Chemical Changes Flashcards
metal + oxygen = ?
metal oxide
metal + water = ?
metal hydroxide + hydrogen
metal + acid = ?
salt + hydrogen
metal oxide + acid = ?
salt + water
metal hydroxide + acid = ?
salt + water
what is oxidation?
the loss of electrons
what is reduction?
the gain of electrons
list the reactivity series.
potassium
sodium
lithium
calcium
magnesium
aluminium
carbon
zinc
iron
sulfur
lead
hydrogen
copper
silver
gold
platinum
metal carbonate + acid = ?
salt + water + carbon dioxide
what happens in a displacement reaction?
a more reactive metal will displace a less reactive metal from a compound
which metals react with cold water?
- K, Na, Li, and Ca fizz in cold water
- Mg will fizz slightly over a longer period of time
which metals react with dilute acids?
most more reactive than hydrogen (potassium, sodium, lithium, calcium, magnesium, zinc, iron)
what do metals form when they react?
positive ions
what is a spectator ion?
an ion that doesn’t change within a reaction
what is the reduction half equation?
x^+ + e^- = x
what are the 2 oxidation half equations?
- x^- = x + e^-
- x = x^+ + e^-
what are the diatomic elements?
hydrogen, nitrogen, fluorine, oxygen, iodine, chlorine, bromine (have no fear of ice cold beverages)
what is an ore?
a rock containing a metal compound which metal can be extracted from for a profit
what are 3 types of metal extraction?
- electrolysis
- displacement using carbon (any less reactive than carbon)
- thermal decomposition (mercury, silver)
why does gold not need to be extracted from ores?
it is unreactive so is found pure in the earth
what is the formula for hydrochloric acid?
HCl
what salt does hydrochloric acid form?
chloride
what is the formula for nitric acid?
HNO3
what salt does nitric acid form?
nitrate
what is the formula for sulphuric acid?
H2SO4
what salt does sulphuric acid form?
sulphate
what is an acid?
a substance which contains H+ ions which are released when it is dissolved in water
what does a low pH mean?
high concentration of H+ ions
what is a strong acid?
where all molecules ionise - dissociate into ions
what is a weak acid?
where only small fraction of molecules ionise - dissociate into ions - reversible and never goes to completion
what is a concentrated acid?
lots of acid dissolved - high number of moles per dm^3
what is a dilute acid?
small amount of acid dissolved - low number of moles per dm^3
give the ionic equation for a neutralisation reaction
H^+ + OH^- → H2O
what is pH?
a measure of the H+ concentration in solution
what happens as pH decreases by 1 unit?
concentration of H+ ions increase by a factor of 10
what is an alkali?
a substance which releases OH- ions when added to water
what is a base?
a compound which neutralises acids
give 3 examples of bases
metal oxides, metal hydroxides, metal carbonates
what is electrolysis?
splitting of a compound using flow of charge
what is an electrolyte?
ionic compound that is molten or dissolved in water that conducts electricity and is decomposed by it
what is an electrode?
unreactive material which can conduct electricity - usually graphite
why is graphite used for electrodes?
- it has a high MP
- it is inert
- it conducts electricity
what is the charge of anode and cathode in electrolysis?
positive anode, negative is cathode
what is the product at the anode in electrolysis?
halogen gas (if anion is group 7) or oxygen (if anion is not group 7)
what is cryolite?
aluminium compound with a lower melting point than aluminium oxide
why is cryolite used in electrolysis?
using molten cryolite as a solvent reduces some of the energy costs involved in extracting aluminium by allowing the ions in aluminium oxide to move freely at a lower temperature.
what is the process at the anode in electrolysis?
oxidation
give the half equation at the anode in electrolysis
X^- = e^- + X
what is the product at the cathode in electrolysis?
metal (if cation is less reactive than hydrogen) or hydrogen (if cation is more reactive than hydrogen)
what is the process at the cathode in electrolysis?
reduction
give the half equation at the cathode in electrolysis
X^+ + e^- = X
what is an anion?
negative ion
what is a cation?
positive ion
what is uncertainty?
systematic error which affects everything the same
what colour is phenolphthalein?
- pink in alkali
- colourless in acid
what is titration used for?
to make a soluble salt from an acid and soluble base
it is the best method to make sure reactants are mixed in correct proportions
what are the control variables in titrations?
concentration and volume of acid
what are concordant results?
within 0.1 of each other
a piece of magnesium is placed in a solution of copper(II) sulfate; describe what you would observe.
magnesium would displace copper so a brown solid appears over the magnesium and the blue solution becomes paler
compare the electrolysis of molten magnesium chloride with the electrolysis of aqueous magnesium chloride.
in MOLTEN:
- high temperature required to melt MgCl2
- Mg2+ ions attracted to cathode - Mg2+(l) + 2e- ⇒Mg(s)
- Cl- ions attracted to anode - 2Cl- ⇒Cl2(g) +2e-
in AQUEOUS:
- carried out at RT
- mixture of ions present: Mg2+, H+, Cl-, OH-
- Mg2+ and H+ ions attracted to cathode; hydrogen is less reactive than Mg and is more easily reduced so 2H+(l) + 2e- ⇒ H2(g)
- Cl- and OH- ions attracted to anode; chlorine is a halogen so 2Cl-(l) ⇒ Cl2(g) + 2e-
