1e-Chemical formulae, equations and calculations Flashcards
Question: What is a word equation?
Answer: A word equation shows the reactants and products of a chemical reaction using their names. Example: Hydrogen + Oxygen → Water
Question: What is a balanced chemical equation?
Answer: A balanced equation shows the number of atoms of each element is the same on both sides. Example: 2H₂ + O₂ → 2H₂O
Question: Why are state symbols used in equations?
Answer: State symbols show the physical state of substances: (s) solid, (l) liquid, (g) gas, (aq) aqueous.
Question: How do you calculate relative formula mass (Mr)?
Answer: Mr is the sum of the relative atomic masses (Ar) of all atoms in a formula. Example: Mr of H₂O = (2 × 1) + 16 = 18
Question: What is a mole (mol)?
Answer: A mole is the unit of the amount of substance, containing 6.022 × 10²³ particles (Avogadro’s number).
Question: How do you calculate the number of moles?
Answer: Moles = Mass / Mr
Question: How do you calculate the mass of a substance?
Answer: Mass = Moles × Mr
Question: What is percentage yield, and how is it calculated?
Answer: Percentage yield compares the actual and theoretical yield:Percentage yield = (Actual yield / Theoretical yield) × 100
Question: What is an empirical formula?
Answer: The simplest ratio of atoms of each element in a compound.
Question: What is a molecular formula?
Answer: The actual number of atoms of each element in a compound.
Question: How do you calculate the empirical formula from experimental data?
Answer:
Find the mass of each element.
Calculate the moles of each element (Mass / Ar).
Divide by the smallest number of moles.
Write the ratio as the empirical formula.
Question: How do you determine the formula of a metal oxide by combustion?
Answer: Example: Magnesium oxide
Weigh magnesium before combustion.
Burn magnesium in air.
Weigh the magnesium oxide formed.
Use the mass difference to calculate the oxygen mass and determine the formula.
Question: How do you determine the formula of copper(II) oxide by reduction?
Answer:
Weigh copper(II) oxide before heating.
Heat with hydrogen to remove oxygen.
Weigh the remaining copper.
Calculate the ratio of copper to oxygen to find the formula.