Lecture 6 Flashcards
What are water molecules attracted to each other by?
Electrostatic interactions between the partial charges
A dipole-dipole interaction
In the water molecule what atom is more electronegative?
Oxygen so the electrons are closer to oxygen than the hydrogen atoms
What are the dipole-dipole interactions in water called?
Hydrogen bonding
Unusually strong
Is water a polar molecule?
Yes
What is unusual about waters density?
It is more dense when it is melted
So solid floats in liquid
What is unusual about waters properties?
It has very high melting and boiling points
Why does water have such high melting and boiling points?
Because of the strong hydrogen bonding
What happens to the freezing point of water when the pressure increases?
It decreases
Eg ice skater melts ice
What is key about waters surface tension and heat capacity?
They are very large
Water retains its heat
What is unusual about waters concentration?
It is very high 55.5molL at 25 degrees
What do the molecules in liquid water do?
Move around close to each other
Making/breaking hydrogen bonds
What do the molecules in solid water do?
Held rigidly in a structure that maximises the possible number of hydrogen bonds.
Which structure liquid or solid water is more open and less dense?
Solid (ice)
Is water a good solvent for electrolytes?
Yes
What is an electrolyte?
Substances that give ons when dissolved
What happens when NaCl is out in water?
It dissolves spontaneously despite strong electrostatic forces holding NaCl together
What does solvation (water as a solvent) do to high energy ions?
Helps stabilise the ions
How does solvation stabilise ions?
Interaction of charged ions with the dipoles of water molecules
What are all ions in water surrounded by?
Water molecules
When water is a solvent, what is this called?
Hydration
Why is water a good solvent for polar molecules?
Because ‘like’ polarity dissolves in each other
Are non-polar molecules generally soluble?
No but their solubility is not zero
Why are non-polar molecules sometimes soluble in water?
The permanent dipole of water can induce a dipole in the non-polar molecule
What does the magnitude of the induced dipole on non-polar molecules depend on?
The size (number of electrons) and shape of the gas molecule
What is a solution?
When one or more chemical species dissolve in a liquid
What is a solute?
A substance that dissolves in a liquid. Can be solid, liquid or gas
What is a solvent?
A liquid in which the solute dissolves
What is a dilute solution?
Has less amount (mol) solute than solvent
What is a non-electrolyte?
Dissolves without the formation of ions eg glucose/urea
What are the two types a solute can be classified as?
Electrolyte
Non-electrolyte
What can the electrolyte be?
Weak (partially dissociated)
Strong (completely dissociated)
What do non-electrolyte molecule do in water?
- uniformly distribute
- unchanged in bonding
- no ions formed
If ionic solids are not very soluble in water are they still considered strong electrolytes?
Yes because all the solid dissolves completely dissociated to ions
