Reactions and calculations

• Acids are proton donors that release hydrogen ions when mixed with water, they produce H+ ions in aqueous solution.
• Hydrogen ions are never by themselves in water, they combine with hydrogen to produce hydroxonium ions (H3O+)
• Bases are proton acceptors and remove H+ ions from aqueous solution
• Bases soluble in water are alkalis, they release OH- ions in solution.

• It is a base
• NH3
• It dissolves in water so is alkali.
• It accepts protons from acids to make an ammonium ion which then can form an ammonium salt.
• Doesnt directly produce hydroxide ions because the reaction with ammonia and water produces hydroxide ions.

• Reaction between acid and water and base and water is reversible, both forwards and backwards reaction will be happening.
• Depending on whether the forwards or backwards reaction is more prevalent and to what extent the acid or base is ionised in solution acids and bases can be classified as strong or weak.
• E.g- HCl is almost 100% ionised in solution so it is a strong acid the forwards reaction is favoured asnd nearly all H+ ions released, NaOH the forwards reaction is favoured so nearly all the base dissociates in water and lots of OH- ions are released.
• Weak acids the backwards reaction is favoured so only a small amount of the acid dissociates and a few H+ ions are released, it is written as a reversible reaction.
• Weak bases ionise slightly in water and backwards reaction is favoured so a small amount of base dissociates and a few OH- ions released, written as a reversible reaction.

If a hydrogen ions are replaced by metal ions or ammonium ions you get a salt.

Sulfuric acid produces salts called sulfates.

Hydrochloric acid produces salts called chlorides.

Nitric acid produces salts called nitrates.

Acid + base = salt and water.

Metal + acid = salt + hydrogen.

metal oxide + acid = salt + water.

Metal hydroxide + acid = Salt + water.

metal carbonate + acid = salt + carbon dioxide + water.

• Metal Hydroxides are usually alkalis eg sodium hydroxides and potassium hydroxides. 
• They release OH- ions into water which then accept H+ ions from an acid to form water molecules.

• All solids consist of a lattice of positive and negative ions. In some salts, water molecules are incorporated in the lattice too.
• In water the O atoms are attracted to the positively charged ions in the lattice.
• The H atoms in water are attracted to negatively charged ions in the lattice.
• Waters in a lattice are waters of crystalisation.
• A salt containing waters of crystalisation are hydrated.
• A salt is anhydrous if it doesnt contain waters of crystalisation.
• One mole of a particular hydrated salt always has the same number of moles of waters of crystalisation.

• Find mass of water lost
• Find moles of water lost
• Find moles of anhydrous salt produced
• Work out ratio of moles of salt to water
• Scale the ratio so its 1:n

conc X volume (cm3) / 1000

• Polyprotic acids are acids that donate more than 1 proton.
• Diprotic acids donate 2 protons, eg H2SO4.
• Triprotic acids donate 3 protons, eg H3PO4.
• Compared to monoprotic acids when working out amount of moles of base to neutralise a diprotic acid you need to double the number and then triple it for triprotic acids.

• Theoretical yield is the mass of product that should be formed in a chemical reaction.
• It assumes no chemicals are lost in the process.
• You can use masses of reactants and a balanced equation to calculate the theoretical yield for a reaction.
  • 1. Work out moles of limitiing reactant
  • 2. use equation to work out how many moles of product you would expect that much reactant to make
  • 3. calculate the mass of that many moles of product- and thats the theoretical yield.

• Reasons for actual mass of product being less than theoretical yield:
  • not all chemicals react properly
  • chemicals get lost
• You can work out percentage yield from theoretical yield
• Percentage yield = actual yield / theoretical yield x 100

• A measure of the proportion of reactant atoms that become part of the desired product in the balanced chemical equation.
• Percentage yield doesnt mean how wasteful the reaction is itself. A reaction that has 100% yield could be very wasteful if a lot of atoms from the reactants wind up in by-products rather than the desired product.
• Efficency of a reaction is measured by percentage yield which tells you how wasteful the process is based on how much product is lost.
• Atom economy =
• Mr of desired product/ sum of molecular masses of all products X 100
• To calculate atom economy find molecular masses of products youre interested in then add up Mr of all products and put both into the formula.

• addition, reactants combine to form a single product
• atom economy always 100% no product lost
• substitution, some atoms from one reactant are swapped with atoms from another.
• This always results in at least 2 products.
• atom economy always less than 100%

• Atom economy and percentage yield measure different things.
• A reaction with a high atom economy could have a low percentage yield.
• Atom economy is a way to measure the atomswasted when making a chemical. The higher the atom economy, the 'greener' the process. 100 per cent atom economy means that all the atoms in the reactants have been converted to the desired product.
• The calculated or expected amount of product is called the theoretical yield. The amount of product actually produced is called the actual yield. 

• Reactions with low atom economies are less sustainable.
• Many raw materials are in limited supply so it makes sense to use them as efficently as possible.
• This will allow them to last as long as they can.
• Low atom economies mean lots of waste product.
• It costs money to separate the desired product from the waste product and more money to dispose of waste products safely.
• Disposing of them safely means they dont harm the environment.
• Companies usually have paid good money to buy the reactant chemicals.
• Its a waste of money if a high proportion of them end up as useless products.
• Reactions with a low atom economy may still be used if waste products could be used for something else.