Fizzy carbonated water, salty sea water, a dental filling, even the air we breathe: all of them are solutions. So is the Pb²⁺ or Cd²⁺ mixed into water, only you cannot see it. Two questions then: how many kinds of solution are there, and what force keeps one substance dissolved inside another?
1. Seven kinds of solution
Both the solvent and the solute can be solid, liquid or gas. By physical state, solutions come in seven kinds. The book names each one as state of solvent + state of solute, so the first word is the solvent. “Liquid + gas” therefore means a gas dissolved in a liquid.
First, the gas as solute. Gas + gas is air. Liquid + gas is carbonated water. Solid + gas is H₂ dissolved in palladium.
Now the liquid or solid as solute. Liquid + liquid is gasoline. Solid + liquid is dental amalgam. Liquid + solid is sea water. Solid + solid is pewter, which is 96% Sn and 4% Cu.
Now match them yourself. Seven examples go into seven boxes, one in each.
match themthe first word is the solvent
Solvent first
Pick up an example, then drop it in a box. In the book's name the first word is the solvent and the second is the solute.
Right. Next one.
Not yet. First ask which part is present in the larger amount, the solvent; its state is written first. Then the state of what is dissolved in it.
All seven in place. The seven names always run solvent + solute.
2. The rule of mixing and six forces
How does a pollutant stay dissolved in water or another medium? The basic rule is one line: like dissolves like. That likeness works through six kinds of force. Take them one by one, with the book's examples.
Ion-dipole force (10 to 50 kJ/mol). A Na⁺ ion in water forms a hydration shell of water molecules around it. Pb²⁺, Cd²⁺, As³⁺ and Cr³⁺ stay in water in just this way.
Hydrogen bonding. Alcohols (R-OH), amines (R-NH₂) and amino acids stay dissolved in water by this bond.
Dipole-dipole force. CH₃CHO stays dissolved in CHCl₃. Both are polar molecules, so the dipole of one holds the other.
Ion-induced dipole force. Fe²⁺ and O₂ in haemoglobin are held by this force. Cl⁻ dissolved in gasoline stays there by the same force.
Dipole-induced dipole force. O₂ and N₂ in water stay this way. CO, CO₂, SO₂ and SO₃ mixed with N₂ and O₂ are held by it too.
Dispersion force. This is the one that acts for non-polar substances.
Seven examples for the six forces follow. Look for an ion, then ask whether the molecule is polar or non-polar, and the force gives itself away. Fe²⁺ and Cl⁻ are both ion-induced dipole, and both are offered.
match themlook for an ion
How each one mixes
Pick up an example, then drop it in a box. First ask: is there an ion?
Right. Next one.
Not yet. What kind of particle is it: an ion, a polar molecule or a non-polar one? And what is the medium around it? Those two questions fix the force.
All in place. Fe²⁺ and Cl⁻ both stay by the ion-induced dipole force.
3. How strong is each force
The strengths in kJ/mol (Figure 1.31): dipole-dipole 3-4, dipole-induced dipole 2-10, ion-induced dipole 3-15, dispersion 1-10, hydrogen bond 10-40 and ion-dipole 10-50. The two strongest are ion-dipole and the hydrogen bond. The ranges overlap, so there is no strict order. We simply sort by the top of each range.
sort theman ion or an H bond is strongest
Small or big
Pick up a force, then drop it in a box. Ask: how high does its range go?
Right. Next one.
Not yet. Recall the ranges: ion-dipole 10-50, hydrogen bond 10-40. The other four top out at 15 or less.
All correct. Reaching 40 are ion-dipole (10-50) and the hydrogen bond (10-40). The rest: ion-induced dipole 3-15, dipole-induced dipole 2-10, dispersion 1-10, dipole-dipole 3-4.
4. Check yourself
Three questions, one at a time.
check yourselfpick one answer
Question 1
What kind of solution is air (by the book's naming)?
Liquid + gas is carbonated water; in air the solvent is not a liquid.
Solid + gas is H₂ in palladium, not air.
Solid + solid is pewter, not air, whose solvent is a gas.
Right. In air both solvent and solute are gases, so it is gas + gas.
In the second, match a force to its example.
check yourselfpick one answer
Question 2
By which force does an alcohol (R-OH) stay dissolved in water?
Right. A hydrogen bond forms between the O-H of the alcohol and water.
An alcohol is not an ion, so it is not the ion-dipole force.
Dispersion force is for non-polar substances; an alcohol mixes in water by H bonds.
The ion-induced dipole force needs an ion; an alcohol is not one.
The last asks you again which particle stays by which force.
check yourselfpick one answer
Question 3
What kind of solution is carbonated water?
Right. The solvent is a liquid (water) and the solute a gas (CO₂); so liquid + gas.
Gas + liquid is not the book's form; the book writes the solvent first, so this is reversed.
Liquid + liquid is gasoline; in carbonated water the solute is a gas.
Solid + liquid is dental amalgam, not carbonated water.
The whole note on six cards.
cut from the notetap to turn over
Six cards
QuestionHow does the book name a solution? What does 'liquid + gas' mean?
AnswerState of solvent + state of solute; liquid + gas means a gas dissolved in a liquid (such as carbonated water).
QuestionWhat kinds of solution are gasoline, dental amalgam, sea water and pewter?