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AS OCR A CHEM > amount of substance > Flashcards

amount of substance Flashcards

1
Q

What is the relative mass of electron

A

1/2000

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2
Q

Why is the proton number significant

A

Each element has a unique number of protons - determines which element the atoms belongs to if the proton number changes the whole element changes

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3
Q

Which letter is used to represent the atomic number of an atom ?

A

Z

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4
Q

Which letter represents the mass number ?

A

A

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5
Q

Define isotope

A

Atoms of the same element with different numbers of neutrons ( same number of protons ) and different masses

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6
Q

What is an atom

A
  • smallest part of an element that can take place in CR
    -mostly empty space
    -mass concentrated in nucleus
    ( P+N)
    -atoms are neutral same n.o P +E
  • negative E orbit nucleus
  • electrostatic attraction beteeen positive N and negative E holds atom together
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7
Q

What are ions

A

Atoms that either gained or lost an electron

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8
Q

What are cations

A

Positive charged - lost E P>E

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9
Q

What are anions

A

Negatively charged ion gained E E>P

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10
Q

What is the symbol of isotopes

A

Chemical symbol - mass number eg Carbon -12

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11
Q

What are the difference between isotopes and atoms

A

Same chem properties but diff physical

Chemical :
Same - same number of E in outer shell - E take part in CR

Physical :
Diff neutrons - add mass
Diff in mass and density

.

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12
Q

What is the history of the atom .

A

1807- John Dalton
1897-JJ Thompson PPM
1909-Ernest Rutherford - Gold leaf experiment
1913- Neil Bohr. Fixed energy shells
James Chadwick neutrons
Atomic model today

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13
Q

What did John Dalton believe .

A

A- spheres each element has diff spheres
A can’t be divided
All A in Element same

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14
Q

What was JJ Thompson plum pudding model

A

Negative electrons embedded in a sea of positive charge
Discovered the electron

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15
Q

What was the gold leaf experiment and what Rutherford discover

A

Discovered nucleus - very small + positively charged
Mainly empty space with a cloud of negative electrons

Gold foil experiment - AP fired at gold foil most went through = empty spaced
Some deselected at large angles - hit a positive nucleus concentrated in the centre where all the mass is concentrated

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16
Q

What did Niels Bohr ?

A

Electrons orbit nucleus in fixed distanced in shells
-most of the atom is empty space
most of the mass is in the nucleus

Prob with Rutherford model : cloud of electrons would collapse into positive nuclei due to electrostatic forces of attraction between positive nucleus and negative electrons

Proof :
When EM Radiation abosorbed electrons move between shells into height energy level
Emit this radiation when electrons move down to lower energy shells

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17
Q

What is the atomic model today .

A

E don’t have the same energy in shells
Have subshells
Explains ionisation trends

TINY central nucleus – contains protons (+) and neutrons (0)
electrons (–) move around outside nucleus in orbits / shells / energy levels
most of the atom is empty space
most of the mass is in the nucleus

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18
Q

What is relative atomic mass

A

Is the weighted mean mass of an atom of an element compared to 1/12th of the mass of an atom of carbon-12

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19
Q

What is the relative molecular mass

A

Is the mean mass of a molecule , compared to 1/12th of the mass of an atom of carbon-12- based on the mass of a 12 C atom , the standard for atomic masses

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20
Q

What is the relative isotopic mass

A

Is the mass of an atom of an isotope compared to 1/12th of the mass of an atom of carbon -12- based on the mass of a 12 C atom , the standard for atomic masses

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21
Q

Why does different isotopes of the same element react in the same way

A

Neutrons have no impact on the chemical reactivity
Reactions inv electrons isotopes have same n.o E in same arrangement
-same CR as they
have same electron
configuration but physical
properties like density may be
diff

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22
Q

What is the unit used to measure atomic masses

A

Unified atomic mass (U)

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23
Q

What is the unit of relative atomic mass

A

No units

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24
Q

How to calculate the relative molecular mass and relative formula mass

A

Both : calculated adding relative atomic masses of each of the atom making up the molecule or formula

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25
Q

What is mass/charge m/z

A

Mass of isotope divided by charge as most have +1 charge this is the same as isotopic mass

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26
Q

Describe mass spectra -isotopes graphs - mass spectrum

A

Y-axis abundance -% add up to 100 -relative abundance and both isotopes should add up to 100
X-axis M/z

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27
Q

How to calculate relative atomic mass

A

mass of element given as relative atomic mass (Ar) using average mass of isotopes
relative atomic mass element calc using relative abundance values
(relative abundace x mass isotope 1 ) x (relative abundance x mass isotope 2 ) / 100

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28
Q

what is the basic process of mass spectrometry

A

sample vapourised
sample ionised to form positive ions
ions are accelerated
Ions pass through the apparatus + are separated according to mass to charge ratio
Heavy ions move slower / are less deflected(so the ions of each isottope is seperated)
ions detected on a mass spectrum -as a mass-to-charge ratio, written m/z
Compute analyses the data and produces mass spectrum
Each ion produces a signal, larger the signal,= greater abundance
mass spectra produced used to calc - relative atomic mass of element + its isotopes

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29
Q

What are the uses of mass spectrometry

A

Identify unknown compounds
Find relative abundance of each isotope of an element
Sterile structural information

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30
Q

what happens if their are too many neutrons in an isotope ?

A

Sometimes the extra neutrons
make the nucleus big and unstable
– this makes the isotope
radioactive

31
Q

how is the mass of atoms calculated ?

A

standard isotope is needed on which to base all the atomic masses = carbon -12
one atom o f carbpn 12 -1.992646538x10^-26
-carbon-12 isotope is defines as 12amu(12u)
-the standard mass for atomic mass is 1u - mass of 1/12th of carbon -12 atom
-TF = 1u is app mass of proton/neutron

32
Q

what is 1U ?

A

1.6x10^-27

33
Q

what does relative atomic mass take into account ?

A

the isotopic mass of each isotope
the abundance of each isotope

34
Q

what is mass spectrometry ?

A

Establish the relative atomic mass of an element and the relative abundance of its isotopes

Establish the relative molecular mass of a molecule/compound

35
Q

How is the mass spectrometry detected ?

A

positive ions pick up an electron
at the detector= a current to flow,
-the more ions that hit at any tiime , the bigger the current.

Lighter ions travel at a higher
speed so reach the detector first.

Ions with same mass/charge
ratio arrive at the detector at the
same time.

The flight times are recorded.

36
Q

how is the mass spectrometry analysed

A

The height of the peak gives the
relative isotopic abundance of each
ion.

37
Q

what are binary compounds ?

A

Contains 2 elements
Metal ion always come first
The ending of the second element is -ide

38
Q

what are polyatomic compounds

A

More than one element bonded together

39
Q

what is the charge of ammonium ?

A

NH4 = 1+

40
Q

what is the charge of hydroxide ?

A

OH = -

41
Q

what is the charge of nitrate ?

A

NO3 = -

42
Q

what is the charge of nitrite ?

A

NO2 = -

43
Q

what is the charge of hyrdrogencarbonate

A

HCO3 = -

44
Q

what is the charge of manganate ?(permanagate)

A

MnO4 = -

45
Q

what is the charge of carbonate ?

A

CO3 = 2-

46
Q

what is the charge of sulfate ?

A

SO4= 2-

47
Q

what is the charge of sulfite ?

A

SO3= 2-

48
Q

what is the charge of dichromate ?

A

Cr2O7= 2-

49
Q

what is the charge of phosphate ?

A

PO4= 3-

50
Q

why is every measurement subject to some uncertainty ?

A

When assessing uncertainty, a number o. issues have to be considered. :
● Resolution of instruments
● Manufacturer’s tolerance on these instruments
● Judgments made by the person carrying out the exp
● Adopted procedures eg repeated readings
● The size of increments available such as the size of drops from a pipette.

51
Q

what is reading uncertainty ?

A

Uncertainty in a reading for a specific instrument is said to be plus or minus half of the smallest division. E.g. thermometer

52
Q

what is measurement uncertainty ?

A

Both of uncertainties in a measurement must be taken into account

eg uncertainty of the zero marker + the uncertainty of the measurement point. E.g. ruler

53
Q

how do you estimate uncertainty ?

A

1) by considering the resolution of measuring instruments

2) from the range of a set of repeat measurements
uncertainty = range
2

54
Q

what do you do with uncertainty on graphs ?

A
55
Q

what is random error ?

A

where repeating the measurement gives a randomly different result

the more measurements you make, and then average, the better estimate you generally can expect to get.

56
Q

what is sytematic error ?

A

where the same influence affects the result for each of the repeated measurements

you learn nothing extra just by repeating measurements. Other methods are needed to estimate uncertainties due to systematic effects, e.g. different measurements, or calculations

If a straight-line graph through the origin is expected but the line of best fit of the plotted points does not pass through the origin, then this is an indication of a systematic error. If there is a large scatter of points around the line of best fit this is an indication of a large uncertainty possibly due to random errors.

57
Q

what is avagrados law for ideal gases ?

A

Equal amounts in moles of gases occupy the same volume under the
same conditions of temperature and pressure.

The volume of one mole of any gas at room temperature and pressure
(20oC and 1 atmosphere pressure) is 24 dm3 (24,000 cm3)

58
Q

how to find the volume of a substance ?

A

v= n/c

59
Q

how to find the volume of a gas

A

v = n x 24

60
Q

what would 1 mol of O2 be ?

A

32g

61
Q

what does ideal gases mean ?

A

An ideal gas is a model of a gas that
behaves in an ideal way.
-random motion

-elastic collisions (no loss of energy)

negligible size of the molecules themselves

no forces between molecules

62
Q

what does a molar volume of a gas depend on ?

A

gas molecules so far apart - the
vol o.the G = mostly cuz space between molecules + doesnt depend on the size of the , only on the number o.molecules.

1 mole of any gas contains the same
n.o molecules- occupy same
vol -depends on the pressure
+ temp

The volume of one mole of gas =
molar volume (units = dm3 mol-1)

molar vol of any G at room
temp + pressure (RTP, about 20°
C +1 atmosphere pressure) is approx
24 dm3 (or 24000 cm3)

63
Q

what is the idea gas equation ?

A

pV = nRT

where
p = pressure (Pa)

V = volume (m3)

n= amount in mol (mol)

R = ideal gas constant = 8.314 (Jmol−1K−1)

T = absolute temperature (K)

64
Q

what is the ideal gas equation mean ?

A

possible to predict how a certain amount of gas will behave when the conditions of temperature and/or pressure are changed.

65
Q

(The ideal gas equation ) How to convert 1 atm to 101 kPa

A

1.01×105 Pa

66
Q

(The ideal gas equation ) what is 1m3 in dm3 and cm3

A

1 m3 = 1×103 dm3 = 1×106 cm3

67
Q

(The ideal gas equation ) what atm to pa ?

A

multiply by 1.01×105

68
Q

(The ideal gas equation ) what is kPa to Pa

A

multiply by 10^3

69
Q

(The ideal gas equation ) what is dm3 to m3

A

multiply by 10−3

70
Q

(The ideal gas equation ) what is cm3 to dm3

A

multiply by 10−6

71
Q

(The ideal gas equation ) what is °C to K

A

add 273

72
Q
A
73
Q
A

AS OCR A CHEM (5 decks)

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