Concentration, pH, Temperature and

Pressure

A solution is a homogeneous mixture of one substance (the solute) dissolved in another substance (the solvent).

Concentration is a ratio of the amount of solute to the amount of solvent.

Concentration

The concentration of a solution is a measure of the

amount of solute that is dissolved in a given quantity

of solvent. A dilute solution is one that

contains a small amount of solute.

A concentrated solution contains a large amount of

solute.

• Behavior of solutions depend on

compound itself and on how much is present, i.e. on the concentration.

• Two solutions can contain the same compounds but behave quite different because the proportions of those compounds are different.

Concentrations of Solutions

Concentration of a solution: the more solute in

a given volume of solvent, the more concentrated

1 tsp salt (NaCl)/cup of water vs 3 Tbsp salt/cup water

Concentrations of Solutions

pH Scale

• Based on concentration of hydrogen ions

• All solutions have pH between 0 and 14

• Pure water pH = 7• Acidic solutions pH less than 7• Basic solutions pH more than 7• Each whole number represents a factor

of 10 on pH scale. pH 5 has 10 times more hydrogen ions than pH 6.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Neutral

pH Scale

Acidic Basic

You know that salt easily mixes with

water by dissolving in it. But did you know that salt can dissolve at different rates?

The temperature of the water, the size of the salt particles, and how you stir the solution are factors that affect how quickly the salt dissolves.

Rate of Dissolving

Temperature

Temperature affects the rate of dissolving in a solution.

The particles of a substance are always moving.

When heat is added, the particles move faster making it dissolve faster in a liquid.

Think about adding sugar to ice tea vs. hot tea. Which one dissolves faster?

Solubility: Temperature Dependence

• All solubilities are temperature dependent

• Most solids are more soluble at higher temperatures. Exceptions exist.

Another factor that affects the rate of

dissolving is particle size. The smaller the solute particles are, the faster

they dissolve. If you have ever made a cup of hot chocolate,

you dissolved powder into milk. If you put a piece of a chocolate bar in the

milk, it would take a longer time to dissolve.

Particle Size

Stirring also affects the rate of

dissolving. When adding particles to a liquid, you

stir or shake the liquid. This action makes the solute dissolve

more quickly. What happens if you pour a drink mix

into a container without stirring?

Stirring