AQA Part 1 C3 Revision

• When an acid dissolves in water, it forms H⁺ ions
  • These Hydrogen atom is a proton because as a Hydrogen atom only only 1 proton and 1 electron, and with the Hydrogen atom giving away an electron (H⁺), this leaves only a proton. This makes it a PROTON DONOR

OH^- (aq) + H⁺ (aq) → H₂O (l)

• When an alkali dissolves in water, it forms OH^-  ion s
  • The OH ions react with the H ions from the acid to form water. This makes it a PROTON ACCEPTOR as it accepted the Hydrogen proton. 

To test the the acidity/alkalinity of the solution, add universal indicator and check the pH scale.

Strong acids are COMPLETELY ionised in water. Their concentration is 1mol/dm. If it's a weak acid then their concentration will be much less.

They worked independently of each other and developed the ideas that acids are proton donors and alkalis are proton acceptors. Their ideas explained the behaviour of  acids/alkalis in all solvents so their ideas were greatly accepted.

It was Arrhenuis who, however, was the first person to attempt to explain these ideas. His ideas were not accepted though because sub-atomic particles had not yet been accepted and his ideas didn't explain the behaviour of acids/alkalis in solvents other than water. 

Titrations are used to find the exact quanity required for an alkali to neutralise an acid (or vice versa). When an acid and alkali react, they form a salt and neutralise. 

Burette- Used to measure & find the exact amount of acid needed for the neutralisation.

Pipette- Used to measure out a fixed amount

End point- The point at which the acid and alkali have fully reacted

• Strong acid + strong alkali – use any indicator
• weak acid + strong alkali – use phenolphthalein
• strong acid + weak alkali – use methyl orange

You will need to be able to explain the steps for a titration and how to do calculations involving titrations. 

Exothermic- Temperature of surroundings get higher. It makes bonds and releases this as chemical energy so heat energy is reduced. We say that the change in energy is negative – which we write as ΔH -ve. The energy of the reactants is greater than the energy of the products.

Endothermic- Temperature of surroundings get lower. It breaks bonds and releases more energy. We say that the energy is positive which we write as ΔH +ve. The energy of the products is greater than the energy of the reactants. 

Energy level diagrams show us the change. The activation energy is the minimum energy required to start a reaction.We use bomb calorimeters & simple calorimeters to measure the energy change. 

4.2 joules of energy raises 1g of water by 1°C

To increase solubility in liquids:

• Increase temperature

To increase solubilty in gases:

• Decrease temperature
• Increase pressure

A saturated solution means a solution in which as much of the solute has dissolved.

A solubility curve shows us the solubility of a solute. It can be used to a) predict how much solute will dissolve into a solvent at any given temperature, and b) predict how much solute will form again when we cool down a hot solution.

Water from earth EVAPORATES -> Water CONDENSES -> Water PERCIPITATES

Hard water:

Calcium or Magnesium ions get dissolved in the water through dissolving from the rocks.

Most contain calcium (or magnesium) hydrogencarbonate. The calcium carbonate comes from the limestone on buildings, the hydrogen comes from water and the carbon dioxide comes from the atmosphere. All these react to form calcium (or magnesium) hydrogencarbonate.

This is TEMPORARILY hard water as you can thermally decompose this calcium hydrocarbonate to make calcium carbonate (aka limescale). Although the limescale reduces efficiency in kettles as pipes as it makes them work slower and heat to a lower temperature, it does still remove the hardness of temporarily hard water.

Permenantly hard water contains CALCIUM SULFATE

To remove hardness in water you can use distillation. This is expensive due to the cost of heat, but it does remove hardness is large amounts.

Treating water to make sure it's clean:                                                                 You can also use a filter jug. This contains activated carbon, silver and an ion-exchange column. The carbon removes organic compounds, silver discourages the growth of bacteria and the ion-exchange column exchanges the ions which make it the water hard.

Removing hardness:                                                                                         1)Use an ion-exchange column. This contain sodium or hydrogen solid resins which exchange with the magnesium/calcium ions as the hard water enters the column. This columns have to have a salr put into the every so often.

2)Add washing soda (sodium bicarbonate) When added, it precipitates out calcium and magnesium ions as insoluble carbonates. Once these ions are no longer in the water the water has become soft.

Ca²⁺ (aq) + CO₃^2- (aq) → CaCO₃ (s)

Hard water can cause SCUM. This is caused by reaction between the soap stearates and the hard water. The soap which contains sodium stearates react with the calcium/magnesium ions. This produces sodium ions, and calcium/magnesium stearate which is SCUM.   This means it takes longer than soft water for the soap to create a lather  so it's more expensive.

Another problem is SCALE. Scale is the reaction between the hard water and heat. It causes calcium carbonate (limescale) to form due to the thermal decomposition. This reduces efficiency in pipes.