7. Solutions Flashcards
1
Q
The Physical State of Matter Depends on ……….
A
…..a balance between the kinetic energy of particles, which tends to keep them apart, and the attractive forces between them, which tends to bring them together
2
Q
The Gaseous State
A
- kinetic energy increases as temperature increases
- at high temperatures, particles possess a high kinetic energy and move so fast that the attractive forces between them are too weak to hold them together - the gaseous state
3
Q
The Liquid State
A
- at lower temperatures, less kinetic energy means particles move more slowly to the point where the forces of attraction between them have some effect. When the temperature is low enough, a gas will condense - the liquid state
4
Q
The Solid State
A
- when the temperature is even lower, particles don’t have enough kinetic energy to counteract the attractive forces between them, and so the particles stop moving past each other. Each particle will have a set of nearest neighbours that will not change - the solid state
5
Q
Solution
A
- an homogeneous mixture whereby a solute is dissolved in a solvent
- distribution of particles in a solution is uniform ie. every part of the solution has the same composition and properties
- components of a solution do not separate upon standing
- solution cannot be separated into its components by filtration
- for any given solute and solvent, it is possible to make solutions of many different compositions
- solutions are almost always transparent
- solutions can be separated into pure components by methods such as distillation and chromotography
- separation is a physical change, not chemical.
6
Q
Solvent
A
- generally the substance in a solution that is present in largest quantity
- if one substance is a liquid, it is normally considered to be the solvent
- when water is present, it is assumed to be the solvent
7
Q
Solute
A
- a substance dissolved in a solvent
8
Q
Solubility
A
- the maximum amount of solute that can be dissolved in a solvent at a specific temperature and pressure
- a physical property
9
Q
Saturated Solution
A
- a solution that contains as much dissolved solute as it can hold while in equilibrium with undissolved solute
10
Q
Supersaturated Solution
A
- a solution in which there is more solute in the solvent than it can normally hold at a given temperature under equilibrium conditions
- a supersaturated solution is unstable and when disturbed the excess solute will precipitate + the solution will return to equilibrium ie. a saturated solution
11
Q
Miscible
A
- two liquids are said to be miscible if they are soluble in each other in all proportions
12
Q
Factors Affecting Solubility
A
- ‘like dissolves like’
- temperature
- pressure
13
Q
- ‘Like Dissolves Like’
A
- polar compounds dissolve in polar solvents because the positive dipole of one molecule will be attracted to the negative dipole of another molecule
- non-polar compounds dissolve in non-polar solvents
14
Q
- Temperature
A
- in general, the solubility of most solid + liquid substances in a liquid solvent increases with increasing temperature
- for gases in liquids, increasing the temperature decreases the solubility
15
Q
- Pressure
A
- in general, pressure has very little effect on the solubility of liquids or soluds in liquid solvents
- the solubility of gases always increases with an increase in pressure
16
Q
Henry’s Law
A
- the solubility of a gas in a liquid is directly proportional to the pressure
17
Q
Gas Tension
A
- the amount of gas held in solution
- it is proportional to the pressure of the gas in the liquid
18
Q
Concentration
A
- the amount of a solute dissolved in a given quantity of solvent
19
Q
Percent Concentration
A
For solid in liquid:
weight/volume (w/v)% = (mass of solute / volume of solution) x 100
weight/weight (w/w)% = (weight of solute / weight of solution) x 100
For liquid in liquid:
volume/volume (v/v)% = (volume of solute / volume of solution) x 100
20
Q
Molarity
A
- the number of moles of solute dissolved in one litre of solution - moles/litre
Molarity (M) = moles of solute (n) / volume of solution (L)
21
Q
Dilution
A
Solutions are frequently prepared by diluting concentrated solutions rather than measuring out pure solvent. Because only solvent is added during dilution, the number of moles of solute remains unchanged.
before dilution M1V1 = moles
after dilution M2V2 = moles
and therefore M1V1 = M2V2
Also %1V1 = %2V2
22
Q
Parts per Million
A
ppm = (grams of solute / grams of solution) x 106
23
Q
Parts per Billion
A
ppb = (grams of solute / grams of solution) x 109
24
Q
Water as a Solvent
A
- most of the important chemical reactions in living tissue occur in aqueous solution
- water is used as a solvent transporting reactants and products from one place in the body to another
- water is also a reactant or product in many biochemical reactions
- water is a good solvent because of its polarity and its hydrogen bonding capacity
25
Hydration
- when a solid ionic compound is added to water, water molecules surround the ions at the surface of the crystal. The anions attract the positive pole of the water molecule, and the cations attract the negative pole of the water molecule. Each ion attracts multiple water molecules. When the combined force of attraction to water molecules is greater than the force of attraction of the ionic bonds that keep the ions in the crystal, the ions will be completely dislodged. Water molecules now surround the ions removed from the crystal - the ion is hydrated (or solvated for other solvents). The surrounding layer of solvent molecules - the solvation layer - acts as a cushion preventing the hydrated cations and anions from colliding and thereby keeping them in solution
26
Hydrates
- substances that contain water in their crystals
- caused by the attraction between ions and water molecules being so strong that the water molecules become part of the crystal structure
- water molecules in a crystal are called 'water of hydration'
- often, to remove the water, the crystals must be heated for some time at high temperature
- the crystal without its water of hydration is called 'anhydrous'
- some crystals rehydrate by absorbing water vapour from the air - these crystals are 'hydroscopic'
27
Electrolyte
- a substance that conducts an electric current when dissolved in water or when in the molten state
- ions in solution migrate from one place to another independently of one another, and it is this migration that constitutes an electric current
- cations migrate to the cathode (negative electrode)
- anions migrate to the anode (positive electrode)
- a non-electrolyte is a substance that does not conduct electricity
- electric conductance depends on the concentration of ions: the higher the ion concentration, the greater the electric conductance of the solution
- strong electrolytes are compounds that dissociate completely
- weak electrolytes are compounds whereby only partial dissociation occurs
- electrolytes help to maintain the acid-base balance and the water balance in the body
28
Covalent Compounds in Water
- some covalent compounds dissolve in water to produce ions and therefore they behave as electrolytes
- most covalent compounds that dissolve in water have their entire molecule solvated
- provided the solute molecule is fairly small, the solute will form hydrogen bonds with water
- hydrogen bonding is possible between two molecules if one of them contains an O, N or F atom (a hydrogen bond acceptor), and the other contains an O-H, N-H or F-H bond (a hydrogen bond donor). Water has both an O atom and an O-H bond and therefore can behave as a donor or acceptor
- in general, for a molecule to be small enough to be soluble in water, it should have no more than three C atoms for each O or N atom
- usually, covalent molecules that do not contain O or N atoms are insoluble in water, the exception being where the covalent molecules react with water
29
Water in the Body is Important:
- dissolves ionic substances and some covalent compounds
- hydrates all polar molecules
- a vehicle to transport most of the organic compounds, nutrients and fuels used by the body
- a vehicle to transport waste material in the body
- hydration of macromolecules such as proteins, nucleic acids and polysaccharides allows the proper motions within these molecules necessary for functions such as enzyme activity
30
Colloid
- mixture in which particles of one of the components are of a size intermediate between those in a true solution + those in a suspension ie. 2 - 500nm
- colloidal particles usually have a very large surface area which means they scatter light, making them appear turbid, cloudy or milky
- can exist in each of the three phases, forming stable dispersions so they do not separate and settle out
- most colloidal particles carry a large solvation layer which moves with the particle and cushions it from other colloidal particles. It is only the solvation layers that touch and therefore the particles do not stick together - they stay in solution
- the large surface area of colloidal particles acquire charges from the solution. All colloids in a particular solution acquire the same charge ie. either positive or negative. This leaves a net positive or negative charge in the solvent. When a colloidal particle collides with another, the two repel each other
- the combined effects of the solvation layer and the surface charge keep colloidal particles in a stable dispersion
- to remove a colloidal dispersion, we can remove the solvation layer by adding a solvent and/or we can remove the surface charge by adding an electrolyte. In each case, the colloidal particles become unprotected and therefore when they collide they will stick together and precipitate from the solution
31
Suspension
- relatively large particles of one substance are suspended in another
- the particle size is \> 500nm
- suspensions settle and separate upon standing as the large particles collide and stick together
32
Emulsion
- a system consisting of a liquid, with or without an emulsifying agent, in an immiscible liquid, usually as droplets of larger than colloidal size
33
Colligative Property
- property of a solution that depends only on the number of solute particles and not on the chemical identity of the solute
eg. freezing point depression, boiling point elevation, osmotic pressure
34
1. Freezing Point Depression
- decrease in freezing point of a liquid caused by adding a solute
- one mole of any particle, whether it be molecule or ion, dissolved in 1000g of water lowers the freezing point of the water by 1.86°C
- nature of the solute does not matter, only the number of particles
- if a solute is ionic, each mole will dissociate to two or more moles of particles, and the freezing point of the water will be lowered directly proportionally to the number of dissociated particles
35
2. Boiling Point Elevation
- increase in the boiling point of a liquid caused by adding a solute
- one mole of any particle, whether it be molecule or ion, dissolved in 1000g of water raises the boiling point of the water by 0.512°C
- nature of the solute does not matter, only the number of particles
- if a solute is ionic, each mole will dissociate to two or more moles of particles, and the boiling point of the water will be raised directly proportionally to the number of dissociated particles
36
3. Osmotic Pressure
- the amount of external pressure that must be applied to the more concentrated solution to stop the passage of solvent molecules across a semi-permeable membrane
37
Osmosis
- passage of solvent molecules from a less concentrated solution across a semi-permeable membrane into a more concentrated solution
- semi-permeable membrane is a thin slice of some material that contains very tiny holes that allows only solvent molecules to pass through
- solvated solute particles are much larger than solvent particles and cannot pass through
38
Osmolarity
- molarity of the solution multiplied by the number of particles produced by each formula unit of solute
- osmotic pressure generated by a solution is dependent on the osmolarity of the solution
- two solutions with the same osmolarity are 'isotonic'
39
Hemolysis
- an osmotic process in which water flows into red blood cells throgh the cells' semi-permeable membrane, causing the cells to burst
40
Crenation
- an osmotic process in which water flows out of red blood cells and into solution through the cells' semi-permeable membrane causing the cells to shrivel
41
Hypertonic Solution
- a solution that has greater osmotic pressure than that with which it is being compared
42
Hypotonic Solution
- a solution that has lesser osmotic pressure than that with which it is being compared
43
Dialysis
- process in which a solution containing particles of different sizes is placed in a bag made of a semi-permeable membrane. The bag is placed into a solvent or solution containing only small molecules. The solution in the bag reaches equilibrium with that outside, allowing the small molecules to diffuse across the membrane but retaining the large particles
44
Hemodialysis
- dialysis of blood
