Chem topic 5

• What is the symbol for amount of substance?

  n
• What is the unit used to measure amount of substance?

  Mole
• What does the Avogadro constant represent?

  The number of atoms per mole of the carbon-12 isotope
• How to calculate the mass of 1 mole of an element?

  Mass of 1 mole = relative atomic mass in grams
• How to calculate moles when mass and molar mass are given?

  Moles (mol) = mass (g) / molar mass (g mol^-1)
• What is an empirical formula?

  Simplest whole number ratio of atoms of each element present in a compound
• How to calculate empirical formula?

  Divide the amount of each element by its molar mass, then divide by the smallest value obtained
• What is Avogadro's law?

  Under the same temperature and pressure, one mole of any gas would occupy the same volume
• How much volume does a gas occupy at room temperature and pressure?

  24 dm^3 or 24000 cm^3
• What is molar gas volume?

  The volume per mole of gas molecules
• Why do different gas particles occupy the same volume?

  The gas particles are very spread out, hence individual differences have no effect
• How to calculate moles when gas volume is given?

  Moles (mol) = volume (dm^3) / 24 or Moles (mol) = volume (cm^3) / 24000
• What are the ideal ways in which gases behave?

  ● They are in continuous motion

  ● No intermolecular forces experienced

  ● Exert pressure when they collide with each other or container

  ● No kinetic energy is lost in the collisions

  ● When temperature increases, kinetic energy of gases also increase
• What is the ideal gas equation?

  pV = nRT
• What is 1 atmospheric pressure equal to in pascals?

  101325 Pa
• What is 0°C equal to in kelvins?

  273 K
• What does concentration of a solution mean?

  It is the amount of solute dissolved in 1 dm^3 of solvent
• How to calculate moles when concentration and volume are given?

  Moles (mol) = concentration (mol dm^-3) * volume (dm^3)
• What is a standard solution?

  A solution of known concentration
• What are the steps to prepare a standard solution?

  1. Weigh the solute using the weigh by difference method
  2. In a beaker dissolve the solute using the solvent
  3. Pour the solution into a volumetric flask
  4. Rinse the beaker using the solution and add it to the flask
  5. Add solvent to the flask carefully until it reaches the graduation line
  6. Mix the solution thoroughly to ensure complete mixing
• What is a species in a chemical reaction?

  Any particle that takes part in a reaction
• What do the terms concentrated and dilute mean?

  Concentrated - large amount of solute per dm^3 of solvent, Dilute - small amount of solute per dm^3 of solvent
• What are the four common state symbols?

  1. Solid (s)
  2. Liquid (l)
  3. Gaseous (g)
  4. Aqueous (aq)
• What does percentage yield mean?

  The efficiency of which reactants are converted into products
• What are the reasons for not obtaining 100% yield?

  ● Reaction may be at equilibrium

  ● The reactants may be impure

  ● Side reactions could happen

  ● Reactants or products may be left behind while transferring

  ● Loss of products during separation and purification
• How is percentage yield calculated?

  Percentage yield = (actual amount of product (mol) / theoretical amount of product (mol)) * 100
• What does atom economy tell us about?

  The proportion of desired products compared with all the products formed in the reaction
• How is atom economy calculated?

  Atom economy = (molecular mass of desired product / sum of the molecular masses of all products) * 100
• Does 100% yield mean 100% atom economy?

  No, even if all the reactants are converted into products, not all products of the reaction will be the required products
• Which type of reaction has 100% atom economy?

  Addition reactions (two or more reactants are combined to form a product)
• What does systematic error mean?

  The same error appears in each measurement
• How can the error of mass measurement be reduced?

  By using the weighing by difference method
• How to measure using the weighing by difference method?

  1. Measure the mass of the container
  2. Add the chemical to the container and weigh the container
  3. Calculate the mass of the chemical
  4. Transfer the chemical and remeasure the empty container
  5. Calculate the mass of the chemical transferred
• Is the percentage error higher or lower when the quantity measured has been reduced?

  Higher