C4 - Predicting and Identifying Reactions and Products Flashcards
where are group 1 elements found
- placed in the vertical column on far left of the periodic table
what are group 1 elements known as and why
- Alkali metals
> because they react with water to produce an alkaline solution (metal hydroxide) + hydrogen gas
what properties do group 1 metals have
- shiny when freshly cut
- good conductors of heat
- solid at room temp but are soft enough to cut with knife
what are the general trend going down group 1
- density increases
- melting point decreases
- softer metals
- reactivity increases
what do group 1 meals react with
- water
- oxygen
- acids
what does the reaction of group 1 metals with water produce
- metal hydroxide + hydrogen
> e.g. sodium reacts with water to form sodium hydroxide + hydrogen
why are group 1 metals stored in oil
- because they react rapidly with oxygen in air and water
what does the reaction of group 1 alkali metals with acids produce
- salt + hydrogen gas
> these reactions are more violent than the ones with water - dangerous to do in school lab
what is the trend of reactivity down group 1 metals and why
- elements get more reactive as you go down the group
> because the outer electron becomes further away from the positive nucleus and so the attraction between them becomes weaker
> this means that the attractive force is more easily broken, so less energy is required to remove the electron - the easier it is for a group 1 atom to lose its outer shell electron the more reactive the element is
what is the general ionic equation for group 1 elements
M —-> M+ + e-
(loses electron)
what charge do group 1 metals carry
+1
> they lose on electron to obtain a full outer shell and a stable electron configuration
why do elements in the same group have similar chemical properties
- because they have a similar electron configuration (same number of outer shell electrons)
what are group 7 elements also known as
- halogens
what some properties of group 7 elements
- non metals
- brittle in solid state
- poor conductors of electricity
- exist as diatomic molecules
> with weak intermolecular forces
what is the colour + state of fluorine at room temperature
- pale yellow gas
what is the colour + state of chlorine at room temperature
- green gas
what is the colour + state of bromine at room temperature
- orange-brown liquid
> easily vaporises
what is the colour + state of iodine at room temperature
- shiny grey-black crystalline solid
> sublimes to form purple vapour
describe the trend in boiling point down group 7
- boiling points increase
describe the trend in density down group 7
- density increases
what do group 7 elements react with
- halogens react with metals to form salts
> the reactions are typically vigorous with group 1 metals, especially if the metal is heated first
what is the trend of reactivity down group 7
- reactivity decreases
> because the outer shell becomes further away from the positive nucleus and so the attraction becomes weaker
> it’s harder for the electron to get attracted to the outer shell so reactivity decreases - the easier it is for a halogen atom to gain an electron the more reactive the element is
what is the general ionic equation for group 7 elements
X2 + 2e- —-> 2X-
(gains electron)
what charge do halide ions carry
-1
> they gain one electron to complete a full outer shell to obtain a stable electron configuration
what is a halide
- a compound containing a group 7 elements + one other element (usually hydrogen or a metal)
apart from metals what else can halogens react with
- metal halides in solutions
what are displacement reactions in halogens
- a halogen will displace a less reactive halogen from its halide ions in solution
e.g. chlorine displaces bromine from bromides and iodine from iodides
why are halogen displacement reactions carried out
- they are used to confirm the order of reactivity of chlorine, bromine and iodine
how can you carry out halogen displacement reactions
- wear eye protection
- place a small volume of halide salt (potassium chloride/bromide/iodide) solution in a spotting tile
- add a few drops of halogen solution (chlorine/bromine/iodine water)
- note down the observations - if you see a colour change the reaction has occurred
- repeat for different combos of halide salt + halogen
what colour are solutions of chlorine, bromine and iodine
- chlorine water = colourless
- bromine water = orange
- iodine = brown
what do you observe when chlorine is added to each of the halide salt solutions
- potassium chloride = no reaction
- potassium bromide = orange
- potassium iodide = brown
what do you observe when bromine is added to potassium iodide
- brown colour
what are the half equations for the displacement reaction when: chlorine displaces bromine from bromide ions
Cl2 + 2e- —-> 2Cl- reduction
2Br- —-> Br2 + 2e- oxidation
- combine to make ionic equation
Cl2 + 2Br- —-> 2Cl- + Br2
what are group 0 elements known as
- noble gases
why are noble gases called what they are
- because they are so unreactive + take part in very few chemical reactions due to having a full outer shell
what state are group 0 elements
- gas at room temp
- non-metals
why are noble gases so unreactive
- they have a complete outer shell
> they don’t have the tendency to lose/gain electrons to form ions in reactions or to share electrons to form molecules in reactions
> as a result they are very unreactive
the noble gases are monatomic, explain what that means
- they exist as single atoms with very weak forces of attraction between them
why do noble gases have low boiling points
- because they have weak intermolecular forces between the atoms which require little energy to overcome
> this is why they are all gases at room temp
what trends going down noble gases are present
- attractive forces between atoms get stronger
- boiling point increases (as atoms become larger)
- density increases
why do noble gases have very low densities
- because their atoms are far apart in the gas state, so there is very little mass in a given volume
> as you go down group 0 the density increases
where are transition metals in the periodic table
- between groups 2 + 3
what are the properties of transition metals
- metals
- shiny when freshly cut
- good conductors of electricity
- strong
- malleable (can be bent into shape)
in comparison to group 2, the transition metals are:
- stronger + harder
- have higher densities
- have higher melting points (except mercury which is liquid at room temp)
what are the chemical properties of transition metals
- they are less reactive than alkali metals
> they react slowly, if at all
transition metals: what happens when iron reacts slowly with water / oxygen
- produce hydrated iron (III) oxide = rust
do gold, platinum and iridium react with water/oxyegn
no
transition metals produce _____ ionic compounds
- coloured
unlike alkali metals which can only form +1 ion charges what can transition metals do
- they can form more than one type of ion
> as they have complex electron configuration
> e.g. iron can be Fe2+ or Fe3+
transition metals are often good ____
- catalysts
> because of their ability to form different ions as they have complex electron configuration
metals form positive ions in reactions, the more easily this happens _____
- the more reactive the metal is
when can metals react with water / dilute acids
- if the metal is more reactive than hydrogen
metals react with water to produce ____
- metal + water —> metal hydroxide +hydrogen
metals react with acids to produce ____
- metal + acid —> salt + hydrogen
what can be used to put metals in order of their reactivity + why
- reactions of metals with water/dilute hydrochloric acid
> produces hydrogen
> the more reactive the metal, the greater the rate of hydrogen production
> so more vigorous bubbling
> so you measure the rate at which hydrogen gas is produced
when carrying out metal + water/ dilute hydrochloric acid reactions what mustn’t you do
- boil the water/acid because it would bubble when boiled, so you wouldn’t be able to tell if the bubbles were due to a reaction
> it would also be unsafe to boil the acid as it could splatter everywhere
what are metal displacement reaction
- a more reactive metal can displace a less reactive metal from solutions of it’s compounds
> e.g. copper is more reactive than silver so it can displace silver from silver nitrate solution
displacement reactions are an example of ____
- redox reactions
> e.g. Cu(s) + 2AgNO3(aq) —-> Cu(NO3)2(aq) + 2Ag(s)
Cu(s) —–> Cu2+(aq) + 2e- (oxidation)
Ag+(aq) + e- —–> Ag(s) (reduction)
how can you carry out metal displacement reactions
- place small volume of the metal salt solution in a spotting tile
- add a piece of the metal
- note your observations
- repeat with other combos of metal + metal salt
metals in groups 1 + 2 are more _____
- reactive than transition metals and other metals
how can you test for carbon dioxide
- using limewater
> limewater = calcium hydroxide solution - limewater turns cloudy when carbon dioxide is bubbled through it
> because calcium hydroxide + carbon dioxide = water + white precipitate of calcium carbonate
how can you test for chlorine
- hold a piece of damp blue litmus paper over the substance
- if chlorine is present, it will bleach the paper white
> it will be red at first for a bit because chlorine solution is acidic
how can you test for hydrogen
- place a lighted splint near the mouth of the container of gas
- if hydrogen is present a squeaky pop will be produced
> because hydrogen burns with oxygen in air to form water
how can you test for oxygen
- place a glowing splint near the mouth of the container of gas
- if oxygen is present, the splint should relight
what can you use to test for cations
- flame tests
- hydroxide precipitate tests
what are flame tests used to detect
- metal ions
- the different metal ions give off different colours of light
why do metal ions give off different flame colours
- when metal ions are heated, energy is transferred to their electrons
> this allows the electrons to momentarily jump up to a higher energy shell, before falling back to their normal position - when they fall back they release energy to the surroundings as radiation, which you see as light
> different metal ions produce different colours of light
how can you carry out a flame test
- collect equipment: nichrome wire loop, Bunsen burner, hydrochloric acid, samples to test, distilled water
- clean nichrome wire loop by dipping into hydrochloric acid then rinsing with distilled water - if clean, there will be no change in colour of Bunsen burner flame when you hold the loop in it
- dip the clean loop into test power / solution
- use a handle to hold the loop in the edge of a roaring blue flame
- record the flame colour
- clean the wire loop and repeat with other substances
why is a nichrome wire loop used to carry out flame tests
- because it’s inert
> so won’t react with the test substance and doesn’t emit a colour of its own in the flame
what colour flame does lithium ion produce
crimson red
what colour flame does sodium ion produce
yellow
(sodium just seems yellow)
what colour flame does potassium ion produce
lilac
(potassium sounds like a sweet flower which is lilac - also p for purple but it’s actually lilac)
what colour flame does calcium ion produce
orange-red
(bones surrounded by orange + red like blood??)
what colour flame does copper ion produce
green-blue
(copper rusts to this colour)
what is another way to test for metal cations
- hydroxide precipitate tests
what reagent is used for hydroxide precipitate tests
- sodium hydroxide solution
> it’s water soluble so you can see the precipitate form
> group 1 metal hydroxides are soluble in water but most other metal hydroxides are insoluble
how do you carry out hydroxide precipitate tests
- add a drop of sodium hydroxide solution to a solution containing the metal ions and note the colours of the hydroxide precipitate formed
what is the colour precipitate of calcium ions when reacted with sodium hydroxide + give ionic equation
- white
Ca2+(aq) + 2OH- (aq) —-> Ca(OH)2 (s)
what is the colour precipitate of zinc ions when reacted with sodium hydroxide + give ionic equation
- white at first but turns colourless in excess of sodium hydroxide (NaOH)
Zn2+(aq) + 2OH- (aq) —-> Zn(OH)2 (s)
what is the colour precipitate of iron (II) ions when reacted with sodium hydroxide + give ionic equation
- green
Fe2+(aq) + 2OH-(aq) —-> Fe(OH)2 (s)
what is the colour precipitate of iron (III) ions when reacted with sodium hydroxide + give ionic equation
- brown
Fe3+(aq) + 3OH-(aq) —-> Fe(OH)3 (s)
what is the colour precipitate of copper (II) ions when reacted with sodium hydroxide + give ionic equation
- blue
Cu2+(aq) + 2OH- —-> Cu(OH)2 (s)
how can you distinguish between calcium hydroxide and zinc hydroxide
- as both form white precipitates
> add an excess of sodium hydroxide solution as zinc hydroxide dissolves to form a colourless solution but calcium hydroxide doesn’t dissolve
what are the different anions you need to test for
- carbonate ions
- sulfate ions
- halide ions
how can you detect sulfate ions
- barium ions react with sulfate ions to produce white, insoluble barium sulfate
> add a few drops of dilute hydrochloric acid
> add a few drops of barium chloride solution
> if sulfate ions are present, a white precipitate forms
how can you detect carbonate ions
- hydrogen ions from dilute acids react with carbonate ions to produce carbon dioxide
+ water
> add a few drops of dilute hydrochloric acid
> if carbonate ions are present, bubble of gas will be produced
> to confirm if the gas is carbon dioxide, bubble it through limewater
how do you detect halide ions
- add a few drops of dilute nitric acid
- add a few drops of silver nitrate solution
- if one of the halide ions are present, a coloured precipitate forms
what colour precipitate does silver chloride produce
white
what colour precipitate does silver bromide produce
cream
what colour precipitates do silver iodide produce
yellow
why is acid added in sulfate + halide ions tests
- to remove carbon impurities as they can often result in false positive result
what is the ionic equation for reaction of sulfate ions with barium chloride
Ba2+(aq) + SO42-(aq) —-> BaSO4(s)
what is the ionic equation for the reaction of carbonate ions with acid
CO32-(aq) + 2H+(aq) —-> CO2(g) + H2O(l)
what are instrumental methods of analysis
- instrumental analysis relies on machines to carry out analysis of a substance
what are some advantages of instrumental analysis
- sensitivity - can analyse very small amounts of substances - useful if substance is expensive or difficult to obtain
- accuracy - instruments are very accurate + can be calibrated using internationally accepted standards
- speed - instruments can carry out analysis quickly + can run all the time
what are some disadvantages of instrumental analysis
- costly
- needs highly skilled operators
- large equipment
- needs setting up
how can you interpret gas chromatograms
- each peak represents a substance present in the mixture
- areas under each peak show the relative amounts of each substance in the mixture
- the retention time (time taken for a substance to travel through the chromatography column) is different for different substances
what does a mass spectrometer measure
- the masses of atoms + molecules to help work out the structure of unknown substances
how does mass spectrometry work
- samples are fired through a machine
- samples are ionised to form molecular ions (always positive)
- these ions can break to form fragments which the machine separate and detect
