Module 2 key information Flashcards
What is the relative mass of a proton, neutron and electron?
Proton= + 1 neutron= 1 electron= 1/1836
What is the charge of a proton, neutron and electron?
Proton= +1 neutron = 0 electron= -1
What is an isotope?
Atoms of the same element with different numbers of neutrons but the same number of protons.
So the same atomic number but a different mass number.
Do isotopes have the same properties?
They have similar chemical properties because of the same electronic configuration
They have slightly different physical properties because of the different masses
What is relative isotopic mass?
The mass of an isotope relative to 1/12th of the mass of an atom on carbon-12
What is relative atomic mass?
The weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12
What is relative molecular mass?
(Mr)= the sum of all atomic masses in the molecule
Used for simple molecules
What is relative formula mass?
sum of all atomic masses in the molecule
Used for compounds with giant structures
How to complete mass spec?
the sample is vaporized, ionised, accelerated, deflected, detected
What is mass spec used to find out?
relative isotopic masses and abundance
What is the nitrate ion?
NO3-
What is the sulphate ion?
SO4(2-)
What is the carbonate ion?
CO3(2-)
What is the hydroxide ion?
OH-
What is the ammonium ion?
NH4(+)
What is the zinc ion?
Zn2+
What is the silver ion?
Ag+
What is the charge on a tin or lead ion?
+2
How to balance a chemical equation?
1) balance metals
2) balance non-metals except oxygen and hydrogen
3) balance oxygen and hydrogen
What are the units for molar mass?
g mol-1
How to convert cm3 to dm3?
divide by 1000
How many cm3 is 1ml?
1cm3=1ml
How to convert cm3 to m3?
divide by 1000 then divide by 1000 again
What is the empirical formula?
The simplest whole-number ratio
What is the molecular formula?
the number and types of atoms of each element in a molecule
How to work out moles from mass?
mass= mr X mol
What is Avogadro’s constant?
The number of particles per mol
= 6.02 x 10(23)
How to work out the number of particles?
moles x Avogadro’s constant
How to work out the volume using molar gas volume?
Molar gas volume ( at rtp it is 24 in dm3) x mol
How to work out the moles using concentration?
Moles= concentration x volume
What is the ideal gas equation?
PV= nRT P= pressure in pascals V= volume in m3 n= moles R= gas constant (8.314) T= tempreture in Kelvin
How to convert degrees to kelvin?
+273
What does anhydrous mean?
Contains no water molecules in the structure
What does hydrated mean?
Contains water molecules in its crystalline structure
What is water crystallisation?
a number of water molecules present in a crystalline structure.
How to carry out the water of crystallization?
weight out the empty crucible
add the hydrates salt into the weighed crucible and then weigh again
pipe-clay triangle to heat gently then strongly
leave crucible to cool and then weigh anhydrous and crucible
What assumptions do we make when carrying out the water of crystallisation?
1) How do you know all the water has been extracted ( heat till mass is constant)
2) There may be further decomposition ( colour change)
How to calculate the formula of hydrated salt from percentage composition?
100%- percentage composition= % composition of the other molecule.
divide percentage by molar mass and compare the ratio
eg: 36%/18
How to calculate the formula of the hydrated salt from the mass composition?
the molar mass of the whole composition - the molar mass of the salt= molar mass of H20
the molar mass of water/ 18= ratio
Why gas syringe can be inaccurate?
1) gas can escape before you insert the bung
2) some gasses dissolve
How to calculate the percentage yield?
(Actual yield/ theoretical yield) x100
Why a reaction may not reach its theoretical yield?
1) reaction may not be completed
2) Other side reactions
3) Purification methods have resulted in the loss of some of the products
How to work out the atom economy?
Sum of molar masses of desired products/Sum of molar masses of all products
*MAKE SURE TO HAVE A BALANCED EQUATION
What is the atom economy of a reaction that produces only 1 product?
100%
Why the atom economy and percentage yield is important?
Sustainability of natural resources to improve efficiency
You can get a large proportion of your desired product and little waste
Makes industrial processes more efficient
Preserves raw materials
Reduces waste
What is an acid?
Release H+ into aqueous solutions therefore is a proton donor
What is a strong acid?
An acid that completely dissociates in aqueous solutions to form H+ and anions
HCL
H2SO4
HNO3
What is a weak acid?
An acid that partially dissociates in aqueous solutions
CH3COOH
What is a base?
Neutralises an acid to form a salt
What is an alkali?
a base that dissolves in water, releasing hydroxide ions into the solution
What is the ionic equation for neutralisation reactions?
H+ + OH- ————H20
What is an amphoteric substance?
Substances that act as bases and acids
What is titration?
A volumetric analysis method can be used to determine the exact volume of one solution that is required to react exactly with another
Why is titration used?
Finding the concentration of a solution
Identification of unknown chemicals
Finding the purity of a substance
What is the standard solution?
The standard solution of known concentration
How to make a standard solution?
Solid is weighed accurately
dissolved in a beaker with distilled water
It is transferred to a volumetric flask
Wash beaker and glass rod with distilled water and add to the volumetric flask
Fill flask till graduation line until the bottom of meniscus reaches the line
Invert the volumetric flask slowly
How to carry out titration?
- Add the measured volume of one solution to a conical flask with a pipette.
- Add the other solution to a burette, and record the initial burette reading to the nearest 0.05cm3.
- Add a few drops of indicator to the solution.
- Run the solution in the burette into the solution in the conical flask, swirling the conical flask throughout to mix the solutions. The endpoint of the titration is when the indicator changes colour.
- Record the final burette reading. The volume of solution added from the burette is the titre, calculated by doing: initial burette reading - final burette reading.
- A quick titration is first carried out to find the approx. titre.
- The titration is repeated. Further titrations are carried out until the two accurate titres are concordant (agreeing to 0.10cm3)
How to calculate the unknown concentration of the solution in a conical flask?
Pipette 25.00cm3 of 0.100 mol dm-3 KOH(aq) Mean titre from burette 25.70cm3 of H2SO4(aq) Unknown information? Concentration of H2SO4
Calculation:
n(KOH) = c x V/1000 = 0.100 x 25.000/1000 = 0.00250 mol
2KOH(aq) + H2SO4(aq) → K2SO4(aq) + 2H2O(l)
2 mol 1 mol
0.00250 mol : 0.00125 mol
3. n(H2SO4) = c x V/1000
c = 1000 x n/V = 1000x0.00125/25.70
= 0.0486 mol dm-3
therefore the concentration of H2SO4(aq) is 0.0486 mol dm-3
What is the oxidation number of an element?
0
Is the +/- before the oxidation number?
before
What is the oxidation of H in metal hydrides?
-1
What is the oxidation of O in peroxides?
-1
What is the oxidation of O bonded to F?
+2
What is does oxidation and reduction mean in terms of electron transfer
Reduction: gain of electrons
Oxidation: loss of electrons
What is does oxidation and reduction mean in terms of changes in oxidation number?
Reduction: decrease in oxidation number
Oxidation: increase in oxidation number
What is an orbital?
The region around the nucleus which can hold up to 2 electrons with opposite spins.
What are nodes?
Space where electrons cannot exist between electron shells
What is the shape of the S-orbital?
Spherical
What is the shape of the P-orbital?
Dumbell shape
How many different d-orbitals are there?
5
How many different f-orbitals are there?
7
Why does 4s orbital fill before 3d?
3d comes after 4s because 3d is at a higher energy level, so 4s fills first
*Electron configuration focuses on the shell order rather than the order of filling and so 3d comes before 4s, even though 4s fills first.
Why is chromium an exception in its electron configuration?
Chromium should be [Ar]3d4 4s2
BUT chromium [Ar]3d5 4s1
It is energetically more favourable to have full d orbitals half full S orbital
Why is copper an exception in its electron configuration?
[Ar]3d9 4s2
BUT copper [Ar]3d10 4s1
What is an ionic bond?
electrostatic attraction between oppositely
What is a giant ionic lattice?
A repeating pattern of oppositely charged ions held together by the electrostatic force of attraction
What are the physical properties of ionic compounds?
—-High melting and boiling point (solid)
High temperatures (= high energy) is needed to overcome the strong electrostatic attraction between the ions
–Soluble (solid)
Often dissolve in polar solvents
Ionic lattice must be broken down → water molecules attract and surround ions
—-Electrical conductivity
Solid ionic compounds do not conduct electricity because there are no mobile charge carriers as ions are in fixed positions
When liquid or aqueous, they do conduct electricity
Because the lattice breaks down, allowing the ions to move as charge carriers
What is a covalent bond?
the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Why do atoms want to form covalent bonds?
energy is released so they become more stable after each covalent bond is made
What bond is between N2?
triple bond
What is a dative covalent bond?
A covalent bond in which both of the electrons in the share have been provided by the same atom
What’s another word for a dative bond?
Co-ordinate bond
3 bond pairs?
trigonal planar
120 degrees
4 bond pairs?
tetrahedral
109.5 degrees
3 bond pairs and 1 lone pair?
Pyramidal
107 degrees
2 bond pairs and 2 lone pairs?
Non-linear
104.5 degrees
6 bond pairs?
Octahedral
90 degrees
2 bond pairs?
linear
180 degrees
What is electronegativity?
the ability of an atom to attract the bonding electrons in a covalent bond;
What is a dipole?
A dipole is a separation of opposite charges
What effects electronegativity?
nuclear charge
Atomic radius
How to know if a molecule is polar?
Polar bonds
asymmetrical
What is Induced dipole-dipole interactions (London forces)
In polar and non-polar molecules
Electrons at any instant of time move closer to one atom=instantaneous dipole
What affects the strength of Induced dipole-dipole interactions (London forces)
The number of electrons
The shape of the molecule
What are the Permanent dipole-dipole interactions?
Only in polar molecules
One of the bonded atoms is more electronegative than the other.
Between molecules
Why is the boiling point of molecules that have PDD higher than those that only have IDD?
Boiling points are higher in compounds with permanent dipole-dipole interactions because extra energy is needed to break it
What is hydrogen bonding?
intermolecular bonding between molecules containing N, O or F and the H atom of –NH, –OH or HF
What is the solubility rule of simple molecular substances?
like dissolves like
What are the anomalous properties of water
ice is less dense than water
H bonds hold water molecules apart in an open lattice structure
Water molecules in ice are further apart than in water
its relatively high melting and boiling points due to relatively strong bonding
Can covalent compounds conduct electricity?
Electrical conductivity
No mobile charged particles = non-conductors of electricity
