quantitative chemistry

• How to calculate percentage yield

  actual yield/theoretical yield x 100
• An actual yield is the mass of a product actually obtained from the reaction. It is usually less than the theoretical yield. The reasons for this include:

  • incomplete reactions, in which some of the reactants do not react to form the product
  • practical losses during the experiment, such as during pouring or filtering
  • side reactions (unwanted reactions that compete with the desired reaction)
• Copper oxide reacts with sulfuric acid to make copper sulfate and water. In an experiment, 1.6 g of dry copper sulfate crystals are made. If the theoretical yield is 2.0 g, calculate the percentage yield of copper sulfate.


  actual yield / theoretical x 100

  1.6/2=0.8 x 100= 80%
• In an experiment, the theoretical yield is 3.2 g but the actual yield is only 2.4 g. Calculate the percentage yield.

  2.4/3.2=0.75x100 = 75%
• what is the theoretical mass


  A theoretical yield is the maximum possible mass of a product that can be made in a chemical reaction.
• what is concentration?


  A solution forms when a solute dissolves in a solvent. The concentration of a solution is a measure of how 'crowded' the solute particles are. The more concentrated the solution, the more particles it contains in a given volume.
• concentration equation


  mass of solute (g) /volume (dm^3)
• concentration is the amount of particles in a given solution
• concentration equation

  concentration= mass/volume
• The concentration of a solution affects its properties such as boiling point, freezing point, density, and viscosity.
• resolution definition

  smallest apparatus a piece of apparatus can make
• what is a mole ?

  a measurement used to count particles, where 1 mole of substance = 6.02x10^23. this number is known as avogadros constant.
• why is 1 mole exactly 6.02x10^23

  If you divide the charge on a mole of electrons by the charge on a single electron you obtain a value of Avogadro's number of 6.02214154 x 1023 particles per mole
• The number of atoms or molecules in a mole is known as the __________ constant.

  Avogadro constant. The Avogadro constant is approximately 6.022 x 10^23.
• Which is greater: the number of atoms in one mole of carbon, or the number of atoms in one mole of iron?


  they are the same
• moles equations

  moles=mass/mr

  moles=concentration x volume
• what is titration?


  A titration is a technique where a solution of known concentration is used to determine the concentration of an unknown solution. 
• How do you get from Cm³ to dm³ ?


  x by 1000
• Calculate the mass of 0.25 mol of carbon dioxide molecules. (Mr of CO2 = 44)


  Mass = relative formula mass × amount

  = 44 × 0.25

  = 11 g
• concentration equation


  Concentration = Amount of Solute / Volume of Solution
• what is the limiting reactant?


  The limiting reactant is the reactant that is completely used up in a reaction and limits the amount of product formed.
• titration equation


  Concentration₁ × Volume₁ = Concentration₂ × Volume₂
• give some reasons why the percentage yield is less than 100%

  reaction may be incomplete, side reactions taking place and losses during transfer (Between glassware)
• 1 dm3 = 1000 cm3
• The concentration of an acid can be determined by titration. An indicator is added to an alkali in a flask. Name an indicator that can be used in this titration.


  methyl orange from yellow to red / orange / pink

  or

  phenolphthalein (1) from pink to colourless (1)
• concentration = moles / volume (dm³)
• Conservation of Mass


  mass of reactants = mass of products
• • Percentage yield formula:

  Percentage yield = (actual yield / theoretical yield) × 100
• Rate of reaction:


  Rate = change in concentration / time
• How do you calculate the volume of a gas at room temperature and pressure (RTP)?

  gas volume (dm³) = Moles × 24
• What is the Haber Process used for?

  Produces ammonia (NH₃) for fertilizers.
• • What are the raw materials used in the Haber Process?

  Nitrogen (N₂) from the air and hydrogen (H₂) from natural gas or water electrolysis.
• • Write the balanced equation for the Haber Process.

  N₂ + 3H₂ ⇌ 2NH₃
• What are the conditions required for the Haber Process?

  • Temperature: 450°C

  • Pressure: 200 atmospheres

  • Catalyst: Iron
• Why is the temperature set to 450°C in the Haber Process?

  Higher temperatures favor the reverse reaction, but 450°C is a compromise: fast enough rate without sacrificing too much yield.
• Why is a pressure of 200 atmospheres used?

  High pressure favors the formation of ammonia, as it has fewer molecules on the right side of the equation (increasing yield).
• What role does the iron catalyst play in the Haber Process?

  Speeds up the reaction without affecting the equilibrium position.
• How does the Haber Process demonstrate Le Chatelier’s principle?

  High pressure and moderate temperature shift the equilibrium towards more ammonia production.
• How does increasing temperature affect the Haber Process?

  • It shifts the equilibrium to the left, decreasing ammonia yield (because the forward reaction is exothermic).
• How does increasing pressure affect the Haber Process?

  • It shifts the equilibrium to the right, increasing ammonia yield.