Chapter 10 Chem water and solutions

10.1 Water and Its Solutions 

• Water is unique since it is necessary for life as we know it.

• It can naturally be found in all 3 states (ice, water, and vapor) on Earth.

  • Big, blue marble—name given by astronauts

• Water is bent, polar (acts like a magnet), and can form hydrogen bonds.

  • The hydrogen bond is responsible for some fairly unique properties of water.

Surface tension

1. Inward pull that minimizes surface area

2. Tends to hold drops in a round shape.

3. Think of it like a thin film or skin on the surface.

4. Can be broken with surfactant (surface active agent).

vapor pressure

1. Low for such a simple liquid.

2. Slow evaporation

   1. If water had a vapor pressure, fast evaporation 

      1. Lots of rain

Heat capacity

1. High for a liquid

2. Heats up slowly. 

3. Important for weather and beaches

Solid water 

1. Less dense than liquid water (ice floats).

2. Most dense at 4 °C, then slowly expands as it freezes (important for fish in ponds).

Solvent

what does the dissolving

Solute

what gets dissolved

Water is called

the universal solvent

Dissolves most ionic and polar solvents 

• Does not dissolve non-polar substances like oil

Like dissolve like

• Polar dissolves polar

• non polar dissolves non polar 

Electrolytes

• conduct current when dissolved in water

  • Salt - yes

  • Sugar - no

Solution formation 

• 3 factors affect how fast a solution forms.

1. String or agitation (increasing)—strong and using are the same.

2. Temperature (increases when warmer)  

3. Particles size (smaller = faster)

Solubility 

• How much of the solute will dissolve

• Usually expressed in grams per 400g of water

Solutions  have 3 possible situations 

Saturated, unstaturated and superstaurated

Unsaturated

can still dissolve more 

Saturated

dissolves all possibility, (extra slate does not dissolve, sinks to the bottom)

Super saturated

1. holds more than it should (forms in a special situation)

Temperature and pressure (for gases) affect solubility  

• Usually higher solubility when warmer for solids; lower for gases

• More gas can dissolve under higher pressure (soda)  

Dilute

small amounts of solute 

Concentrated

large amounts of solute

Can be measured with molarity (M)

molarity

moles of a substance per liter (mol/L) of solution

Ex: What is the molar salt in 500 mL of water

• 2/0.500 = 4M

Colligative properties

• depend on the amount of solute dissolved

  • Depends on the nature of the solute

Vapor pressure depression

• VP lowers when the solute is present

Freezing point depression 

• Fp lowers when solute is present (ex, salt in water)

• 1.86 per mol 1 L of water

Boiling point elevation 

• BP is raised when the solute is present 

• 0.51C per mole   of  L of water

What causes water to have a high surface tension, low vapor pressure, and less dense solid than liquid?

hydrogen bonds

Why is Florida not as hot as Texas in the summer? Explain with chemistry terms.

water has a large heat capacity and it evaporates, which is the cooling process.

One ionic compound, sodium sulfate, will dissolve in water but another, barium sulfate, will not. Why?

Which one of the chemicals, if either, would be an electrolyte? Explain.

The electrostatic forces of Ba are too strong. Sodium sulfate is the electrolyte because ions can separate.

What would happen to the solubility of a gas if the temp is raised? A solid?

gass would lower and most solids would higher

Explain what is wrong with using the terms concentrated and dilute in chemistry class, even though they

are good terms.

not specific enough

Why might it be bad to dump a large amount of hot water, say from a factory, into a nearby lake, even if the

water does not contain contaminants?

lower solubility of O2, the fish will suffocate