Transcript Families of Chemical Compounds

Families of Chemical Compounds
Chapter 3
Solution Chemistry
• Classification of compounds based on physical &
chemical properties
• Acids, Bases, & Salts - most abundant families
What is a solution?
• Solution – the even distribution of molecules of
one substance into another substance
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Uniform throughout
Dissolved molecules too small to be seen
Do not settle over time
All consist of basic properties
• Solute – substance that is dissolved
• Solvent – substance that does the dissolving
▫ A.k.a. “dissolving medium”
• Most common solutions have a liquid as its
solvent
▫ Water most common solvent
▫ Alcohol (solvent) makes a solution called a tincture
• Solutes can be solid, liquid, or gas
• Particles in a solution are individual atoms, ions,
or molecules
▫ So small they do not scatter light, therefore
appearance is clear
• Not easily separated by simple means like filtration
• Some physical changes such as evaporation or boiling
can separate parts of some solutions
• Ability or inability to conduct electricity
▫ Any solution that contains ions is a good conductor
• Electrolytes – substances whose water solutions
conduct an electric current
▫ most are ionic compounds
▫ Pure water not a conductor until electrolytes such as potassium
chloride, sodium chloride, or silver nitrate are added
• Non-electrolytes – substances whose water solutions
do not conduct electric currents
▫ Most covalent compound are non-ecectrolytes
▫ Ex. Solution of sugar and water
Making Solutions
• Every solution has particular solvent & solute
• Types of Solutions
▫ Miscible – 2 liquids dissolving in each other
▫ Alloys – solid solutions consisting of metals; mixing
melting metals
 Ex. Brass, bronze, wrought iron
• Rate of Solutions
▫ Stirring or shaking moves molecules faster
▫ More molecules of solute brought in contact w/solvent
sooner, therefore solute dissolves faster
▫ Occurs at the surface therefore if surface area is
increase, rate of solution increased
▫ Heat also increase rate of solution due to high/faster
movement of molecules
• Solubility – measure of how much of that
solute can be dissolved in a given amount of
solvent under certain conditions
▫ Depends on the nature of both solute & solvent
▫ Ex. salt & water  high solubility
salt & alcohol  low solubility
• 2 Factors affect solubility
▫ Temperature
 Usually increase in temp. increases solubility of solid in liquid
 Increase of temp. decreases solubility of gas in liquid
▫ Pressure
 Solids & liquids dissolved in liquids pressure has not effect
 Gases dissolved in liquids; increase in pressure increases
solubility
• Concentration – amount of solute dissolved in
a certain amount of solvent
▫ Concentrated solution – a lot of solute is dissolved
in a solvent
▫ Dilute solution – little solute dissolved in a solvent
▫ Neither terms is precise
• Saturated Solution – contains all the solute it
can possible hold at a given temperature
▫ If more solute is added it will settle undissolved
• Unsaturated Solution – contains less solute than
it can possibly hold at a given temperature
▫ More solute can be dissolved
• Supersaturated Solution – under special
circumstances, able to hold more solute than
normal for that temperature
▫ unstable
• Special Properties
▫ Freezing point depression – the dissolving of a
solute in a liquid solvent lowers the freezing point
of the solvent
 Ex. Ethylene glycol – a.k.a. antifreeze added to
automobile cooling systems
▫ Boiling point elevation – addition of solute in a
pure liquid solvent raises the boiling point
 Salt added to water, raises the boiling point
therefore water boils at a higher temp decreasing
cooking time
Acids and Bases
• Found in common everyday items
• Important role in life processes in human body
• Manufacturing of many products
Properties of Acids
• Acids have certain physical & chemical
properties when dissolved in water
• Physical property – sour taste
▫ Lemons contain citric acid
▫ Vinegar contains acetic acid
• Indicators – compounds that show a definite
color change when mixed with an acid or a base
▫ Litmus paper – common indicator
 Changes from blue to red in an acid
▫ Phenolphthalein – colorless in an acid solution
• Acids reacts w/metals to form hydrogen gas &
metal compounds
▫ Corrodes the metal & leaves a residue
 Ex. Car batteries
• Acids contain hydrogen
▫ When dissolved in water, produce positive
hydrogen ions or protons; a.k.a. proton donors
Common Acids
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3 most common acids in laboratory & industry
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Sulfuric Acid
Nitric Acid
Hydrochloric Acid
All strong acids = good electrolytes (conductors of
electricity)
Ionize to a high degree in water & produce hydrogen
ions
Weak Acids = poor electrolytes
Acetic Acid
Carbonic Acid
Boric Acid
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Do not ionize to a high degree in water, produce few
hydrogen ions
Properties of Bases
• When dissolved in water – all share common
physical & chemical properties
▫ Bitter taste, slippery to touch
▫ Can be poisonous & corrosive
▫ Turn litmus paper from red to blue; phenolphthalein
to bright pink
▫ Emulsify or dissolve fats/oils to form soap
 Ex. Ammonium hydroxide (household cleaner) “cuts” grease
▫ All bases contain hydroxide ion
 When dissolved in water produce ion
▫ A.k.a. “proton acceptor”
Common Bases
• Strong bases
▫ dissolve readily in water to produce large numbers of
ions
▫ Good electrolytes
▫ Ex. Potassium hydroxide, sodium hydroxide, calcium
hydroxide
• Weak bases
▫ Do not produce large numbers of ions when dissolved
in water
▫ Poor electrolytes
▫ Ex. Ammonium hydroxide, aluminum hydroxide
Acids & Bases in Solution: Salts
• pH scale – used to measure the acidity of a
solution (pH= power of Hydrogen)
▫ The pH of a solution is a measure of hydronium ion
concentration
 Formed by the attraction btwn a hydrogen ion from an acid & a
water molecule
▫ Series of numbers btwn 0 and 14
▫ Middle of scale is 7 = neutral solution
 Ex. Water
▫ Less than 7 = acid
 Strong acids = low pH number
▫ More that 7 = base
 Strong bases = high pH number
Determining Solution pH
• Indicators – show a specific color change
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Litmus paper
Phenolphthalein
pH paper
Methyl orange
Bromthymol Blue
• pH meters are used for accuracy
• Common household indicators
▫ Red cabbage
▫ Grape juice
Formation of Salts
• Salts are formed when acids react chemically
with bases
• Salts – compound formed from the positive ion
of a base and a negative ion of an acid
▫ Neutral substance
• Neutralization- reaction of acids with a base
produce a salt and water
▫ Properties of acids and bases lost in process
▫ Many salts formed are insoluble in water
▫ Crystallize out of solution, remain a solid
HCl + NaOH ---------- H2O + NaCl
Hydrogen Chloride + Sodium Hydroxide
yields Water and Salt
• Participate – insoluble substance that
crystallizes out of a solution
▫ This process is called Precipitation
• Neutralization reactions are doublereplacement reactions
• Dangerous acids combined with dangerous
bases can produce a harmless salt and water.