Chemical changes Flashcards
What is produce when metals react with oxygen?
metal oxides
Describe reduction and oxidation in terms of loss or gain of oxygen
oxidation is loss of electrons, gain of oxygen or loss of hydrogen
reduction is gain of electrons, loss of oxygen or gain of hydrogen
Why do displacement reactions occur?
when a metal is more reactive than another metal
State the reactivity series
potassium
sodium
calcium
magnesium
aluminium
carbon
zinc
iron
tin
lead
hydrogen
copper
silver
gold
platinum
Why are some metals such as gold found in the earth as metal itself but most are found as compounds?
they have reacted with other elements as they are more reactive
What determines whether a metal can be extracted from its oxide by reduction?
if a metal is less reactive than carbon
What is produces when acids react with some metals?
salts and hydrogen
When acids are neutralised by alkalis and bases what is produced?
salts and water
When acids are neutralised by metal carbonates what is produced?
salts, water and carbon dioxide
What salts are produced in neutralisation reactions?
metal + ide or ate (taken from the acid)
What can reactions be used to make?
soluable salts
What do acids produce in aqueous solutions?
hydrogen ions
What do aqueous solutions of alkalis contain?
hydroxide ions
What is the ph scale and how is it used?
range from 0-14
1-6 = acid
7 = neutral
8-14 = alkaline
What happens in a neutralisation reaction between an acid and an alkali?
hydrogen ions react with hydroxide ions to produce watee
what is the ionic equation for a neutralisation reaction?
NaOH+HCl ->H2O & NaCl
what is the use of universal indicator?
shows us how acidic or alkaline a solution is
What can the volumes of acid and alkali solutions that react with eachother be measured by?
titration using a suitable indicator
How do you carry out titrations?
- fill up a burette with acid
- use a pipette to add alkali to conical flask
- Add an indicator to the alkali
- slowly add the acid into the alkali
- slow the adding of acid when the indicator changes colour
- Stop adding when there is a permanent colour change
How do you calculate the chemical quantities in titrations? ( involving concentrations in mol/dm3 and g/dm3 )
amounts of solute in moles = concentration x volume
What is a strong acid? give an example
an acid that breaks down completely
sulphuric acid or hydrochloric acid
what is a weak acid? give an example
partially dissociates
ethanoic acid
What happens as the pH decreases by one unit?
the hydrogen ion concentration of the solution increases by a factor of 10
What happens to the ions in an ionic compound when it is melted or dissolved in water?
ions are free to move from place to place
What is an electrolyte?
substances that have a natural positive or negative charge when dissolved in water
What happens to ions during electrolysis?
positive ions move to the cathode
negative ions move to the anode
What happens during the electrolysis of molten compounds?
positively charged ions move to the cathode, they receive electrons and are reduced.
Why is electrolysis used to extract some metals?
when a metal is more reactive than carbon it is cheaper to extract by electrolysis
Why are large amounts of energy used in the extraction process?
to melt the compounds and to produce the electrical current
How is aluminium extracted using electrolysis?
positively charged ions gain electrons from the cathode and form molten aluminium
Why is a mixture used as the electrolyte during the extraction of aluminium?
to allow the movement of free ions
Why must the positive electrode be continually replaced during the extraction of aluminium?
the oxygen reacts with the carbon of the positive electrodes forming CO2 so they gradually burn away
What do ions discharges when an aqueous solution is electrolysed using inert electrodes depend on?
the relative reactivity of the elements involved
What will be produced at the negative electrode (cathode) and how is this linked to the break down of water molecules?
hydrogen is produced if the metal is more reactive than hydrogen
What will be produced at the positive electrode (anode) and how is this linked to the break down of water molecules?
oxygen is produced
What happens at the cathode and anode in terms of electrons, oxidation and reduction?
reduction happens at the negative cathode because this is where positive ions gain electrons.
oxidation happens at the positive anode because this is where the negative ions lose electrons
How do you write half equations?
- write down the reactant and the product
- balance the atoms
- write the total charge underneath each species in the equation
- balance the charge by adding electrons
