Chapter 20 The Dissolving Process Part 2

Rate of Solution The rate at which a material dissolves can be affected by: 1.Surface area

Rate of Solution The rate at which a material dissolves can be affected by: 2.Agitation (stirring)

Rate of Solution The rate at which a material dissolves can be affected by: 3.Temperature Temperature not only affects how quickly we can dissolve a solute but also how much solute can be dissolved.

Factors Affecting Solubility Temperature Effects

Temperature and Solubility of Solids TemperatureSolubility (g/100 g H 2 O) KCl(s)NaNO 3 (s) 0° °C °C °C

Temperature and Solubility of Solids TemperatureSolubility (g/100 g H 2 O) KCl(s)NaNO 3 (s) 0° °C °C °C The solubility of most solids increases with an increase in the temperature.

Temperature and solubility

Factors Affecting Solubility Temperature Effects

Temperature and Solubility of Gases TemperatureSolubility(g/100 g H 2 O) CO 2 (g)O 2 (g) 0°C °C °C

Temperature and Solubility of Gases TemperatureSolubility(g/100 g H 2 O) CO 2 (g)O 2 (g) 0°C °C °C The solubility of gases decreases with an increase in temperature.

Thermal Pollution

Thermal pollution can occur when heated water is discharged into cooler streams or rivers. This heated water generally is from power plants or industrial processes. A fish must pump water across its gills to meet its need for oxygen. If the dissolved oxygen in water is low, the gills must move faster to get enough oxygen for the fish to survive.

Unsaturated Solutions Contains less than the maximum amount of solute. No undissolved solute present. Can dissolve more solute. Dissolved solute

Saturated Solutions Contains the maximum amount of solute that can dissolve. Tend to have undissolved solute at the bottom of the container. Solution is in equilibrium with undissolved solute.

What is the solubility of NaCl at room temperature (25°C)? Solubility ≈ 36g NaCl/100g of water

How could I dissolve the extra 4.0g of NaCl without adding more water?

Heat up the water to ≈ 90°C Solubility ≈ 40g NaCl/100g of water If we would cool the water back to room temperature we may create a supersaturated solution.

Supersaturated A supersaturated solution contains more than the maximum amount of solute and is unstable. It returns to a saturated solution if disturbed in some way (i.e.: a seed crystal)

Supersaturated Solutions Show laser disc video of supersaturated solution.

Pressure and Gas Solubility More gas can dissolve at higher pressure.

Nitrogen Narcosis This is a condition that can result from diving too deep, bringing on disorientation, euphoria, errors in judgment and even hallucinations or unconsciousness. Any of those can be fatal.

Nitrogen Narcosis

August 21, 1986 Lake Nyos – Cameroon, Africa 1700 people, thousands of cattle, and many more birds and animals are found dead.

Lake Nyos

Homework Worksheet: The Dissolving Process