Quantitative Chemistry Flashcards
(18 cards)
Q: What is the Law of Conservation of Mass?
A: Mass is neither created nor destroyed in a chemical reaction. The mass of the products equals the mass of the reactants in a closed system.
Q: What is the Relative Formula Mass (Mr)?
A: Mr is the sum of the relative atomic masses (Ar) of all atoms in a formula.
Q: How do you calculate the Mr of a compound like H₂O?
A: Mr of H₂O = (2 × Ar of H) + (1 × Ar of O) = (2 × 1) + (16) = 18
Q: What is a mole in chemistry?
A: 1 mole = 6.02 × 10²³ particles (Avogadro’s number). It’s the amount of a substance that contains the same number of particles as there are in 12g of carbon-12.
Q: How do you calculate the number of moles?
A: Moles = Mass (g) ÷ Relative Formula Mass (Mr)
Q: How do you calculate the mass from moles?
A: Mass = Moles × Mr
Q: What is a limiting reactant?
A: The reactant that is completely used up first in a reaction, limiting the amount of product formed.
Q: How do you find the limiting reactant?
A: Compare the mole ratio of reactants used in the reaction. The one that runs out first is the limiting reactant.
Q: How does a limiting reactant affect the yield of a product?
A: The limiting reactant controls how much product is formed. Once it’s used up, the reaction stops.
Q: What happens to mass in an open system during a reaction?
A: The mass can change because gases may escape or be absorbed into the system.
Q: What happens to mass in a closed system during a reaction?
A: The mass remains the same because no substances can enter or leave the system.
Q: How do you calculate concentration of a solution?
A: Concentration (g/dm³) = Mass of solute (g) ÷ Volume of solution (dm³)
Q: What is a balanced chemical equation?
A: A chemical equation where the number of atoms of each element is the same on both sides of the equation.
Q: Why is it important to balance chemical equations?
A: To satisfy the Law of Conservation of Mass – no atoms are lost or gained.
Q: How do you calculate the theoretical yield?
A: Use the limiting reactant to find the amount of product that should be formed in a reaction (based on stoichiometry).
Q: What is the actual yield?
A: The actual amount of product obtained from a reaction. It may be lower than the theoretical yield due to factors like incomplete reactions or losses during extraction.
Q: What is the percentage yield?
A: Percentage yield = (Actual yield ÷ Theoretical yield) × 100
Q: How can mass changes be used to identify a reaction type?
A: Mass changes can indicate whether a gas has been produced or absorbed during a reaction, revealing whether it’s an exothermic or endothermic reaction.
