Module 2: Foundations in Chemistry Flashcards
Define relative molecular mass.
The mass of that specific molecule, relative to the mass of 1/12 of a carbon-12 atom.
Define relative atomic mass.
The weighted average mass of an atom of an element taking into account all of its naturally occurring isotopes relative to the mass of 1/12 of a carbon atom.
Why is the mass of an atom not proton+neutron+electron?
Due to the strong nuclear force holding protons and neutrons together, some mass is lost, and this is called mass defect.
Why are the radii of two isotopes of the same element the same?
They have the same number of protons and electrons.
What is the empirical formula of a compound?
The simplest whole number ratio of atoms present in a molecule of a compound.
What is the ideal gas equation?
PV=nRT
Define oxidation number.
The number of electrons involved in bonding an element to another.
What is the oxidation number of an element?
0
When is a reaction classified as redox?
In terms of electrons: Electrons are lost and gained
In terms of oxidation numbers: Oxidation numbers increase and decrease
What are the oxidation number exceptions?
- Hydrogen in metal hydrides: -1
- Oxygen in peroxides: -1
- Oxygen when bonded to fluorine: +2
Define disproportionation.
When a single element is both oxidised and reduced in a reaction.
How many electrons does an orbital hold?
Two, which spin in opposite directions.
What are the exceptions when writing electron configuration?
- 4s is filled before 3d, because it has less energy, however it also loses electrons before 3d.
- For chromium and copper, the 4s sub-shell only has one electron while the 3d sub-shell has five and ten electrons respectively. This is because this is more stable.
What is the shape of an S sub-shell and a P sub-shell?
- S: Spherical
- P: Dumbbell shaped
Which elements don’t follow the octet rule?
- 8 > Boron
- 8 < Sulfur
Define coordinate / dative covalent bonding.
When one atom provides both electrons in a covalent bond.
How does solubility change as ionic charge increases?
It decreases.
Are metals soluble in water?
No, they don’t dissolve, they react.
What shape and angle does a molecule with 0 LPs and 2 BPs have?
Shape: Linear
Angle: 180
What shape and angle does a molecule with 0 LPs and 3 BPs have?
Shape: Trigonal planar
Angle: 120
What shape and angle does a molecule with 1 LPs and 2 BPs have?
Shape: Non-linear
Angle: 119
What shape and angle does a molecule with 0 LPs and 4 BPs have?
Shape: Tetrahedral
Angle: 109.5
What shape and angle does a molecule with 1 LPs and 3 BPs have?
Shape: Trigonal pyramidal
Angle: 107
What shape and angle does a molecule with 2 LPs and 2 BPs have?
Shape: Non-linear
Angle: 104.5
What shape does a molecule with 0 LPs and 5 BPs have?
Shape: Trigonal bipyramidal
What shape does a molecule with 0 LPs and 6 BPs have?
Shape: Octahedral
Define electronegativity.
An atom’s ability to attract the electron density in a covalent bond to itself.
Define bond polarity.
Difference in electronegativity between two bonded atoms.
What is a dipole and when does a molecule have permanent dipole?
A dipole is the difference in charge as a result of bond polarity and a molecule had a permanent dipole when the charges don’t cancel out.
What are the three types of intermolecular forces?
- Induced dipole-dipole interactions (London forces)
- Permanent dipole-dipole interactions
- Hydrogen bonds
What types of bonds result in hydrogen bonds
- O-H
- N-H
- F-H
What modifications can be made to the method of an experiment where you are trying to find the water of crystalisation to make it more accurate?
-Use a greater mass of hydrated salt
-Use a scale with a higher resolution
-Keep heating until mass no longer changes
What is an acid?
Proton donor
What is a base?
Proton acceptor
What is an alkali?
Water soluble base, releases hydroxide ions in water
What is the difference between a strong acid and a weak acid?
A strong acid fully dissociates, while a weak acid partially dissociates
What does amphoteric mean?
Something that can behave as an acid or a base
What are the uses of titration?
- Finding concentration of solution
- Identification of unknown solution
- Finding the purity of a substance
What is a standard solution?
A solution of known concentration
What are concordant titres?
Titres with 0.1cm⁻³ of each other
Why is it important to fill the space below the tap in the burette before beginning an accurate titration?
It will fill during titration and cause titre to be too high and appear to have more moles of acid.
Why does rinsing the inside of the conical flask with water improve the accuracy of each titre?
Ensures no solution is lost / ensures all reagents are in the reaction mixture.
What indicators are used in titrations?
Phenolphthalein: Pink in strong alkalis, colourless once neutralised
Methyl orange: Orange in strong acids, colourless when neutralised
