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Chemistry > C12 -Chemical Analysis > Flashcards

C12 -Chemical Analysis Flashcards

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1
Q

What is a pure substance ?

A

-A pure substance is not mixed with any other substance , it only contains a single elemnt or single compound .

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2
Q

What is the simplest way to determine if a substance is pure ?

A

-Measure its melting point and boiling point .

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3
Q

When does a pure substance melt and boil ?

A

-A pure substance melts at a specific fixed temperature . -A pure substance also has a specific fixed boiling point .

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4
Q

When do Impure substances melt and poil ?

A

-Impure substances melt and boil over a range of temperatures .

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5
Q

What does graph one show ?

A

THe melting and boiling of water (an example of a PURE substance ) .

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6
Q

Stage one of graph one ?

A

-We start with ice and are gradually increasing the temperature .

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7
Q

What happens at star one ?

A

-At a certain point the temperature STOPS RISING .
-This is the MELTING POINT .
(In the case of water this is FIXED at 0 degrees . )

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8
Q

What happens at star two ?

A

-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 .)

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9
Q

So how do we know water is pure ?

A

-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 .

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10
Q

What does graph 2 show ?

A

A graph for a mixutre of water and a impurity .

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11
Q

What happens in graph 2 ?

A

-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 .

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12
Q

What is a formulation ?

A

-A formulation is a complex mixture , that has been designed as a useful product .

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13
Q

What is special about formulations ?

A

-In a formulation , the quanitty of each component is carefully measures , so that the product has the properties we need .

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14
Q

Examples of formulations ?

A

-Fuels
-Cleaning products
-Paints
-Medicine
-Alloys
-Fertilisers
-Food

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15
Q

What is the melting point ?

A

The temperature at which a solid turns into a liquid and a liquid turns into a solid .

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16
Q

What is the boling point ?

A

When a substance changes from a liquid to a gas and then a gas to a liquid .

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17
Q

what is 24 carat gold ?

A

Pure gold - contains no other metal .

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18
Q

How do you workout the fraction of gold present .

A

Divide the carat number by 24 .
e.g —> 9/24=0.375 = 37.5%

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19
Q

What is a pure substance ?

A

All the particles are the same .

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20
Q

What is a mixture ?

A

Contains different particles .

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21
Q

What is an element ?

A

A susbatnce made up of only one type of atom .

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22
Q

What are compounds ?

A

Substances amde of different types of atoms joined together .

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23
Q

How does paper chromatogrpahy do ?

A

Allows us to separate substances based on their dffierent solubilities .

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24
Q

first stage of papepr chromatogrpahy

A

take a piece of chromatography paper .
-draw a pencil lne near th botom .

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25
Q

second stage of paper chromatogrpahy .

A

-put dots of our colours (substance) on a pencil line .

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26
Q

third stage of paper chromatogrpahy .

A

now put paper into solvent
(a liquid that will dissolve substances ).

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27
Q

fourth stage of paper chromatogrpahy

A

The solvent now makes it way up the paper and dissolves the ink and coloured dots , which are also carried by the paper .

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28
Q

Why is paper in chromatography called stationary phase and the solven called mobile phase ?

A

Paper called stationary pahse as it does not move .
SOlvent called mobile pahse as it moves .

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29
Q

A pure compound …

A

will produce a sinlge spot in all solvent ,

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30
Q

a compound in a mixture (mixture of colours )

A

may sepearate into a different spots depending on the solvent .

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31
Q

More soluble substances…

A

travel further up the paper .

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32
Q

Why do we draw the starting line un pencil

A

As if we draw the line in pen , the pen ink would also move up with the solvent effecting the results

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33
Q

How to figure out unknown substance using chromatogrpahy .

A

-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 ,.

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34
Q

Rf value facts .

A

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

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35
Q

RQP for paper chromatogrpahy .

A

Sample of food chemicals ,
4 known food coloruings (a -d)

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36
Q

First stage pf paper chromatogrpahy rp ?

A

First stage pf paper chromatogrpahy rp ?

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37
Q

Second stage of paper chromatogrpahy rp ?

A

Mark five pencils pots at equal spaces across line .
-make sure there 1cm clear on each side of the paper .

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38
Q

Third stage of paper chromatogrpahy rp ?

A

use a capiallary tube to put a small spot of eak of the known colours and the unkown colours ontol pencil spot

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39
Q

fourth stage of paper chromatogrpahy rp ?

A

now pour water into beaker depth of 1cm water in this case solvent .

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40
Q

fifthstage of paper chromatogrpahy rp ?

A

attach a glass rod using tape and lower paper into a glass beaker ,bottom of paper should dip into water .

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41
Q

pencil line with psots must be above the surface of water why ?

A

or water will wash off the line .

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42
Q

the sides of the paper must not touch side walls why >

A

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 .

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43
Q

sixth stage of paper chromatogrpahy rp ?

A

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

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44
Q

where are the unkwon colours ..

A

the spots that line up with the unknown colour is unkown colour .

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45
Q

explain y referring to sgtationary and mobile phases , why samples mov ar different speed in an experimetn .

A

-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 .

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46
Q

check the chromatography question in the book .

A

In chemistry exercise boo - on Rf value , dangerous food colouring

47
Q

Test for hydrogen gas ?

A

-A test tube that contains a gas that might be hydrogen .
-To test for hydorgen , remove the bung and insert the burning splint .

48
Q

What is the observation from the hydrogen gas .

A

Hydrogen gas burns rapidly and produces a ‘pop’ sound .

49
Q

Test for oxygen gas ?

A

-A test tube that contains a gas that might be oxygen .

50
Q

Observation for oxygen

A

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 ).

51
Q

Testing for carbondioxide?

A

To test for carbondioxide , use limewater .
-Limewater is an aqueous solution of calcium hydroxide .

52
Q

Testing for carbondioxide (1)

A

-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 .

53
Q

Observation for Carbondioixde

A

-If we repeat this several times , the limewater may turn cloudy .
-Telling us the gas is carbondioxide .

54
Q

Test for chlorine

A

-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 .

55
Q

Word equation and balanced symbol equation for ccombustion of magnesium and hydrochloric acid .

A

Magnesium+hydrochloric acid —> Magnesium Chloride and hydrogen .

56
Q

Explain why hydrogen pops with a lighted splint ?

A

Combustion . The flame ignites the hydrogen .

57
Q

Explain why oxyen relights a glowing splint ?

A

-Concentration of oxygen higher in the tube than in the air /

58
Q

Write a word equation for the catalyitic decompostion of hydrogen peroxide .

A

Hydrogen perioxide —> water +oxygen .

59
Q

Calcium carbonate +hydrochloric acid —>

A

Hydrogen peroxide —> water +oxygen

60
Q

Limewater is a solution of calcium hydroixde in water .
-Explain why it goes miklky when carbon dioxide is bubbled through it .

A

A precipitate of calcium carbonate is formed .

61
Q

check page 184 in textbook alnd learn the equations .

A

.

62
Q

Check exercise book for the following

A

.

63
Q

Negative ion for carbonate

A

.

64
Q

reaction for carbonate

A

.

65
Q

Negative ion for sulfate

A

.

66
Q

Reaction for sulfate

A

.

67
Q

What three halide ions are we using an their negative ions ?

A

Chloride
Bromide
Iodidie
jsut put a - against their symbol

68
Q

First step for testing a carbonate ion

A

1.Add diilute acid to our sample

69
Q

Second step for testing a carbonate ion

A

2.The acid will react with carbondioxide gas .
-We will see effervescence (fizzing) .
-That does not prove we have carbondioxide gas .

70
Q

Third step for testing a carbonate ion

A

-BUbble the gas through limewater .
-If the limewater goes cloudy , then this proves we have carbondioixde . That mean we started with a carbonagte ion .

71
Q

First step for testing for Halide ions

A

Add dilute nitric acid to a sample

72
Q

Second step for testing halide ions

A

Add a dilute silver nitrate solution

73
Q

Third step for testing halide ions

A

Halide ions produce a reciitate of the silver halide .
-Each halide makes a different coloured precippitate .

74
Q

Chloride ions

A

A white precipitate of silver chloride .

75
Q

Chloride ions

A

A white precipitate of silver chloride .

76
Q

bROMIDE IONS

A

pRODUCE A CREAM PRECIPITATE OF SILVER BROMIDE

77
Q

Iodide ions

A

produce a yellow precipitate of silver iodide .

78
Q

Test for sulfate ions ?

A

-Add dilute HCL into our sample
-Add barium chloride solution
-If sulfate ions are present , we will see a white precipitate .

79
Q

What are flame tests used for ?

A

-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 .

80
Q

How does a flame test work ?

A

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 .

81
Q

What colour flame does lithium produce

A

A CRIMSON flame (must say this colour in the exam . )

82
Q

What colour flame does Sodium produce ?

A

Sodium produces a YELLOW FLAME .

83
Q

What colour flame does Potasium produce ?

A

Potassium produces a lilac flame .

84
Q

What colour flame does Calcium porduce ?

A

-Calcium porduces an oragne red-flame .

85
Q

What colour falme does copper produce ?

A

-Copper ions produce a green flame .

86
Q

What is one problem with flame tests ?

A

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 .

87
Q

What is another problem with flame tests ?

A

2.Sometimes a sample contains a mixture of metal ions , which can mask the colour fo the flames .

88
Q

What is the solution for problem 2 ?

A

-Instead of using flameesrs , sicentits often use a technique called flame emission spectroscopy .

89
Q

What is the solution for problem 2 ?

A

-Instead of using flameesrs , sicentits often use a technique called flame emission spectroscopy .

90
Q

S1 FOR FLAME EMMISON SPECTROSCOPY .

A

1.a SAMPLE OF THE METAL ION N SOLUTION IS PLACED INTO A FLAME .

91
Q

S2 FOR FLAME EMMISON SPECTROSCOPY .

A

2.The lgiht given out is thin and [asses into a machine called a pectroscope .

92
Q

S3 FOR FLAME EMMISON SPECTROSCOPY .

A

3.The spectroscope converts the line into line spectrum .

93
Q

S4 FOR FLAME EMMISON SPECTROSCOPY .

A

-We can use this to indentify ,the metal ion in the sample .

94
Q

What can flame emission spectroscopy also tell ?

A

-Flame emision spectroscopy can also tell us the concentration of the metal ion .
-Lines become MORE INTENSE at a higher concentrations .

95
Q

Flame emission spectroscopyy is an example of an INSTRUMENTAL METHOD (carried out by a machine )

A

.

96
Q

One advanatge of instrumental methods :

A

-ThEY ARE RAPID , WE COULD USE FLAME EMISISON SPECTROSOCPY TO ANALYSE SAMPLES MORE RAPIDLY THAN WE COULD USING FLAME TESTS .

97
Q

Another advanatge of instrumental methods :

A

-instrumental methods are senstiive , Flame emission spectroscopy will work even on TINY samples of metal compounds .

98
Q

Final advanatge of instrumental methods .

A

-Instrumental methods are accurate , flame emission spectroscopy is more likely to identify a metal ion correctly than using a flame tests.

99
Q

How else can we test for cetrian metal ions ?

A

-using their reaction with (soidum hydroxide solution (NaOh).

100
Q

What will happen if we add Soium hydroixde to Calcium (Ca2+) , Magnesium (Mg2+) , and aluminium ions 9Al3+).

A

-They ll produe a white precipitate .
PROBLEM –> we cannot distinguish between these three tests becuse they all produce a white precipitate .

101
Q

How can we tell which one is aluminium ?
How do we tell which one is calcium ?

A

-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 .

102
Q

Do the balanced symbol equation and word equaiton for Calcium

A

Calcium nitrate +sodium hydroixde —> sodium nitrate +Calcium hydroixide .
-Check sheet for balanced quation .

103
Q

Do the balanced symbol equation and word equaiton for Magnesium

A

Magnesium nitrate +sodium hydroixxde —> sodium nitrate +calcium hydroixde

104
Q

Do the balanced symbol equation and word equaiton for Aluminium .

A

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 :))

105
Q

-How can wetell that it is a precipitate that has formed >

A

-As precipitates have the state symbol for solids .
tHE HREE INSOLUBLE METAL HYDROXIDES FORMED ARE - calcium hydroixde , Magnesium hydroixide , and aluminium hydroixde .

106
Q

Sodium hydroixde can aslo test for thre other metal ions :

A

-Coperr (ii) ions
-Iron (ii) ions
-Iron (iii) ions

107
Q

Coper (ii) ions ?

A

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

108
Q

Iron (ii) ions ?

A

-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

109
Q

Iron (iii) ?

A

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

110
Q

Do ionic equaitons for all the positive ins

A

-CHECK EXERCISE BOOK ON THURSDAY 29TH OF sEPTEMRBER 2022

111
Q

Disadvanatages for instrumental analysis ?

A

-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 .

112
Q

Explain why metal ions heated i na flame emit light energy and how this can be used to identify metal ions .

A

–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 .

113
Q

In a spectrometer …

A

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 .

Chemistry (20 decks)

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