Solvents and Solutes Flashcards
Define a solution?
A homogenous mixture of 2 or more substances. It is a solute dissolved in a solvent.
It can be a solid in a liquid; a liquid in a liquid; a gas in a liquid. Or a solid in a solid (metal alloy)
Solutions are different to non homogenous mixtures such as suspensions and colloid.
How would you describe the constituents of room air?
A mixture of gases.
Why is water a good solvent?
Water is a good solvent as it is polar in nature (O slightly negatively charged, H slightly positively charged).
Furthermore it has a much higher melting/boiling
point, heat of vaporisation and surface tension that
would be predicted due to the hydrogen bonds it form with other water molecules.
Each water molecule can form 4 Hydrogen bonds (1 on each H atom and 2 on the O atom)
Explain why Ice floats?
As water freezes its H bonds form a 3D structure and it expands. As it expands it becomes less dense than liquid water (which is most dense at 4 degrees)
Which substances dissolve well in water?
Polar substances dissolve well in water as it is polar. (Like dissolves in like)
You can also think of it as hydrophilic substances dissolve well in water and hydrophobic substances do not.
Molecularly how do solute dissolve in water?
Simple hydration shells form around simple polar salts,
In which the polar salt molecule forms a weak attraction to either the H or O of the H2O.
Where larger non polar substances are dissolved in water a larger complex hydration shell is formed: a cage-like structure known as clathrate formation
Which factors affect solubility?
Pressure (more applicable in gases): as you increase the pressure you increase the solubility of a gas in a liquid.
Temperature: As temp increases you increase the solubility of a solid in a liquid, but you decrease the solubility of a gas in a liquid.
Important to note that temperature effects the degree of solubility differently for different solutes. (KCL solubility increases more than NaCl’s with an increase in temp)
The characteristics of the solvent and solute i.e polar solutes tend to dissolve well in polar solvents, non polar solutes (oil) tend to dissolve well in non polar solutes (benzene)
Define solubility and how is it expressed?
A measure of the maximum amount of solute that can dissolve per amount of solvent under specified conditions of temperature and pressure.
It is expressed as concentration of a mass in a mass, or as a percentage.
Lidocaine 1% means it has 1g in 100g this is equivalent to 1g in 100ml (as 1ml of water is 1g)
1g in 100ml = 1000mg in 100ml
So can also be thought of as 10mg per ml
What is the difference between a suspension and a colloid?
Suspensions are mixtures that will eventually separate after a certain amount of time.
Colloids are a type of mixture where a substance is dispersed evenly through another.
A colloidal system is made up of an:
+ Internal phase of small particles 1-1000 nm in diameter, i.e. the dispersed substance
+External phase within which the internal phase is dispersed
A liquid liquid colloid is known as an emulsion. A solid liquid colloid will not settle with gravity, unlike a suspension which will settle overtime.
Define an emulsion?
An emulsion is a liquid liquid colloid.
It is a mixture of 2 or more liquids which have become evenly dispersed after the input of energy.
Overtime emulsions will revert back to the constituent liquids and cease being an emulsion.
How do emulsifiers work?
To prevent reversion, emulsifiers can help stabilise the emulsions including surfactants such as egg yolk and soya lecithin.
Emulsifiers binds electrostatically to the internal phase to help maintain their position in relation to the molecules in the other substance through electrostatic forces.
Propofol is an example which is lipid soluble held in a watery base through the help of egg and soya
lecithin emulsifiers.
What are the different types of colloid fluids in medicine?
Gelatin colloid: molecular weight of 30 000 Da, made from collagen in animal tissue, risk of anaphylaxis
Dextran colloids: made from polymerisation of glucose, vary in molecular weight
Starch colloids: large range of molecular weights (up
to 200 000 Da) and will remain within the circulation for up to 24 hours. Reduced risk of anaphylaxis, but expensive and can cause coagulopathy and pruritus.
What is Raoult’s law?
Raoult’s Law: The overall vapour pressure of a solution depends on the vapour pressure of each component in solution.
What is a colligative property?
Physical properties of a solution that vary by the number of dissolved particles rather than by the identity of the solute.
Explain the relationship between solutes in solution and vapour pressure?
As you add a solid solute (NaCl) to a solvent the vapour pressure will drop.
If you takes Raoult’s Law: The overall vapour pressure of a solution depends on the vapour pressure of each component in solution. Total vapour pressure = (n1 x VP1) + (n2 x VP2)
As the amount solute added increases the mole fraction of the solvent decreases. A solid solute such as NaCl does not exert a vapour pressure.
Therefore although the SVP of the solvent remains static, as the mole fraction of the solvent decreases the overall vapour pressure will decrease.
