concentration of the solution.

How do you convert equivalents to milliequivalents?

To convert equivalents to milliequivalents, you multiply the number of equivalents by 1,000, since 1 equivalent equals 1,000 milliequivalents. The formula is:

$\mathrm{mEq}=\mathrm{Eq}1000$

For example, if you have 0.5 equivalents, the number of milliequivalents is:

$0.51000=500$

So, 0.5 equivalents is equal to 500 milliequivalents.

What is the formula for normality in chemistry?

The formula for normality in chemistry is:

$N=\frac{\mathrm{Equivalents}}{\mathrm{Liters}}$

Normality (N) represents the concentration of equivalents per liter of solution. To calculate normality, you divide the number of equivalents by the volume of the solution in liters. For example, if you have 3 equivalents of an ion in 2 liters of solution, the normality is:

$\frac{3}{2}=1.5$

So, the normality is 1.5 N.