Chapter 13 - Physical properties of solutions

What is a solution?

A mixture of a solvent and one or more solutes - can either be solid, liquid or gas.

Difference between solvent & solute?

The solution is the product that the solvent ends up dissolving - often times the solution is the one with a smaller quantitiy.

What determines he physical state of the solution?

The solvent is what determines the physical state of a solution

Examples of gas-gas, gas-liquid & gas-solid?

Air, carbonated water & h2 gas in a palladium.

liquid-liquid, liquid-solid & solid-liquid & solid-solid

ethanol in water , mercury in silver , saltwater & brass

Unsaturated

A solution with less than the maximum amount of solute that can be dissolved

Saturated

A solution with the maximum amount of solute dissolved.

Supersaturated

a solution that contains more dissolved solute than the maximum - generally unstable - often created in high temperatures and crystallizes when returned to room temperature.

State saturation of the following grams of Navl in 100g of H2O where solubility is 36g/100H2O : 40g, 36g & 32g

Oversaturated, saturated, unsaturated

Phase match brass, carbonated bev and O2 in a palladium where its a solute-solvent solution.

Solid-solid, Gas-liquid, & Gas-solid.

Solavtion process

When a solute dissolves in a solvent, the molecules of the solute are separated and therefore individually surrounded by solvent molecules.

Solvation process interactions

Solute-solute, solvent-solvent & solute-solvent

Describe the three conceptual steps in dissolution

First stage: pure solute and pure solvent not mixed

First → second stage: Holes must be created in the solvent to hold the solute particles. Separation of solvent particles occurs. Heat energy must be supplied from the environment (Enthalpy change (Change in ss) must be positive.

Second → third stage: Solute particles do what the solvent particles were doing in stage 2, change in Huu is positive. This is interchangable with step 2.

Third→ fourth: an exothermic reaction occured as the separated particles of the solute occupt the holes in the solvent, creating a solution. The enthalpy change of the system in this step (change in Hus) is negative.

change in Hsoln = Change in Hss + Change in Huu + Change in Hus. If Change in Hsoln is smaller than 0 its exothermic and endothermic if larger than zero.

Dissolution is encouraged when exothermic and discouraged when endothermic.

What intermolecular force occurs when the charge of an ion is attracted to the partial charge on a polar molecule? AKA NaCl or KI in H2O

Ion-dipole between an ion and a polar molecule

What molecular force occurs when a partial cahrge on a polar molecule induces a temporary partial charge on a neighboring nonpolar molecule or atom? AKA He or CO2 in H2O

Dipole

The charge of an ion induces a temporary partial charge on a neighboring nonolar molecule or atom AKA Fe2+ and O2

Ion-dipole between a non-polar molecule and an ion

What is molarity?

The molar concentration or the number of moles of solute per liter of solution so Moles/liters

2.34g NaCl is dissolved in enough water to make 250 mL solution, calculate the molarity of this solution. given the molar mass of Nacl is 58.44 g/mol

0.160 mol/liters

Mole fraction

The # of moles of a component divided by the total number of moles in a mixture OR Moles of A / Sum of moles of all components.

A commercial bleach solution contains 3.62% NaOCl by mass in water, caluclate the mole fraction of NaOCl in this solution. (hint, just convert % to grams always) Givem mm of NaOCl is 74.44 g/mol and 18.02 g/mol for H2O

Step 1. 3.62g/74.44 g/mo= 0.0486 mol AND 96.38/18.02g/mol =5.35 so 0.0486/5.35= 0.00901 mole fraction of NaOCl

Molality

Number of moles of a solute dissolved in 1 kg of solvent so Moles of solute/mass of solvent in kg

A solution containing equal masses of glycerol (C3H8O3) And water has a density of 1.10 g/mL. calculate the molality and molarity of glycerol in this solution. there is 10g of glycerol and 10g of water given molar mass of glycerol is 92.09 g/mol

Molality: moles of glycerol: 10g of 92.09g/mol= 0.1086 that over the mass of water in kg (0.0100) becomes 0.1086mols/0.0100kg = 10.86 mol/kg

Molarity: volume=mass/density so divide the TOTAL mass of the solution over the given density= 20.0g/1.10 g/mL=18.18 mL=0.01818 L and THEN divide moles of glycerol over the liters.

Percent by Mass (%m/m)

The ratio of the mass of an individual component tot he total mass SO: mass of solute/mass of solute+mass of solvent x 100

calculate the mass percent of NaCl in a solution containing 1.50 g NaCl dissolved in 50.0 g of water

(1.50/50+1.50) ×100 = 2.91%

ppm & ppb

parts per million: the ratio of the mass of an individual component to the total mass multiplied by 10^6

parts per billion: the ratio of the mass of an individual component to the total mass multiplied by 10^9

EQUATION: mass of solute/mass of solution x 10^ (6 or 9)

a solution is made by dissolving 0.0171g of glucose C6H12O6 in enough water to make a liter of solution. The density of the solution is 1.062 g/mL the molar mass of glucose is 180.2 g/mol. express the concentration of the solution in ppm and ppb

1L x 1000mL/L x 1.062 g/mL = 1062g and (0.0171g/1062g) x 10^6 =16.102 17.04 ppm and 10^9 17,040

how is molarity effected by temperature ?

the volume of a solution increases with temperature which would change molarity

which concentration units are independent from temperature and why?

mass percent, mole fraction, molality, ppm and ppb because the mass and moles do not change with temperature

how does the solubility of gasses in water react with increasing temperatures? why?

decreases because the temp can effect the kinetic energy of the gas molecules which are then able to break intermolecular forces and escape from the solution

How is the solibility of solids and liquids effected by pressure? how do they compare to gases?

the solubility of solid and liquid solvents are not effected by pressure unlike gases because the solubility of gas is proportional to the pressure, which is given by henry’s law c=kP

What is henry’s law? what do the letters stand for?

c=kP.

C: Solubility (M) of the dissolved gas.

P: Pressure of the gas over the solution

k: constant for each gas (mol/Lxatm) that depends only on temperature

As pressure decreases, the concentration also decreases.

calculate the concentration of CO2 in water @ 25 degrees celsius when the pressure of CO2 over the solution is 4.0 am. Henry’s law constant for co2 in water=3.1X10-² mol/Lxatm

4.0 atm x 3.1×10^-2 = 0.124 mol/L

Electrolyte

A compound that conducts an electric current when it is in an aqueous solution or melted. To conduct a current, substance has to contain mobile ions that can move. All ionic compounds are electrolytes.

Nonelectrolyte

A compound that does not conduct an electric current. Sugar and ethanol are nonelectrolyes which is why they would not work as well when melting snow like salt. They do not produce ions when dissolved in water.

Vapor pressure

The pressure exerted by the vapor in the headspace of a closed container.

Raoult’s law

Quantifies the amount of vapor pressure lowering that is observed in a nonvolatile solute. The equation is Psoln=xsolvent P^0 solvent where

Psoln: vapor pressure of the solvent above the solution

P^0: vapor pressure of the solvent above the pure liquid solvent

Xsolvent: mole fraction of the pressure

THIS WORKS BEST WITH IDEAL SOLUTIONS WHERE CONCENTRATION IS LOW AND INTERMOLECULAR ATTRACTIONS ARE SIMILAR

The vapor pressure of water is 42.2 mmHg Torr at 25 degrees celsius. a 225g sample of glucose is added to 575g of water to form a solution calculate the vapor pressure of this solution. given molar masses of glucose and water are 180.2 and 18.02

step 1. calculate the moles of water and solution: 225/180.2=1.249 and 575/18.02=31.909.

step 2. Mole fraction (xsolvent) Moles of water/total moles of solution so 31.91/31.91+1.249=2.249 0.09623

step 3. multiply by given pressure of water 0.9623 × 42.2 mmHg = 40.63 mmHg

Boiling point elevation

Change of tb=tb-t^0b where T^0b is bigger than Tb and change of Tb is bigger than 0

Change of Tb is the boiling point elevation

Boiling point elevation is proportional to the number of solute particles present and can be related to molality where change of tb (boiling point) = kb x m

Where m is molality and Kb is molal boiling point elevation constant (C/m) for a given solvent and the value of Kb DEPENDS ONLY ON THE IDENTITY OF THE SOLVENT

Calculate the boiling point of 0.50 m solution of glucose in ethanol where Kb=1.22 c/M AND THE BOILING POINT IS 78.4

step 1. calculate change of tb BY 1.22 times 0.50 m =1 ft 7.685 in 0.61 C amd then add the boiling point

Freezing point depression:

Change of tf=tf^0-tf w

Where its Freezing point depression - freezing point of pure solvent - freezing point of the solution

ethylene glycol is a common autombile antifreeze it is water soluble and vairly nonvolatile at bp of 197 c the molar mass of glycol is 62.07 and f and Kb for water are 1.86 and 0.52 C/m Calculate freezing point and boiling point of a solution containing 685g of ethylene and 2075g of water

1. moles of glycol= 685/62.07 - 11.03 mol

2. molality = 11.03 over 2.075 kg of water (remember its solute moles of solvent kg)

3. plug and play where change of freezing point is the given freezing point is 1.86 times molality

4. change boiling point is 0.52 times molality

5. Change of Tf is 9.90 and change of Tb is 2.72. C

Osmotic pressure

the new movement of a solvent through a sempipermeable membrane towards the solution with greater solute concentration where it goes from lower solute to higher solute concentration. the osmotic pressure the whats required to stop osmosis

(osmotic pressure looks like pi) = MRT which is molarity times the gas constant times the absolute given temp in kelvin

The average osmotic pressure of blood is 7.7 atm at 25 degrees celsius what molarity of glucose will be isotonic with blood?

1. rearrange original equation to solve for M where it becomes (osmotic pressure) over RT so 7.7/R times 298 K (273+25)

2. thats it, 0.314

define isotonic, hypotonic and hypertonic

Isotonic: two solutions of equal concentrate

Hypotonic: a solution have LOWER osmotic pressure

Hypertonic: a solution having GREATER osmotic pressure

What is the constant for vant hoff factor for electrolyte i?

number of solution after dissolation over the number of formula units initiallt dissolved