Problem 96 - Chemistry Matter and Change

Question

RDA of Selenium The recommended daily allowance \((\mathrm{RDA})\) of selenium in your diet is \(8.87 \times 10^{-4} \mathrm{mol}\) . How many atoms of selenium is this?

Step-by-Step Solution

Answer

The RDA of selenium, $8.87 \times 10^{-4}\ \mathrm{mol}$, contains approximately \(5.34 \times 10^{20}\) atoms of selenium.

Step 1: Write down the given RDA value

The given RDA of selenium is \(8.87 \times 10^{-4}\ \mathrm{mol}\).

Step 2: Write down Avogadro's constant

Avogadro's constant, \(N_A\), is the number of atoms in one mole of any substance. It is given as \(N_A = 6.022 \times 10^{23}\ \mathrm{atoms/mol}\).

Step 3: Calculate the number of atoms of selenium

To calculate the number of atoms of selenium, we will multiply the given RDA value of selenium in moles by Avogadro's constant. Number of atoms = RDA of Selenium in moles × Avogadro's constant Number of atoms = \(8.87 \times 10^{-4}\ \mathrm{mol} \times 6.022 \times 10^{23}\ \mathrm{atoms/mol}\)

Step 4: Carry out the calculation and simplify the units

After multiplying the given values, we can cancel out the units of moles and obtain the answer in atoms. Number of atoms = \(5.34 \times 10^{20}\ \mathrm{atoms}\) The RDA of selenium contains approximately \(5.34 \times 10^{20}\) atoms of selenium.

Key Concepts

Selenium

Selenium is an essential trace element in the human diet. It plays a crucial role in various bodily functions. Despite its importance, it's needed only in small amounts.
Selenium contributes significantly to a healthy immune system and supports the antioxidant activities that prevent cellular damage. In the context of chemistry, selenium is a non-metal element belonging to group 16 of the periodic table.
It often forms compounds with other elements to perform its roles in biological systems. Since it is ingested in small amounts, understanding its presence and concentration is key to ensuring adequate dietary intake without exceeding the recommended levels.

Avogadro's Constant

Avogadro's constant is a fundamental number in chemistry, representing the number of atoms, molecules, or particles in one mole of a substance. The value of Avogadro's constant is precisely defined as \(6.022 \times 10^{23}\) atoms/mol.
It serves as a bridge between the atomic scale and the macroscopic scale. By using Avogadro's constant, chemists can convert between the number of atoms and the amount of substance in moles.
This constant is named after the Italian scientist Amedeo Avogadro, who noticed how equal volumes of gases, at the same temperature and pressure, have the same number of molecules. This observation laid the groundwork for the mole concept we use today.

Atoms

Atoms are the basic building blocks of all matter, comprising protons, neutrons, and electrons. Each chemical element consists of atoms that are distinct for that element, characterized by the number of protons in the nucleus, known as the atomic number.
The concept of atoms dates back to ancient Greek philosophy but has been refined and confirmed through scientific research over centuries.

• Protons and neutrons form the nucleus, which holds the atom's mass.
• Electrons orbit this nucleus and are involved in chemical reactions and bonding.

Understanding atoms is fundamental in calculating chemical quantities and understanding reactions. For example, knowing the number of atoms in a given mass of selenium allows nutritionists and scientists to assess selenium's presence in dietary contexts.