Equivalents: Videos & Practice Problems

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 essential for quantifying the amount of individual ions in body fluids and intravenous solutions. An equivalent, often abbreviated as eq, represents the number of moles of charge contributed by an ion in a solution. Specifically, one equivalent corresponds to one mole of positive or negative charge. It is crucial to note that equivalents can only be expressed as positive values.

For instance, when considering sodium ions (Na⁺), one mole of sodium contributes a charge of +1, resulting in 1 equivalent. In contrast, for iron (III) ions (Fe³⁺), one mole contributes a charge of +3, which translates to 3 equivalents. To calculate the number of equivalents for any ion, the formula is straightforward: multiply the ion's charge by the number of moles of that ion present.

Additionally, the term milliequivalent is commonly used to express equivalence in smaller units, where 1 equivalent equals 1,000 milliequivalents. Thus, the relationship can be summarized as follows: equivalent = ion charge × moles of ions. For example, with sodium ions, the charge is +1 and the number of moles is 1, yielding 1 equivalent. For iron (III) ions, the charge is +3 with 1 mole present, resulting in 3 equivalents. This understanding is vital when calculating the equivalence of any ionic solution.

Equivalents Example 1

To calculate the number of equivalents for ions, you can use the formula:

Equivalents = Ion Charge × Moles of Ion

For calcium ions (Ca²⁺), the ion charge is +2. If you have 1 mole of calcium ions, the calculation would be:

Equivalents of Calcium = 2 × 1 = 2 equivalents

For phosphate ions (PO₄^3-), the ion charge is -3. If you have 2 moles of phosphate ions, the calculation would be:

Equivalents of Phosphate = 3 × 2 = 6 equivalents

Thus, the number of equivalents for calcium ions is 2, and for phosphate ions, it is 6.

Equivalents Concept 2

Normality is a crucial concept in chemistry that refers to the concentration of ions in an aqueous solution. It is denoted by the variable N and is defined as the number of equivalents of a solute per liter of solution. To understand normality, it's essential to first grasp the concept of equivalence, which can be calculated using the formula:

Equivalence = Ion Charge × Moles of Ions

With this understanding, normality can be expressed mathematically as:

Normality (N) = Equivalence / Liters of Solution

This relationship highlights how normality provides a measure of the reactive capacity of a solution, making it particularly useful in titrations and other chemical reactions where the number of reactive species is important. By knowing the normality of a solution, chemists can predict how it will behave in various chemical processes.

Equivalents Example 2

To calculate the normality of magnesium ions in a solution, we start with the formula for normality, which is defined as the number of equivalents of solute per liter of solution. The equation can be expressed as:

Normality (N) = \frac{Equivalents}{Liters of Solution}

In this scenario, we have 0.35 moles of magnesium ions in 300 milliliters of blood. First, we need to convert the volume from milliliters to liters:

Volume in liters = 300 \, \text{mL} \times \frac{1 \, \text{L}}{1000 \, \text{mL}} = 0.300 \, \text{L}

Next, we calculate the number of equivalents. The number of equivalents is determined by multiplying the charge of the ion by the number of moles of that ion. For magnesium, which has a charge of 2+, the calculation is as follows:

Equivalents = Ion Charge \times Moles of Ions = 2 \times 0.35 \, \text{moles} = 0.70 \, \text{equivalents}

Now, we can substitute the values into the normality formula:

Normality = \frac{0.70 \, \text{equivalents}}{0.300 \, \text{L}} = 2.33 \, \text{N}

Thus, the normality of the magnesium ions in the blood is approximately 2.3 N. This calculation is essential for understanding the concentration of ions in biological fluids, which can have significant implications in medical and physiological contexts.

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

Answer: (D)

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

Answer: (B)

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

Answer: (C)

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

Answer: (A)

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.