Lecture 6

Question 0

What are water molecules attracted to each other by?

Answer 0

Electrostatic interactions between the partial charges

A dipole-dipole interaction

Question 1

In the water molecule what atom is more electronegative?

Answer 1

Oxygen so the electrons are closer to oxygen than the hydrogen atoms

Question 2

What are the dipole-dipole interactions in water called?

Answer 2

Hydrogen bonding

Unusually strong

Question 3

Is water a polar molecule?

Answer 3

Yes

Question 4

What is unusual about waters density?

Answer 4

It is more dense when it is melted

So solid floats in liquid

Question 5

What is unusual about waters properties?

Answer 5

It has very high melting and boiling points

Question 6

Why does water have such high melting and boiling points?

Answer 6

Because of the strong hydrogen bonding

Question 7

What happens to the freezing point of water when the pressure increases?

Answer 7

It decreases

Eg ice skater melts ice

Question 8

What is key about waters surface tension and heat capacity?

Answer 8

They are very large

Water retains its heat

Question 9

What is unusual about waters concentration?

Answer 9

It is very high 55.5molL at 25 degrees

Question 10

What do the molecules in liquid water do?

Answer 10

Move around close to each other

Making/breaking hydrogen bonds

Question 11

What do the molecules in solid water do?

Answer 11

Held rigidly in a structure that maximises the possible number of hydrogen bonds.

Question 12

Which structure liquid or solid water is more open and less dense?

Answer 12

Solid (ice)

Question 13

Is water a good solvent for electrolytes?

Answer 13

Yes

Question 14

What is an electrolyte?

Answer 14

Substances that give ons when dissolved

Question 15

What happens when NaCl is out in water?

Answer 15

It dissolves spontaneously despite strong electrostatic forces holding NaCl together

Question 16

What does solvation (water as a solvent) do to high energy ions?

Answer 16

Helps stabilise the ions

Question 17

How does solvation stabilise ions?

Answer 17

Interaction of charged ions with the dipoles of water molecules

Question 18

What are all ions in water surrounded by?

Answer 18

Water molecules

Question 19

When water is a solvent, what is this called?

Answer 19

Hydration

Question 20

Why is water a good solvent for polar molecules?

Answer 20

Because ‘like’ polarity dissolves in each other

Question 21

Are non-polar molecules generally soluble?

Answer 21

No but their solubility is not zero

Question 22

Why are non-polar molecules sometimes soluble in water?

Answer 22

The permanent dipole of water can induce a dipole in the non-polar molecule

Question 23

What does the magnitude of the induced dipole on non-polar molecules depend on?

Answer 23

The size (number of electrons) and shape of the gas molecule

Question 24

What is a solution?

Answer 24

When one or more chemical species dissolve in a liquid

Question 25

What is a solute?

Answer 25

A substance that dissolves in a liquid. Can be solid, liquid or gas

Question 26

What is a solvent?

Answer 26

A liquid in which the solute dissolves

Question 27

What is a dilute solution?

Answer 27

Has less amount (mol) solute than solvent

Question 28

What is a non-electrolyte?

Answer 28

Dissolves without the formation of ions eg glucose/urea

Question 29

What are the two types a solute can be classified as?

Answer 29

Electrolyte

Non-electrolyte

Question 30

What can the electrolyte be?

Answer 30

Weak (partially dissociated)

Strong (completely dissociated)

Question 31

What do non-electrolyte molecule do in water?

Answer 31

• uniformly distribute
• unchanged in bonding
• no ions formed

Question 32

If ionic solids are not very soluble in water are they still considered strong electrolytes?

Answer 32

Yes because all the solid dissolves completely dissociated to ions