Topic 3 - Chemical Changes Flashcards
What is the pH scale?
A measure on how acidic or alkaline a solution is
Ranges fro 0-14
How can you measure the pH of a solution?
Using an indicator and comparing what colour that shows up on the periodic table
What do acids and bases do together?
They neutralise each other
How can neutralisation reactions be shown?
As an ionic equation
Acids produce what ions in water?
Hydrogen ions
Acids can be strong or what?
Weak
What are strong acids?
e.g. hydrochloric, sulfuric, nitric
Ionise almost completely in water. They tend to have low pHs (0-2)
What are weak acids?
e.g. citric, carbonic acids
Do not fully ionise in solution. Only a small proportion of the acid molecules. Their pHs tend to be around 2-6
What is the difference between a strong and concentrated acid?
The acid strength tells you what proportion of acid molecules ionise the water
The concentration tells you how much acid there is within a litre (1 dm^3) of water. Concentration is how watered down your acid is.
Can you have a dilute strong acid?
Yes
The acid can be watered down, so there is less acid per dm^3, however it can be strong in terms of the proportion of acid molecules using the pH scale
Salts form when acids react with what?
Bases
What are salts?
Ionic compounds
A salt is formed in what type of reaction?
A neutralisation reaction
Acid + metal oxide -> salt + water
Give some examples
2HCl + NaOH -> NaCl +H2O
H2SO4 + ZnO -> ZnSO4 +H2O
Acid + metal hydroxide -> salt + water
Give some examples
HCl + NaOH -> NaCl +H2O
H2SO4 + Zn(OH)2 -> ZnSO4 + 2H2O
Acid + metal -> salt and hydrogen
Give an example
2HCl + Mg -> MgCl2 +H2
How do you test for hydrogen?
Using a light splint. A popping sound should be heard
Acid + metal carbonate -> salt + water + carbon dioxide
Give an example
2HCl + Na2CO3 -> WNaCl + H2O + CO2
What is the test for carbon dioxide
Using limewater. If carbon dioxide is present, the limewater will turn cloudy
How do you make soluble salts?
By reacting an acid with an alkali
What is oxidation?
Oxidation is the loss of electrons, but gain of oxygen
What is reduction?
The gain of electrons but the loss of oxygen
What is electrolysis?
The breaking down of a substance using electricity
An electric current is passed through the electrolyte, causing it to decompose
What do half equations show?
How electrons are transferred during reactions
What are cations, and where do they go during electrolysis?
Positive ions. They move towards the cathode (negative electrode) and become reduced
What are anions, and where do they go during electrolysis?
Negative ions.
They move towards the anode (positive electrolyte) and are oxidised
In molten ionic solutions, there’s only one source of ions.
True or false?
True
They can be electrolysed because the ions can move freely and conduct electricity
Why is hydrogen gas sometimes form in electrolysis?
In aqueous solutions, H+ and metal ions will be present.
Hydrogen gas will be produced if the metal is more reactive than hydrogen
If the metal is less reactive than hydrogen, a solid layer of pure metal is formed
