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The Mole Concept in Physical Chemistry

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Questions and Answers

What is the molar mass of carbon dioxide ($CO_2$)?

32.00 g/mol

28.01 g/mol

12.01 g/mol

44.01 g/mol (correct)

How many moles of sodium chloride (NaCl) are present in 58.44 grams of NaCl?

10 moles

1 mole (correct)

0.5 moles

2 moles

What is the mass of 2.5 moles of water ($H_2O$)?

18.02 g

22.52 g

45.05 g (correct)

90.10 g

How many atoms are present in 0.25 moles of magnesium (Mg)?

1.51 x 10^23 atoms Signup and view all the answers

What is the molarity of a solution containing 0.5 moles of potassium chloride (KCl) dissolved in 2.0 liters of water?

0.25 M Signup and view all the answers

How many grams of glucose ($C_6H_{12}O_6$) are needed to prepare 500 mL of a 0.25 M glucose solution?

22.5 g Signup and view all the answers

A chemical reaction requires 2 moles of sodium (Na) to react with 1 mole of chlorine gas ($Cl_2$) to form 2 moles of sodium chloride (NaCl). What is the mole ratio of sodium to chlorine gas in this reaction?

2:1 Signup and view all the answers

If 10 grams of magnesium (Mg) react with excess hydrochloric acid (HCl), how many grams of magnesium chloride ($MgCl_2$) are produced?

30 g Signup and view all the answers

What is a direct relationship between the concepts of moles and Avogadro's number?

One mole of any substance contains Avogadro's number of elementary entities. Signup and view all the answers

What is the best explanation for relating 'moles' and 'molar mass' in chemistry?

Molar mass is the mass of one mole of a substance. Signup and view all the answers

Study Notes

The Mole Concept in Physical Chemistry

The mole (mol) is the fundamental unit of amount of substance in the International System of Units (SI).
It represents the amount of substance containing as many elementary entities (e.g., atoms, molecules, ions, electrons) as there are atoms in 12 grams of carbon-12.
This number, known as Avogadro's number (N_A), is approximately 6.022 x 10²³.

Molar Mass

The molar mass of a substance is the mass of one mole of that substance.
It is expressed in grams per mole (g/mol).
Molar mass is crucial for converting between mass and amount of substance (in moles).
For elements, the molar mass is numerically equal to the atomic mass (from the periodic table), but has units of g/mol.

Relationships Between Moles, Mass, and Number of Particles

Moles to Mass: Mass (grams) = Moles (mol) × Molar Mass (g/mol)
Moles to Number of Particles: Number of particles = Moles (mol) × Avogadro's Number (N_A)
These relationships allow for calculations between mass, amount of substance, and the number of individual particles.

Using Moles in Chemical Reactions

Chemical reactions are balanced in terms of moles.
The stoichiometric coefficients in a balanced chemical equation represent the mole ratios of reactants and products.
This allows for calculating the amount of reactants needed or the amount of products that can be formed from a given amount of reactants.

Molarity

Molarity (M) is a measure of the concentration of a solution.
Defined as the number of moles of solute per liter of solution.
Formula: Molarity (M) = Moles of solute (mol) / Liters of solution (L)
Essential for expressing and working with solutions in various chemical procedures.

Other Concentration Units

Other concentration units exist, such as molality (mol/kg), normality, and parts per million (ppm), each with specific applications in different contexts.
These units provide alternative ways to quantify the amount of solute in a given amount of solvent or solution.

Calculating Moles in Solution

The volume of a solution can be used to determine the amount of solute (in moles) if the concentration (in molarity) is known.
Example calculations involving dissolving a given mass of solute in a specified volume of solvent and subsequently calculating the molarity or molality will utilize the relationships described above.

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Description

Explore the essential concepts of the mole in physical chemistry, including its definition and significance in the SI units system. Understand the relationship between moles, mass, and the number of particles, along with how to calculate molar mass and utilize Avogadro's number.