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Terms in this set (11)
Define and calculate M, m, %weight, mole fraction, ppm, N
M- molarity (moles of solute/L solution)
m- molality (moles solute/kg solvent)
%weight- (mass solute/mass solute+solvent) x 100
mole fraction- (mole solute/total mole)
ppm- (g solute/g solvent) x 1,000,000
N- moles (mass/molar mass)
describe dissolving at the particle level
The particle model can provide a simple representation of dissolving in terms of mixing to show what happens when a solid dissolves. If a solid dissolves on mixing its particles break apart and form a loose association with the liquid (solvent) particles. A solid will not dissolve in a liquid if its particles are unable to form links to the liquid particles.
describe characteristics of solutions
A solution is a homogeneous mixture of two or more substances.
The particles of solute in a solution cannot be seen by naked eye.
A solution does not allow beams of light to scatter.
A solution is stable.
The solute from a solution cannot be separated by filtration (or mechanically).
It is composed of only one phase
describe interactions in solution process
When one substance dissolves in another, the particles of the solute disperse uniformly throughout the solvent. The solute particles occupy positions that are normally taken by solvent molecules. The ease with which a solute particle may replace a solvent molecule depends on the relative strengths of three types of interactions:
describe energy changes in solution process
It is the enthalpy change when one mole of a solute dissolves to form an infinitely dilute solution.
The process of dissolving can be broken down into two steps:
1. The solid ionic compound is split up into a gas of ions (requires the energy equal to the lattice energy to be supplied).
2. The ions dissolve in solution and become hydrated; the energy equal to the hydration energies of the two ions is given out.
describe role of disorder in solution process
The entropy of a system increases when a solute dissolves, as it becomes more disordered as the ions spread out through the solution.
An increase in entropy favours dissolving- even if a small amount of energy is needed.
So substances with a small positive enthalpy change of solution are still able to dissolve, provided there is a sufficient increase in entropy.
predict if certain compounds will dissolve in specific solvents
Solubility is the relative ability of a solute (solid, liquid, or gas) to dissolve into a solvent and form a solution.
To predict whether a compound will be soluble in a given solvent, remember the saying, "Like dissolves like." Highly polar ionic compounds such as salt readily dissolve in polar water, but do not readily dissolve in non-polar solutions such as benzene or chloroform.
describe and calculate the effect of solution concentration on vapor pressure of a solution
The pressure on the surface of a solution has very little effect on the solubilities of solids and liquids. It does have an enormous effect on the solubility of gases. As the partial pressure of a gas in the atmosphere above the surface of a solution increases, the solubility of that gas increases.
describe and calculate the effect of solution concentration on boiling point of a solution
The boiling point of the solvent above a solution will be greater than the boiling point of the pure solvent whether the solution contains a non-volatile solute or a volatile solute. However, for simplicity, only non-volatile solutes will be considered here.
Experimentally, we know that the change in boiling point of the solvent above a solution from that of the pure solvent is directly proportional to the molal concentration of the solute.
change in boiling point = boiling point constant x molar concentration
describe and calculate the effect of solution concentration on freezing point of a solution
The freezing point of the solvent in a solution will be less than the freezing point of the pure solvent whether the solution contains a non-volatile solute or a volatile solute. However, for simplicity, only non-volatile solutes will be considered here.
Experimentally, we know that the change in freezing point of the solvent in a solution from that of the pure solvent is directly proportional to the molal concentration of the solute.
describe and calculate the effect of solution concentration on osmotic pressure of a solution
We need to know the molar concentration of dissolved species in order to calculate the osmotic pressure of an aqueous solution
pi = MRT
3.14= molar concentration x 0.08206 x Kelvin
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