Lesson 12 Notes

What Happens When Substances Are Mixed With Water?

1. Solutions are homogeneous mixtures of two or more substances.

a. The substance present in the larger proportions in a solution is the solvent.

b. The substance in the smaller proportion is the solute.

c. Solutions can consist of both liquid solvents and a solid solute, but they can appear in other phases too.

i. Liquids and gasses dissolve in water

ii. Alcoholic drinks consist mainly of a solution of alcohol and water.

iii. Oxygen dissolved in water

iv. Sulfur dioxide dissolves in rainwater to form acid rain.

2. Solutions in which water is the solvent are called aqueous solutions.

a. When a solvent dissolves a solute, the particles of the solute disperse throughout the solvent.

3. Aqueous solutions can be divided into two groups.

a. Electrolytes conduct electricity.

b. Nonelectrolytes do not conduct electricity.

c. Dissociate are electrolytes split into ions when added to water.

i. Ex: common salt (sodium chloride, NaCl) dissolves in water to form an electrolytic aqueous solution:

ii. NaCl(s) Na +(aq) + Cl-(aq)

d.Strong Electrolyte Soldium chloride solutuionr eadily conduct electricity because its ions migrate to an electrode of opposite charge.

d. weak electrolytes – Many electrolytes incompletely dissociate; therefore, they conduct electricity less effectively.

e. Polar molecule – Water is a particularly good solvent for charged particles because the shape of the water molecule gives it a different charge at each end.

f. Solvation – a configuration causes water molecules to rapidly surround those of a similarly polar or ionic solute.

g. Hydrogen bonding – sucrose dissolves readily in awter because its hydroxyl (or OH) groups readily bond with water molecules.

h. Heat of solution – absorption of heat that occurs when sodium nitrate is dissolved in water.

i. Enthalpy – change in the internal energy.

j. Hydration – the solution is the result of the breakup of crytal lattices and subsequent connection with water.