The equivalent mass of an atom, also known as its equivalent weight, is found by dividing its gram atomic weight by its valence (combining power). This concept is crucial in understanding stoichiometry, especially in reactions involving elements that don't have a simple 1:1 combining ratio.
Understanding Key Terms
Before diving into the calculation, let's clarify the key terms:
- Gram Atomic Weight: This is the atomic mass of an element expressed in grams per mole. You can typically find this value on the periodic table.
- Valence (Combining Power): This represents the number of chemical bonds an atom can form with other atoms. It's essentially the atom's capacity to combine with other elements.
Calculating Equivalent Mass: Step by Step
Here's how you calculate the equivalent mass of an atom:
- Identify the element: Determine the atom you want to find the equivalent mass for.
- Find the gram atomic weight: Refer to the periodic table to find the atomic mass of the element in grams per mole. This is the gram atomic weight.
- Determine the valence: Identify the common valence or combining power of the element, which can be ascertained based on its position in the periodic table and common chemical compounds it forms.
- Divide: Divide the gram atomic weight by the valence.
Examples of Equivalent Mass Calculation
Here are some examples based on the provided reference:
| Element | Gram Atomic Weight (g) | Valence | Equivalent Weight (g) |
|---|---|---|---|
| Silver (Ag) | 107.868 | 1 | 107.868 |
| Magnesium (Mg) | 24.312 | 2 | 12.156 |
| Aluminium (Al) | 26.9815 | 3 | 8.994 |
| Sulphur (S) as sulphide | 32.064 | 2 | 16.032 |
- Silver (Ag): Has a gram atomic weight of 107.868 g and a valence of 1. Therefore, its equivalent weight is 107.868/1 = 107.868 g.
- Magnesium (Mg): Has a gram atomic weight of 24.312 g and a valence of 2. Thus, its equivalent weight is 24.312/2 = 12.156 g.
- Aluminium (Al): Has a gram atomic weight of 26.9815 g and a valence of 3. The equivalent weight is 26.9815/3 = 8.994 g.
- Sulphur (S): As a sulphide, sulphur has a gram atomic weight of 32.064 g and a valence of 2. Its equivalent weight is 32.064/2 = 16.032 g.
Importance of Equivalent Mass
Understanding equivalent mass helps in:
- Predicting Combining Ratios: In chemical reactions, knowing the equivalent masses allows you to determine the exact amounts of reactants needed to completely react with each other, particularly useful for titrations.
- Electrochemical Calculations: In electrochemistry, equivalent masses are used to understand the amount of substance deposited or dissolved during electrolysis.
- Neutralization Reactions: It is important to know the equivalent mass of an acid or base in a neutralization reaction.
In summary, finding the equivalent mass of an atom involves using its gram atomic weight and valence to determine its combining capacity. The equivalent mass helps us to understand the quantitative relationship of different elements in chemical reactions.
