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level: Masses of atoms and molecules (3.1 - 3.5)

Questions and Answers List

level questions: Masses of atoms and molecules (3.1 - 3.5)

QuestionAnswer
Scientists have defined unified atomic mass in terms of what isotope?Carbon-12
Unified atomic massone twelfth of the mass of a carbon-12
Relative atomic massratio of the average mass of the atoms of an element to the unified atomic mass units
Values of the relative atomic mass in the Periodic Table are determined by what...Determined by using the weighted average mass of the atoms of a particular elements
What term do we use for the mass of a particular isotope of an element which has the Avogadros number of atoms (6.02 x 10^23)Relative isotopic mass
How do we find the relative molecular massBy adding up the relative atomic masses of all the atoms present in one molecule
For silicon dioxide the formula is SiO2. This is also known as its?Formula units
What term do we use compounds containing ionsRelative formula mass
Compounds can form crystals which have water as part of their structure. What is this water called?Water of crystallisation
A compound containing water of crystallisation is called?Hydrated compounds
A compound which does not contain water of crystallisation is called?Anhydrous compounds
What is the main use of mass Spectrometry?Main use of mass spectrometry is in the identification of organic compounds.
What is fingerprinting?Other form of spectroscopy, a substance can be identified by matching its spectrum against the spectra of known substances stored in a database.
The peak at highest mass-to-change ratio is caused by the ....ion?Molecular ion
How is a molecular ion formed?A molecular ion is formed when 1 electron is removed from a molecule to form an ion with a single positive charge.
Fragmentation of a compound in a mass spectrometer causes what?Fragmentations of a compound in a mass spectrometer causes certain bonds to break
The breaking of single bonds such as C-C , C-O or C-N is the most common cause of what?Fragmentation
What does the formula of a compound show us?Formula of a compound shows us the number of atoms of each element present in one formula unit or one molecule of the compound
Explain Avogadro constantNumber of particles equivalent to the relative atomic mass or relative molecular mass of a substance in grams.
What is the numerical value for Avogadro constant6.02 x 10^23
Define term mole, in terms of Avogardros constant.A mole is the amount of substance which contains 6.02 x 10^23 specified particles
What is meant by the stoichiometry of the equation?Ratio of moles of the reactants and products
What do we use in order to find the mass of products formed in a chemical reaction? (3)- Mass of reactants - Molar mass of reactants - balanced equations
The reactant which has number of moles in excess is calledExcess reagent
The reactant which is not in excess is calledlimilting reagent
What must you remember in calculating which reactant is limiting? (2)- work out number of moles of reactant - take into account ratio of the reactants shown in equation (the stoichiometry)
Use the formula of a compound and relative atomic masses to calculate percentage by mass of a particular element in a compound.%by mass = Atomic mass x number of moles of particular elements in a compound ------------------------------------------------------------- Molar mass of compounds
In many chemical reactions, especially organic reactions, not all reactants are changed to products you want, why? (3)- other reactions going on at same time - reactants or products are lost in atmosphere - Reaction does not go to completion
What is the formula when calculating percentage yield?actual yield --------------------------------------------- x100 predicted yield (theoretical yield )
What is actual yieldmoles of product obtained by experiment
What is predicted yield?moles or mass of product obtained by calculation if no side products are formed and all of a specific reactants is converted to specific products
What is the empirical formula of a compound?Simplest whole number ratio of elements present in one molecule or formula unit of compound
In order to deduce the molecular formula we need to know what (2)?- relative formula mass of the compound - empirical formula