Chemical Changes Flashcards
What is PH?
A measurement of how acid or alkaline a substance is
What are the most acidic and alkaline PHs?
PH 0 and PH 14
What are the ways to measure the PH of a solution?
- Use an indicator
- Use a ph probe connected to a ph meter
What happens when you react an acid and a base?
acid + base → salt + water
The acid and base neutralise each other.
What is an acid?
An aqueous solution with a ph less than 7
What ions do acids form in water?
H+
What is a alkali?
An aqueous solution with a ph above 7
What ions do alkalis form in water?
OH-
What is the purpose of titration?
It calculates the exact concentration of acid needed to neutralise a base and vise versa.
What is the method for titration?
Say you want to find the concentration of acid it takes to neutralise an alkali:
- First use a pipette and a pipette filter to measure out a set volume of alkali into a conical flask,
- Add two or three drops of indicator
- Use a funnel to fill a burette with some acid of known concentration,
- Record the initial volume of the acid
- Slowly drip down the acid so that you can tell what volume is left in the burette,
- Do this until the solution changes colour, this means the solution has neutralised,
- Record the final volume of the acid and find the amount of acid dripped down into the solution by finding the difference. This is the volume of a certain concentration of acid to neutralise the known volume of alkali.
How do you increase the accuracy of your titrations?
- Take several readings
- Ignore anomalies
- Take a mean of your trials
- Use a high resolution burette.
What indicators can you use for titration?
> Litmus (blue in alkali → red in acids)
Phenolphthalein (pink in alkalis → colourless in acids)
Methyl Orange (yellow in alkalis → red in acids)
What are strong acids?
Acids that ionise fully in water, all the acid particles disassociate to release H+ ions.
What are weak acids?
Acids don’t ionise fully in water, not all the acid particles disassociate to release H+ ions.
Which acid forms a reversible reaction? (Strong or Weak)
Weak, it cause an equilibrium.
e.g. CH3COOH ⇌ H+ + CH3COOH-
Why are strong acids more reactive?
There are more H+ ions to react in the solution, so, the rate of reaction is faster because there are more reactants.
What is the relation between PH and concentration of H+ ions in an acid?
Factor H+ ion concentration changes by = 10^-x
so if the the PH falls from 7 to 4 the PH changes by -3 so 10^-(-3) = 10^3 = 1000, so the concentration of H+ ions has increased by 1000
What is the difference between strong acids and concentrated acids?
Acid concentration is the proportion of acid in the aqueous solution,
Acid strength is the proportion of molecules in the acid that ionise in water
What are the products of Acid + Metal oxide?
Acid + Metal oxide → Salt + Water
What are he products of Acid + Metal hydroxide?
Acid + Metal hydroxide → salt + water
What are the products of Acid + Metal carbonate?
Acid + Metal carbonate → salt + water + Carbon dioxide
How do you make soluble salts using an insoluble base?
- You need to pick the right acid and insoluble base,
- Gently heat up the dilute acid using a Bunsen burner, then turn of the Bunsen burner,
- Add the insoluble base to the warm acid a bit at a time,
- You know when the reaction is done because the excess insoluble solid will sink to the bottom,
- Then filter out the excess solid to get a salt solution,
- Use crystallisation to get the pure solid crystals of he salt.
What is the reactivity series? (definition not order)
Lists the metals in order of their reactivity towards other substances.
What is the order of the reactivity series?
Potassium Sodium Lithium Calcium Magnesium Carbon > non-metal Zinc Iron Hydrogen > non-metal Copper
What are the products of Acid + metal?
Acid + Metal → salt + hydrogen
What are the products of Metal + Water?
Metal + Water → Metal Hydroxide + Hydrogen
What is Reduction?
The gain of electrons
What is Oxidation?
The loss of electrons
How can you remember reduction and oxidation?
> O - oxidation > I - is > L - loss > R - reduction > I - is > G - gain
`What reactions is this:
2Mg + O2 → 2MgO
Oxidation:
reacting in oxygen, electrons are lost
What reaction is this:
2CuO + C → 2Cu + CO2
Reduction:
Separating a metal oxide, electrons are gained
How do you extract metals form metal oxides under carbon in the reactivity series?
Use carbon to displace the metal in a reduction reaction, this looks like:
Metal oxide + Carbon → Metal + Carbon Dioxide
What method is used to extract metals that are of higher reactivity than carbon?
Electrolysis
How do extract metals that are not very reactive at all?
They tend to be found naturally pure because they don’t react with anything.
What is a Redox reaction?
A reaction where electrons are transferred:
e.g. Fe + 2H+ → Fe2+ + H2
The Fe takes two electrons from the H2 it becomes reduced
The H2 loses 2 electrons so it oxidises.
What is an example of a Redox reaction?
A displacement reaction:
In this reaction, the metal always gains electrons is reduced
What is the difference between an ionic equation and a regular balanced equation?
Ionic equations only focus on the ions/ important sections of the equation.
What is electrolysis?
This is the process of passing direct current through a solution of melted ionic compound to move the ions apart and so break the compound down and discharge some of the elements at the electrodes.
What is an electrolyte?
A molten ionic compound.
What is the method of electrolysis?
- A circuit is created by dipping an anode and a cathode into an electrolyte. The electrolyte can conduct electricity because they have free flowing ions and will therefore complete the circuit.
- The Anode is positively charge and lacks electrons,
The Cathode is negatively charged and has an abundance of electrons, - The ions form the electrolyte (Positive metal and negative electron) attract to the anode and cathode,
- The anion (non-mental) attracts to the anode and the cation (metal) attracts to the cathode.
- The molten metal is now neutral form taking electrons from the cathode and sinks to the bottom of the electrolysis tank where it can be collected.
What side of the battery/power pack is the anode connected to?
Positive
What side of the battery/power pack is the cathode connected to?
Negative
What are the electrodes usually made of?
A nonreactive substance such as: graphite or expensive platinum metal.
What bonds are used in an electrolyte?
Ionic bonds
Why don’t solid ionic compounds conduct electricity?
- They do not have free flowing ions because they are rigid in place since the structure of a solid is an organised arrangement.
- Therefore, there is little movement of the ions, this means electricity cannot be conducted.
