Solutions and Acid/Base

Solutions

Solutions

• Solute – substance in lower concentration, dissolved

• Solvent – substance in higher concentration• Water is a universal solvent

Electrolyte vs. Non-electrolyte

• Electrolyte conducts electricity in solution due to the formation of ions• Acids, bases, most salts (ionic compounds)

• Non-electrolyte does not conduct electricity• Sugar, ethanol (many covalent compounds)

Rate of solution formation

• Stirring• Temperature• Surface area

• How would each of these affect solution formation?

Solubility

• Amount of solute that will dissolve in a given quantity of a solvent at a specific temperature and pressure to produce a saturated solution

• Expressed in grams of solute per 100 g of solvent

Solubility

• Unsaturated – able to dissolve more solute if added• Saturated – maximum amount of solute dissolved for the temperature

and pressure• Supersaturated – contains more solute than possible due to a slow

temperature drop

Factors affecting solubility

• Temperature – most increase solubility with temperature, but a few drop• Solubility of gases in liquid solvent is higher at lower temperatures• Best seen on solubility graph

• Pressure – does not affect solids or liquid solutes as much as gas solutes• Solubility increases with pressure

Solubility Graphs• Think: How does

solubility change as temperature increases? • Is there any

compound that does not follow the trend? Why might that be?

1. A solution of sodium nitrate at 20 ⁰ C has 100 g dissolved. Is it saturated, unsaturated, or supersaturated?

2. How much KNO3 would need to be added to a solution containing 25 grams at 37 ⁰C in order to make the solution saturated?

1. A solution of sodium nitrate at 20 ⁰ C has 100 g dissolved. Is it saturated, unsaturated, or supersaturated? above the line = super saturated

2. How much KNO3 would need to be added to a solution containing 25 grams at 37 ⁰C in order to make the solution saturated? 25 grams

Concentration calculations

• Molarity = Moles of solute / liters of solution

• Dilutions = M1 x V1 = M2 x V2

• Percent by volume = (V solute/V solution) x 100%

• Percent by mass = (mass solute / mass solution) x 100%

Molarity

• Intravenous (IV) saline solutions are often administered to patients in the hospital. One saline solution contains 0.90 g NaCl in exactly 100 mL of solution. What is the molarity of the solution?

• Molarity = moles per liter• 0.90 g NaCl / 58.44 g/mol = 0.015 mol• 100 mL = 0.1 L• 0.015 mol/0.1 L = 0.15 M (0.15 mol/L)

Molarity

• Household laundry bleach is a dilute aqueous solution of sodium hypochlorite (NaClO). How many moles of solute are present in 1.5 L of 0.70 M NaClO?

Dilutions

• How many milliliters of aqueous 2.00 M MgSO4 solution must be diluted with water to prepare 100.0 mL of aqueous 0.400 M MgSO4?

Percent by volume

• What is the percent by volume of ethanol (C2H6O) in the final solution when 85 mL of ethanol is diluted to a volume of 250 mL with water?

Percent by mass

• If you were making a 2000 g solution of glucose that has a 2.8% (m/m) concentration, how much glucose should you use?

Colligative property summary

• http://www.chemistryexplained.com/Ce-Co/Colligative-Properties.html

• Freezing point depression (solute lowers point of freezing)• Boiling point elevation (solute raises point of boiling)

Acids, Bases, SaltsChapter 19

Acids

• Hydrogen-containing compounds that ionize to yield hydrogen ions in aqueous solution• Acids are hydrogen-ion donors

Acids

• Properties• Sour taste• Electrolytes• React with metals• Change color of indicator• (litmus paper red)• (phenolphthalein clear)

• Examples• Acetic acid (vinegar)• Citric acid (in candy, citrus fruit,

soda)• HCl, H2SO4, HNO3

Bases

• Compounds that ionize to yield hydroxide ions in aqueous solution• Bases are hydrogen-ion acceptors

Bases

• Properties• Bitter taste• Slippery feel• Electrolyte• Change color of indicator• (litmus paper blue)• (phenolphthalein pink)

• Examples• Soap• Milk of magnesia

Ionization (dissociation)

• Ionization – becoming an ion• Dissociation – breaking into smaller particles• All dissociate, only some ionize

Strong and weak

• Strong – dissociate almost completely in water

• Weak – only dissociate slightly in water

Concentration vs. Strength

• Concentrated/dilute – how much (moles) dissolved in water

• Strong/weak – how ionized/dissociated in solution

• HCl is a strong acid, but can be made into a dilute solution. • Vinegar is a dilute solution of a weak acid.

Acid Base Neutralization Reaction

• Acids and bases react to neutralize and form salt and water

• HCl + NaOH NaCl + H2O

• Salt = anion from an acid and cation from a base

Ion product constant for water

• For aqueous solutions, the product of the hydrogen-ion concentration and the hydroxide-ion concentration equals 1.0 x 10-14

• Kw = [H+] x [OH-] = 1.0 x 10-14

• Acidic [H+] greater than [OH-] • (greater than 1 x 10-7)

• Candies are slightly acidic. If the [H+] in a solution is 4.5 x 10-6 M, is the solution acidic, basic, or neutral? What is the [OH-] of this solution?

pH scale and indicators

• 0-14• Negative logarithm of the hydrogen-ion concentration• pH = -log [H+]

pH scale and indicators

• pH = -log [H+]

Neutral solution is [H+] = 1 x 10-7 M pH = -log (1 x 10-7)pH = 7.0

• What is the pH of a solution with a hydrogen-ion concentration of 5.67 x 10-11 M?

• The pH of an unknown solution is 11.34. What is its hydrogen-ion concentration?

pOH

• pOH = -log[OH-]

• pH + pOH = 14

• What is the pH of a solution if [OH-] = 5.6 x 10-3 M?

Summary Questions

1. Give the pH range for acids and bases.2. What are the units for molarity? 3. You are making hot chocolate. Describe how you will ensure the

best saturation of the solution. 4. What is the difference between a weak acid and a strong acid? 5. If the pH of the solution is 6.5, what is the [H+] concentration?

What is the pOH? 6. When you open a pop bottle what happens to the pressure? How

does this change the solution? What role would temperature play?