Amount Of Substance Flashcards
What order should you balance an equation?
1) Metal
2) Non-Metal
3) Oxygen
4) Hydrogen
What is Avogadro’s Constant?
L
6.02x10^23
What is a mole?
1 mole of a substance is the amount of that substance which contains the same number of particles as there are carbon atoms in 12 grams of carbon-12
How to work out number of particles?
No. Particles = Avogadro’s Constant (L) x No. moles
How to work out Relative Atomic Mass?
RAM = Average mass of an atom of an element x12 divided by the mass of one atom of carbon 12
How do you work out the Relative Formula/ Molecular Mass of a compound?
Mr= Average mass of ‘entity’ x 12 divided by mass of one atom of carbon 12
What is electronegativity?
The power of an atom to attract the pair of electrons in a covalent bond
What is electronegativity scaled on?
What does this depend on?
The Pauling Scale
The nuclear charge of the atom
The Atomic radius of the atom
The number of PELs the atom has
The higher the nuclear charge of an atom the ______ the electronegativity
Greater
The smaller the radius of an atom the _____ the electronegativity
Greater
The fewer the number of PELs in an atom the _____ the electronegativity
greater
Which atom has the greatest electronegativity?
Why?
Florine (F)
It has a small radius with a high nuclear charge
When is a bond non-polar?
When the atoms are the same
What is an Ionic Bond?
A metal transfers it’s electrons to a non-metal and then there is a strong electrostatic force of attraction between the oppositely charged ions
What are the properties of ionic compounds?
1) Solid at room temperature as they have a giant ionic lattice structure and so their melting and boiling points are very high. This is due to the strong electrostatic attraction between oppositely charged ions
2) do not conduct electricity in solid state as ions aren’t free to move and carry charge
3) they are brittle and shatter upon impact - layers slide on impact so like charged ions line up
Describe metallic bonding
A lattice of positively charged metal ions attracted to a sea of delocalised electrons
What does delocalised mean
The electrons have no fixed position
If the charge is greater in an ion, what happens to its size
The greater the charge the smaller the ion
The number of delocalised electrons is proportional to those lost by the metal ions, how does this affect the bonding?
The more electrons donated the stronger the metallic bonding
Why do most metals have a high melting point
The strong electrostatic force of attraction between the positive ions and negative delocalised electrons
Why are metals good conductors
The delocalised electrons are free to move and flow - carry a current
How does the radius affect metallic bonds?
The smaller the radius, the stronger the bonding
Why are metals malleable and ductile?
The layers of ions can slide over each other
What is a covalent bond
The sharing of pair(s) of electrons between two atoms
How does sharing electrons make a bond?
There are more attractive forces than repulsive forces
Which is the strongest intermolecular force?
Weakest?
Hydrogen Bonding
Van der Waals
How do Van der Waals’ forces occur
Electrons are constantly moving and could all move to once side of a molecule so it suddenly becomes more negative - this is a temporary dipole. This means the electrons of the neighbouring molecule will be repelled, creating partial charges which attract the two molecules
What affects the strength of Van der Waals forces
Size of molecule (bigger = more VDW)
Mr of Molecule (bigger = more)
Surface area contact (more SA = more VDW)
Where is Dipole- Dipole forces found?
Why do they form?
In polar molecules only
Different electronegativity causes partial charges to form
Where does Hydrogen Bonding form?
Why?
It occurs between molecules which have a hydrogen directly bonded to Oxygen, Nitrogen, or Fluorine
Why elements are most electronegative so there is a big difference in electronegativity and so the electrons in the bond are pulled strongly towards them, leaving the hydrogen with a strong positive partial charge. The lone pair of electrons on a neighbouring molecule is attracted the hydrogen
When drawing hydrogen bonding, what must you remember?
To include:
All partial charges
All lone pairs
Hydrogen Bond clearly shown between the lone pair and positive hydrogen nucleus
Why is ice less dense than water?
H20 molecules spread out to form more hydrogen bonds. Water molecules are further apart on ice so there are more gaps/ spaces between molecules.
Acid + metal —>
salt + hydrogen
acid + oxide —>
salt + water
acid + metal hydroxide—>
salt + water
acid + metal carbonate —>
salt + water + CO2
acid + hydrogen carbonate —>
salt + water + CO2
acid + ammonia —>
ammonium salt
Metal carbonate —> (on heating)
metal oxide + CO2
When writing ionic equations, what must you do?
1) Split up aqueous ionic compounds (including acids) into separate ions
2) cancel out spectator ions (these appear on both sides)
3) write out final equation
In a reaction, which reagent is the limiting reagent?
The reagent that is not in excess
How do you work out the maximum mass?
1) Work out moles of all reactants
2) the one with the smaller amount of moles is the limiting reagent
3) work out the moles of the product(s) using the limiting reagent’s moles
How to work out density in g/cm3
Mass in g
—————
Volume in cm3
How to work out percentage yield
1) work out moles of reactant
2) use mole ratio to work out theoretical moles of product
3) use theoretical moles to work out theoretical mass
Actual mass
—————————- x100
Theoretical mass
How to convert from cm3 to dm3
Divide by 1000
What is the Relationship between concentration and Mr
Concentration in g/dm3 = concentration in mol/dm3 x Mr
What colour does phenolphthalein go in
a) acid
b) alkali
a) colourless
b) pink
What colour does methyl orange go in
a) acid
b) alkali
a) red
b) yellow
In a back titration how much of the products in the first reaction should be carried on to the second?
The unreacted amount
How to work out mass of an atom
Mass= Mr/ L
