CHEMISTRY OCR GATEWAY C4

• HISTORY OF THE ATOM
• ATOM - TINY PARTICLE OF MATTER WHICH MAKE UP EVERYTHING IN THE UNIVERSE
• 19TH CENTURY - JOHN DALTON DESCRIBED ATOMS AS SOLID SPERES
• 1897 - JJ THOMSON CONCLUDED THAT ATOMS WERE NOT SOLID BUT A POSITIVE MASS THAT MUST CONTAIN NEGATIVLY CHARGED PARTICLES - PLUM PUDDING MODEL
• 1909 - RUTHERFORD CONDUCTED GOLD FOIL EXPERIMENT - FIRED POSITIVELY CHARGED PARTCLES AT THIN SHEET OF GOLD. MOST PARTICLES PAST THROUGH GOLD ATOMS - DISPROVED PLUM PUDDING MODEL. NUCLEAR ATOM THEORY DEVELOPED - POSITIVE NUCLEUS SURROUNDED BY 'CLOUD' OF NEGATIVE ELECTRONS, MOST OF ATOM EMPTY SPACE
• LATER - BOHR MODEL DEVELOPED. SCIENTISTS REALISED THAT LOSE ELECTRONS WOULD BE ATTRACTED TO NUCLEUS, CAUSING ATOM TO COLLAPSE. BOHR SUGGESTED THAT ELECTRONS EXIST IN FIXED ORBITS OR SHELLS, EACH SHELL HAVING A FIXED ENERGY. ACCEPTED BY MANY SCIENTISTS AT TIME. VERY CLOSE TO CURRENTLY ACCEPTED VERSION OF ATOM
• SCIENTIFIC THEORIES
• DEVELOPMENT OF SCIENTIFIC KNOWLEDGE - NEW EVIDENCE PROMPTS CREATION OF NEW, IMPROVED IDEAS - USED TO MAKE PREDICTIONS WHICH ARE PROVED CORRECT, GIVING INDICATION THAT IDEAS ARE RIGHT. PEER REVIEW - SCIENTISTS SEE OTHERS IDEAS AND DEVELOP THEM OR USE THEM TO DEVELOP THEIR OWN.

THE ATOM

NUCLEUS - IN THE MIDDLE OF ATTOM, CONTAINS PROTONS AND NEUTRONS, HAS A POSITIVE CHARGE BECAUSE OF PROTONS. ALMOST ALL OF ATOMS MASS CONCENTRATED ON NUCLEUS

ELECTRONS - MOVE AROUND NUCLEUS IN SHELLS, NEGATIVELY CHARGED, TINY BUT COVER A LOT OF SPACE, VOLUME OF THEIR ORBITS DETERMINE SIZE OF ATOM, VIRTUALLY NO MASS

TOTAL MASS OF ATOM = ABOUT 10 TO THE POWER OF -23 GRAMS

TOTAL CIRCUMFERENCE OF ATOM = ABOUT 10 TO THE POWER OF -10 METRES

NEUTREL ATOMS

SAME AMOUNT OF ELECTRONS TO PROTONS - CHARGES SAME SIZE - CHARGES CANCEL OUT

ATOMIC NUMBER AND MASS NUMBER

MASS NUMBER - TOTAL NUMBER OF PROTONS AND NEUTRONS

ATOMIC NUMBER - NUMBER OF PROTONS (AND ELECTRONS)

ISOTOPES

ISOTOPES - DIFFERENT FORMS OF THE SAME ELEMENT, WHICH HAVE THE SAME NUMBER OF PROTONS BUT A DIFFERENT NUMBER OF NEUTRONS

SAME ATOMIC NUMBER BUT DIFFERENT MASS NUMBERS

EXAMPLE - CARBON-12 AND CARBON-14

CARBON-12 - 6 PROTONS, 6 ELECTRONS, 6 NEUTRONS - ATOMIC NUMBER 6, MASS NUMBER 12

CARBON-14 - 6 PROTONS, 6 ELECTRONS, 8 NEUTRONS - ATOMIC NUMBER 6, MASS NUMBER 14

ELECTRON SHELLS

ELECTRONS ALWAYS OCCUPY SHELLS

THE LOWEST ENERGY LEVELS ARE ALWAYS FILLED FIRST

ONLY A CERTAIN NUMBER OF ELECTRONS ARE ALLOWED IN EACH SHELL - 1ST=2, 2ND=8, 3RD=8

WORKING OUT ELECTRON CONFIGURATIONS

FIND OUT NUMBER OF ELECTRONS BY LOOKING AT ATOMIC NUMBER - E.G. MASS NUMBER 5 = 5 ELECTRONS

DRAW THE FIRST SHELL WITH TWO ELECTRONS IN IT AND THEN WORK OUT HOW MANY THERE ARE LEFT TO PUT IN THE SECOND AND THIRD SHELL (ONLY UP TO 8 IN 2ND AND THIRD) E.G. MASS NUMBER 11 = 3 SHELLS, 1ST SHELL 2, 2ND SHELL 8, 3RD SHELL 1

IONIC BONDING

IONIC BONDING - TRANSFERRING ELECTRONS - ATOMS LOSE OR GAIN ELECTRONS TO FORM CHARGED PARTICLES (IONS) WHCIH ARE STRONGLY ATTRACTED TO ONE ANOTHER (ATTRACTION OF OPPISITE CHARGES)

ATOMS LIKE TO HAVE ONLY FULL SHELLS OF ELECTRONS

ATOMS THAT CONTAIN OUTER SHELL WITH ONE OR TWO ELECTRONS (GROUP 1 OR 2) - WANT TO GET RID OF IT/THEM - LEAVES A POSITIVE ION (ONE ELECTRON MISSING MEANS MORE PROTONS THAN ELECTRONS)

ATOMS THAT CONTAIN OUTER SHELL WITH SIX OR SEVEN ELECTRONS (GROUP 6 OR 7) - WANT TO GAIN ONE OR TWO - LEAVES NEGATIVE ION

GROUP 1 OR 2 ATOM GIVES OUTER SHELL ELECTRON TO GROUP 6 OR 7 ATOM - LEAVES TWO ELECTRONS, ONE POSITIVE ONE NEGATIVE - ATTRACT EACHOTHER AND LATCH ON TO EACHOTHER

DOT AND CROSS DIAGRAM OF IONIC BONDING

GIANT IONIC LATTICES

GIANT IONIC LATTICE - A CLOSELY PACKED, REGULAR LATTICE ARRANGEMENT CREATED BY METALS AND NON METALS FORMING IONIC BONDS WITH EACHOTHER

DON'T CONDUCT ELECTRICITY WHEN SOLID - ELECTRONS AREN'T FREE TO MOVE AROUND

VERY STRONG CHEMICAL BONDS BETWEEN ALL THE IONS

EXAMPLES - MgO AND NaCl

HIGH MELTING AND BOILING POINTS - VERY STRONG ATTRACTIONS BETWEEN OPPISITELY CHARGED IONS MEANS THAT THE BONDS TAKE A LOT OF ENERGY TO BREAK DOWN

MgO - HIGHER MELTING POINT - MADE OF 2+ AND 2- ATOMS, MEANING THAT EACH ION HAS TWICE THE CHARGE, MAKING ATTRACTION HARDER TO OVERCOME

PARTICLES IN MgO SMALLER - PACK TOGETHER MORE TIGHTLY - HIGHER MELTING POINT

BOTH CONDUCTORS WHEN LIQUID - IONS ARE FREE TO MOVE AROUND WHEN SOLID STRUCTURE MELTS

NaCl DISSOLVES - IONS SEPERATE OUT AND ARE FREE TO MOVE IN SOLUTION - SOLUTION CONDUCTS ELECTRICITY

SIMPLE IONS

ION - A CHARGED ATOM (E.G. Cl-) OR GROUP OF ATOMS (E.G. NO-3)

STABLE ELECTRONIC STRUCTURE - STRUCTURE OF ATOMS WITH FULL OUTER SHELLS E.G. IONS THAT HAVE BONDED

METALS - GROUP 1 OR 2 ELEMENTS - LOSE ELECTRONS TO BECOME POSITIVELY CHARGED IONS WIT A STABLE ELECTRONIC STRUCTURE

NON - METALS - GROUP 6 OR 7 - GAIN ELECTRONS TO BECOME NEGATIVELY CHARGED IONS WITH A STABLE ELECTRONIC STRUCTURE

NUMBER OF ELECTRONS LOST OR GAINED = CHARGE OF ION E.G. IF AN ION HAS LOST TWO ELECTRONS, IT'S CHARGE WOULD BE 2+

WORKING OUT THE FORMULAE OF AN IONIC COMPOUND

BALANCE THE POSITIVE AND NEGATIVE CHARGES

E.G. POTASSIUM OXIDE - POTASSIUM ION IS 1+ AND OXYGEN ION IS 2- SO THERE WOULD NEED TO BE TWO POTASSIUM IONS TO REACT WITH ONE OXYGEN ION TO BALANCE OUT THE CHARGES

EQUASION - 2K+ + O2- -----> K2O

REQUIREMENTS FOR EXAM

- LEARN NOTES

- RECOGNISE AN ION, AN ATOM AND A MOLECULE FROM GIVEN FORMULAE

- DRAW A 'DOT AND CROSS' DIAGRAM

- PREDICT AND EXPLAIN PROPERTIES OF COMPOUNDS WITH A GIANT IONIC STRUCTURE

THE PERIODIC TABLE

SHOWS ELEMENTS IN ORDER OF ASCENDING ATOMIC NUMBER

GROUPS - VERTICLE COLUMNS - CORRESPONDS TO NUMBER OR ELECTRONS IN OUTER SHELL

PERIODS - ROWS - CORRESPONDS TO NUMBER OF FULL SHELLS OF ELECTRONS ATOM HAS

HISTORY OF THE PERIODIC TABLE

DOBEREINER - TRIED TO ORGANISE ELEMENTS INTO TRIADS

1800S - ONLY MEASURABLE NUMBER WAS ATOMIC MASS - ELEMENTS ORGANISED IN ORDER OF ATOMIC MASS

1828 - DOBEREINER ORGANISED ELEMENTS INTO GROUPS OF THREE, THE MIDDLE ONE BEING THE AVERAGE RAT OF THE OTHER TWO E.G. Cl, Br, AND I WERE A GROUP

NEWLANDS - LAW OF OCAVES

1864 - NEWLANDS NOTICED THAT EVERY EIGHTH ELEMENT HAD SIMILAR PROPERTIES - LISTED THEM IN ROWS OF SEVEN

PATTERN BROKE DOWN ON THIRD ROW - TRANSITION METALS BROKE IT UP - HE LEFT NO GAPS

WORK CRITICISED - GROUPS COMTAINED ELEMENTS WHICH DIDN'T HAVE SIMILAR PROPERTIES - MIXED UP METALS AND NON METALS - DIDN'T LEAVE ANY GAPS FOR ELEMENTS WHICH WERE YET TO BE DISCOVERED

DMITRI MENDELEEV - LEFT GAPS AND PREDICTED NEW ELEMENTS

1896 - MENDELEEV ARRANGED 50 KNOWN ELEMENTS INTO TABLE OF ELEMENTS (WITH VARIOUS GAPS) IN ORDER OF ATOMIC MASS - KEPT ELEMENTS WITH SIMILAR PROPERTIES IN SAME VERTICAL GROUPS - GAPS ALLOWED HIM TO PREDICT PROPERTIES OF UNDISCOVERED ELEMENTS

COVALENT BONDING

SHARING PAIRS OF ELECTRONS - OCCURS IN NON METALS - EACH ATOM HAS FULL OUTER SHELL

EACH ATOM INVOLVES MAKES ENOUGH COVALENT BINDS TO FILL SHELL - EACH BOND PROVIDES ONE EXTRA SHARED ELECTRON FOR EACH ATOM

SIMPLE MOLECULAR SUBSTANCES

ATOMS FORMED FROM COVALENT BONDS USUALLY HAVE SIMPLE MOLECULAR STRUCTURES E.G. H20 AND CO2

ELEMENTS IN MOLECULES HELD TOGETHER WITH VERY STRONG COVALENT BONDS BUT FORCES OF ATTRACTION BETWEEN EACH MOLECULE IS VERY WEAK - MAKES MELTING AND BOILING POINT VERY LOW - MOLECULES EASILY PARTED FROM EACHOTHER - MOST MOLECULAR SUBSTANCES ARE GASES OR LIQUIDS AT ROOM TEMPERATURE

DON'T CONDUCT ELECTRICITY - NO FREE ELECTRONS

ALKALI METALS

LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, FRANCIUM

AS YOU GO DOWN GROUP 1, ALKALI METALS BECOME MORE REACTIVE - OUTER ELECTRON MORE EASILY LOST BECAUSE THERE IS A LARGER ATOMIC RADIUS (FURTHER FROM NUCLEUS) - LESS ENERGY NEEDED TO REMOVE IT

ONE OUTER ELECTRON - MAKES THEM VERY REACTIVE AND GIVES THEM SIMILAR PROPERTIES

LOW MELTING AND BOILING POINT, LOW DENSITY, VERY SOFT

OXIDATION - LOSS OF ELECTRONS

GROUP 1 METALS KEEN TO LOSE ELECTRON TO BECOME A 1+ ION WITH A STABLE ELECTRONIC STRUCTURE - ALWAYS FOR IONIC COMPOUNDS

BURNING COLOURS

WIRE LOOP DIPPED INTO HYDROCHLORIC ACID TO CLEAN AND MOISTEN IT, DIPPED INTO POWDERED SAMPLE OF GROUP 1 COMPOUND AND THEN PLACED OVER BLUE BUNSEN BURNER FLAME

        LITHIUM - RED FLAME                   SODIUM - YELLOW/ORANGE FLAME                  POTASSIUM - LILAC FLAME

REACTION WITH COLD WATER

WHEN LITHIUM, SODIUM OR POTASSIUM ARE PUT IN WATER, THEY REACT VERY VIGOROUSLY

MOVE AROUND ON SURFACE, FIZZING FURIOUSLY - PRODUCE HYDROGEN GASS

REACTIVITY WITH WATER INCREASES AS YOU GO DOWN THE GROUP - REACTION WITH POTASSIUM GETS HOT ENOUGH TO IGNITE IT

SODIUM AND POTASSIUM MELT IN HEAT OF REACTION

ALKALI FORMS - THE HYDROXIDE OF THE METAL

METAL + WATER ------> METAL HYDROXIDE + HYDROGEN

HAPPENS WITH ALL ALKALI METALS

REQUIREMENTS FOR EXAM

- LEARN NOTES

- WRITE OUT BALANCED EQUASION FOR ALL ELEMENTS REACTING WITH WATER

- INTERPRET INFORMATION ON FLAME TESTS TO DEDUCE ALKALI METAL PRESENT FROM FLAME COLOURS

HALOGENS

FLOURINE, CHLORINE, BROMINE, IODINE, ASTATINE

AS YOU GO DOWN THE GROUP 7 ELEMENTS, THE HALOGENS BECOME LESS REACTIVE BECAUSE THERE IS A LARGER ATOMIC RADIUS (OUTER SHELL FURTHER FROM NUCLEUS) - LESS INCLINATION TO GAIN ELECTRON

SEVEN ELECTRONS IN OUTER SHELL

CHLORINE - FAIRLY REACTIVE, POISONOUS, DENSE GREEN GAS (LOW BOILING POINT)

BROMINE - DENSE, POISONOUS ORANGE LIQUID

IODINE - DARK GREY CRYSTALINE SOLID (HIGH BOILING POINT)

REDUCTION - GAIN OF ELECTRONS

KEEN TO GAIN ELECTRONS TO BECOME A 1- ION WITH A STABLE ELECTRONIC STRUCTURE

MORE REACTIVE THE HALOGEN, MORE KEEN IT IS TO GAIN ELECTRON

REACTION WITH ALKALI METALS

HALOGENS REACT VIGOROUSLY WITH ALKALI METALS TO FORM SALTS CALLED METAL HALIDES

SODIUM + CHLORINE -----> SODIUM CHLORIDE

2Na + Cl2 -----> 2NaCl

DISPLACEMENT REACTIONS

MORE REACTIVE HALOGENS WILL DISPLACE LESS REACTIVE ONES

CHLORINE + POTASSIUM IODIDE -----> IODINE + POTASSIUM CHLORIDE

REQUIREMENTS FOR EXAM

- LEARN NOTES

- BE ABLE TO WRITE EQUASIONS FOR REACTIONS BETWEEN ALL SEVEN GROUP 1 AND GROUP 7 ELEMENTS

- BE ABLE TO WRITE DISPLACEMENT REACTIONS FOR ANY TWO HALOGENS

- PREDICT PROPERTIES OF FLOURINE AND ASTATINE (PHYSICAL, MELTING/BOILING POINT, DISPLACEMENT REACTIONS) GIVEN PROPERTIES OF OTHER HALOGENS

TRANSITION METALS - METALS IN THE MIDDLE OF THE PERIODIC TABLE

A LOT OF EVERYDAY METALS ARE TRANSITION METALS E.G. COPPER, IRON, ZINC, GOLD, SILVER

TYPICAL METALLIC PROPERTIES - UNHEARD OF TRANSITION METALS FOLLOW ALL THE SAME PROPERTIES AS OTHER TRANSITION METALS

CATALYSTS

TRANSITION METALS MAKE GOOD CATALYSTS

IRON - CATALYST IN THE HABER PROCESS

NICKEL - USEFUL FOR HYDROGENATION OF ALKENES (MAKING MARGERINE)

COLOURS OF COMPOUNDS

COLOURFUL DUE TO TRANSITION METAL ION THEY CONTAIN

IRON (II) COMPOUNDS - LIGHT GREEN

IRON (III) COMPOUNDS - ORANGE/BROWN (RUST

COPPER COMPOUNDS - BLUE

THERMAL DECOMPOSITION

THERMAL DECOMPOSITION - BREAKING DOWN WITH HEAT

TRANSITION METAL CARBONATES (COMPOUNDS WITH CO3 IN THEM) BREAK DOWN WHEN HEATED INTO MTEAL OXIDE AND CARBON DIOXIDE, RESULTING IN COLOUR CHANGE

COPPER (II) CARBONATE -----> COPPER OXIDE + CARBON DIOXIDE

TEST FOR CARBON DIOXIDE - BUBBLE GAS THROUGH LIME WATER - IF CO2 PRESENT, LIME WATER TURNS MILKY

PRECIPITATION 

PRECIPITATION - TWO SOLUTIONS REACT AND AN INSOLUBLE SOLID FORMS IN SOLUTION

SOLID ID SAID TO 'PRECIPITATE OUT' - SOLID KNOWN AS THE 'PRECIPITATE'.

SOME SOLUBLE TRANSITION METAL COMPOUNDS REACT WITH SODIUM HYDROXIDE TO FORM AN INSOLUBLE HYDROXIDE WHICH THEN PRECIPITATES OUT

COPPER (II) SULFATE + SODIUM HYDROXIDE -----> COPPER HYDROXIDE + SODIUM SULFATE

CuSO4 + 2NaOH -----> Cu(OH)2 + Na2SO4

PRECIPITATION TEST

SOME INSOLUBLE TRANSITION METAL HYDROXIDES HAVE DISTINCTIVE COLOURS - USED TO TEST WHICH TRANSITION METAL IONS A SOLUTION CONTAINS

COPPER (II) HYDROXIDE - BLUE SOLID

IRON (II) HYDROXIDE - GREY/GREEN SOLID

IRON (III) HYDROXIDE - ORANGE/BROWN SOLID

REQUIREMENTS FOR EXAM

- LEARN NOTES

- IDENTIFY WHETHER AN ELEMENT IS A TRANSITION METAL ELEMENT BY ITS POSITION ON THE PERIODIC TABLE

- CONSTRUCT WORD AND BALANCED SYMBOL EQUASIONS FOR THERMAL COMPOSITION REACTIONS GIVEN

- CONSTRUCT BALANCED SYMBOL EQUASIONS FOR REACTIONS BETWEEN CU2+, FE2+, FE3+ AND OH- GIVEN FORMULAE OF IONS

CRYSTAL STRUCTURES

ALL METALS HAVE THE SAME BASIC PROPERTIES, DUE TO SPECIAL TYPE OF BONDING THAT EXISTS IN METALS CALLED METALLIC BONDS WHICH ALLOW OUTER ELECTRONS OF EACH ATOM TO MOVE FREELY

CREATES 'SEA' OF DELOCALISED ELECTRONS THROUGHOUT METAL WHICH GIVES IT THESE PROPERTIES:

HIGH MELTING AND BOILING POINTS AND HIGH DENSITY 

STRONG ATTRACTIONS BETWEEN DELOCALISED ELECTRONS AND CLOSELY PACKED POSITIVE IONS CAUSING VERY STRONG METALLIC BONDING - A LOT OF ENERGY NEEDED TO BREAK APART

STRENGTH OF METALLIC BOND AND MELTING POINT DECREASES AS ATOMIC RADIUS INCREASES

STRONG BUT BENDY AND MALLUABLE

HIGH TENSILE STRENGTH (STRONG AND HARD TO BREAK) BUT CAN BE HAMMERED INTO DIFFERENT SHAPES

GOOD CONDUCTORS OF HEAT AND ELECTRICITY

SEA OF DELOCALISED ELECTRONS CAN MOVE FREELY THROUGH METAL, CARRYING ELECTRICAL CURRENT (OR HEAT ENERGY) WITH THEM

METAL AND ITS USES

STAINLESS STEEL

GOOD CONDUCTOR OF HEAT, DOESN'T RUST EASILY, CHEAP - SAUCEPANS

COPPER

GOOD CONDUCTOR OF ELECTRICITY, EASILY BENT - ELECTRICAL WIRING

ALUMINIUM OR TITANIUM

LOW DENSITY, STRONG, DOESN'T CORRODE - AEROPLANES

STEEL

STRONG (IRON AND CARBON - CARBON MAKES IT LESS BRITTLE) - BRIDGES

SUPERCONDUCTORS

METALS HAVE SOME ELECTRICAL RESISTANCE - HEAT UP ELECTRICAL ENERGY THAT FLOWS THROUGH THEM - SOME ENERGY WASTED AS HEAT

AT VERY LOW TEMPERATURES, SOME METALS RESISTANCE DISAPPEARS COMPLETELY AND THEY ARE SAID TO BECOME SUPER CONDUCTORS

THIS MEANS THAT NO ENERGY IS WASTED AS HEAT SO, IF ONE WAS TO START A CURRENT FLOWING THROUGH A SUPERCONDUCTING CIRCUIT AND TOOK THE BATTERY OUT, THE CURRENT WOULD CARRY ON FLOWING FOREVER.

USES

POWER CABLES THAT TRANSMIT ELECTRICITY WITHOUT LOSS OF POWER

STRONG ELECTROMAGNETS THAT DON'T NEED A CONSTANT POWER SOURCE

TEMPERATURES

METALS ONLY START SUPERCONDUCTING AT LESS THAN -265 DEGREES CELCIUS - VERY EXPENSIVE - LIMITS USE

SCIENTISTS ARE TRYING TO DEVELOP ROOM TEMPERATURE SUPERCONDUCTORS THAT WORK AT ABOUT 20C

WATER RECOURCES

SURFACE WATER - ARTIFICIAL LAKES, RIVERS, RESERVOIRS - IN UK, RECOURCES START TO RUN DRY IN SUMMER 

GROUND WATER - AQUIFIERS (ROCKS THAT TRAP WATER UNDERGROUND) - PARTS OF SOUTH EAST WHERE SURFACE WATER IS LIMITED, 70% OF DOMESTIC WATER SUPPLY COMES FROM GROUND WATER

UNPURIFIED WATER

BEFORE WATER IS PUROFIED, IT MAY CONTAIN DISSOLVED SALTS AND MINERALS, MICROBES, POLLUTANTS, INSOLUBLE MATERIALS

PURIFYING - THREE STAGES

FILTRATION - WIRE MESH SCREENS OUT LARGE TWIGS ETC. AND THEN GRAVEL AND SAND BEDS FILTER OUT ANY OTHER SOLID BITS

SEDIMENTATION - IRON SULFATE OR ALUMINIUM SULFATE IS ADDED TO THE WATER - MAKES FINE PARTICLES CLUMP TOGETHER AND SETTLE AT THE BOTTOM

CHLORINATION - CHLORINE GAS IS BUBBLED THROUGH TO KILL HARMFUL BACTERIA AND OTHER MICROBES

IMPURITIES IN TAP WATER

SOME POLLUTANTS CAN'T BE FILTERED OUT. TAP WATER IN THE UK HAS STRICT SAFETY STANDARDS BUT SMALL TRACES CAN STILL BE FOUND

NITRATE RESIDUES - FROM EXCESS FERTILISERS THAT RUN OFF INTO RIVERS AND LAKES - CAN CAUSE SERIOUS HEALTH PROBLEMS, ESPECIALLY FOR YOUNG BABIES IF TOO MUCH PRESENT - PREVENT BLOOD FROM CARRYING OXYGEN PROPERLY

LEAD COMPOUNDS - FROM OLD LEAD PIPES - POISONOUS, PARTICULARLY IN CHILDREN

PESTICIDE RESIDUES - FROM SPRAYING TOO NEAR RIVERS AND LAKES

DISTILLING SEA WATER

PRODUCES PURE WATER - DONE IN DRY COUNTRIES

NEEDS LOADS OF ENERGY - EXPENSIVE - NOT PRACTICAL FOR LARGE AMOUNTS OF SEA WATER 

TEST FOR SULPHATE IONS

ADD DILUTE HYDROCHLORIC ACID TO SAMPLE THEN ADD TEN DROPS OF BARIUM CHLORIDE SOLUTION. IF YOU SEE A WHITE PRECIPITATE, SULPHATE IONS ARE PRESENT

BARIUM IONS + SULPHATE IONS -----> BARIUM SULPHATE

TEST FOR HALIDE IONS

ADD DILUTE NITRIC ACID TO TEST SAMPLE THEN ADD TEN DROPS OF SILVER NITRATE SOLUTION. IF PRECIPITATE FORMS, HALLIDE IONS PRESENT

CHLORIDE IONS - WHITE PRECIPITATE   BROMIDE IONS - CREAM PRECIPITATE  IODIDE IONS - YELLOW PRECIPITATE

SILVER NITRATE + SODIUM HALIDE -----> SILVER HALLIDE + SODIUM NITRATE

REQUIREMENTS FOR EXAM

- LEARN NOTES

- CONSTRUCT BALANCED SYMBOL EQUASIONS FOR BARIUM SULPHATE AND SILVER NITRATE TESTS

- INTERPRET SIMPLE DATA ON WATER RECOURCES IN THE UK