Chemistry Class 11: Mole Concept Quiz

Chemistry NCERT Class 11: Mole Concept

The mole concept is a fundamental concept in chemistry, which helps simplify calculations and solve problems related to chemical compounds. This article will focus on key subtopics related to the mole concept, including Avogadro's number, stoichiometry, molar volume, molar mass, and empirical formula.

Avogadro's Number

Avogadro's number (NA) is a fixed numerical value of the Avogadro constant, which is approximately equal to $$6.022 \times 10^{23}$$ molecules, atoms, or other elementary entities. It is defined as the amount of a substance that contains exactly one mole of that substance. For example, one mole of carbon-12 (12C) has a mass of exactly 12 grams.

Stoichiometry

Stoichiometry is the study of the quantitative relationships between reactants and products in chemical reactions. It helps in understanding the ratios at which substances react and the number of moles of each substance involved in the reaction. In this context, the mole concept is used to simplify calculations and determine the stoichiometry of a reaction.

Molar Volume

Molar volume is the volume of gas occupied by one mole of a particular substance at a specific temperature and pressure. It is calculated using the ideal gas law, which states that the pressure (P) of an ideal gas is directly proportional to the number of moles (n) and the volume (V) it occupies, and inversely proportional to the temperature (T) in Kelvin.

$$PV = nRT$$

Where:

• P is the pressure of the gas in Pascals (Pa)
• V is the volume of the gas in cubic meters (m³)
• n is the number of moles of the gas
• R is the ideal gas constant (8.314 J/(mol·K))
• T is the temperature in Kelvin (K)

Molar Mass

Molar mass is the mass of one mole of a particular substance and is expressed in grams per mole (g/mol). It is calculated by dividing the mass of a specific number of moles of a substance by the number of moles in that substance.

Empirical Formula

The empirical formula of a compound is the simplest ratio of the number of different atoms present in that compound. It is determined by dividing the molar mass of the compound by the mass of each element in the compound and rounding to the nearest whole number. The empirical formula is usually represented as a quotation, such as $$C_2H_5O_4$$, where $$C$$ represents carbon, $$H$$ represents hydrogen, and $$O$$ represents oxygen.

For example, consider a compound with a molar mass of 90.00 units. If the mass of carbon is 12.01 units, the mass of hydrogen is 3.94 units, and the mass of oxygen is 34.04 units, the empirical formula would be $$C_2H_5O_4$$.

Empirical Formula vs. Molecular Formula

While the empirical formula gives the simplest ratio of the number of different atoms, the molecular formula gives the actual number of atoms present in a molecule. The molecular formula is often represented as a chemical formula, such as $$H_2O$$ for water or $$NaCl$$ for sodium chloride. The empirical formula of water is $$H_2O$$, but its molecular formula is $$H_2O_4$$, indicating that each water molecule contains two hydrogen atoms and one oxygen atom.

In conclusion, the mole concept is a crucial concept in chemistry, as it simplifies calculations and helps in understanding the quantitative relationships between various substances in chemical reactions. Avogadro's number, stoichiometry, molar volume, molar mass, and empirical formula are all essential aspects of the mole concept that aid in solving complex chemical problems.