C3 Quantitative Chemistry

• What is the conservation of mass?

  In a chemical reaction, the total mass is the products is equal to the total mass of the reactants.

  Mass is conserved because no atoms are lost or made.
• Why must chemical equations be balanced?

  To show that mass is conserved.
• What can a half equation show?

  What happens to one reactant in a chemical reaction, with electrons written as e-
• What are ionic equations used for?

  Simplifying complicated equations.

  They just show the species that are involved in the reaction.

  The spectator ions (ions not involved in the reaction) are not included.
• What is the relative formula mass (Mr)?

  The sum of all the relative atomic masses (Ar) of all the atoms shown in the formula of a compound.
• Where are the atomic masses shown?

  In the periodic table.
• How do relative formula masses relate to conservation of mass?

  The sum of the relate formula masses of all the reactants is always equal to the sum of the relative formula masses of all the products.
• Why do some reactions appear to have a change in mass?

  This happens when reactions are carried out in a non closed system and include a gas that can enter or leave.
• What is a mole (mol)?

  A measure of the number of particles (atom, ions or molecules) contained in a substance.
• What is Avogrado's constant?

  One mole of any substance contains the same number of particles - 6.02 x 10^23
• What is the mass of any one mole of a substance?

  It's relative atomic mass or relative formula mass in grams.
• How do you calculate the amount of substance (number of moles)?

  Mass of substance (g) ÷ atomic (or formula) mass (g/mol)
• What do balanced equations show?

  The number of moles of each product and reactant.

  They can be used to calculate the mass of the reactants and products.

  The numbers needed to balance and equation can be calculated from the masses of the reactants and the products using moles.
• What is the limiting reactant?

  When one chemical is used up in a reaction, it stops the reaction going any further, it is called the limiting reactant.

  The other chemical, which is not used up, it is said to be in excess.
• What volume does one mole of a gas take up?

  24 dm³, at room temperature and pressure.
• How do you calculate volume of a gas?

  Amount (mol) x 24 dm³
• How is concentration of a solution measured?

  Mol/dm³

  g/dm³
• How do you calculate concentration?

  Amount of substance (mol) ÷ volume (dm³)
• What do acids and alkalis react together to form?

  A neutral solution
• What is titration?

  An accurate technique that can be used to find out how much of an acid is needed to neutralise an alkali
• What happens when neutralisation takes place?

  The hydrogen ions (H+) from the acid join with the hydroxide ions (OH-) from the alkali to form water (neutral pH).

  H+(aq) + OH-(aq) > H2O(l)
• What indicators can be used for strong acids and alkalis?

  Methyl orange or phenolphthalein.
• What are examples of strong acids?

  Hydrochloric acid, nitric acid and sulfuric acid.
• What are examples of strong alkalis?

  Aqueous sodium hydroxide and aqueous potassium hydroxide.
• What needs to be known in titration to find the concentration of an acid or alkali?

  The relative volumes of acid and alkali used.

  The concentration of the other acid or alkali.
• How do you calculate the concentration from tritration?

  Write a balanced equation for the reaction to determine the ratio of acid to alkali involved.

  Calculate the number of moles in the solution of known volume and concentration, you can work out the number of moles in the other solution from the equation.

  Calculate the concentration of the other solution.
• What do atoms do in a chemical reaction?

  They are never lost or gained, only rearranged from the reactants to form the products.
• What is it not always possible to do in a reaction?

  Obtain the calculated amount of product
• Why might a reaction not obtain the calculated amount of product?

  If the reaction is reversible, it might not go to completion.

  Some product could be lost when it is separated from the reaction mixture.

  Some of the reactants may react in different ways to the expected reaction.
• What is the yield?

  The amount of product obtained.
• What is the percentage yield?

  Used to compare the actual yield obtained from a reaction with the maximum theoretical yield.
• How do you calculate percentage yield?

  (Yield from reaction ÷ Maximum theoretical yield) × 100
• What is atom economy?

  A measure of the amount of reactant that ends up in a useful product.
• What reaction pathway do scientists try to choose?

  Ones with a high atom economy
• Why is a high atom economy important?

  Economic reasons and sustainable development, as more products are made and less waste is produced.
• How do you calculate atom economy?

  (Relative formula mass of the desired product ÷ Sum of all the relative formula mass of all the products/ reactants) × 100
• How can ethanol be produced?

  Hydration and Fermentation.
• What happens in hydration?

  Ethene is reacted with steam to form ethanol.

  C2H4 + H2O > C2H5OH
• What type of reaction is hydration?

  An addition reaction- all the reactants atoms end up in the desired products.

  It has a 100% atom economy.
• What happens during the fermentation of glucose?

  Ethanol is produced.

  C6H12O6 > 2C2H5OH + 2CO2