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Chemistry Alevel OCR > 2.1 Atoms And Reactions > Flashcards

2.1 Atoms And Reactions Flashcards

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1
Q

What is the definition of Relative Isotopic Mass?

A

The MASS of an atom of an ISOTOPE compared to ONE-TWELFTH of the mass of an atom of CARBON-12.

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2
Q

What is the definition of relative atomic mass (Ar)?

A

The WEIGHTED MEAN MASS of an atom of an element compared to ONE-TWELFTH of the mass of an atom of CARBON-12

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3
Q

What is Carbon-12 used for?

A

.As atoms are so small, instead of measuring them directly we measure the mass relative to something else (we use a relative scale)
-We use the Carbon-12 isotope as the international standard measurement for the unified atomic mass unit (u.)
-1u is a tiny mass =1.660540210x10^27kg
-the mass of an atom of carbon-12 is defined as 12u
-so the mass of one twelfth of an atom of carbon-12 is 1u

We ignore the mass of electrons in this measurement as they are so small

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4
Q

How do you find the relative molecular mass (Mr) in simple molecules or the relative formula mass in giant structures?

A

-By adding together the relative atomic masses (mass number) of all the elements making the molecule
-For this you do not take into account the big number in front of formulas only the subscript numbers.

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5
Q

How do you calculate the relative atomic mass Ar of an isotope?

A

Ar=(RIM x percentage abundance) + (RIM x percentage abundance)
———————————————————————————————-
100

RIM-relative isotopic mass (elements mass number)

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6
Q

What are the steps to calculate an empirical formula?

A
  1. Divide the mass of each element(or the percentage you are given) by its relative molecular mass to get the number of moles.
    2.Divide the number of moles of each by the smallest number of moles this will give you a 1:x ratio
    3.If necessary multiply the answer to get a whole number .e.g. 1:1.5 x 2= 2:3
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7
Q

How do you calculate the molecular formula from the empirical formula and relative molecular mass?

A
  1. Find the empirical formula mass e.g. CH2 =12+(1.0 x 2)= 14.0
  2. Do the Mr/ empirical formula mass .e.g. 56/14=4
    3.Times the molecular formula mass by this answer e.g. (4 x CH2)= C4H8
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8
Q

State the ideal gas equation and the units

A

pV=nRT

P= pressure in Pa (1atm =101kPa)
V=volume in m^3
n=number of moles
R=the gas constant =8.314 Jmol^-1K^-1
T=Temperature in K

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9
Q

How do you convert from kPa to Pa?

A

kPa x 1000=Pa

Pa/1000=kPa

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10
Q

Convert from cm^3 to dm^3 to m^3

A

Cm^3 / 1000 = dm^3

dm^3 / 1000= m^3

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11
Q

What is the gas constant?

A

8.314 Jmol^-1 K^-1

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12
Q

Convert from degrees Celsius to kelvin

A

Add 273 to the degrees celsius measurement
E.g. 0 degrees celsius + 273= 273k

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13
Q

What is the equation for moles of a gas at room temp(25 degrees Celsius ) and pressure (101kPa)

A

n= V/ 24dm3mol-1

V= volume in dm3

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14
Q

What is the equation for the amount of moles in a solution ?

A

n=cV

n= amount of substance in moles
c=concentration in molsdm^-1
V= volume of solution in dm^3

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15
Q

Define amount of substance

A

The quantity that has moles as its units. Chemists use amount of substance as a way of counting atoms

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16
Q

Define a mole

A

-units mol
-the unit for amount of substance
-the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope

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17
Q

What is the Avogadro constant?

A

-Na
-the number of particles per mole 6.02x10^23 mol^-1

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18
Q

Define molar mass

A

-M
-The mass per mole of a substance , units gmol^-1

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19
Q

Formula for number of moles

A

-n=m/RMM

-m= mass in g
-RMM= relative molecular mass in gmol^-1

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20
Q

Equation to calculate number of particles

A

Number of = 6.02x10^23 x number of moles
Particles

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21
Q

What did Democritus believe about the atom?

A

-In the fifth century Ancient Greek philosopher Democritus developed the first idea about the atom.
-His theory was merely philosophical and theological reasoning
-He believed you could only divide a sample of matter a certain amount of times. He believed you would end up with a particle that could not be split any further.
-In his view there were many different types of atoms

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22
Q

What was John Dalton’s atomic theory?

A

-In 1803 Dalton presented his atomic theory. It stated that:
.all atoms of a given element are the same
.matter is made of atoms which cannot be created ,destroyed or divided
.atoms from one element are different from those of every other
.atoms combine together to form new substances.

Dalton used his own symbols to represent atoms of different elements. He also developed first table of atomic masses.

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23
Q

What model did J.J Thompson propose?

A

-1897-1906
-Cathode rays from cathode ray tubes had recently been discovered. Using a cathode-ray tube he conducted an experiment which discovered cathode rays were actually electrons
-Thompson concluded the electrons must have come from within the atoms of the electrodes.
-This disproved dalton and the ancient Greeks.
-Based on his investigation he proposed the plum pudding model.

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24
Q

Describe the plum pudding model

A

-proposed by jj Thompson after discovery of electrons
-Negatively charged particles in a sea of positive charge.In Thompson model the atom is neutral

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25
Q

What was the gold foil experiment?

A

-in 1909 Rutherford carried out a gold foil experiment.Where they shot positively charged alpha particles at a thin sheet of gold foil. Based on plum pudding model they expected particles to pass through foil as positive charge of nucleus was thought to be evenly spread out.

26
Q

What were the results of the gold foil experiment ?

A

-Most particles as expected were not deflected at all
- However a small percentage of particles were deflected at large angles. Some were deflected directly back
-These results did not support the plum pudding model. In 1911 Rutherford proposed the nuclear model

27
Q

Describe the nuclear model

A

-This model consists mainly of empty space with the nucleus at the centre and electrons orbiting in paths around the positive nucleus

28
Q

What was the Bohr model?

A

-In 1913 Niel’s Bohr altered Rutherford’s model
-His model allowed electrons to follow only certain paths in fixed shells located at set distances from the nucleus.Every orbital had different energy associated with it , higher energy orbitals being further from nucleus
-This was the planetary atom where electrons orbited a central nuclear sun in shells
-This model showed why the atom does not collapse inwards
-His model and calculations agreed with experimental results

29
Q

What did the Bohr model help to explain ?

A

-Spectral lines seen in emission spectra
- The energy of electrons at different distances from the nucleus

30
Q

What did Henry Moseley discover?

A

-The link between X-ray frequencies and the elements atomic number (its order in the periodic table). At the time he could not explain this

31
Q

Who discovered the proton?

A

-In 1918 Rutherford discovered the proton from his work on bombarding nitrogen gas and observing the hydrogen nuclei being emitted from the gas
-This was able to explain Moseley’s finding as atomic number tells us number of protons.

32
Q

What did Louis de Broglie and Erwin Schrödinger suggest about wave and particle behaviour?

A

-In 1923 Louis de Broglie suggested particles could have the nature of both a wave and a particle
-In 1926 Erwin Shrödinger suggested that an electron had wave-like properties in an atom.He also introduced the idea of atomic orbitals

33
Q

Who discovered the neutron?

A

-In 1932 James Chadwick observed a new type of radiation emitted from some elements.
-He found out that this new type of radiation was made up of uncharged particles with approximately the same mass as a proton.These uncharged particles became known as neutrons

34
Q

What is the modern understanding of atoms?

A

It is now thought that protons and neutrons are made up of even smaller particles called quarks

35
Q

What is an isotope?

A

Atoms of the same element with different numbers of neutrons but the same number of electrons and protons.
They have different masses

36
Q

What can a mass spectrometer be used for?

A

-to identify an unknown compound
-to find the relative abundance of each isotope of an element
-to determine structural information of an element

37
Q

What is the equation for percentage yield?

A

% yield= actual amount in mol, of product
—————————————————- X 100
theoretical amount in mol, of product

38
Q

What is the equation for atom economy?

A

Atom economy= molecular mass of the desired product
——————————————————————- X100
Sum of molecular masses of all products.

39
Q

What do acids do in aqueous solution?

A

Release H+ ions

40
Q

What do alkalis do in aqueous solutions?

A

Release OH- ions

41
Q

How do strong acids dissociate?

A

-they readily give up H+ ions
-they fully dissociate

42
Q

How do weak acids dissociate?

A

-only partially disassociate
-once a H+ ion is released from a weak acids they are quickly taken back again
-weak acids are excellent at accepting H+ ions back

43
Q

What is an amphoteric substance?

A

A substance that can behave as an acid and a base

44
Q

What is the difference between a base and an alkali?

A

A base is a something that can react with an acid to form water and a salt. An alkali is any base that is soluble in water.

45
Q

How can a salt be produced?

A

-by neutralising acids with bases (proton acceptors) such as:
.carbonates
.metal oxides
.alkalis

46
Q

What is the general equation for the reaction between an acid and a carbonate ( CO3^2-)

A

Acid + carbonate ——-> salt +carbon dioxide+water

47
Q

What is the general equation for the reaction between an acid and a metal oxide?

A

Acid + metal oxide ——> salt + water

48
Q

What is the general equation for the reaction between an acid and an alkali?

A

Acid + alkali ———-> salt + water

49
Q

What is the general equation for the reaction between an acid and a metal?

A

Acid+metal ——->salt +hydrogen

50
Q

What happens when acids are neutralised by aqueous ammonia NH3 ?

A

-ammonium salts are formed
-containing the ammonium ion

51
Q

What happens when ammonium nitrate is in solution?

A

-it is found as 2 ions
-NH₄⁺
-NO3-

52
Q

What are the rules for assigning oxidation numbers?

A

-in the elemental state = 0 (e.g Na or O₂)
-combined oxygen= -2 (e.g CaO)
-combined oxygen in peroxides= -1 (e.g H₂O₂)
-oxygen bonded to fluorine = +2
-combined hydrogen= +1
-combined hydrogen in metal hydrides= -1 (e.g LiH)
-Simple ion= charge on ion
-combined fluorine = -1 (e.g NaF )

53
Q

What is oxidation?

A

-Loss of electrons, it is an increase in oxidation number

-oxidation is gain of oxygen

54
Q

What is reduction?

A

-gain of electrons, it is a decrease in oxidation number

-it is the loss of oxygen

55
Q

What does the term hydrated mean?

A

Refers to a crystalline compound containing water molecules

56
Q

What does anhydrous mean?

A

Refers to a substance that contains no water molecules

57
Q

What is water of crystallisation?

A

Refers to water molecules that form an essential part of the crystalline structure of a compound.

58
Q

How do you use experimental results to calculate the formula of a hydrated salt?

A

1- find the moles of the anhydrous salt
2-find the moles of the water
3- divide through by smallest number
4-use this to determine the dot formula of the hydrated salt

59
Q

How do you use the empirical formula to work out the formula for a hydrated salt?

A

1- use the number of hydrogen atoms in the empirical formula to work out how many water molecules are present
2-use the remaining atoms to determine the formula of the main salt, and how many molecules are present
3-construct the dot formulae

60
Q

What is a dot formula used for?

A

Used to indicate the ratio of water in a hydrated crystal.
Relative number of water molecules go after the dot

61
Q

What is a standard solution?

A
  • a solution of a known concentration

Chemistry Alevel OCR (9 decks)

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