3A1 Mole Concept Flashcards
Explore how the mole concept applies to chemical systems and calculations.
Define:
Avogadro’s law
Equal volumes of any gas contain the same number of particles at the same temperature and pressure.
Amedeo Avogadro first described this law in 1811.
Mathematically expressed as V ∝ n.
Who first observed the relationship that led to Avogadro’s gas law?
The French scientist Gay-Lussac.
His observations of the relationships between pressure and temperature of a gas were made in 1808. Avogadro incorporated this theory into his own work on the mole concept.
Define:
a mole
A unit to measure an amount of matter or particles.
The concept simplifies counting and measuring small particles or atoms, since one mole represents 6.02 x 10²³ particles.
Which unit is larger, a dozen or a mole?
A mole.
A mole represents 6.02 x 10²³, while a dozen represents 12.
How do you convert moles to atoms?
Multiply the number of moles by Avogadro’s number (6.02 x 10²³).
This provides the total number of atoms in the sample.
Avogadro’s number is used for mole-to-particle and particle-to-mole conversions.
Define:
molar mass
The mass of one mole of a substance, expressed in grams per mole (g/mol).
It is calculated by summing the atomic masses of the elements in the substance.
Example: The molar mass of water (H₂O) is 18 grams/mol.
Calculated by adding the molar masses of hydrogen and oxygen.
Define:
atomic mass unit
(amu)
A unit used to express the mass of atoms or molecules.
1 amu is defined as one-twelfth the mass of a carbon-12 atom.
List the steps to determine molar mass.
- Write the chemical formula.
- Count atoms of each element.
- Multiply atomic masses by the number of atoms.
- Add results.
These steps use atomic masses from the periodic table.
Example: The molar mass of ethanol (C₂H₆O) is 46.068.
Calculate: (2×12.01) + (6×1.008) + (1×16.00).
State the relationship between molar mass and molecular mass.
- Molar mass is the mass of one mole.
- Molecular mass is the mass of one molecule.
Molar mass is in g/mol, and molecular mass is in amu.
Molar mass is used to convert between moles and grams.
State the mole formula.
Mole = Mass / Molar Mass
It is used to find moles from a given mass and vice versa.
State why scientists use moles in calculations.
- They allow for consistent measurements of particles.
- They simplify comparisons.
Moles relate atomic-scale quantities to macroscopic measurements.
True or False:
The molar mass of a compound depends on its chemical formula.
True
The chemical formula indicates the number and type of atoms, determining the molar mass.
Define:
molarity
The number of moles of solute per liter of solution.
Molarity quantifies solute concentration in a solution.
It allows chemists to quantify the number of particles in reactions.
A solute is the substance dissolved in a solution while a solvent is the substance in which the solute is dissolved.
Which formula is used to calculate molarity?
Molarity (M) = Moles of solute / Volume of solution (L)
This formula relates solute quantity to solution volume.
True or False:
The molarity of a solution depends on the mass of the solvent.
False
Molarity depends on the total volume of the solution, not just the solvent.
Define:
mole ratio
A ratio that shows how the number of moles of two substances in a chemical reaction are related.
Mole ratios are derived from the coefficients in a balanced chemical equation.
Define:
stoichiometry
It is the calculation of quantities in chemical reactions based on mole ratios.
It involves using balanced equations to relate reactants and products.
What is the stoichiometry of the reaction between Na and Cl₂ to form NaCl?
2 moles of Na react with 1 mole of Cl₂ to form 2 moles of NaCl.
The balanced reaction ensures the same number of atoms on both sides.
Which coefficients are used to find the mole ratio in the reaction: 2H₂ + O₂ → 2H₂O?
2 moles H₂ / 1 mole O₂ / 2 moles H₂O
Coefficients indicate the proportion of reactants and products.
How do you calculate the amount of product formed using mole ratios?
Multiply the given moles of a reactant by the mole ratio to find moles of the product.
Ensure the equation is balanced before determining the mole ratio.
Fill in the blank:
The mole ratio of O₂ to H₂O in the reaction 2H₂ + O₂ → 2H₂O is ____.
1:2
One mole of O₂ produces two moles of H₂O.
Define:
chemical formula
A representation of a compound’s elements.
It shows the types and quantities of atoms present in a compound. For instance, H₂O represents water, with two hydrogen atoms and one oxygen atom.
Define:
structural formula
The arrangement of atoms and bonds.
Structural formulas represent how atoms are bonded in a molecule and can include electron-dot diagrams or line structures to show shared electron pairs, like the bond between H and O in H₂O.
What is a balanced chemical equation?
An equation with equal numbers of each type of atom on both sides.
Balancing ensures the conservation of mass and correct relationships between substances.
Unbalanced equations give incorrect mole ratios.
True or False:
Mole ratios can be used to convert between masses of reactants and products.
True
Mole ratios allow conversion between moles, which can then relate to mass.
What is the mole ratio of N₂ to NH₃ in the reaction N₂ + 3H₂ → 2NH₃?
1:2
One mole of N₂ reacts to produce two moles of NH₃.
Define:
percent composition
It is the percentage by mass of each element in a compound.
It is used to determine the empirical formula.
It is calculated using the formula: (Mass of element / Molecular mass) × 100.
The molecular mass is the sum of the atomic masses of all the elements in a compound.
How do you calculate the percent composition of NaOH?
- Determine the molecular mass.
- Calculate the mass contribution of each element.
- Use the percent composition formula.
Molecular mass of NaOH is 40 g/mol.
Mass contribution of Na is 23g, O is 16g, and H is 1g.
Percent composition:
- Na = 23/40 x 100 = 57.5 %
- O = 16/40 x 100 = 40 %
- H = 1/40 x 100 = 2.5 %
List two applications of percent composition.
- Determining the purity of compounds.
- Designing concrete mixes in construction.
It ensures the correct proportions of components in materials or mixtures.
Fill in the blank:
The percent composition of _______ in H₂O is approximately 88.89%.
Oxygen
Water’s molecular mass is 18 g/mol, and oxygen’s mass is 16 g/mol.
How is percent composition used in the food industry?
It is used in nutrition labels to show the proportions of nutrients in food.
This helps consumers maintain dietary balance.
Define:
empirical formula
It is the simplest whole-number ratio of atoms in a molecule.
It represents the proportions of elements, not the exact number of atoms.
How do you calculate the empirical formula from percent composition?
- Convert percentages to grams.
- Convert the grams to moles.
- Divide the moles by the smallest mole value.
- Adjust to whole numbers if needed.
This method assumes a 100g sample for simplicity.
Percent composition helps calculate the empirical formula by determining the ratio of elements.
Define:
molecular formula
A formula that shows the exact number of each type of atom in a molecule.
It provides detailed information compared to the empirical formula.
Which formula represents sugar’s molecular formula?
C₆H₁₂O₆
Sugar’s empirical formula is CH₂O, the simplest ratio.
Fill in the blank:
The empirical formula for N₂O₄ is _____.
NO₂
Divide all subscripts by 2, the greatest common factor.
State the relationship between empirical and molecular formulas.
The molecular formula is a whole-number multiple of the empirical formula.
Molecular mass is needed to determine the molecular formula.
True or False:
All compounds have different empirical and molecular formulas.
False
Some compounds, like Methane (CH₄) and carbon dioxide (CO₂), have identical empirical and molecular formulas.
