Amount of substance

• What is the key concept for chemical calculations?

  The mole
• How is the mole defined in terms of carbon-12?

  It is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.
• What is Avogadro's Number?

  
  

  6.022x10^23
• What are the three equations used to calculate moles at A-level?

  1. For pure solids, liquids, and gases
  2. For gases: $PV =$$nRT$
  3. For solutions: $\text{concentration} =$$\frac{\text{moles}}{\text{volume}}$
• What is the unit of mass in chemical calculations?

  Grams
• What is the unit of moles?


  mol
• What is the unit of pressure (P)?

  Pa
• What is the unit of volume (V) in the Ideal gas equation?

  m^3
• What is the unit of temperature (T)?

  K
• What is the unit of concentration?

  mol dm^-3 or M
• How do you convert cm^3 to dm^3?

  Divide by 1000
• How do you convert cm^3 to m^3?

  Divide by 1,000,000
• How do you convert dm^3 to m^3?

  Divide by 1000
• How do you convert °C to K?

  Add 273
• What is relative atomic mass?

  The average mass of one atom compared to one twelfth of the mass of one atom of carbon-12
• What is relative molecular mass?

  The average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12
• How should the relative molecular mass (Mr) be quoted?

  To 1 decimal place (1dp)
• How is the molar mass (Mr) for a compound calculated?

  By adding up the mass numbers of each element in the compound from the periodic table
• What is the unit of significant figures for answers?

  Same number of significant figures as the data given in a question
• What is Avogadro's Constant (L)?

  It is the number of particles in one mole, which is 6.022 x 10^23.
• What is the unit of density?

  g cm^-3
• How is density calculated?

  $\text{density} =$$\frac{\text{mass}}{\text{volume}}$
• What is the difference between a molecular formula and an empirical formula?

  • Molecular formula: Actual number of atoms of each element in the compound.
  • Empirical formula: Simplest ratio of atoms of each element in the compound.
• How do you calculate moles from mass and molar mass?

  moles = mass / Mr
• What is the relationship between moles and concentration?

  Concentration = moles / volume
• What happens when soluble ionic solids dissolve in water?

  They dissociate into separate ions
• What are the steps to make a solution?

  • Weigh the sample bottle with solid
  • Transfer to beaker and reweigh
  • Add distilled water and stir
  • Heat if necessary to dissolve
  • Pour into volumetric flask and rinse
  • Make up to the mark with distilled water
  • Invert flask to ensure uniform solution
• What is the purpose of using a volumetric pipette over a measuring cylinder?

  It has a smaller uncertainty and is more accurate
• What happens when you dilute a solution?

  • Amount of moles of solute remains the same
  • Volume of solution increases
  • Concentration decreases
• How do you calculate the new diluted concentration after dilution?

  new diluted concentration = original concentration x original volume / new diluted volume
• What are the safety precautions when handling acids and alkalis?

  • Wear goggles for irritants and corrosives
  • Keep away from flames for flammable substances
  • Wear gloves for toxic substances
  • Avoid contact with oxidizing agents
• What is the ideal gas equation?

  PV = nRT
• What is the unit of pressure in the ideal gas equation?

  Pa
• What is the unit of volume in the ideal gas equation?

  m³
• What is the unit of temperature in the ideal gas equation?

  K
• How do you convert temperature from Celsius to Kelvin?

  Add 273
• How do you calculate the moles of Cl₂ gas using the ideal gas equation?

  moles = PV / RT
• How do you calculate the molar mass of a volatile liquid using the ideal gas equation?

  Mr = mass / moles
• What are potential errors when using a gas syringe?

  • Gas escapes before bung is inserted
  • Syringe sticks
  • Some gases are soluble in water
• Why is it important to note temperature and pressure when measuring gas volume?

  Because the volume of a gas depends on these conditions