2.3 Solutions

Objectives 9. Define solution, solute, solvent, and concentration 10. Explain the dissociation of water 11. Contrast properties of acids and bases 12. Describe the use of pH scale 13. Explain the action of buffers

Obj 9: Define solution, solute, solvent, and concentration Solution – mixture of one or more substances that are uniformly distributed in another substance Solute – substance dissolved in solution Solvent – substance in which the solute is dissolved

Example Example Sugar – solute Sugar – solute Water – solvent Water – solvent Mixed = solution of sugar water Mixed = solution of sugar water Neither sugar or water molecules are altered chemically Neither sugar or water molecules are altered chemically If solution boiled, sugar would remain If solution boiled, sugar would remain

Solutions vary in concentration – measurement of amount of solute dissolved in fixed amount of solution Example Example 2% saltwater solution = 2 g of salt dissolved in enough water to make 100 mL of solution 2% saltwater solution = 2 g of salt dissolved in enough water to make 100 mL of solution More solute the greater the % More solute the greater the % Saturated solution – one in which no more solute can dissolve Saturated solution – one in which no more solute can dissolve

Aqueous solutions – solutions in which water is the solvent Example Example Marine organisms – the sea Marine organisms – the sea Plants get nutrients from aqueous solution Plants get nutrients from aqueous solution Body cells in aqueous solution Body cells in aqueous solution

Obj 10: Explain the dissociation of water Dissociation – breaking apart of the water molecules into 2 ions of opposite charge Example Example H 2 O ↔ H + + OH - H 2 O ↔ H + + OH - Forms 2 ions Forms 2 ions H + and OH - H + and OH - Hydroxide ion = OH- Hydroxide ion = OH-

The free H+ ion can react with other water molecule The free H+ ion can react with other water molecule H + + H 2 O ↔ H 3 O + H + + H 2 O ↔ H 3 O + H 3 O + = hydronium ion H 3 O + = hydronium ion Acidity or Alkalinity measure of relative amounts of hydronium and hydroxide ions Acidity or Alkalinity measure of relative amounts of hydronium and hydroxide ions If hydronium ions = hydroxide ions the solution is neutral If hydronium ions = hydroxide ions the solution is neutral Pure water Pure water

Obj 11: Contrast properties of acids and bases Acid - # of hydronium ions greater than hydroxide ions in a solution Example Example HCl – hydrogen chloride – a gas dissolved in water HCl – hydrogen chloride – a gas dissolved in water Molecules dissociate for form H + and Cl - Molecules dissociate for form H + and Cl - HCl ↔ H + + Cl - HCl ↔ H + + Cl -

Free H+ combine with water Free H+ combine with water H+ + H 2 O ↔ H 3 O+ H+ + H 2 O ↔ H 3 O+ Solution has more hydronium ions (H 3 O+) than hydroxide ions (OH-) = acidic solution Solution has more hydronium ions (H 3 O+) than hydroxide ions (OH-) = acidic solution Acids have sour taste Acids have sour taste Concentrated forms are highly corrosive Concentrated forms are highly corrosive

Base – solution contains more hydroxide ions than hydronium ions NaOH ↔ Na + + OH - NaOH ↔ Na + + OH - Alkaline - refers to bases, an adjective Alkaline - refers to bases, an adjective Taste bitter Taste bitter Feel slippery Feel slippery

Acids and Bases

Obj 12: Describe the use of pH scale Compares relative concentrations of hydronium (H 3 O + ) and hydroxide (OH - ) ions Compares relative concentrations of hydronium (H 3 O + ) and hydroxide (OH - ) ions Ranges from 0-14 fig 2-10 Ranges from 0-14 fig = very acidic 0 = very acidic 7= neutral 7= neutral 14 = very basic 14 = very basic

Ammonia = 11.5 Ammonia = 11.5 Internal fluid = 8 Internal fluid = 8 Blood = 7.5 Blood = 7.5 Water = 7 Water = 7 Urine = 6 Urine = 6 Vinegar = 3 Vinegar = 3 Stomach acid = 2 Stomach acid = 2

Measure on logarithmic scale Measure on logarithmic scale Each unit is a ten fold change Each unit is a ten fold change Example Example pH of 4 has 10 x more hydronium ions (H 3 O + ) than a solution with a pH of 5 pH of 4 has 10 x more hydronium ions (H 3 O + ) than a solution with a pH of x more hydronium ions (H 3 O + ) than a solution with a pH of x more hydronium ions (H 3 O + ) than a solution with a pH of 6

Measure with litmus paper Measure with litmus paper Color changes with pH Color changes with pH

pH Scale

Obj 13: Explain the action of buffers Chemical substances that neutralize small amounts of either an acid or base added to a solution Chemical substances that neutralize small amounts of either an acid or base added to a solution Buffers maintain internal fluids at normal and safe levels Buffers maintain internal fluids at normal and safe levels

Review Objectives 9. Define solution, solute, solvent, and concentration 10. Explain the dissociation of water 11. Contrast properties of acids and bases 12. Describe the use of pH scale 13. Explain the action of buffers