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Chemisty > MOD8 > Flashcards

MOD8 Flashcards

1
Q

What is the analysis of inorganic substances?

A

It is the analysis of ions which are commonly found as environmental pollutants

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2
Q

What are the 2 ways we monitor organic substances?

A

Qualitative and quantitative

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2
Q

Why do we monitor ions?

A

As ions are found as environmental pollutants which often enter waterways, which are important resources, which can impact our health. We use waterways for drinking, agriculture and habitat for animals

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3
Q

What is Qualitative?

A

What ions exist

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4
Q

What does quantitative mean?

A

How many ions exist

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5
Q

What is mg/L equal to?

A

Ppm

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6
Q

What are the health effects of lead exposure(3)?

A

Acute positioning
Chromic positioning
Children behaviour

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6
Q

What is acute positioning?

A

Significant exposure over a short time
-Muscle weakness
-Loss of appetite
-nausea

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7
Q

What are the 2 case studies for why we monitor ions?

A

1- lead (toxic heavy metal)
2- Eutrophication

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8
Q

How can people get lead in their body? (2)

A

Through exposure to
- lead based paints
- Old leaded petrol

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9
Q

What is chromic positioning?

A

Low exposure over a long time
-Kidney disease
-Impaired memory

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10
Q

What does lead exposure do to children?

A

Behaviour problems such as retared intellectual development

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11
Q

What is eutrophication?

A

Is algae bloom, this is where NO3- and PO32- (fertilisers) run off into waterways causing excessive algae to grow which restrict the sunlight from entering and it also cause the algae to take up all the oxygen, as the bacteria will consume all the oxygen when decomposing the dead algae in the water and then aquatic animals will die.

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12
Q

What are the qualitative tests on monitoring ions?(3)

A

-colour of solution
-flame test
-precipitate tests

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13
Q

What is the colour of cu2+ solution?

A

Blue

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14
Q

What is the colour of Fe2+ solution?

A

Pale green

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15
Q

What is the colour of Fe3+ solution?

A

Yellowish brown

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16
Q

Is seeing the colour of the solution reliable?

A

NO it is not very reliable as many salt solutions are colourless and some might have the same colour.

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17
Q

Why can’t anions be seen?

A

As it is not in the visible spectrum rather the infrared spectrum

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18
Q

What are the steps of a flame test ?

A

1- place the pt wire into HCL
2- then flame
3- repeat like 3 times
4- Put the pt wire into the sample
5- then flame
6- observe the colour

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19
Q

What is the colour Barium metal ion turn in a flame test?

A

Apple green

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20
Q

What is the colour Sodium metal ion turn in a flame test?

A

Yellow orange

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21
Q

What is the colour potassium metal ion turn in a flame test?

A

Pale purple

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22
Q

What is the colour copper metal ion turn in a flame test?

A

Blue green

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23
Q

What is the colour calcium metal ion turn in a flame test?

A

Brick red

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24
Q

What are the advantages of the flame test?

A

Quick and cheap
Help to confirm precipitation test

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24
Q

How does the colour in a flame test exhibits?

A

The electron gets excited as the electron absorbs energy and moves to a higher energy level then it moves back down to its original shell and causes radiation to be released and this is what we see in flame tests.

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25
Q

What Are the Disadvantages of the Flame test?

A

Only apply to certain cations NOT anions
Cant distinguish ions of the same element (Fe3+, Fe2+)

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26
Q

How do we test if OH- is present?

A

We use a red litmus paper and watched it turn blue
(red) 4.5—- 8.3 (blue)

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27
Q

How do we test for Co32- and Ch3C00-?

A

By adding and acid (HNO3-)
CO32- will release bubbles (co2) and ch3c00 will smell like vinegar

CO32- +2H+—> CO2 +H20

CH3C00- + H+ —–> CH3C00H(aq)

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28
Q

How do we test for So42- and Po43-, and how do we get rid of the ambiguity ?

A

Using a Ba2+ test as it can precipitate, and we use acidified conditions as Ba2+ will only precipitate with so42-, as equilibrium in HPO42- lies further to the left, as Ba2+ can’t react with PO43-

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29
Q

How to test for Po43- ?

A

add Baso4 Using NH3(aq) (BASIC conditions) as it allows for Ba2+ to precipitate with PO43-

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30
Q

How do we test for CL-, Br- and I-, colours?

A

Using Ag+ as
CL- +Ag+ —> AgCl (s): white ppt
Br- + Ag+ —> AgBr(s): pale yellow ppt
I- +Ag+ —–> AgI(s) : yellow ppt

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31
Q

Why do we use HNO3- for what substances?

A

CO32- and CH3c00

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32
Q

Why do we use Ba2+ for what substances?

A

SO42- and PO43-

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33
Q

Why do we use Ag+ for what substances, whatarethere according coours?

A

Cl(white ppt)-, I-( yellow ppt) and Br- (plae yellow ppt)

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34
Q

How do we differentiate between BrAg (pale yellow) and AgI (yellow)?

A

We add Conc.NH3 and AgBr dissolves to form a colourless complex ion
While AgI doesn’t dissolve

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35
Q

What colour forms when Ag+ + OH- —-> Ag(OH)?

A

Brown precipitate

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35
Q

What are the disadvantages of the precipitation test?

A

-Only gives qualitative information
-Time consuming

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36
Q

What is the advantage of precipitation tests?

A

-Can identify both cations and anions
-More reliable than simple flame tests

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37
Q

How do electrons move to the ground state to the excited state and back?

A

The electron absorbs energy and moves from ground state to excited state, and the electron releases energy and moves back to the ground state.
As the electron will release the same energy as they return to their ground state

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37
Q

Why do we use ASS?

A

-Highly accurate, as it provides a conc. Close To ‘true value’
-sensitive as it detects very low conc. (PPM/PPB)
- it can analyse ions without interference from other ions.

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37
Q

What is AAS?

A

Atomic Absorption spectrum

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38
Q

What is the equipment in the AAS(5)?

A
  • lamp
  • flame (with sample)
  • lens (for focus)
  • prism/ monochromator
  • photomultiplier
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39
Q

What is inside the lamp?

A

There is a cathode which is made of the same substance of the sample,
The cathode is then electrified and it is excited and emits a specific wavelength which will be absorbed by the sample.

39
Q

What does a photomultiplier do?

A

Selects a specific wavelength that is only absorbed by the sample/ and the cathode

40
Q

How is the absorbance calculated?

A

We can use by measuring the intensity with no sample (I0) then compare it with the sample (I),

41
Q

What can AAS be used to monitor?

A

Toxic heavy metal that are pollution
To ensure public health as it can help to prevent poisoning.

41
Q

What is absorbance also directly proportional to?

A

Concentration as absorbance increases concentration increases

42
Q

Why is interpolation valid but not extrapolation?

A

Interpolation is valid but extrapolation is invalid as it assumes the will still gives the same trend(linear relationship) of values that are not tested for experimentally.

43
Q

What are the limitations of AAS?

A
  • expensive
  • lacks portability
  • unique cathode
  • cannot be used to analyse anions
44
Q

What is calorimetry?

A

Measure the absorbance of light at a certain wavelength passing through a coloured solution, and then the concentration of the analyte can be determined.

45
Q

What does the detector do, in calourmetry?

A

Measures the intensity of light that pass through the sample

45
Q

How does calorimetry work(5)?

A

light source
filter
sample
detector
recorder

46
Q

What is the UV-Vis?

A

ultraviolet visible spectroscopy, it involves analysing a solution with light in the visible and ultraviolet range.

46
Q

What does a filter do in calorimetry?

A

Selects the complementary colour

46
Q

What colour is strongly absorbed by the sample?

A

The complementary colour is absorbed

47
Q

What is the difference between a calorimetry and Uv-vis spectrometer?

A

Uv-vis spectrometer uses a monochromator rather than a filter

48
Q

What is absorbance directly proportional to?

A

Concentration

49
Q

What are the 3 formulas of absorbance?

A

A=kC
A=εlC
A=log10(Io/I)

A= absorbance
ε= molar absorptivity (L mol/cm)
C= concentration (mol/L)
Io= intensity of light entering sample cell
I= intensity of light exiting the sample cell

50
Q

What is the aim of the sulphate content in lawn fertiliser?

A

To determine the sulphate content of a fertiliser by gravimetric analysis.

51
Q

What is the method of the sulphate content in lawn fertiliser?

A

1- accurately weigh out a known mass of crushed fertiliser and dissolve in HCL solution.
2- filter off any insoluble materials
3- hat the solution until almost boiling then add excess BaCl2 dropwise (stir)
4- gently leave the mixture for 30 min so the particles can come together to form larger ppt the allow to cool
5- weigh the filter paper + filter the ppt
6- add more BaCl2 then rinse the ppt 2-3 times with distilled water and ethanol
7- dry the ppt until constant mass is attained +weighted

52
Q

Why do we add acid in step one?

A

So that co3^2- can be released into co2(g)
And po4^3- changes into HPO4^2- which is not able to form a ppt with Ba^2+

53
Q

Why do we add BaCl2 dropwise in step3?

A

So it doesn’t get too small otherwise it will go through the filter paper.

54
Q

And why do we heat the solution in step 3?

A

To increase the solubility of BaCl2

55
Q

Why do we cool the solution in step 4?

A

To reduce the solubility of BaSo4

56
Q

Why do we add distilled water and ethanol in step 6?

A

To remove the absorbed Ba2+and Cl- ion, we add ethanol to dry the ppt

57
Q

What are 2 problems that may arise in the sulphate content in lawn fertiliser?

A

Underestimation
Overestimation

58
Q

What is the underestimation problem in sulphate content in lawn fertiliser?

A

BaSo4 can form small particles that may pass through the filter, by dumping all the BaCl2 all at once.

59
Q

What is the overestimation problem in sulphate content in lawn fertiliser?

A

Baso4 contains impurities like Po4^3- and CO3^2-
Ppt has not completely dried (mass of precipitate + water)

60
Q

How can we prevent underestimation?

A

Form the precipitate slowly
-Increased Particle size by letting the solution digest
-Cool the ppt before filtration to decrease solubility

61
Q

How to test for carboxyl?

A

U can use a blue litmus paper if turn red it is carboxyl group
Add a acid and if bubble of co2

61
Q

How can we prevent overestimation?

A

Add Hcl to prevent Po463- and Co3^2- from precipitating
Rinse with distilled water to remove excess Cl- and Ba2+
Use vacuum filtration to dry if available.

61
Q

How to test for alkenes(c=c)?

A

Bromine water test, if reaction occurs it is alkene.

62
Q

How to test for alcohol (O-H)?(3)

A

Add Na metal (sodium), as it reacts with the alcohol and na slowly dissolves and a gas is produced -> H2(g), formula
2CH3OH(l) + 2Na(s) —> 2NaCH3O(no state as it dissolve in CH3OH) +H2(g)

Test using strong oxidants like acidified Cr2O7^2- or MnO4^-
As primary and secondary alcohols will readily oxidised and undergo a colour change

Tertiary alcohol we use the lucas test where react the tertiary alcohol with HCl/ZnCland a substitution reaction occurs forming a haloalkane results in a cloudy laye

63
Q

What is the order of reactivity of alcohols in lucas reagent?

A

Tertiary alcohol immediately react to form a cloudy layer
Secondary slowly react with Lucas reagent after several minutes to form a cloudy layer
Primary alcohol do not react with Lucas reagent
Tertiary> secondary> primary

64
Q

What is a Lucas Test?

A

Involves a substitution reaction with a lucas regent(HCL or ZnCl2) and alcohol, to form a cloudy haloalkane

65
Q

What does mass spectrometry involve?

A

Involves ionising a vaporizer sample and measuring the mass to charge ratio (m/z)and relative intensities of the ions formed.

65
Q

What Are the steps of mass spectrometry?

A
  1. Inlet-which introduce the vaporised sample
  2. and the sample enter the heated filament part where it is bombarded with high energy electrons to produce a radical cation: M(g) + e- —-> M^(.+) +2e-
  3. Then the ions are then into a fine beam through narrow slits and are accelerated through an electric field into a magnetic field
  4. When ions enter the magnetic field they deflect into a circular path
  5. Detector which analysed on the computer to calculate the m/z ratio
66
Q

What does the radius of curvature depend on?

A

-Mass of particle
-Charge of particle
-Magnetic field
-Initial voltage applied

66
Q

What do we do to analyse all ion sizes?

A

Vary the electromagnetic field

67
Q

What is the parent peak?

A

Last peak it has to be more than 1% (like 5% is fine)

67
Q

What is the relative abundance of 35 Cl and 37 Cl?

A

35—> 75%
37—> 25%
So the ratio is 1:3

68
Q

Do lighter ions undergo larger or smaller deflection?

A

Larger deflection so smaller radius

69
Q

What are the 2 isotopes of CL?

A

35 Cl and 37Cl

70
Q

What is the base peak?

A

The highest peak

71
Q

What are the 2 isotopes of BR?

A

79Br and 81 Br

72
Q

What is the relative abundance of 79Br and 81 Br ?

A

79Br —> 50%
81 Br —>50%
So the ratio is 1:1
And the highest one is usually 79

73
Q

What is the advantage of the mass spectrum?

A

-Very accurate providing m/z ratio
-Can be used to identify molecular mass and chemical formula

74
Q

What are the disadvantages of the mass spectrum?

A

Expensive

75
Q

What are the advantages of the infrared spectrum?

A

-quick process that provide information about the function group present
-Can be used to identify unknown samples

76
Q

What is the disadvantage of the infrared spectrum?

A

-relatively expensive
-limited info about H-NMR and C-NMR

77
Q

What is NMR?

A

Nuclear magnetic resonance, used to determine the different hydrogen environments

78
Q

What happens when ppm gets larger?

A

higher chemical shift so closer to electronegative atoms and frequency is higher

79
Q

What does the integration mean on the spectrum?

A

Number of hydrogens in each chemical environment

80
Q

What doe the splitting pattern mean on the spectrum?

A

Number of hydrogen on the neighbouring carbon and we use the n+1 rule so we minus 1

81
Q

What is the table we should use for the H NMR?

A

Ppm, Integration, splitting, Neighbour, conclusion

82
Q

How do we find the empirical formula if we are given percentages ?

A

We put everything to 100g and then using the percentage we find the mass then we find moles then we divide everything be the lowest, if decimals like .5 then we multiply by 2,until we get whole numbers

83
Q

What Is the table we use for the C NMR?

A

Ppm, conclusion
We look at the structure on the reference sheet

84
Q

How to find the molecular formula if you have the empirical formula and the mass spectra?

A

MF= (CnHnOn)x
MF= the mass
Find the molar mass of CnHnOn
Then find for x

85
Q

What does availability of reagents mean?

A

Having reacts readily available and cheap

86
Q

What are 3 reaction conditions?

A

Equilibrium yield
rate of reaction
economics

86
Q

What is yield?

A

Refers to the quantity of product that can be formed when a reactant is completely consumed

87
Q

How to find the % yield?

A

Actual yield/ theoretical yield x100

87
Q

What does purity mean?

A

Refers to the quality of the product

88
Q

How to find the %purity?

A

Mass(useful product)/mass of sample x100

89
Q

What is the haber process?

A

Making ammonia(NH3), through
N2(g) +3H2(g) <—-> 2NH3(g)

90
Q

What are some use of ammonium?

A

Fertilisers
Household cleaners

90
Q

Is haber exothermic or endothermic?

A

Exothermic

91
Q

How to increase the reaction rate?(3)

A

-High temp- increases the kinetic energy more successful collisions
-High pressure- more closely packed means more successful collisions
-Catalyst- provides alternatives reaction pathway by lowering the activation energy, which mean more collisions which can overcome the activation energy

92
Q

What are the actual conditions of the haber process? (6)

A

-Moderate temperatures (we maximise yield by lower temp, but it will take along time as the reaction rate is slow)
-High pressure
-Catalyst → allows low temps to be used
-Liquify NH3 so the equilibrium will shift to the right
-We recycle unreacted gases back
-Use a stoichiometric ratio of 3:1 of H2+N2 which avoids having excess reactants which improves cost

Chemisty (2 decks)

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