Chapter 9: Solutions

Solutions (basic)

Homogenous mixtures

• Have two components

What are the solvent and solute distributions in solutions?

Solute: present in smaller amounts

Solvent: present in larger amounts

How do solutions form?

When there is sufficient attraction between solute and solvent molecules

• When solute-solvent interactions are large enough to overcome solute-solute and solvent-solvent interactions

What states of matter can solvents and solutes be in?

Both: gas, liquid, or solid

What happens to the solute when mixed with a solvent (state change)

Mixes with the solvent so that the solute and solvent have the same physical state

Solutes

Mixed into the solvent

• Spread evenly throughout the solution

• Cannot be separated by filtration, but can be separated through evaporation

• Are not visible, but can give the solution a color

Water as a solvent

One of the most common solvents in nature

Why is water a polar molecule?

Due to the polar O-H bonds

• Hydrogen bonds

What is the rule about the dissolving of solutes in a solvent?

“Like dissolves like“

• Both must be polar or nonpolar

Water w/ polar solutes

• Why?

Polar molecules such as CH₃OH are soluble in water due to the -OH group to form hydrogen bonds with water

Water w/ nonpolar solvents

Iodine, grease, oil and other nonpolar molecules are not soluble in water because there are no attractions between the two.

Electrolytes (in the body)

They play an important role in maintaining the proper function of the cells and organs

• Can be measured in a blood test

What does it mean to “dissociate“

Fall apart into ions

Strong Electrolytes

• Dissociate 100% in water, producing positive and negative ions

• Form solutions that can conduct an electric current strong enough to light a lightbulb

Weak Electrolytes

• Dissociate only slightly in water

• Forms a solution with a few ions and mostly undissociated molecules

• Mildly conducts electricity

Nonelectrolytes

• Dissolve as molecules in water

• Do not produce ions in water

• Do not conduct an electric current

Do polyatomic break down?

Nope

What are some examples of strong, weak, and non- electrolytes?

SE: Ionics, strong bases (have OH), strong acids, salts

WE: Weak acids (usually begin with H except for ammonia)

NE: Carbon compounds

What are the types of particles in a solution with strong, weak, and non-electrolytes?

SE: Only ions

WE: Mostly molecules a few ions

NE: Only molecules

Equivalents of Electrolytes

The amount of an electrolyte or an ion that provides one mole of electrical charge (+ or -)

Equivalents of Electrolytes (in solution…)

• The charge is always balanced by the charge of the negative ions

How are the concentration of electrolytes in intravenous fluids expressed?

Milliequivalents per liter (mEq/L)

• 1 Eq = 1000 mEq

If you have 2.2 mol of NaCl solution, then how many mole equivalents of each ion do you have?

Na⁺ = 2.2 Eq Na⁺

Cl⁻ = 2.2 Eq Cl⁻

If there are 25 mEq/L of Na⁺ and 4 mEq/L of K⁺ what is the total positive charge, and what concentration of Cl⁻ would make sense?

Total positive charge: 29 mEq/L

Cl⁻ = as the only anion has to be 29 mEq/L

Concentration: 8.8 mEq/L

How many moles of calcium ions in 0.50L

Calcium ions = 2+

0.5 L (8.8 mEq Ca²⁺/1 L)(1 Eq Ca²⁺/1000 mEq Ca²⁺)(1 mole Ca²⁺/2 Eq Ca²⁺) = 0.0022 moles of Ca²⁺

Solubility

The maximum amount of solute that dissolves in a specific amount of solvent

• Temperature sensitive for solutes

How is solubility expressed?

As grams of solute in 100g of solvent (usually water)

g of solute/100g water

Unsaturated Solutions

• What do they look like?

Contain less than the max amount of solute

• Can dissolve more solute

• Is clear

Saturated Solutions

Contain the max amount of solute that can dissolve

• Have undissolved solute at the bottom of the container

What happens in saturated solution? (equilibrium process)

Some solute dissolves and some recrystallize

solute dissolves

solute + solvent ⇌ saturated solution

solute recrystallizes

What happens to the solubility when the temperature increases?

• Most solids

• Gasses

Solids = Increases (direct relationship)

Gasses = Decreases (inverse relationship)

Henry’s Law

The solubility of a gas is directly related to the pressure of the gas above the liquid

• At higher pressures, more gas molecules dissolve in the liquid

  • Gas is pushed into the liquid

• When the pressure of a gas above a solution decreases, the solubility of the gas in the solution also decreases

What types of ionic compounds are soluble in water?

Ionic compounds that contain a soluble cation or anion

What happens if an ionic compound with no soluble cations or anions is placed in water?

• Why?

It will form a solid

• The ionic bonds are too strong for the polar water molecules to break

What can we use the solubility rules to predict?

Whether an ionic compound will dissolve in water or not

What are the solubility rules?

What DOES dissolve in water:

Positive Ions = Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH₄⁺

Negative Ions = No₃⁻, C₂H₃O₂

• Cl⁻, Br⁻, and I⁻ except when bonded with Ag⁺, Pb²⁺, or Hg₂²⁺

• SO₄²⁻ except when bonded with Ba²⁺, Pb²⁺, Ca²⁺, Sr²⁺, or Hg₂²⁺

What are the three types of equations?

Complete Molecular Equation:

• What we’re used to

Total Ionic Equations

• Uses subscripts and charges

Net Ionic Equations

• Cancels out repetitive parts

How do you write a net ionic equation?

First, form the complete molecular equation, balancing and all

Next, form the total ionic equation by separating the aqueous solutions into their ions = by using the subscripts as coefficients and writing in the charges

• Do not split polyatomic or solids or liquids or gasses

Lastly, cancel out any of the same ions from either side of the equation

How do you calculate the concentration of a solution? What are the units for each part?

Amount of solute/Amount of solution

Solute = grams, milliters, or moles

Solution = grams, milliters, or liters

Mass Percent (m/m) Formula

mass of solute g/mass of solute g + mass of solvent g(mass of solution g) x 100%

Volume Percent (v/v) Formula

volume of solute mL/volume of solution mL x 100%

Mass/Volume Percent (m/v) Formula

mass of solute g/volume of solution mL x 100%

What does the “x 100%“ mean in the m/m, v/v, and m/v formulas?

It means that, technically, the g of solute is over 100g of solution

ex. 5% (m/m) = 5g solute/100g solution

What is the conversion factor displayed by 8.50% (m/m) NaOH

8.50g NaOH/100g 8.50% (m/m) NaOH Solution

• Yes lots of words :<

Molarity

The moles of solute per volume(L) of solution

• Very specific; only in unites of moles and liters

What is the formula for molarity

Moles of solute/Liter of solution

What conversion factor is represented by 1.00M of NaCl?

1.00 moles NaCl/1 L NaCl solution

What is the molarity of a solution of 6.00g of NaOH in 500mL of solution?

First, we need to make grams into moles

6.00g (1 mol NaOh/40.00g NaCl) = 0.150 mole NaOH

Now, we need to make the 500mL solution into liters, which would be 0.500 L

Lastly use the molarity formula (mole/L)

0.150 mol NaOh/0.500L NaOH solution = 0.300M NaOH

What does a capital M mean?

Molar/Molarity

Dilution

A solvent, usually water, is added to a solution which increases it’s volume and decreases the concentration of the solution

True or False: In dilution, the mass of the solute stays the same

True

In the initial and diluted solutions, what formula relates their concentration?

C₁V₁ = C₂V₂

What is C in C₁V₁ = C₂V₂

Percent concentration(m/m, v/v, m/v) or molarity

What other formula has basically the same use as C₁V₁ = C₂V₂

M₁V₁ = M₂V₂

Solutions (described)

Transparent

• Do not separate

• Contain small particles, ions, or molecules that cannot be filtered nor can they pass through the semi-permeable membrane

• Homogenous

• Particles do not settle

Colloids

• Medium-sized particles

• Cannot be filtered

• Can be separated by semipermeable membranes

• Homogenous

• Particles do not settle

Suspensions

• Heterogeneous, nonuniform mixtures

• Have very large particles that settle (rapidly)

• Can be filtered

• Must be stirred to stay suspended

What is the Tyndal Effect and what type of mixture is it?

When particles are large enough and light shines through, it gets scattered

• Colloids

What are the two separation methods, and how large are the pores in each?

Filter Paper: 10⁻⁷m (larger)

Semipermeable Membrane: 10⁻¹⁰m (smaller)

Which mixture particles can pass through a semipermeable membrane?

Solution particles

• Not colloids or suspensions

Which mixture particles settle out and can be separated by a filter?

Suspensions

When does a liquid boil?

When it’s vapor pressure matches the external atmospheric pressure

When a solute is added to water, what physical properties change?

• What are these properties called and what do they depend on?

• Vapor pressure above solution decreases

• Boiling point increases

• Freezing point decreases

They are called colligative properties and depend only on the concentration of solute particles in the solution

Vapor Pressure Lowering (added solute)

Increasing the concentration of solute particles in the solution

• Decreases the # of solvent particles at the surface of the solution

• Prevents some of the solvent particles from leaving the solute

  • The solute takes up space at the top so the water cannot become vapor

Boiling Point Elevation (added solute)

Increasing the concentration of nonvolatile particles in the solution raises the boiling point of the solution

• More solute in solution decreases the vapor pressure

• Solution boils at a higher temperature than normal

  • More energy is needed to make water into vapor

Freezing Point Lowering (added solute)

Adding salt to an icy road(for example) when temperatures drop below freezing…

• Allows salt particles to mix with water

• Lowers the freezing point of the ice

What types of particles can lower the freezing point of water?

Strong electrolytes

• The stronger the electrolyte, the lower the freezing point

Osmosis

An ongoing process where water flows from a lower to a higher solute concentration through the membrane

• The level of the solution with the higher solute concentration rises

• The concentrations of the two solutions become equal over time

Osmotic Pressure

Equal to the pressure that would prevent the flow of additional water into the more concentrated solution

• Greater as the # of dissolved particles in the solution increases

Isotonic Solutions

Exert the same pressure as body fluids such as red blood cells (RBCs)

• Most IV solutions used in hospitals are isotonic solutions

What are the m/v% (RBCs) that classify as an isotonic solution?

• 5.0% (m/v) glucose

• 0.90% (m/v) NaCl

Hypotonic Solutions

Have a lower solute concentration than red blood cells

• Water flows INTO the cells by osmosis

  • The fluid increase causes the cells to swell and burst = hemolysis

Hypertonic Solutions

Have a higher solute concentration than red blood cells

• Water flows OUT OF the cells by osmosis

  • The cells shrink, look spiky: crenation

Dialysis

A process used to remove waste products and excess water from the blood

How does dialysis work?

Solvent and small solute particles pass through an artificial membrane

• Large particles are retained inside

What is hemodialysis

Part of Dialysis

• Waste particles such as urea from the blood are removed using an artificial kidney