quatatative chemistry

• What does the Law of Conservation of Mass state?


  No matter is lost or gained during a chemical reaction.
• Why must all chemical equations be balanced?


  Because the total mass of the reactants is equal to the total mass of the products.
• What is the relationship between the relative atomic/molecular masses of reactants and products?


  The sum of the relative atomic/molecular masses of the reactants equals the sum of the products.
• What is a precipitation reaction?


  A reaction in which two solutions react to form an insoluble solid called a precipitate.
• What happens to the total mass in a closed reaction flask?


  The total mass remains constant.
• What is produced when calcium chloride reacts with sodium sulfate?


  A precipitate of calcium sulfate.
• What is the balanced equation for the reaction between calcium chloride and sodium sulfate?

  CaCl₂ (aq) + Na₂SO₄ (aq) ⟶ CaSO₄ (s) + 2NaCl (aq)
• What happens to the total mass in an open reaction flask?


  The total mass changes as gaseous products can escape.
• What is produced when hydrochloric acid reacts with calcium carbonate?


  Carbon dioxide gas.
• What is the balanced equation for the reaction between hydrochloric acid and calcium carbonate?


  2HCl (aq) + CaCO₃ (s) ⟶ CaCl₂ (aq) + H₂O (l) + CO₂ (g)
• What could cause the mass of a reaction flask to increase?


  One of the reactants may be a gas from the air, while products are solids or liquids.
• What is the key principle regarding matter in chemical reactions?


  Matter cannot be created or destroyed.
• What are the steps to represent reactions as equations?

  • Chemical symbols represent reactants and products.
  • No subscript means one atom of that element.
  • A subscript indicates the number of atoms of the preceding element.
  • A subscript after brackets applies to all elements inside.
  • Balance equations to have equal numbers of each atom on both sides.
• Which non-metals must be written as molecules in chemical equations?


  H₂, N₂, O₂, F₂, Cl₂, Br₂, and I₂.
• How do you balance a chemical equation?


  Work across the equation from left to right, checking one element at a time.
• What are the steps to balance the equation for aluminium reacting with copper(II) oxide?


  1. Balance aluminium atoms first.
  2. Balance oxygen atoms next.
  3. Finally, balance copper atoms.
• What is the balanced equation for the reaction of aluminium with copper(II) oxide?


  2Al (s) + 3CuO (s) ⟶ Al₂O₃ (s) + 3Cu (s)
• What is the process for balancing the equation when magnesium oxide reacts with nitric acid?


  1. Write the unbalanced equation.
  2. Balance hydrogen atoms.
  3. Check the equation for balance.
• What is the balanced equation for the reaction between magnesium oxide and nitric acid?


  MgO (s) + 2HNO₃ (aq) ⟶ Mg(NO₃)₂ (aq) + H₂O (l)
• What is a common mistake when balancing symbol equations?


  Adding, changing, or removing small numbers in the chemical formula of a substance.
• What is the symbol for relative atomic mass?


  A
• How is relative formula mass calculated?


  By adding the relative atomic masses of all the atoms present in the formula.
• What is the relative formula mass of common substances?


  • Water (H₂O): 18
  • Potassium carbonate (K₂CO₃): 138
  • Calcium hydroxide (Ca(OH)₂): 74
  • Ammonium sulfate ((NH₄)₂SO₄): 132
• What is the relative formula mass of sodium chloride (NaCl)?


  58.5
• What is the relative formula mass of copper oxide (CuO)?


  79.5
• What is the relative formula mass of magnesium nitrate (Mg(NO₃)₂)?


  148
• What does the Law of Conservation of Mass imply about reactants and products?


  The sum of the relative molecular masses of the reactants equals that of the products.
• What is the process for calculating the % mass of an element in a compound?


  1. Find the relative formula mass of the compound.
  2. Find the relative atomic mass of the element.
  3. Use the formula: % mass = (mass of element / mass of compound) x 100.
• What does the Law of Conservation of Mass state?


  The sum of the relative molecular masses of the reactants equals the sum of the products.
• How do you calculate the relative formula mass of sodium chloride (NaCl)?


  NaCl = 23 + 35.5 = 58.5
• What is the relative formula mass of copper oxide (CuO)?


  CuO = 63.5 + 16 = 79.5
• Calculate the relative formula mass of magnesium nitrate (Mg(NO₃)₂). What is the formula?


  Mg(NO₃)₂ = 24 + (14 x 1 x 2) + (16 x 3 x 2) = 148
• Where can you find the relative atomic mass of elements?


  On the Periodic Table.
• How do you calculate the percentage by mass of an element in a compound?


  • Use the formula:

  \[

  \text{% mass of an element} = \frac{Ar \times \text{number of atoms of the element}}{Mr \text{ of the compound}} \times 100

  \]
• What is the percentage by mass of hydrogen in water (H₂O)?


  Percentage of hydrogen = \(\frac{2 \times 1}{18} \times 100 = 11.1\%\)
• What is the percentage by mass of oxygen in water (H₂O)?


  Percentage of oxygen = \(\frac{1 \times 16}{18} \times 100 = 88.9\%\)
• What should the total percentage by mass of all elements in a compound add up to?


  100%
• What is a common mistake when calculating percentage composition?


  Calculating values above 100%.
• How do you calculate the percentage of carbon in glucose (C₆H₁₂O₆)? What is the answer?


  Percentage of carbon = \(\frac{6 \times 12}{180} \times 100 = 40\%\)
• What is the percentage by mass of nitrogen in ammonium nitrate (NH<sub>4</sub)NO₃)? What is the answer?


  Percentage of nitrogen = \(\frac{2 \times 14}{80} \times 100 = 35\%\)