CHEM CALC

• What does the molecular formula show?

  Number and type of each atom in a molecule
• What is the empirical formula?

  It is the simplest whole number ratio of atoms
• How is the empirical formula calculated?

  • From the ratio of masses of each element
  • By determining the mass of each element in a sample
  • From percentage compositions by mass of elements
• How do you determine the empirical formula from mass?

  By calculating the ratio of masses of elements
• How do you determine the empirical formula from percentage composition?

  By using the percentage of each element
• What does the molecular formula provide?

  Exact numbers of atoms of each element
• How is the molecular formula found from the empirical formula?

  By dividing the relative formula mass of the molecular formula by the empirical formula mass
• How do you calculate the relative mass of the empirical formula C4H10S?

  By summing the atomic masses of its elements
• What is water of crystallisation?

  Water included in the structure of some crystals
• What is a hydrated compound?

  A compound containing water of crystallisation
• What is an example of a hydrated compound?

  CuSO4∙5H2O
• How is the formula of a hydrated compound written?

  With a dot separating the compound and water
• What is an anhydrous compound?

  A compound without water of crystallisation
• How can the degree of hydration be calculated?

  From experimental mass measurements before and after heating
• What is the ideal gas equation?

  PV = nRT
• What does P represent in the ideal gas equation?

  Pressure in pascals (Pa)
• What does V represent in the ideal gas equation?

  Volume in cubic metres (m3)
• What does n represent in the ideal gas equation?

  Amount of substance in moles (mol)
• What does R represent in the ideal gas equation?

  The gas constant, 8.31 J mol-1 K-1
• What does T represent in the ideal gas equation?

  Temperature in Kelvin (K)
• Why is it important to convert units to SI units in gas calculations?

  To ensure consistency and accuracy in calculations
• How do you convert kPa to Pa?

  Multiply by 1000
• How do you convert cm3 to m3?

  Divide by 1,000,000
• How do you convert Celsius to Kelvin?

  Add 273
• How can the ideal gas equation be used for volatile liquids?

  At temperatures above their boiling point
• How do you determine the molecular formula from empirical data?

  By calculating the molar mass and comparing
• What is the percentage composition formula?

  percent mass of an element = (Ar × number of atoms) / Mr of compound × 100
• How do you calculate the percentage by mass of calcium in calcium carbonate?

  Using the percentage composition formula
• Why must chemical equations be balanced?

  Atoms cannot be created or destroyed
• What are the steps for balancing equations?

  1. Write the formulae of reactants and products
  2. Count the atoms in each reactant and product
  3. Balance the atoms one at a time
  4. Use appropriate state symbols
• How do you balance the equation for magnesium and oxygen?

  2Mg + O2 → 2MgO
• What are spectator ions?

  They do not take part in the reaction
• What does an ionic equation show?

  Only the ions participating in a reaction
• How do you write the ionic equation for zinc and copper(II) sulfate?

  Zn (s) + Cu2+(aq) → Zn2+(aq) + Cu (s)
• How do balanced equations relate to chemical reactions?

  • Show number of particles in reactions
  • Allow calculation of moles involved
  • Help calculate masses and volumes
• What are displacement reactions?

  Reactions where a more reactive element displaces another
• What is an example of a displacement reaction?

  Br2 (aq) + 2KI (aq) → I2 (aq) + 2KBr (aq)
• What are neutralisation reactions characterized by?

  Presence of acids and bases forming salt and water
• What is the ionic equation for neutralisation?

  H+ (aq) + OH- (aq) → H2O (l)
• What are precipitation reactions?

  Reactions forming a solid from two aqueous solutions