module 2 Flashcards
isotope definition
atoms of same element with different numbers of neutrons and different masses
why do isotopes all react in same ways
- diff isotopes of same element have same number of electrons but diff number of neutrons
- the number of neutrons in an element has no effect on reactions of an element
relative isotopic mass definition
mass of an isotope relative to 1/12th of the mass of an atom of carbon 12
relative atomic mass definition
- also known as Ar
- weighted mean mass of an atom of an elememt relative to 1/12th of the mass of an atom of carbon 12
how does a mass spectrometer work
- sample is placed in mass spectrometer
- sample is vapourised then ionised to form positive ions
- the ions are accelerated. heavier ions move more slowly and are more difficult to deflect than lighter ions so the ions of each isotope are separated.
- the ions are detected on a mass spectrum as a mas to charge ratio (m/z).
- each ion reaching the detector adds a signal so the greater the abundance, the larger the signal
binary compound
contains two elements only
ammonium ion charge
NH4 1+
hydroxide ion
OH-
nitrate ion
NO3 1-
carbonate ion
CO3 2-
sulfate ion
SO4 2-
manganate ion
MnO4 1-
dichromate ion
Cr2O7 2-
what is avogadros constant
6.02 x 10 ^23
its the number of particles in each mole of carbon 12
equation linking mass, mole and Mr
moles = mass / molar mass (Mr)
molecular formula
number of atoms of each element in a molecule
empirical formula
simplest whole number ratio of atoms of each element in a compound
relative molecular mass
compares mass of molecule with mass of an atom of carbon 12
relative formula mass
compares mass of a formula unit with mass of an atom of carbon 12
what are some assumptions/reasons why real experiments might not give u the same water of crystalisation number/ratio
- we assume all the water has been lost. good solution is to heat till constant mass when the crystals are reheated till the mass of the residue no longer changes suggesting all water has been removed
- many salts can decompose further when heated such as wen u heat copper sulfate, it can decompose to form black copper oxide, this can be difficult to judge if theres no colour change
equation linking concentration moles and volume
conc = mols / volume
what is the molar gas volume
volume per mole of gas molecules at a stated temperature and pressure
what is the molar gas volume at room temperature and pressure
24dm3/mol
v in dm3 -> V/24
v in cm3 -> V/24000
ideal gas equation
pV = nRT
p is pressure in Pa
V is volume in metres cubed
n is amount of gas molecules
R is ideal gas constant = 8.31
T is temperature in kelvin (degrees c + 273)
what are the assumptions made for the molecules making up an ideal gas constant
- random motion
- elastic collisions
- negligible size
- no intermolecular forces
reasons why theoretical yield from percentage yield is not made
- reaction may not have gone to completion
- other side reactions may have taken place alongside main reaction
- purification of the product may have resulted in loss of some product
what is a strong acid
an acid that releases all its hydrogen atoms into solution as H+ ions and completely dissociates in aqueous solution
what is a weak acid
it only releases a proportion of its available hydrogen atoms into solution as H+ ions. it partially dissociates in aqueous solution
what is an alkalai
a base that dissolves in water releasing hydroxide ions into the solution.
acid + alkalai
salt + water
- same as metal oxides.
- H+ + OH- -> H20
acid + carbonate
salt + water + carbon dioxide
three things that titrations can be used for
- finding concentration of a solution
- identifying unknown chemicals
- finding purity of a substance
what is a standard solution
- a solution of known concentration
how to prepare a standard solution
- weigh solid accurately
- dissolve solid in a beaker using less distilled water than will be needed to fill volumetric flask
- transfer this solution to volumetric flask and rinse the last traces of the solution with distilled water
- carefully fill flask to graduation line by adding distilled water drop by drop till bottom of meniscus lines up exactly with mark
- place lid and slowly invert the volumetric flask several times to mix solution thoroughly
what would happen if too much water is added to the volumetric flask
the solution will be too dilute and must be prepared again
what would happen if u do not invert the volumetric flask before performing your titration
the titration results are unlikely to be consistent as solution is not mixed thoroughly enough
oxidation number of oxygen
- normally -2
- in peroxides it is -1
- when bonded to F it is +2
oxidation number of hydrogen
- normally +1
- in metal hydrides it is -1
oxidation number of fluorine
always -1
