C3 Flashcards
what does it mean that in a chemical reaction mas is always conserved
that no atoms are destroyed or created, mass of a reaction stays the same
whats the reason for a mass increase in a reaction usually
one of the reactants is probably a reactant that’s in the air, e.g. oxygen and it is not contained in the container but once reacted it is found in the container and causing mass to increase
whats the reason for a mass decrease in a reaction usually
if any of the products are solid liquid or aqueous and any products are a gas, some of the gas might escape from the container so you don’t account it for mass anymore and mass decreases
what does carbonate have in it, with the charge
CO3 (2-)
what does sulfate have in it, with the charge
SO4 (2-)
what does hydroxide have in it, with the charge
OH (-)
what does nitrate have in it, with the charge
NO3 (-)
how do you work out the formula of an ionic compound
overall charge of an ionic compound is always 0 so you can always work out the ratio of the compound
whats the chemical formula of calcium nitrate
Ca(NO3)2
balance the equation Fe + Cl2 –> FeCl3
2Fe + 3Cl2 –> 2(FeCl3)
what does aqueous mean
dissolved in water
how do you tyurn an equation into an ionic equation
first, write out the equation showing all the ions separately cross out anything that’s the same on both sides
write ionic equation for HNO3 + NaOH –> NaNO3 + H2O
H + OH –> H2O
what does e- stand for in an equation
one electron
when can you write half equation
when oxidation or reduction happens
what should happen to the charges on a half equation
the half equation should have balanced charges on each side
how can you combine half equations to create a full ionic equation
by combining two half equations with different charges you can create a full ionic equation with no extra electrons
write a half equation to show a hydrogen molecule gaining electrons to become hydrogen ons
2H + 2e- –> H2
why do reactions stop
when one reactant is used up. this reactant is called the limiting reactant.
what does it mean fro a reactant to be in excess
a reactant which doesn’t all react, limited by limiting reactant.
calculate the mass of aluminium oxide formed when 135g of aluminium is burned in air
equation 4Al + 3O2 –> 2Al2O3
255g
equation for moles
mass = mr x moles
whats mr
the combined Ar - atomic number
Paula burns a metal, X in oxygen. Given 24.5g of x burns with 3.2g of oxygen, write a balanced equation for this reaction
Ar of X = 63.5 and Mr of x oxide = 143.0
(pg 40)
4X + O2 –> 2X2O
whats an exothermic reaction
a reaction which gives out energy, usually in the form of heat and results in a rise in temperature of the surroundings
whats an endothermic reaction
a reaction which takes in energy, usually in the form of heat, resulting in a fall in temperature of the surroundings
how do reaction profiles show if a reactions exo or endothermic
if products are lower than reactants its a exothermic reaction
if products are higher than reactants its an endothermic reaction
whats activation energy
the minimum amount of energy required needed for bonds to break and a reaction to start
draw a reaction profile for an endo and exothermic reaction
search up answer
what type of reaction is bond breaking
an endothermic reaction as energy needs to be supplied for the reaction to take place
what type of reaction is bond forming
an exothermic reaction as energy is released
how do you calculate the overall energy change
energy required to break bonds - energy released by forming bonds
what type of substance is a substance with a pH less than 7
an acid
what type of substance is a substance with a pH more than 7
A base
whats an alkali
a base that dissolves in water
what are the two ways to measure pH
an indicator and pH meter
whats an indicator
what colours indicate which substance
a dye that changes colour depending on whether its above or below neutral
the more purple it is, the more alkaline it is
the more red it is, the more acidic it is
if it is green it means that the pH is neutral
what a pH metre and how do you use it
you attach a pH probe in a solution to a pH meter and displays the pH level of the solution. it provides a higher level of accuracy than an indicator
whats the reaction called between and acid and an alkali, what does it produce
neutralisation and it produces salt and water
whats a strong acid
acids produce hydrogen, for a strong acid a high proportion of their molecules are hydrogen. They ionise almost completely in water. They tend to have a low pH number
whats a weak acid
in a weak acid only a small proportion of the molecules are hydrogen. they don’t fully ionise in water and tend to have a pH around 2-6
what happens to the pH when you change the concentration of hydrogen ions
if you increase hydrogen ions by a factor of 10, pH decreases by 1, if you increase hydrogen concentration by 100, pH decreases by 2
what pH is the stomach
2
what happens when metals react with acid, what is often produced
salt
how to carry out practical, making soluble salts
add an acid which is the limiting reactant, then add an insoluble reactant make sure use all acid. heat acid until almost boiling use spatula to add the insoluble reactant. they will react and insoluble reactant will seem to disappear. Keep adding insoluble reactant (copper oxide) until visible at bottom of the beaker, all of the acid has reacted. remove the remaining copper oxide using filter paper. then with remaining solution, add it to bowl and place it above boiling water until half solution remains. Then leave it for 24 hours in cool place and crystals will be present after. left with pure crystals of salt.
whats a redox reaction
if electrons are transferred, its a redox reaction. A loss of electrons is called OXidation and a gain of electrons is called REduction. these reactions happen at the same time and is known as a redox reaction
whats OILRIG
a synonym for Oxidation Is Loss
Reduction Is Gain
(in terms of electrons)
how do half equations show weather something has been oxidised or reduced
they show how electrons move during a reaction and how a substance binds to electrons. For example if a positive substance bids with 2 electrons to neutralise, it gains electrons so the substance is reduced
Fe + 2H+ –> Fe2+ + h2
how does iron and hydrogen bind to each other through oxidation and reduction
hydrogen is reduced as it binds with iron which has electrons so its gained electrons
iron is oxidised as it loses electrons
how does electrolysis related to oxidation and reduction
electrolysis is the breakdown of a substance using electricity. The positive ions (cations) move towards the cathode (negative electrode and are reduced (gain electrons. the negative ions (anions) do the same and move to the anode (positive electrode) and are oxidised (lose electrons)
can ions be electrolysed
no as the ions are in fixed positions, unless molten where the ions move freely and conduct electricity.
why is electrolysis with an aqueous solution more complicated
as there will be hydrogen ions and hydroxide ions from the water and they can be attracted to the anode and the cathode
how do you carry out an electrolysis practical for copper sulfate
get two electrodes weigh them, and place them in a beaker filled with your electrolyte and connect the anode and cathode to a power supply through crocodile clips and let the reaction carry out for 30 mins. you will notice a change in mass as the copper oxide has transferred from the anode to the cathode
what are two chemical processes that are used to extract metals from their ores
electrolysis and reduction with carbon
when should metals be extracted by carbon reduction
when the metal is less reactive than carbon (reactivity series
how is a metal oxide reduced with carbon
the metal oxide is reacted with carbon, this produces a product of the pure metal and carbon dioxide
when is electrolysis used to extract metals and why is it not always used
electrolysis is used for metals more reactive than carbon
whats process for using electrolysis when metals are solid
metal oxides are solid meaning the ions can’t moved and need to be molten
to molten it you first add cryolite to the metal oxide which lowers the m.p then you can melt it
then electrolysis can be performed where the element becomes discharged and pure
whats the reactivity series
potassium
sodium
lithium
calcium
carbon
zinc
iron
hydrogen
copper
whats the rule for which element will be discharged at the cathode
the ion of the least reactivity will be discharged
so H+ is always discharged unless the other element is Cu
whats the rule for which element will be discharged at the anode
will always be OH- unless a halide (group 7 element) is present
what is discharged at the anode and cathode for CuSo4
Cu2+
So4 2-
cathode - cu
anode - OH-
