Topic 4 Flashcards
What is the Ph scale?
A measure of how acidic or alkaline a solution is.
What Ph does a Alkali have?
Greater than 7
What Ph does a acid have?
Lower than 7
What Ph is neutral?
7
How can you measure the pH of a solution?
1) indicator
2) pH probe
How is an indicator used?
It changes colour depending on the pH. Some contains a mixture of dyes that means they gradually change colour over a broad range of pH. These are called wide range indicators, They estimate the pH solution.
How is a pH probe used?
The pH probe is attached to a pH meter and is places in the solution, the pH value will appear on the display as a numeric value.
What is an acid?
A substance that forms aqueous solutions with a pH of less than 7.
What ions to acids form?
Hydrogen ions
What is a base?
A substance with a pH greater than 7.
What is an alkali?
A base dissolved in water to form a solution with a pH greater than 7.
What ions are in alkali solution
Hydroxide ions
What is the neutralisation reaction?
acid + base > salt + water
What does it mean by a strong acid?
Strong acids ionise completely in water, all acid particles dissociate to release hydrogen.
What are weak acids?
Weak acids do not fully ionise in a solution. Only a small portion dissociate to release hydrogen ions.
The ionisation of a weak acid sets up an equilibrium between the undissociated and dissociated acid as it is a reversible reaction. The position of equilibrium lies on the left.
What is pH the measure of?
The concentration of hydrogen ions
How do you measure the concentration on the pH scale?
For every decrease of 1 on the scale the concentration of H+ ions increases by a factor of 10.
Factor H+ ion concentration changes by =10-x
How is concentration different from strong acids?
Concentration measures how much acid there is in a certain volume of water.
A strong acid tells you what proportion of the acid molecules ionise in water.
Metal oxide and metal hydroxide formula
acid + metal oxide > salt + water
Acid and metal carbonates formula
Acid + Metal Carbonate > salt + water + carbon dioxide
Making soluble salts using an insoluble base (Practical)
1) you need the right acid and insoluble base such as an insoluble metal oxide, hydroxide or carbonate e.g. if you want to make copper chloride you could mix hydrochloric acid and copper oxide
2) gently warm the dilute acid using a bunsen burner then turn off the bunsen burner
3) add the insoluble base to the acid a bit at a time, until no more reacts. You will no when all the acid has been neutralised because even after stirring the excess solid will just sink to the bottom of the flask
4) filter out excess solid to get slat solution
5) to get pure, solid crystals, gently heat solution using a water bath or an electric heater to evaporate some of the water and then stop heating it and leave the solution to cool. Crystals of the salt should form which can be filtered out of the solution and then dried (Crystallisation)