Chemical Changes (1)

• anything that forms a solution with a pH of less than 7 the lower the pH, the more acidic the solution

anything that forms a solution with a pH of greater than 7 (a base that is soluble in water) the higher the pH, the more alkaline the substance is

neither acidic nor alkaline substances which have a pH of exactly 7 e.g. pure water

The type of ions that are released by the dissolved substance. Acids release hydrogen ions when they are aqueous Alkalis release hydroxide ions when they are aqueous

a substance that reacts with an acid to produce a salt and water

The higher the concentration of ions in a solution, the more acidic it is, so the lower the pH will be. So, as concentration of hydrogen ions increases, pH decreases. In alkaline solutions, the higher the concentration of hydroxide ions, the higher the pH.

a dye that changes colour depending on whether it’s above or below a certain pH

acidic - red neutral - purple alkaline - blue

acidic - red neutral - yellow alkaline - yellow

acidic - colourless neutral - colourless alkaline - pink

Base + Acid -> Water + Salt BAWS

• Measure out 150cm^3 of dilute hydrochloric acid into a conical flask (Use a pipette or a measuring cylinder for this). • Measure out 0.5g of calcium oxide to the hydrochloric acid. • Wait for the base to completely react, then record the pH of the solution, using either a pH probe or universal indicator paper. • Repeat steps 2 to 4 until all the acid has reacted. (You’ll know you’ve reached this point when unreacted calcium oxide starts to collect at the bottom.) • You can then plot a graph to see how pH changes with the mass of base added.

the proportion of acid particles that dissociate to produce hydrogen ions in solution

an acid that ionises almost completely in water (most of the acid particles dissociate to release hydrogen ions) e.g. sulfuric, hydrochloric and nitric acid

an acid that only partially ionises in water (only some of the acid molecules will ionise and release hydrogen ions) e.g. carboxylic, citric, carbonic, ethanoic acids

how much acid there is in 1 dm^3 of water (1L) (not to be confused with acid strength)

The pH of an acid is dependent on the acid’s concentration - increasing the concentration of hydrogen ions leads to a decrease in the pH If the concentration of hydrogen ions increases by a factor of 10, the pH decreases by 1.

bases

Base + Acid -> Water + Salt BAWS

Metal + Acid -> Salt + Hdrogen MASH

• Collect the gas in a test tube. • Put a lit splint into the test tube. • If there is a ‘squeaky pop’, hydrogen gas is present. (This noise comes from the hydrogen burning quickly with the oxygen in the air to form water.)

metal Carbonates + Acid -> Water + Carbon dioxide + Salt CAWCS

Bubble the gas through limewater (aqueous calcium hydroxide). If the solution turns cloudy then there is carbon dioxide present. (The cloudiness is caused by the formation of calcium carbonate.)

If the salt contains any of the ions then it is soluble in water. - Sodium - Nitrates - Ammonium - Potassium - Ethanoate If it contains chlorine then it is soluble except for silver chloride and lead chloride. If it contains sulfate then it is soluble except for lead, barium and calcium sulfate.