Section 1 7 atoms molecules and stoichiometry
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SECTION 1 (7%): ATOMS, MOLECULES AND STOICHIOMETRY. Uses of isotopes (e.g. radioactive dating & leak detection) Mass spectrometer (e.g. determination of relative atomic or molecular mass from relative intensities of peaks in mass spectrum)

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SECTION 1 (7%): ATOMS, MOLECULES AND STOICHIOMETRY

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Section 1 7 atoms molecules and stoichiometry

SECTION 1 (7%): ATOMS, MOLECULES AND STOICHIOMETRY


Section 1 7 atoms molecules and stoichiometry

  • Uses of isotopes (e.g. radioactivedating & leak detection)

  • Mass spectrometer (e.g. determination of relative atomic or molecular mass from relative intensities of peaks in mass spectrum)

  • Electrolysis (e.g. calculation involving volume of gas evolved / mass of solid deposited / thickness of electroplating layer, oxidation states of metals)


Section 1 7 atoms molecules and stoichiometry

  • Ideal gas equation (e.g. calculation of partial pressure & densities for a mixture of gases at 2 different temperature)

  • Calculation involving volumetric analysis / back titration (e.g. determination of % by mass of active chlorine in bleaching solution, % of mass of N in ammonium fertilizer)

  • Balancing nuclear reactions


1 1 the atomic structure

1.1 THE ATOMIC STRUCTURE

  • Relative atomic mass:

  • Atomic number: equal to the number of p_____ in the nucleus

  • Mass number:number of protons plus no. of neu_____s

  • Isotopes:e.g. 12C, 13C, 14C; 35Cl, 37Cl


1 2 radioactivity

1.2 RADIOACTIVITY

  • Radioactivity: the disinte________ of certain unstable nuclei with emission of ra______

  • 3 types of radiation from radioactive substance

    1. ray ( particle)

    2. ray (particle)

    3. ray


Section 1 7 atoms molecules and stoichiometry

  • Nuclear equations: all the following equations which involve changes in the number of neutrons and / or protons are known as nuclear equations. (balancing in both mass and atomic number on both sides) e.g.9Be + 4He 12C + 1n

    9Be + 1H 10B + 

baX+dcY feZ

b + d = f

a + c = e


Section 1 7 atoms molecules and stoichiometry

  • decay:

  • mass no.-4, atomic no. –2

  •  decay:

  • mass no. no change, atomic no. +1


Section 1 7 atoms molecules and stoichiometry

  • Half life:

    the time for the radiation to be halved, or for the radio-nuclei to be reduced to half.

  • Radioactive decay:

    ln Io / It = kt & k = ln 2 / t1/2

    (t1/2 : half life)


Uses of radioactivity

Uses of radioactivity

  • Leak detection

  • radiotherapy:  ray in cancer treatment

  • nuclear power

  • tracers: for studying metabolism in living organism

  • carbon-14 dating


1 3 relative isotoric atomic and molecular masses

1.3RELATIVE ISOTORIC, ATOMIC AND MOLECULAR MASSES

  • Isotope:atoms with the s______ number of protons but dif_____ numbers of neutrons.

  • Relative atomic mass:

    e.g. relative atomic mass of Cl atom = 0.75 * 35 + 0.25 * 37 = 35.5

  • Relative molecular mass:

    e.g. the relative molecular mass of water H2O = (2 * at. mass H) +(at. mass O)


Section 1 7 atoms molecules and stoichiometry

  • Mass spectrometer: used for the determination of relative masses of particles. It responds to the mass-charge ratio.

NOT mass!


Section 1 7 atoms molecules and stoichiometry

  • Mass spectrum:

    (i) y-axis  peak height (or relative intensity) is directly proportional to the % abundance of the ionized species (e.g. 14N+ or CO2+),

    (ii) x-axis  m/e ratio


1 4 the mole concept p v t relationships of gases

1.4 THE MOLE CONCEPT, P-V-T RELATIONSHIPS OF GASES

  • A mole: the amount of a substance (6.02 * 1023).

  • Avogadro’s law:equal volumes of gases at same conditions  equal no. of moles.

  • Molar volume of gas at s.t.p.:22.4 dm3 in volume.

  • Ideal gas equation:PV = nRT


Section 1 7 atoms molecules and stoichiometry

  • Relationship between density & molar mass:the ideal gas equation can be rewritten for the calculation of the gas density (, in g m-3 [or kg m-3]). For a gas of mass m (in g [or kg]) & a molar mass of M (in g mol-1 [or kg mol-1]), a volume of V (in m3) at a pressure P (Nm-2, Pa):

    PV =nRT &  =m/V  PV = (m/M)RT  P = (/M)RT


Section 1 7 atoms molecules and stoichiometry

  • Partial Pressure:in a gas mixture, the partial pressure of each component gas is the pressure that the gas would exert if it were the only gas occupying the total volume at that temperature.

  • Dalton’s Law of Partial Pressure:for three gases 1, 2 and 3 in mixture P total = P1+ P2 + P3

    rewritten as P total = (n1+n2+n3)(RT/V) = n total (RT/V)


Section 1 7 atoms molecules and stoichiometry

  • Mole fraction:

    the mole fraction (I) of a component in a mixture is defined as the no. of moles of that component over the total no. of moles of gases,

    i.e. 1 = n1/(n1+n2+n3) = n1/ntotal

  • Partial pressure of component gas i is given by Pi = i * P total where i = ni/ntotal


1 5 the faraday and the mole

1.5 THE FARADAY AND THE MOLE

  • Charge [Q] = current [I] *time [t]

    Unit: Cunit: Aunit: s

  • No. of moles of e- = no. of faradays = charge / 96500 C


1 7 chemical equations and stochiometry

1.7 CHEMICAL EQUATIONS AND STOCHIOMETRY

  • Primary standard: a substance that can be used to prepare a standard solution without standardization (i.e. by dissolving a known mass of that substance in a solvent to give a known volume of the solution, the molarity of that solution can be calculated), e.g. (COOH)2.2H2O [acid], aminosulphonic acid (sulphamic acid) NH2SO3H [acid], anhydrous Na2CO3(s) [base], K2Cr2O7(s) [OA], KIO3(s) [OA], Na2C2O4(s) [RA], Fe(NH4)2(SO4)2.6H2O ammonium iron(II) sulphate(VI)-6-water [RA]


Section 1 7 atoms molecules and stoichiometry

  • Primary stand must be very pure / with constant composition does not absorb moisture or lose water easily, stable in air, soluble.

  • Preparation of primary standard:

  • Standardization involving redox agents:

  • Preparation of standard I2(aq):

  • Titration of iodine (in flask) against thiosulphate (in burette)

  • Standardization of other oxidizing agents:

  • Back titration


Common errors in section 1

Common Errors in Section 1


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