CHEM 122 Lab Final

Objectives of Lab 2 (Colligative Properties: Freezing Point Depression)

-Define colligative properties

-Use the freezing point depression constant of cyclohexane to determine the concentration and identity of an unknown solution

What do colligative properties depend on?

Only the ratio of the number of solute particles to the number of solvent particles, and not the identity of the solute

What properties are considered colligative

Boiling point, osmotic pressure. vapor pressure. and freezing point

What reagents were used in lab 2?

Cyclohexane and NaCl (solid)

True or False: Kf depends on the identity of the solute

False, its dependent on the solvent

Adding a solute to a solvent wil:

Elevate boiling point, decrease vapor pressure, increase osmotic pressure, and depress the freezing point

Objectives of Lab 3 (Titration Antacid Analysis)

-Set up and perform a neutralization titration

-Describe how antacids function to neutralize stomach acid

-Calculate the amount of acid neutralized by an antacid tablet

Why is acid needed in the digestive process?

To activate the enzyme, pepsin, which helps with breaking down food

What color will the phenolphthalein indicator turn in basic solutions (high pH)?

Pink

What causes someone to feel heartburn?

Overeating or eating specific foods, which causes the stomach to secrete more HCl than is needed

Antacids provide relief from:

Gastric hyperacidity

Why are HCl and NaOH considered safety hazards in the lab?

They are corrosive to the skin and eyes

What reagents were used in lab 3?

-Antacid (tums, aka-seltzer, gaviscon)

-HCl

-NaOH

-Phenolphthalein indicator

Objectives of Lab 4 (The Iodine Clock: Reaction Kinetics)

-Describe the factors that influence reaction kinetics

-Calculate the molarity of a solution

-Discuss how increasing the concentration of a reactant influences the rate of the reaction

Define kinetics

The study of reaction rates

True or False: In general, increasing temperature increases the reaction rate

True

Reaction Mechanism

The step or series of steps (pathway) by which the reactants form products

Chemical nature of the reacting species

The chemical structure and composition of the reacting substances govern how fast a reaction takes place

Concentration of reacting species

Can be molarity for liquids or partial pressure for gases. Any increase in the number of reacting species in a given volume results in an increase in collisions, increasing the odds of a collision with sufficient energy and correct orientation. This increases the rate

Surface area in heterogeneous reactions

Species involved in heterogeneous reactions can react only where the two phases touch; small particles have a larger surface area than larger particles

Catalysts

Alter the mechanism of the reaction by interacting with the reactants to provide a new pathway with lower activation energy (meaning a high percentage of the reacting species has sufficient energy to react)

What reagents were used in lab 4?

-KIO3

-Bisulfite

Rate Law

The relationship between the rate of a chemical reaction and the concentration of the reactants, if all other factors are held constant

Objectives of Lab 5 (Le Châteliers Principle)

-Explain Le Chǎteliers principle

-Predict the direction of equilibrium shift when a stress is applied to the system

-Describe qualitative changes observed when a system experiences stress

What is Le Chǎteliers principle?

When a stress is applied to a system at equilibrium, the system will adjust so as to relieve that stress

If you spill concentrated HCl, you need to flush the spill with plenty of water followed by a solution of sodium bicarbonate. Why is it necessary to flush with a solution of sodium bicarbonate?

Because sodium bicarbonate is a neutralizer which is necessary to neutralize the reaction of HCl

Adding a reactant

Right shift

Adding a product

Left shift

Removing a product

Right shift

Removing a reactant

Left shift

Decrease in volume

Shifts towards the lower ratio of moles

Increase in volume

Shifts towards the higher ratio of moles

For an endothermic reaction, increasing heat will shift the reaction:

Right

For an endothermic reaction, decreasing heat will shift the reaction:

Left

For an exothermic reaction, increasing heat will shift the reaction:

Left

For an exothermic reaction, decreasing heat will shift the reaction:

Right

Objectives of Lab 6 (Buffers and Salt Hydrolysis)

-Explain how chemists use buffer systems to control pH

-Calculate hydronium and hydroxide ion concentrations

-Explain the process of hydrolysis

What does a buffer do?

It resists large changes in pH upon dilution or addition of small amounts of acid or base

_____ acids have a larger value Ka

Stronger acids

_____ acids have a smaller Ka

Weaker acids

_____ bases have a larger Kb

Stronger bases

____ bases have a smaller Kb

Weaker bases

Blood buffer

Bicarbonate system

What happens if the bicarbonate system is disrupted?

-Acidosis or alkalosis (too much acid or base)

-Symptoms: nausea, migraine, cramps, fainting, coma, death

True or False: Proteins act as buffers

True

Objectives of Lab 7 (Finding Equilibrium Constants: The Solubility of Borax)

-Calculate the solubility constant of Ksp

-Perform a titration

Define Ksp

Ksp is the solubility product constant, which indicates how soluble a solid is in water

Objectives of Lab 8 (Qualitative Analysis: Cations, Anions, and Complex Ions)

-Become acquainted with the chemistry of several elements

-Understand the principles of qualitative analysis

-Identify unknown cations/anions

Qualitative Analysis

Determines presence of substance based on its reactivity

What is qualitative analysis used for?

Speed and mobility

Anode

What's being oxidized

Cathode

What's being reduced

Objectives of Lab 9 (Oxidation-Reduction Reactions)

-Describe the transfer of electrons in an oxidation-reduction reaction

-Illustrate an electrochemical cell and describe the system in terms of half-cells

Calculate the free energy of a given system and state whether the reaction is spontaneous or non spontaneous

A solution contains 0.119 moles of an unknown compound and 200g of acetic acid. The Kf of acetic acid is 3.90 ℃/𝓂 and the normal freezing point of acetic acid is 16.6 ℃. Calculate the freezing point of the solution

~14.26℃

A solution contains 233 g of an unknown compound in 1000 g of cyclohexane. The molality of this solution is 3.6 𝓂. What is the molar mass of the unknown compound?

~65 g/mol

Is NaCl neutral, basic, or acidic?

Neutral

Is ZnBr2 neutral, basic, or acidic?

Acidic

Calculate the Ka of HCH3CO2 (acetic acid) if the Kb of CH3COO- (acetate ion) is 5.6E-10

~1.8E-5

What is the pH of a buffer that contains 0.800 M acetic acid and 1.000 M sodium acetate? The Ka of acetic acid is 1.8E-5

4.84

What is the pH of a 0.25 M NaOH solution?

13.40

The rate law for a reaction rate is rate=k[A][B]. What is the reaction order with respect to reactant A

The reaction order with respect to A is 1

You mix 40 mL of 0.02 M KIO3 with 10 mL of 0.01 M sulfite-starch solution in 70 mL of water. What is the initial concentration of KIO3 in the reaction mixture?

0.0067

Complete the following neutralization reaction: CaCO3 + HCl

CaCO3 + 2HCl -> CaCl2 + H2O + CO2

A titration is performed. 13.2 mL of 2.7 M HCl was required to titrate 25.0 mL of NaOh to the equivalence point. What is the molarity of NaOh at the equivalence point?

1.4 M NaOH

Is a solution of sodium acetate acidic, neutral, or basic?

Basic

Is a solution of ammonium chloride acidic, basic, or neutral?

acidic

Calculate the pH of a 0.100 M KCN solution. The Ka of HCN is 6.2E-10

11.11

What us the Ksp expression for the following equilibrium: AgBr (s) ⇌ Ag+ (aq) + Br- (aq)

Ksp=[Ag+][Br-]

Solid BaF2 is added to pure water, and some of the solid remains undissolved. Analysis of the equilibrium solution indicates that the fluoride ion concentration is 1.5E-2 M

a) Write the chemical equation for the dissociation of the solid into its ions

b) What is the Ksp expression

c) Calculate the Ksp

a) BaF2 (s) ⇌ Ba 2+ (aq) + 2F- (aq)

b) Ksp=[Ba2+][F-]^2

c) 1.7E-6

True or False: For qualitative analysis, ions are grouped according to their reactivity to known specific compounds

True

Barium (Ba 2+) is a Group IV cation. K2CrO4 will precipitate any barium present as a bright yellow precipitate. Write the balanced net ionic equation for the reaction between Ba 2+ and K2CrO4.

Ba^2+ (aq) + CrO4^2- (aq) ⇌ BaCrO4 (s)

Addition of AgNO3 will precipitate any chloride (Cl-) present as a white precipitate. Write the balanced net ionic equation for the reaction between AgNO3 and Cl-

Ag+ (aq) + Cl- (aq) ⇌ AgCl (s)

Watch glass

Buret

pH meter

Hot plate

Pipet

Volumetric pipet

Pipet bulb

Stir Bar

Gradulated cylinder

Thermometer

Clamp

Rubber stopper

Ring stand

Sn^2+ -> Sn^4+ + 2e-

Fe^3+ + e- -> Fe^2+

The standard cell potential for the overall redox reaction is +0.617 V. Calculate Delta G knot for the redox reaction.

-1.191E5 J or -119.06 kj

Calcium (Ca^2+) is a Group IV cation, K2C2O4 will precipitate any calcium present as a white solid. White the balanced net ionic equation for the reaction between Ca^2+ and K2C2O4

Ca^2+ (aq) + C2O4^2- (aq) -> CaC2O4 (s)

Addition of dilute acid (H+) causes vigorous bubbling/fizzing with carbonates. Write the balanced net ionic equation for the reaction between H+ and CO3^2-

2H+ (aq) + CO3^2- (aq) -> H2O + CO2

Complete the following neutralization reaction:

NaHCO3 + HCl ->

NaHCO3 + HCl -> NaCl + H2O + CO2

Complete the following neutralization reaction:

Mg(OH)2 + HCl ->

Mg(OH)2 + 2HCl -> MgCl2 + 2H2O

Complete the following neutralization reaction:

Al(OH)3 + HCl ->

Al(OH)3 + 3HCl -> AlCl3 + 3H2O

rate of reaction

the change in concentration of a reactant or product per unit time

Given the following rate law, how does the rate of reaction change if the concentration of X is doubled?Rate = k[X][Y]4

The rate of reaction will increase by a factor of 2.

Which rate law is [A] vs time? What slope does it have?

Zero order and it has a slope of -k

Which rate law is ln[A] vs time? What slope does it have?

First order and it has a slope of -k

Which rate law is 1/[A] vs time? What slope does it have?

Second order and it has a slope of +k

In experiment 4, how were you able to evaluate temperature change in reaction rates?

performed ice bath at room temp, cold and warm temp

barium

bright yellow precipitate

calcium

white precipitate

Na

bright yellow flame