chemistry topic 4 chemical changes Flashcards
the lower the PH scale what does it tell us ?
the more acidic it is
the higher the PH scale what does it tell us?
the more alkaline it is
what is indicator?
a dye that changes colour depending on whether its above or below a certain PH
what does universal indicator do?
change colour to the PH of the solution
what do acids and bases do?
neutralise each other
what is an acid?
a substance that forms an aqueous solution with a PH of less than 7
what is a base?
any substance will react with an acid to form a salt
what is an alkali?
a base that dissolves in water to form a solution with a PH greater than 7
what is the reaction called between acids and bases?
neutralisation
what is the equation for neutralisation?
acid + base = salt + water
what is the equation for neutralisation using acid and alkali ions?
H+ + OH- = H20
how is reactivity determined in metals?
by how easily they will lose electrons
what happens when metals react with water or acid?
they lose electrons to form positive ions
the higher a metal is in the reactivity series means what?
the more easily it will react with water or acid
what is the equation for an acid reacting with a metal?
acid + metal = salt + hydrogen
what is the speed of a reaction determined by?
the rate at which the bubbles of hydrogen are given off
the more reactive the metal means what?
the faster the reaction will go
what is the equation for the reaction of metals with water?
metal + Water= metal hydroxide + hydrogen
what type of metals wouldn’t react with water?
less reactive metals
what are metals usually found as in the earth?
compounds that need to be extracted before use
how do you do the formation of a metal ore?
oxodisation
how do you extract metals?
reduction
what can some metals be extracted with?
carbon
what happens in reduction with carbon ?
the carbon gains the oxygen that is in the metal
how do metals higher than carbon in the reactivity series have to be reduced ?
using electrolysis
metals below carbon in the reactivity series can be reduced with what?
carbon
what does electrolysis mean?
splitting up with electricity
what happens during electrolysis?
an electric current is passed through n electrolyte
what is an electrolyte?
a molten or dissolved ionic compound
where do the positive ions go in the electrolyte?
they move to the negative electrode where they gain electrons
where do the negative ions go in the electrolyte?
they move to the positive electrolyte where they lose electrons
whats the negative electrode called ?
cathode
what is the positive electrode called?
anode
what happens to the ions when they go to the negative electrode?
they are reduced
what happens to the ions when they go to the positive electrode?
they are oxidised
what happens after the different ions move to the electrodes?
a flow of charge is created through the electrolyte
why cant an ionic solid be electrolysed?
the ions are in fixed positions and cant move
why can molten ionic compounds be electrolysed?
the ions can move freely and conduct electricity
what are molten ionic compounds broken up into?
their elements
why is electrolysis impractical?
its very expensive and requires lots of energy
what material are electrodes made out of so they don’t react with the electrolyte?
an inert material
what is formed at the negative electrode?
metals form positive ions so they are attracted to the negative electrode
what happens at the positive electrode?
non metals form negative ions so they are attracted to the positive electrode
in aqueous solutions what ions are there as well as ions from the ionic compound?
hydrogen ions (H+) and hydroxide ions (OH-)
what happens at the cathode if H+ ions are present?
hydrogen gas will be produced if the metal ions form a metal more reactive than hydrogen
what happens if H+ ions are present and the metal ions are less reactive than hydrogen?
a sold layer of pure metal will be produced instead, it will coat the cathode
what happens if halide ions are present?
at the anode, molecules of chlorine, bromine or iodine will be formed
if no halide ions are present what happens to the OH- ions from the water?
oxygen gas and water will be formed at the anode
how can you test for chlorine after electrolysis?
it bleaches damp litmus paper
how can you test for hydrogen after electrolysis?
squeaky pop test with a lighted splint
how can you test for oxygen after electrolysis?
it will relight a glowing splint
what do half equations show?
reactions at the electrodes
what can you combine the half equations for both reactions to get?
ionic equation of whole reaction
at the cathode where is the added electrons on a half equation?
before the arrow
at the anode where is the added electrons on a half equation?
after the arrow
titration: what would you set up to find the concentration of some alkali?
use a pipette and pipette filler and add a set amount of volume of alkali to a conical flask
titration: what do you use a funnel to fill?
a burette with acid of known concentration
titration: how should you fill the burette?
below eye level so you won’t be looking up if some acid spills over
titration: what do you record in the burette?
the initial volume of acid in the burette
titration: how do you add the acid to the alkali?
a bit at a time, giving the conical flask a regular swirl. go slow when you think the end point is nearly reached
Titrations: what do you record at the end?
the final volume of acid in the burette
how do you fill the pipette in titrations?
to about 3cm above the line
why do you need several consistent readings in titrations?
to spot any anomalous results
what should you calculate and ignore doing titrations?
mean, ignore anomalies
what is the substance colourless in acids but pink in alkali’s for titrations?
phenolphthalein
for titrations, what is the chemical that is red in acids but blue in alkalis?
litmus
for titrations, what is the chemical that goes from red in acids to yellow in alkalis?
methyl orange
what do acids produce in water?
protons
when do acids only ionise?
in aqueous solutions
what happens to strong acids in water?
they ionise completely
what do all acids release when ionised?
H+
what happens to weak acids in solution?
they don’t fully ionise
what kind of reaction Is a weak acid?
they have a reversible reaction
where is equilibrium between in weak acids?
the undissociated and dissociated acid
where does equilibrium usually lie in weak acid reactions and why?
it usually lies on the left since only a few acid particles release H+ iions
what is the PH of an acid or alkali a measure of?
the concentration of H+ ions in the solution
for every decrease of one of the PH scale , what is it a measure of?
the concentration of the H+ ions increases by a factor of 10
what does acid strength tell you?
what proportion of acid molecules ionise in water
what does concentration of an acid measure?
how much acid there is in a certain volume of water
what is the word equation for acid and metal oxides reacting together?
acid + metal oxide/ hydroxide = salt +water
what is the word equation for acid and metal carbonate reactions?
Acid+ metal carbonate= salt + water + carbon dioxide
what do you need to make a soluble salt with an insoluble base?
the right acid plus and insoluble base
what are the four steps to making soluble salts with an insoluble acid?
gently warm dilute acid with Bunsen burner, turn off Bunsen burner, add insoluble base till neutralised, filter excess, crystallisation
how do you know when the acid has been neutralised ?
even after stirring, excess solid will just sink to the bottom
how do you do crystallisation?
gently heat filtered solution in water bath to evaporate water then let it cool, crystals should form where they can be filtered and dried
what does a PH probe attached to a PH meter do when placed in solution?
it measures PH electronically
what acronym helps you remember the reactivity series?
please stop laughing/calling my amazing colourful zebra in the history class she grunts
metals more reactive than hydrogen will react with what?
acids
metals less reactive than hydrogen will react with what?
not acids
what can metals less reactive than carbon do ?
be reduced with carbon
what is oxidation?
gain of oxygen
what is reduction?
loss of oxygen
how does reduction from carbon happen?
the ore is reduced as oxygen is removed from it and carbon gains oxygen so therefore it is oxidised
what is a loss of electrons?
oxidation
what is a gain of electrons?
reduction
what happens in redox reactions of metals reacting with acids?
metal ions lose electrons as they are oxidised by hydrogen and hydrogen ions are reduced by metal as they gain electrons
what is an example of a redox reaction?
a displacement reaction
what happens in a displacement reaction?
more reactive metals will displace less reactive metals
what is there always it metal displacement reactions?
the metal atom always gains electrons and the metal atom always loses electrons
what happens when ions don’t change in ionic equations?
they are spectator ions
what is ONLY in ionic equations?
the substances that are oxidised and reduced
