C12 -Chemical Analysis Flashcards
What is a pure substance ?
-A pure substance is not mixed with any other substance , it only contains a single elemnt or single compound .
What is the simplest way to determine if a substance is pure ?
-Measure its melting point and boiling point .
When does a pure substance melt and boil ?
-A pure substance melts at a specific fixed temperature . -A pure substance also has a specific fixed boiling point .
When do Impure substances melt and poil ?
-Impure substances melt and boil over a range of temperatures .
What does graph one show ?
THe melting and boiling of water (an example of a PURE substance ) .
Stage one of graph one ?
-We start with ice and are gradually increasing the temperature .
What happens at star one ?
-At a certain point the temperature STOPS RISING .
-This is the MELTING POINT .
(In the case of water this is FIXED at 0 degrees . )
What happens at star two ?
-Once the water has melted , the TEMPERATURE RISES AGAIN , and at a certin point , the temperature stops rising , this is the boiling point .
-(The boiling point in the case of water is FIXED at 100 degrees .)
So how do we know water is pure ?
-Because both the melting and the boiling points are at specific fixed tempertures , we know thais water is PURE .
-U WILL GET A SIMILAR SHAPED GRAPH FOR ANY PURE SUBSTANCE .
What does graph 2 show ?
A graph for a mixutre of water and a impurity .
What happens in graph 2 ?
-In this case , the water melts and boils over a RANGE OF TEMPERATURES .
-This tells us water is NOT PURE .
-THIS IS THE SAME GRAPH FOR ANY IMPURE SUBSTANCE .
What is a formulation ?
-A formulation is a complex mixture , that has been designed as a useful product .
What is special about formulations ?
-In a formulation , the quanitty of each component is carefully measures , so that the product has the properties we need .
Examples of formulations ?
-Fuels
-Cleaning products
-Paints
-Medicine
-Alloys
-Fertilisers
-Food
What is the melting point ?
The temperature at which a solid turns into a liquid and a liquid turns into a solid .
What is the boling point ?
When a substance changes from a liquid to a gas and then a gas to a liquid .
what is 24 carat gold ?
Pure gold - contains no other metal .
How do you workout the fraction of gold present .
Divide the carat number by 24 .
e.g —> 9/24=0.375 = 37.5%
What is a pure substance ?
All the particles are the same .
What is a mixture ?
Contains different particles .
What is an element ?
A susbatnce made up of only one type of atom .
What are compounds ?
Substances amde of different types of atoms joined together .
How does paper chromatogrpahy do ?
Allows us to separate substances based on their dffierent solubilities .
first stage of papepr chromatogrpahy
take a piece of chromatography paper .
-draw a pencil lne near th botom .
second stage of paper chromatogrpahy .
-put dots of our colours (substance) on a pencil line .
third stage of paper chromatogrpahy .
now put paper into solvent
(a liquid that will dissolve substances ).
fourth stage of paper chromatogrpahy
The solvent now makes it way up the paper and dissolves the ink and coloured dots , which are also carried by the paper .
Why is paper in chromatography called stationary phase and the solven called mobile phase ?
Paper called stationary pahse as it does not move .
SOlvent called mobile pahse as it moves .
A pure compound …
will produce a sinlge spot in all solvent ,
a compound in a mixture (mixture of colours )
may sepearate into a different spots depending on the solvent .
More soluble substances…
travel further up the paper .
Why do we draw the starting line un pencil
As if we draw the line in pen , the pen ink would also move up with the solvent effecting the results
How to figure out unknown substance using chromatogrpahy .
-normal process of chromtogrpahy ,
measure the distance mvoed by the unkwon chemical (distance from pencil line to center of dot.)
-Measure the distancce moved by solvent .
Calcualtre rf calue distance moved by substance / distanced moved by solvent .
no untis .
look up in data base to find substance ,.
Rf value facts .
Several substacnes may have the same Rf calue , some may need to be repeated using a diffeent solvent .
If a substance has never been analysed before m ti willl have no rf value .
DISTANCE TRAVELLED BY SAMPLE/ DISTANCE TRAVELLED BY SOLVENT .
-this value is less than zero
-has no units
RQP for paper chromatogrpahy .
Sample of food chemicals ,
4 known food coloruings (a -d)
First stage pf paper chromatogrpahy rp ?
First stage pf paper chromatogrpahy rp ?
Second stage of paper chromatogrpahy rp ?
Mark five pencils pots at equal spaces across line .
-make sure there 1cm clear on each side of the paper .
Third stage of paper chromatogrpahy rp ?
use a capiallary tube to put a small spot of eak of the known colours and the unkown colours ontol pencil spot
fourth stage of paper chromatogrpahy rp ?
now pour water into beaker depth of 1cm water in this case solvent .
fifthstage of paper chromatogrpahy rp ?
attach a glass rod using tape and lower paper into a glass beaker ,bottom of paper should dip into water .
pencil line with psots must be above the surface of water why ?
or water will wash off the line .
the sides of the paper must not touch side walls why >
or it will interfere with the way water move s.
-Put a lid on beaker , to reudce the amount of evaporation of he solven t .
sixth stage of paper chromatogrpahy rp ?
at this stage water moeves up paper and colours are carried with it
remove paper when water travleld three quarters up it ,
-use a pencil to mark point how far water
where are the unkwon colours ..
the spots that line up with the unknown colour is unkown colour .
explain y referring to sgtationary and mobile phases , why samples mov ar different speed in an experimetn .
-The forces of attraction between the mobile phase and staitonary pahse depend on the pseeds they travel up the chromatogrpahy paper .
-A substance with stronger forces of attraction between itself and the mobile pahse than between itself and the stationary phase will be carried a greater distace in a givwn time .
check the chromatography question in the book .
In chemistry exercise boo - on Rf value , dangerous food colouring
Test for hydrogen gas ?
-A test tube that contains a gas that might be hydrogen .
-To test for hydorgen , remove the bung and insert the burning splint .
What is the observation from the hydrogen gas .
Hydrogen gas burns rapidly and produces a ‘pop’ sound .
Test for oxygen gas ?
-A test tube that contains a gas that might be oxygen .
Observation for oxygen
To test for oxygen we use a glowing splint .
-If we place the glowing splint into a test tube of oxygen , the splint relights (bursts into falmes ).
Testing for carbondioxide?
To test for carbondioxide , use limewater .
-Limewater is an aqueous solution of calcium hydroxide .
Testing for carbondioxide (1)
-A test tube containing a gas taht moght be carbondioxide , and a test tube containing limewater .
-Draw some of the gas into a plastic pipette .
-Bubble the gas through the limewater .
Observation for Carbondioixde
-If we repeat this several times , the limewater may turn cloudy .
-Telling us the gas is carbondioxide .
Test for chlorine
-To test for chlorine we insert damp litmus paper , into the mouth of the test tube .
-Chlroine bleaches the litmus paper and turns it white .
Word equation and balanced symbol equation for ccombustion of magnesium and hydrochloric acid .
Magnesium+hydrochloric acid —> Magnesium Chloride and hydrogen .
Explain why hydrogen pops with a lighted splint ?
Combustion . The flame ignites the hydrogen .
Explain why oxyen relights a glowing splint ?
-Concentration of oxygen higher in the tube than in the air /
Write a word equation for the catalyitic decompostion of hydrogen peroxide .
Hydrogen perioxide —> water +oxygen .
Calcium carbonate +hydrochloric acid —>
Hydrogen peroxide —> water +oxygen
Limewater is a solution of calcium hydroixde in water .
-Explain why it goes miklky when carbon dioxide is bubbled through it .
A precipitate of calcium carbonate is formed .
check page 184 in textbook alnd learn the equations .
.
Check exercise book for the following
.
Negative ion for carbonate
.
reaction for carbonate
.
Negative ion for sulfate
.
Reaction for sulfate
.
What three halide ions are we using an their negative ions ?
Chloride
Bromide
Iodidie
jsut put a - against their symbol
First step for testing a carbonate ion
1.Add diilute acid to our sample
Second step for testing a carbonate ion
2.The acid will react with carbondioxide gas .
-We will see effervescence (fizzing) .
-That does not prove we have carbondioxide gas .
Third step for testing a carbonate ion
-BUbble the gas through limewater .
-If the limewater goes cloudy , then this proves we have carbondioixde . That mean we started with a carbonagte ion .
First step for testing for Halide ions
Add dilute nitric acid to a sample
Second step for testing halide ions
Add a dilute silver nitrate solution
Third step for testing halide ions
Halide ions produce a reciitate of the silver halide .
-Each halide makes a different coloured precippitate .
Chloride ions
A white precipitate of silver chloride .
Chloride ions
A white precipitate of silver chloride .
bROMIDE IONS
pRODUCE A CREAM PRECIPITATE OF SILVER BROMIDE
Iodide ions
produce a yellow precipitate of silver iodide .
Test for sulfate ions ?
-Add dilute HCL into our sample
-Add barium chloride solution
-If sulfate ions are present , we will see a white precipitate .
What are flame tests used for ?
-Scientists often need to indentify unkown compounds , manh of these contian a metal ion .
-One way of indentifying a metal ion is by using a flame test .
How does a flame test work ?
1.Place a small amount of our chemical onto a wrie mounted in a handle . nichrome wire
2.Place the end of the this into a blue bunsen burner flame .
3.The colour of the flame can be used to workout the metal ions present .
What colour flame does lithium produce
A CRIMSON flame (must say this colour in the exam . )
What colour flame does Sodium produce ?
Sodium produces a YELLOW FLAME .
What colour flame does Potasium produce ?
Potassium produces a lilac flame .
What colour flame does Calcium porduce ?
-Calcium porduces an oragne red-flame .
What colour falme does copper produce ?
-Copper ions produce a green flame .
What is one problem with flame tests ?
1.The colour of a flame test , can be difficult to distinguish .
-This is espeically true if there is only a low concentration of the metal compound .
What is another problem with flame tests ?
2.Sometimes a sample contains a mixture of metal ions , which can mask the colour fo the flames .
What is the solution for problem 2 ?
-Instead of using flameesrs , sicentits often use a technique called flame emission spectroscopy .
What is the solution for problem 2 ?
-Instead of using flameesrs , sicentits often use a technique called flame emission spectroscopy .
S1 FOR FLAME EMMISON SPECTROSCOPY .
1.a SAMPLE OF THE METAL ION N SOLUTION IS PLACED INTO A FLAME .
S2 FOR FLAME EMMISON SPECTROSCOPY .
2.The lgiht given out is thin and [asses into a machine called a pectroscope .
S3 FOR FLAME EMMISON SPECTROSCOPY .
3.The spectroscope converts the line into line spectrum .
S4 FOR FLAME EMMISON SPECTROSCOPY .
-We can use this to indentify ,the metal ion in the sample .
What can flame emission spectroscopy also tell ?
-Flame emision spectroscopy can also tell us the concentration of the metal ion .
-Lines become MORE INTENSE at a higher concentrations .
Flame emission spectroscopyy is an example of an INSTRUMENTAL METHOD (carried out by a machine )
.
One advanatge of instrumental methods :
-ThEY ARE RAPID , WE COULD USE FLAME EMISISON SPECTROSOCPY TO ANALYSE SAMPLES MORE RAPIDLY THAN WE COULD USING FLAME TESTS .
Another advanatge of instrumental methods :
-instrumental methods are senstiive , Flame emission spectroscopy will work even on TINY samples of metal compounds .
Final advanatge of instrumental methods .
-Instrumental methods are accurate , flame emission spectroscopy is more likely to identify a metal ion correctly than using a flame tests.
How else can we test for cetrian metal ions ?
-using their reaction with (soidum hydroxide solution (NaOh).
What will happen if we add Soium hydroixde to Calcium (Ca2+) , Magnesium (Mg2+) , and aluminium ions 9Al3+).
-They ll produe a white precipitate .
PROBLEM –> we cannot distinguish between these three tests becuse they all produce a white precipitate .
How can we tell which one is aluminium ?
How do we tell which one is calcium ?
-If we add EXCESS sodium hydroixde solution , then the aluminum precipate REDISSOLVES , allowing us to tell which one is aluminium .
-We can tell which one is calcium by doign a flame test .
Do the balanced symbol equation and word equaiton for Calcium
Calcium nitrate +sodium hydroixde —> sodium nitrate +Calcium hydroixide .
-Check sheet for balanced quation .
Do the balanced symbol equation and word equaiton for Magnesium
Magnesium nitrate +sodium hydroixxde —> sodium nitrate +calcium hydroixde
Do the balanced symbol equation and word equaiton for Aluminium .
Aluminium nitrate +sodium hydroxide —> soidum nitrate +aluminum hydroixide .
-Check sheet for this , THIS OEN IS DIFFERENT AS IT IS AL3+
-ADD STATE SYMBOLS IN SO YOU KNOW WHICH ONE IS THE PRECIPITATE :))
-How can wetell that it is a precipitate that has formed >
-As precipitates have the state symbol for solids .
tHE HREE INSOLUBLE METAL HYDROXIDES FORMED ARE - calcium hydroixde , Magnesium hydroixide , and aluminium hydroixde .
Sodium hydroixde can aslo test for thre other metal ions :
-Coperr (ii) ions
-Iron (ii) ions
-Iron (iii) ions
Coper (ii) ions ?
Copper (ii) ions react with sodium hydroixide to form a bl precipitate of copper (ii) hydroixide .
-Equation the same as others
just start with ‘Copper’ (ii) nitrate and end with ‘copper (ii) hydroxide.’
-do symbol equation
Iron (ii) ions ?
-Iron (ii) ions react with soidum hydroixide to form a green precipitate of ion (ii) hydroixide .
-Same equation just start with ‘iron (ii) nitrate’
End with ‘iron (iii) hydroixide
-do symbol equation
Iron (iii) ?
reacts with sodium hydroicide to form a brown precipitate of iron )ii) hydroicide ,
Iron (iii) nitraet + sodium hydroxide —> sodium nitrate +iron (iii) hydroixde .
-Check book for symbol equation
Do ionic equaitons for all the positive ins
-CHECK EXERCISE BOOK ON THURSDAY 29TH OF sEPTEMRBER 2022
Disadvanatages for instrumental analysis ?
-Equipment is expensive to buy , run and maintain .
-OFTEN HAVE TO CPOMPARE RESULTS in a database .
-Not eveyrone can do it , need to be trained - takes time and effort .
Explain why metal ions heated i na flame emit light energy and how this can be used to identify metal ions .
–The sample is heated in a flame .
-The energy provided , excites the metal ions , making them jumo into higher energy levels .
-when they gall back to lwoer energy levels , the energy is reeleased as light energy .
In a spectrometer …
The wavelengths of rthe light producd can be analysed by passing it thorugh a spectroscope ..
-Each type of metal ion absorbs and gives out its own characteristic of radiation AKa LINE SPECTRUM
-This can be used to identify gthe emtal ions by comparing it to a databse held on a computer .
