Chapter 4 Solutions

Chemical Interactions

Chapter 4: Solutions

Section 4.1

A Solution is a Type of Mixture

The parts of a solution are mixed evenly.

• A solution is a homogeneous mixture: all portions have identical properties.

• The solute is the substance that is dissolved.

• The solvent dissolves the solute.

• Solutes, solvents, and solutions can be liquids, solids, or gases.

• The solute and solvent can be in the same or in different physical states.

• A suspension is a mixture with large particles. The particles do not dissolve. The mixture is not a solution.

Solvent and solute particles interact.

• When a solid dissolves in a liquid, the solute breaks apart.

• Solute particles are surrounded by solvent particles and are evenly distributed in the solution.

• Ionic compounds break up into individual ions when they dissolve.

• When covalent compounds dissolve, the molecules separate from each other, but covalent bonds remain intact and the individual molecules remain whole.

Properties of solvents change in solutions.

• A solute changes the physical properties of a solvent. The freezing point of a solution is

lower than the freezing point of the pure solvent.

The boiling point of a solution is higher than the boiling point of the pure solvent.

Section 4.2

The Amount of Solute

That Dissolves Can Vary.

A solution with a high concentration contains

a large amount of solute.

• The concentration of a solution is the amount of solute dissolved in it at a particular temperature.

• Solutions can be made more concentrated by adding solute.

• Solutions can be made more dilute by adding more solvent.

Degrees of Concentration

Low Solubility High Solubility

• A saturated solution holds as much of a given solute as it can at a given temperature. If it holds more solute than normal, it

is supersaturated.•Very unstable•Disturbing the solution could cause excess solute to come out of the solution as a precipitate.

• Every substance has a characteristic solubility, the amount that will dissolve in a certain amount of a certain solvent at a given temperature.

The solubility of a solute can be changed.

• Changes in temperature will change the solubility.

• The solubility of liquid and solid solutes are not usually affected by changes in pressure.

Solubility depends on molecular structure.

• Solubility depends on changes of solute particles.

• Molecules with regions of electrical charge (polar molecules) and ions dissolve in polar solvents such as water.

• Nonpolar molecules (oils) do not have charged regions and do not dissolve in polar solvents, but they dissolve in nonpolar solvents.

Section 4.3

Solutions can be Acidic,

Basic, or Neutral

Acids and bases have distinct properties.

• Acids: A substance that can donate a

hydrogen ion to another substance when the acid is dissolved in water.•HCl is an acid and donates a H+ ion in a water solution.

• Acids also:

Taste sour React with carbonates to form CO2. React with many metals. Turn litmus red.

• Common acids: Milk, beer,

cheese, sauerkraut, wine, vinegar, lemon juice

• Bases: A substance that can accept a

hydrogen ion from another substance.

In water, the base NaOH releases a hydroxide ion, which can accept a hydrogen ion.

• Bases also: Taste bitter Feel slippery or

soapy Turn litmus

blue.• Common bases:

Borax, milk of magnesia, ammonia, oven cleaner, peroxide

The strength of acids and bases can be

measured.• Strong acids and bases break apart

completely into individual ions. No complete molecules of the acid

or base remain in the solution

• Weak acids and bases don’t break apart completely into ions. It contains both molecules of the

acid/base and its ions.

• The acidity of a solution is measured on the pH scale. Acids produce higher hydrogen ion

concentration and have a low pH – from 0 – 7.

Bases produce a low hydrogen ion concentration and have a high pH – from 7 – 14.

Solutions of pH 7 are neutral.

Acids and bases neutralize each other.

• When an acid and base come into contact, they undergo a neutralization reaction. The hydrogen ion from the acid and the

hydroxide ion from the base combine to form water.

The negative ion from the acid and the positive ion from the base combine to form a salt.

The products of a neutralization reaction – water and salt – are both neutral substances.

Section 4.4

Metal Alloys are Solid Mixtures

Humans have made alloys for thousands of

years.• Alloy: a solid mixture that has many of

the characteristics of a solution. In an alloy, a solid (usually a metal)

solute is mixed with a solid metallic solvent.

Made by melting the metal components and mixing them in the liquid state.

The physical properties of the alloy are different from those of the solvent metal.

• Two types of alloys: Substitutional alloy: atoms of one

metal are replaced by the other metal (brass).

Interstitial alloy: (Steel) Carbon atoms occupy the gaps between the iron atoms.

Alloys have many uses in everyday life.

• Automotive - pistons, cylinder blocks and liners, sliding bearings, wheels.

• Aerospace - actuators and gears, structural elements, bearings and wheels, gas turbines.

• Oil, gas and chemical - valves, pumps, hydraulic and pneumatic systems.

• Cookware - frying pans, saucepans, knife sharpeners.

• Medical - prostheses. • Printing - anilox rolls.

Chapter 4 Solutions

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Transcript of Chapter 4 Solutions