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)
How does the reactivity series order metals?
In order of most reactive to least reactive
How are metals reactivity determined?
How easily they loose electrons and form positive ions and the it reacts with water or acid
What does an Acid + Metal form?
Salt + hydrogen
What is the speed of the reactions indicated by?
The rate at which bubbles of hydrogen are given off
What happens when there a more reactive metal?
displace the less reactive metal
What does Metal + water form?
Metal hydroxide + Hydrogen
What does oxidation mean?
Gain of oxygen, loss of electrons
What is reduction?
Loss of oxygen, gain of electrons
What happens when metals are extracted by reduction with carbon?
The ore is reduced as oxygen is removed from it, and carbon gains oxygen so is oxidised.
What metals can be used in reduction with carbon?
Only metals less reactive than carbon.
How are metals higher in the reactivity series than carbon extracted?
By electrolysis
What is an example of a metal that is unreactive they are in the earth as the metal itself?
Gold
Redox reactions
What happens to the less reactive metal in the compound when a more reactive metal is placed into the solution of dissolved metal compound?
The more reactive metal will displace the less reactive one
What happens in the metal ion in a displacement reation?
It gains electrons so becomes reduced
What happens to the metal atom in a displacement reaction?
It looses electrons to become oxidised
What do ionic equations show?
The useful bits of a reaction
What does electrolysis mean?
The splitting up of electricity
What happens during electrolysis?
An electric current is passed through an electrolyte and the ions move towards the electrodes, where they react the compound decomposes
What is an electrolyte?
A molten or dissolved ionic compound
What is an electrolyte?
A molten or dissolved ionic compound
Where do the positive ions move to?
Towards the cathode and gain electrons (reduction)
Where do the negative ions move to?
The anode, where they are oxidised
Why can’t an ionic solid conduct electricity?
The ions are in a fixed position and cannot be moved
How is Aluminum extracted?
From the ore of bauxite by electrolysis
Why is Aluminum mixed with cryolite?
To lower the melting point
Why does the molten mixture conduct electricity?
Ions are free to move around
What does the anode produce if a halide is not present?
OH- ions/hydroxide ions
What does the cathode produce?
Hydrogen ions unless there is a metal less reactive than hydrogen
Practical
Chlorine
Bleaches damp litmus paper, turning it white
Hydrogen
Make a squeaky pop with a lighted splint
Oxygen
Relight a glowing splint
