1
Q
SOLUTION DEFINITION
A
- A mixture where the particles of a solute are homogeneously spread amongst the particles of a solvent, the major compete of the mixture by mass
- Can be solid (brass, bronze)
- Can be liquid (sea water or gaseous)
2
Q
AQUEOUS SOLUTION
A
- Liquid solutions were the solvent is water
- Formation; two opposing processes – dissolving and crystallizing
- As solute dissolves the solution concentration INCREASES
- As solute crystallizes it returns some of the dissolved solute to the sold, REDUCING the solute concentration
- When speed of two opposing processes is equal, then the solute concentration is at a MAXIMUM and solution is SATURATED
3
Q
SOLUBILITY
A
- Solubility of a solute is often give as the mass that can dissolve in 100 grams of water
- Solids are INCREASING SOLUBLE with increasing temperature
- Cerium (II) Sulfate is an exception; becomes less soluble with increasing temperature
- Gases are LESS SOLUBLE with increasing temperature
4
Q
SATURATED SOLUTION
A
- Solute can continue to dissolve in water until its solution becomes saturated (contains as much dissolved solute as its solubility at that temperature allows
5
Q
UNSATURATED SOLUTION
A
- Further solute may be added to a saturated solution, and if it does dissolve then this shows the solution is unsaturated
6
Q
SUPER SATURATED SOLUTION
A
- Contains more dissolved solute than the solutes solubility at that temperature will normally allow
- One way to do this is produce a saturated solution at a higher temperature and then cool the solution
- The cooler solution will be super saturated
7
Q
STRONG ELECTROLYTES
A
- When these dissolve in water they are entirely present (or mostly) as independent mobile ions
- All ionic compounds are strong electrolytes
- Covalent molecular compounds that are STRONG acids are strong electrolytes
- HCl, H2SO4, HNO3
8
Q
WEAK ELECTROLYTES
A
- When these dissolve in water they are partly present as independent mole ions (mostly as molecules)
- Covalent molecules that are WEAK ACIDS OR BASS
- CH3COOH, H2S, H2CO2, H2SO3 and NH3
9
Q
NON ELECTROLYTES
A
- When these dissolve in water they don’t produce ions
- They are entirely present as molecules
- Most covalent molecules are non-electrolytes
10
Q
EQUATIONS OF SOLVATION
A
- Dissociation
- Ionisation
- Single Arrow
- Double Arrow
11
Q
DISSOCIATION
A
- When an ionic electrolyte dissolves, the ions present within the ionic solid are released into water to form a solution of independent ions
12
Q
IONISATION
A
- Formation of ions by a molecular electrolyte, during ionization molecules of an electrolyte react with water to form ions not originally present within the substance
- Ionization and Dissociation result in a solution that contains independent mobile electrons
13
Q
SINGLE ARROW
A
- Shows ionization or dissociation goes to completion (strong electrolyte
14
Q
DOUBLE ARROW
A
- Shows the reaction doesn’t go to completion, i.e. Significant concentration of ions and molecules are present, as weak electrolytes tend to recombine to reform the original molecules and not fully ionize/disassociate
15
Q
ELECTRICAL CONDUCTIVITY IN A SOLUTION
A
- Conductivity depends on the ability of positive ions to move freely towards the negative electrode while negative ions move freely towards the positive electrode
- Greater concentration of ions in a solutions, the greater is its ability to conduct a current
- Strong electrolytes always produce a more conducting solution, than weak of the same concentration
- Non-electrolytes always produce non-conducting solutions
- Pure water is a non-conductor of electricity (when an electrolyte dissolves in water the resulting mobile ions allow the solution to conduct a current)
16
Q
IONIC SOLUBTILITY AND SOLVATION
A
- Solubility of ionic compounds depends on the solvation properties of polar solvents
- SOLVATION; involves the attraction of polar solvent molecules to both the positive and negative ions of an ionic solid
- WATER AS A SOLVENT; high polar nature of molecules allows water to be a good solvent for ionic solutes
17
Q
HYDRATION
A
- SOLVATION BY WATER; called hydration; occurs because of electrostatic forces (ion-dipole) that form between an ion and the water of a water molecule
- Ion-Dipole involved slightly positive H atom in a water molecule being attracted to a negative ion, while the slightly negative O atom n the water molecule is attracted to a positive ion
- Forces lead to hydration where each ion in solution is surrounded by several water molecules
- High solubility of ionic solids in water is due to ion-dipole forces overcoming the strong attractive forces between oppositely charged ions in the ionic solid
18
Q
PRECIPITATION REACTIONS
A
- Precipitation reaction occurs when an insoluble solid forms within a previously clear solution
- Can happen with ionic solutes when two solutions containing different ions are combined and mixed
- If any pair of ions in the mixture of two solutions can form an insoluble compound, then the compound will ‘come out’ of the solution, forming a precipitate
- SUSPENSION; during a precipitation reaction, the precipitate is in the form of a suspension
- Consists of tiny particles of a solid that are initially spread through the mixture, the suspension causes the reaction mixture to go cloudy – over time the particles will settle to the bottom of the reaction vessel
19
Q
SOLUBLE
A
- More than 0.10 mol of it can dissolve in 1 L of solution
20
Q
SLIGHTLY SOLUBLE
A
- Between 0.10 and 0.01 mol of it can dissolve in L of solution
21
Q
INSOLUBLE
A
- Less than 0.010 mol of it can dissolve
22
Q
USING PRECIPITATION TO DISTINGUISH COMPOUNDS
A
- Precipitation reactions can be used to verify the presence of a particular ion in solution
- For example, if a solution is thought to contain lead ions then the addition of sodium iodide solution would producing a bright yellow precipitation
- Technique only works if the substances to be distinguished contain at least one ionic with a different pattern of solubility
23
Q
GROUND WATER TREATMENT
A
- Aeration
- Clarification
- Sand Filtration
- Disinfection
- Fluoridation
- pH
24
Q
AERATION
A
- groundwater contains gases like CO2 and H2S which increases acidity of water and gives it a bad odor, spraying GW into the air expels gases and increases concentration of dissolved oxygen, the extra O and added chlorine, oxidize and remove organic compounds reduces the solubility of dissolved iron and manganese, these compounds cause water to be black and brown; staining clothing and surface
25
CLARIFICATION
- Occurs after aeration, involves removal of fine particles in GW, these particles will not normally settle out and presence causes water to be unclear and coloured, clarification is achieve in a large settling tank where alum, lime and CaO is added which causes fine particles to clump together and quickly settle out – the clarified water is then drawn off the top of the tank
26
SAND FILTRATION
- Clarified GW may still be coloured and contain fine particles, to remove these water is passed through filter beds of granulated anthracite (coal with 98% carbon) and coarse sand, it absorbs organic materials that cause water to be colour
27
DISINFECTION
- harmful pathogenic bacteria and viruses are still present, chlorination/chloramination destroys these, it involves using chlorine and ammonia to produce a long lasting disinfection
28
FLUORIDATION
- Present of fluoride ions in water reduces tooth enamel, to maximize public health safety from this fluoride concentration in drinking water is between 0.6-1.0mg L, fluoridation involves adjusting the natural fluoride concentration to this by addling fluorosilicic acid
29
pH
- pH correction is achieved by the addition of lime (increases pH), CaO or by dissolving carbon dioxide gas (lowers pH
30
POTABLE WATER
- Clear, colorless, odorless, contain no pathogens or toxic substances and be pleasant to taste
- Water treatment facilities aim to produce water that is safe to drink and cook with
31
POTABLE WATER FROM SEA WATER DISTILLATION
Distillation; water is evaporated from sea water, and is condensed to produce distilled water (free of dissolved salts)
- Evaporation is carried out in several stages at progressively lower pressure; multi stage flash distillation so less energy is needed in the evaporation process
- Using heat exchange process, the heat released from the condensation of water vapor is transferred to incoming cold sea water – increases energy efficiency by recycling some of the heat used in the evaporation process
- Disadvantage; its high energy demand
32
OSMOSIS
- Osmosis; Obtaining fresh water from sea water in a natural process
- Plants use to draw water from the soil into their roots, cell membrane of plant root cells acts like a semi permeable membrane that allows water molecules to pass through, but not larger molecules (salt ions)
- Is the natural tendency of water to diffuse through a SPM from a solution of low salt concentration to one of a higher concentration until both are the same
- As a result, pure water is drawn into cells saltier interior by osmosis
33
POTABLE WATER FROM SEA WATER REVERSE OSMOSIS
- Commercial reverse osmosis, units use high pressure to force water through a synthetic semi permeable membrane (SPM) in the opposite direction to which water would naturally flow
- Pressure is applied to salty water, that flows on one side an SPM
- Causes water to flow out of the salty water (salty feed water), through the SPM to produce pure water
- The feed water becomes salters as around 45% or more of the water content is removed
- Resulting fresh water is called the permeate
- Ions, larger organic molecules, cellular organisms and viruses do pass through the SPM
34
REVERSE OSMOSIS USE
- Used to produce fresh water at desalination plants
- At plants, permeate water is collected then treated for disinfection with chlorine, also fluoridated before storage
- As produced water by RO is deionized, salts for both taste and health reasons are added; adding carbon dioxide gas and lime, results in suitable pH
- requires one third of the energy input of the most efficient thermal distillation plants
