Unit 7: Solutions – Study Guide

This is what you need to know for the quiz on Monday.

Vocabulary:

Solution: a combination of a solute and a solvent where the molecules of the solute are distributed in the liquid solvent and not clumped together into solid particles. Examples of solutions are salt in water (saline solution), sugar in water or oil in acetone.

Solute: the material being dissolved such as salt or sugar. Solutes can be solid, liquid or gas before being dissolved.  Examples include: sugar (solid) dissolved in water,  isopropal alcohol (liquid) dissolved in water (rubbing alcohol), CO2 gas dissolved in water (caronated water) or in juice (soft drinks).

Solvent: the material, typically a liquid which does the dissolving such as water or acetone or an oil. Water is a polar solvent, oils are non-polar solvents.

Polar molecules: molecules where there is a slight charge separation across the molecule. The most notorious polar molecule is water, where the Oxygen has a slightly negative (-) charge and the Hydrogens have a slightly positive (+) charge.  Other polar molecules, in particular polar covalent molecules such as alcohols, can be dissolved in water since water is a polar solvent. Polar solvents can dissolve some ionic compounds since each ion has + or a – charge and each can be dissolved in water which is a polar solvent. Note that in many ionic solids such as many semiprecious crystals, the ionic bonding forces are stronger than the effect of the charge separation in the water molecule. This means that many ionic compounds are too strongly bonded to be dissolved in water. One example is a granite rock which was demonstrated to not dissolve.

Non-polar: Many covalently bonded molecules do not have a charge separation across the molecule and cannot be dissolved in water. Frequently these materials can be dissolved in non-polar solvents such as oils or other organic solvents (oils, acetone, paint thinner).

Insoluabilty: this happens when you try to dessolve a non-polar solute in a polar solvent. for example try to dissolve cooking oil in water.  This lighter liquid, in this case the cooking oil will float on top.

OK, so here’s Hank to explain it all and even some more stuff…….