Chemistry Definitions

  • Created by: elbungay1
  • Created on: 26-05-19 13:53
Define Relative Atomic Mass
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of Carbon-12
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Relative Isotopic Mass
The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12
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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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Avogadro Constant
The number of atoms per mole of the carbon-12 isotope. 6.02x10(23)
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Molar Mass
The mass per mole of a substance. Units are gmol(-1)
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Molar Gas Volume
Volume per mole of gas. The units of molar volume are dm(3)mol(-1). At room temperature and pressure, the moalr volume is approximately 24.0 dm(3)mol(-1)
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Ideal gas Equation
pV=nRT p=pressure in pascals V=volume in m(3) n=number of moles R=gas constant T=Temperature in Kelvin
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Percentage Yield
Actual amount, in mol, of a product / theoretical amount, in mol, of a product x 100
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Chemical compound formed from an acid when a H+ ion from the acid has been replaced by a metal ion or another positive ion
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Hydrated Salt
Crystalline compound containing water molecules
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Substance that contains no water molecules
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Water of Crystallisation
Water molecules that form an essential part of crystalline structure of a compound
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Region of space within an atom that can hold up to two electrons with opposite spins
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A group of atomic orbitals with the same principal quantum number, n.
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Covalent Bond
A bond formed by a shared pair of electron
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Dative Covalent Bond
A bond formed by a shared pair of electrons that has been provided by one of the bonding atoms only. Also known as coordinate bond
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Ionic Bond
Electrostatic forces of attraction between oppositely charged ions
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Trend in properties that is repeated across each period
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First ionisation energy
Energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
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Oxidation and reduction of the same element in a redox reaction
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Enthalpy, H
The heat content that is stored in a chemical system
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Exothermic Reaction
enthalpy of products is smaller than enthalpy of reactants. Heat loss from chemical system to surroundings. ΔH is negative
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Endothermic Reaction
Enthalpy of products is greater than enthalpy of reactants. Heat gain to the chemical system from surroundings. ΔH has a positive sign because heat has been gained
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Activation energy
The minimum energy required to start a reaction by breaking bonds in reactants
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Enthalpy Change of Reaction
The energy change associated with a given reaction
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Enthalpy change of formation
Energy change that takes place when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions
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Enthalpy change of combustion
Energy change that takes place when 1 mole of a substance in its standard states is completely combusted in oxygen.
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Enthalpy change of neutralisation
Energy change associated with the formation of one mole of water from a neutralisation reaction.
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Quantitative study of energy in a chemical reaction. q=mcΔT q=heat echanged with surroundings (J) m=Mass of substance c=specific heat capacity ΔT=change in temperature
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Specific Heat Capacity
Energy required to raise the temperature of 1g of a substance by 1K
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Average Bond Enthalpy
Mean energy required for 1 mole of a given type of gaseous bond to undergo homolytic fission
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Hess' Law
The enthalpy change in a chemical reaction is independent of the route it takes
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A substance that increases the rate of reaction without being used up during the process
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Dynamic Equilibrium
Concentrations of the reactants and the products remain constant. Rate of forward reaction is the same as the rate of the reverse reaction
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Boltzmann Distribution
Distribution of energies of molecules at a particular temperature, often shown as a graph
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Le Chatelier's Principle
When a system in dynamic equilibrium is subjected to change, the position of equilibrium will shift to minimise the change
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Homologous series
Substances have the same functional group/general formula and successive members differ only by a CH2 unit
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Aliphatic Hydrocarbon
Carbon atoms are joined together in either straight (unbranched) or branched chains
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Alicyclic Hydrocarbon
Carbon atoms are joined together in a ring structure but are not aromatic
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Aromatic Hydrocarbon
There is at least one benzene ring in the structure
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General formula
Simplest algebraic formula for all the organic compounds in a homologous series and can be used to generate molecular formula
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Organic chemicals that contain at least one carbon=carbon double bond
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Compounds that contain only hydrogen and carbon atoms
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Organic compounds that contain only single covalent bonds
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Structural Isomers
Compounds with the same molecular formula but different structural formulae
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Functional Group
Group of atoms that are responsible for the characteristic reactions of a compound
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Organic compounds with the same molecular formula and structural formula but with different arrangements of atoms in space
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E/Z Stereoisomerism
Type of stereoisomerism caused by the restricted rotation around the double bond - two different groups are attached to both carbon atoms of the C=C double bond
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Cis-trans isomerism
A type of E/Z isomerism in which the two substituent groups attached to both carbon atoms are the same.
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Reaction Mechanism
Models that show the movement of electron pairs during a reaction
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Curly Arrow
Model the flow of electrons during reaction mechanisms
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Homolytic fission
Happens when each bonding atom receives one electron from the bonded pair, forming two radicals
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Heterolytic Fission
Happens when one bonding atom receives both electrons from the bonding pair
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Complete combustion
Oxidising a fuel in a plentiful supply of air. Forming CO2 and H2O only
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Incomplete Combustion
Oxidising a fuel in a limited supply of air. Forming a mixture of C, CO, CO2 and H2O
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Electron-pair acceptor
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Addition reaction where hydrogen is added across a C=C double bond. Typically requires 150°C and Nickel catalyst
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Addition reaction in which a halogen is added across C=C double bond
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Addition reaction between a gaseous alkene and steam to form an alcohol. Typically requires 300°C, 65atm and H3PO4 catalyst
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Small molecules that are used to make polymers
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Macromolecules made from small repeating units
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Repeating Unit
Specific arrangement of atoms that occurs in a structure over and over again
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Materials are affected by the action of microorganisms and environmental conditions, leading to decomposition
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Material made from renewable source that is biodegradable
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Primary Alcohol
Has the functional group attached to a carbon atom with no more than one alkyl group
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Secondary Alcohol
Functional group attached to a carbon atom with two alkyl groups
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Tertiary Alcohol
Functional group attached to carbon atom with three alkyl groups
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Constant boiling and condensing of a reaction mixture. This ensures that the reaction goes to completion as fully as possible without losing reactants or products as vapour to the air
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Chemical reaction in which water is lost from an organic compound. Alcohols are dehydrated to alkenes. Requires 170° and H2SO4 catalyst
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Electron-pair donors
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Nucleophilic Substitution
Chemical reaction in which an atom or group of atoms is exchanged for a nucleophile
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Highly reactive species with one or more unpaired electrons
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Separating Funnel
Piece of equipment that separates immiscible liquids
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Molecular Ion, M+
Positive ion formed in mass spectroscopy when a molecule loses an electron. M+ has equal mass to RMM of the compound
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Rate of Reaction
Change in concentration of a reactant or a product per unit time
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The order with respect to a reactant is the power to which the concentrations of the reactant is raised in the rate equation
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Rate Constant, k
Constant that links the rate of reactions with the concentrations of the reactants raised to the powers of their orders in the rate equation
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Overall Order
Sum of the individual orders
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Time taken for the concentration of the reactant to reduce by half
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Rate-determining step
Slowest step in the reaction mechanism of a multi-step reaction
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Arrhenius Equation
Used to describe mathematically the exponential relationship between rate constant and temperature. k=Ae^(-Ea/RT) A=pre-exponential factor Ea=activation energy R=gas constant T=temperature in kelvin
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Homogeneous Equilibrium
Equilibrium in which all the species making up the reactants and products are in the same physical state.
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Heterogeneous Equilibrium
Equilibrium in hwich species making up the reactants and products are in different physical states
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Mole Fraction
Measure of how much of a given substance is present in a reaction mixture. Mole fraction = number of moles of A / total number of moles
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Partial Pressure
Pressure of an individual gaseeous substance would exert if it occupies a whole reaction vessel on its own. Pa = mole fraction x total pressure
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Bronsted-Lowry Acid
Proton, H+, Donor
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Bronsted-Lowry Base
Proton, H+, Acceptor
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A base that dissolves in water forming OH- ions
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Strong Acid
Acid that completely dissociates in solution
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Weak Acid
Acid that partially dissociates in solution
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Logarithmic scale to measure concentrations of H+. -log[H+]
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Ionic Product of Water
At 25°C [H+][OH-] = 1.00x10(-14)
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Buffer Solution
Mixture that minimises pH changes on addition of small amounts of acid or base.
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Equivalence Point
Point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution. This matches the stoichiometry of the reaction taking place.
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End Point
Point in a titration at which there are equal concentrations of the weak acid and conjugate base forms of the indicator. The colour at teh end point is midway between the colours of acid and conjugate base forms.
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Lattice Enthalpy ΔleH
Enthalpy change that accompanies the formation of one moles of an ionic lattice from its gaseous ions under standard conditions
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The standard Enthalpy Change of Atomisation
One mole of gaseous atoms is formed from its element in its standard states
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The second ionisation energy Δl2H
One mole of gaseous 2+ ions are formed from one mole of gaseous 1+ ions
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The first electron affinity Δea1H
One mole of gaseous 1- ions are formed from gaseous atoms
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The second electron affinity Δea2H
One mole of gaseous 2- ions is formed from gaseous 1- ions. Endothermic because electron is repelled.
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The standard enthalpy change of solution
Enthalpy change that takes palce when one mole of a solute is completely dissolved in water under standard conditions
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Standard Enthalpy change of Hydration
Enthalpy change that takes place when dissolving one moles of gaseous ions in water
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Quantitative measure of degree of disorder in a system
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Standard Entropy
Standard entropy of a substance is the entropy content of one mole of the substance under standard condition
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Standard Entropy change of reaction ΔS
Entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products in standard states. ΔS = ΣS products - ΣS reactants
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Free Energy Change, ΔG
Balance between enthalpy, entropy and temperature for a process. ΔG = ΔH - TΔS. Process can react spontaneously when ΔG< 0
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Loss of electrons, or an increase in oxidation number
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Gain of electrons, decrease in oxidation number
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Oxidising Agent
Species that is reduced in a reaction and causes another species to be oxidised
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Reducing Agent
Species that is oxidised in a reaction and causes another species to be reduced
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The Standard electrode potential of a half cell
The e.m.f of a half cell compared with a standard hydrogen half cell, measure at 298K with solution concentrations of 1 mol dm^(-3) and a gas pressure of 100 kPa
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Transition Element
D-blcok element that has an incomplete d-sub-shell as a stable ion
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Complex Ion
A transition metal ion bonded to one or more ligands by coordinate bonds
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A molecule or ion that can donate a pair of electrons to the transition metal ion to form a coordinate bond
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Coordination Number
Total number of coordinate bonds formed between a central metal ion and its ligands
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Ligand Substitution
Reaction in which one ligand in a complex ion is replaced by another ligand
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Simplified version that allows us to make predictions and understand observations more easily
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Electrophilic Substitution
Substitution reaction where an electrophile is attracted to an electron-rich atom or part of a molecule and a new covalent bond is formed by the electrophile accpting an electron pair
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Electrophilic substitution reaction where a hydrogen atom is exchanged for a nitro group. In nitration of Benzene, conc. HNO3 and H2SO4 is required. In phenol, only dilute HNO3 required
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Friedl-Crafts Reaction
A substitution reaction where hydrogen is exchanged for an alkyl or acyl chain
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Directing Effect
How a functional group attached directly to an aromatic ring affects which carbon atoms are more likely to undergo substitution
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A chemical reaction where water causes the breaking of bonds, in a decomposition reaction
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Alkylammonium Salt
Compound where the hydrogen(s) on an ammonium ion have been substituted by alkyl chains
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Optical Isomers
Molecules which are non-superimposible mirror images of each other. They have the same chemical properties but interact with polarised light differently
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Chiral Carbon
Has four different groups attached to it
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Condensation Polymerisation
Chemical reaction to form a long-chain molecule by elimination of a small molecules, such as water
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Organic chemical with a -CN functional group
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Technique used to separate miscible liquids or solutions
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Rf Value
Distance moved by component / distance moved by solvent
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Retention Time
Time between injection and detection of a component in gas chromatography
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Internal standard for both carbon and proton NMR
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Chemical Shift
Scale that compares the frequency of NMR absorption with the frequency of the reference peak of TMS
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Isotope of Hydrogen and does not produce a signal in the proton NMR spectrum
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Equivalent Protons
Hydrogen atoms bonded to the same atoms that therefore experience the same magnetic field in the NMR spectrometer
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Card 2


Relative Isotopic Mass


The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12

Card 3




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Card 4


Avogadro Constant


Preview of the front of card 4

Card 5


Molar Mass


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