CHM120 Exam 4

Solution

A mixture where one more more substances are dissolved in another substance

Solvent

A substance that dissolves another substance to form a solution

Solute

The substance that is dissolved in another substance to form a solution

Aqueous Solutions - Ionic 

When soluble ionic or polyatomic substances are dissolved in aqueous solutions, their ions separate and move around in the substance independently from one another.

Aqueous Solutions - Nonionic

Nonionic substances can also dissolve in aqueous solutions, such as sugar which is very soluble. Another example is ethanol, which has a polar O-H bond that reacts strongly with the O-H bond of water.

“Like Dissolves Like”

Polar solvents will dissolve polar solutes, non polar solvents will dissolve non polar solutes. When polar and non polar substances are put together, they tend not to mix. For example, polar water mixed with non polar petroleum.

Saturated Solution

When a solution contains as much solute as can dissolve at that temperature, the solution is saturated.

Unsaturated Solution

If more solute is added, it will dissolve. 

Concentrated Solution

A solution is a mixture, and when a relatively large amount of solute is dissolved in a solution, that solution is concentrated.

Dilute Solution

When a relatively small amount of solute is dissolved in a solution, that solution is dilute.

Mass %

(Mass of Solute/Mass of Solution) x 100

Molarity

Moles of Solute/Liters Solution

Dilution Equation

M1V1 = M2V2 (molarity x volume)

Stoichiometry Steps 

1. Write the Balanced Equation 

2. Calculate the moles of reactants

3. Determine which reactant is limiting 

4. Calculate the moles of other reactants or products, as required

5. Convert to grams or other units, as required 

Neutralization Reactions

One product of this reaction is always water. The net ionic equation is H⁺(aq) + OH^- (aq) —> H₂O (l)

Arrhenius Definitions

Arrhenius said that an acid produced H⁺ ions in aqueous solutions, while bases produced OH^- ions.

Bronsted-Lowry Definitions

In the Bronsted-Lowry model, the acid is a proton (H⁺) donor, and a base is a proton acceptor. When an acid is dissolved in water, it can best be represented as an acid (HA) donating a proton to a water molecule to form a new acid (the conjugate acid) and a new base (the conjugate base). HA (aq) + H₂O (l) —> H₃O⁺ (aq) + A^- (aq) 

Conjugate Acid

A base plus one H⁺ proton. (H₂O —> H₃O⁺)

Conjugate Base

An acid minus one H⁺ proton (HA —> A^-)

Strong Acid - Strong Electrolyte/Weak Acid - Weak Electrolyte

If the acid is completely ionized or dissociated, then it is a strong acid. If the acid is only partially ionized or dissociated, it is a weak acid. 

Common Strong Acids

Sulfuric acid - H₂SO₄; hydrochloric acid - HCl; nitric acid - HNO₃; perchloric acid - HClO₄

Common Weak Acids

acetic acid - CH₃COOH; phosphoric acid - H₃PO₄; carbonic acid - H₂CO₃; hydrofluoric acid - HF

How to Tell if An Acid Is Strong or Weak

Memorize strong acids - Hi Nasty Sul-perchloric (hydrochloric, nitric, sulfuric, perchloric).

pH Indicator

The lower the pH, the stronger the acid. To find pH, know Kw = [H⁺][OH^-] = 1.0e-14, then pH is -log[H⁺] 

pOH indicator

pOH measures basicity, pOH = -log[OH^-]. Lower pOH means stronger base. pH+pOH = 14.00

Diprotic/Polyprotic Acids

Diprotic acids are acids that can furnish 2 protons, and polyprotic acids are acids that can furnish multiple protons (2-3).

Oxyacids 

Acids in which the acidic hydrogen atom is attached to an oxygen atom.

Organic Acids

Acids are those with a carbon-atom backbone, commonly carboxyl acids (CO attached to OH).

Amphoteric Substances

Substances that can behave either as an acid or a base. The most common is water. We can see this clearly in the ionization of water, where the transfer of one H+ proton to another molecule produces H⁺ and OH^-.

K_w

The ion-product constant, which is [H₃O^+][OH^-] or more simply, [H⁺][OH^-]. Needed to find pH and pOH. 

Types of Aqueous Solutions

acidic, basic, neutral 

Significant Figures in pH and pOH

The number of decimal places must be equal to the number of significant figures in the original number.

pH —> H⁺

10e-pH

pOH —> OH^-

10e-pOH

Buffered Solutions

A solution that resists a change in its pH even when a strong acid or base is added to it.

Buffer

A solution is buffered by the presence of a weak acid and its conjugate base. 

The Collision Model

Chemists believe reactions occur by the molecules colliding with each other. Some collisions are violent enough to break bonds, which allows the reactants to rearrange to form the products.

Effect of Increased Reaction Concentration

Reactions speed up, because more molecules per unit volume means more collisions, and therefore more reaction events.

Conditions that Affect Reaction Rates 

Activation energy, temperature, catalysts, enzymes. 

Activation Energy

Reactions also speed up when the temperature increases. Why? The answer is the fact that not all collisions are strong enough to break bonds, and a minimum energy called the activation energy is needed for reactions to occur. Higher temperature = more energy.

Catalysts

A substance that speeds up a reaction without being consumed. Enzymes are a type of catalyst that allow our bodies to speed up reactions that would be too slow to sustain life. A catalyst provides a new pathway for the reaction to occur that has a lower activation energy than the original pathway. 

Equilibrium

The exact balancing of two processes, one which is the opposite of the other, the forward and reverse reactions.

Law of Chemical Equilibrium

A dynamic where the reactants and products in a reversible reaction remain constant.

Equilibrium Expression

K_eq = [products (g/aq)]^^coefficients/[reactants (g/aq)]^^coefficients  

Equilibrium Position

for concentration and volume

Equilibrium Position (Temperature)

When temperature is changed, the equilibrium constant is changed. We treat heat as a reactant (endothermic) or product (exothermic), and then we treat the change as if a reactant or product were added or removed. (Added - away; removed - towards). 

Application of K_eq

Large K_eq (much larger than 1) means that at equilibrium, the reaction consists of mostly products. Small K_eq means the system at equilibrium consists of mostly reactants.

Solubility Equilibria

K_sp = [product A and charge][product B and charge] (coefficients are numbers of atoms)

Oxidation Process

Oxidation is the loss of electrons. 

Reduction Process

Reduction is the gain of electrons.

Oxidation States

1. The oxidation state of an uncombined element is 0

2. The oxidation state of a monatomic ion is the same as its charge

3. Oxygen is assigned an oxidation state of -2 in most of its covalent compounds

4. In its covalent compounds with nonmetals, hydrogen is assigned the oxidation state of +1.

5. In binary compounds, the element with the greater electronegativity is assigned a negative oxidation state equal to its charge as an anion

6. For an electrically neutral compound, the sum of the oxidation states must be zero

7. For an ionic species, the sum of the oxidation states must equal the overall charge.

Oxidizing Agents

The atom reduced is the oxidizing agent

Reducing Agent

The atom oxidized is the reducing agent 

Electrochemistry

The study of the interchange of chemical and electrical energy. Involves two types of processes

1. The production of an electric current from a chemical (oxidation-reduction reaction)

2. The use of an electric current to produce a chemical change (using an electric current to separate H₂O atoms)

Galvanic Cells

Electrochemical batteries, devices powered by oxidation-reduction reactions. The oxidizing agent is separated from the reducing agent so that the electrons travel through a wire from the reducing agent to the oxidizing agent.

Anode

In a battery, the reducing agent loses electrons (which flow through the wire towards the oxidizing agent and so is oxidized). The electrode where oxidation occurs is the anode.

Cathode

At the other electrode, the oxidizing agent gains electrons and is thus reduced. The electrode where reduction occurs is called the cathode. 

Electrolysis

Forcing a current through a cell to produce a chemical change that would not otherwise occur. One example is forcing a current through a battery to reverse the oxidation-reduction reaction and recharge the battery. Another example is forcing a current through water to break it down into its elements.

Lead Storage Batteries

Used in automobiles. Can function for several years under temperature extremes and incessant punishment from rough roads.

Dry Cell Batteries 

Calculators, electronic watches, and smartphones are powered by these. They are called this because they don’t have liquid electrolyte. 

Corrosion

The process of returning metals to their natural state (the ores they were obtained from), by oxidizing.

Preventing Corrosion

Corroded metal loses its strength and attractiveness, so preventing corrosion is important. The primary means is through coating the metal either with pain or metal plating to protect it from oxygen and moisture. Chromium and tin are often used to plate steel. Alloying is also used to prevent corrosion. Stainless steel contains chromium and nickel, both of which form oxide coatings that protect the steel.

Cathodic Protection

The method most often used to protect steel in buried fuel tanks and pipelines. A metal that loses electrons more easily than iron such as magnesium is connected by a wire to the pipeline so that the magnesium is the reducing agent instead of the iron. 

Radioactive Decay

Many nuclei are radioactive, meaning they spontaneously decompose, forming a different nucleus and producing one or more particles. Nuclear equations represent radioactive decay. In a nuclear equation, both the atomic number (Z) and the mass number (A) must be conserved.

Isotopes

All isotopes of an element have the same number of protons but a different number of neutrons, thus changing the mass of the element. All isotopes of elements with more than 83 protons are radioactive.

Types of Radioactive Decay

alpha particle production, beta particle production, gamma ray production, positron production, electron capture.

Alpha Particle Production

A very common mode of decay for heavy radioactive nuclides. An ⍺-particle is ⁴₂He.

Beta Particles 

Another common decay process. The β-particle is assigned a mass number of 0 because its mass is tiny compared to a proton or neutron. The net effect of a β-particle is to change a neutron to a proton. Expressed as ⁰_-1e

Gamma Ray Production

A 𝛾-ray is a high-energy photon of light. A nuclide in an excited nuclear energy state can release excess energy by producing a 𝛾-ray. Production of a 𝛾-ray results in no change of mass number or atomic number. It is expressed as ⁰₀𝛾

Positron Production

A particle with the same mass as the electron but opposite charge. The production of a positron appears to change a proton to a neutron. Results in no change in mass number and a decrease of 1 in atomic number. Expressed as ⁰₁e

Electron Capture

A process in which one of the inner-orbital electrons is captured by the nucleus. Gamma rays are always produced alongside this process. Expressed as ⁰_-1e on the reactant side with ⁰₀𝛾 on the product side. 

Decay Series

Often a radioactive nucleus cannot achieve a stable (nonradioactive) state through a single decay process. In such case, a series occurs until a stable nuclide is formed. A well known example is the series that starts with U-238 and ends with Pb-206.

Nuclear Transformations

Rutherford observed the first nuclear transformation. He found that bombarding N-14 with ⍺-particles produced nuclide O-17.

Half-Life and Carbon Dating 

The half-life of an element is the time required for half the original sample of nuclei to decay. A given type of radioactive nuclide always has the same half-life. Half-lives are used to date Carbon-14 and determine the age of several ancient articles. 

Geiger Counter

The most familiar instrument for measuring radioactivity levels. High energy particles from radioactivity decay produce ions when traveling through matter. This instrument contains argon gas which has no charge, but can be ionized by the rapidly moving particles. The instrument then counts the ionization to determine radioactivity.

Scintillation Counter

An instrument that turns radioactive particles into light, like a flashlight that only turns on when it is hit by radioactive particles.

Nuclear Energy 

The protons and neutrons in atomic nuclei are bound together with forces that are much greater than the forces that bond atoms together to form molecules. The energies associated with nuclear processes are more than a million times those associated with chemical reactions. 

Nuclear Fusion

Combining two light nuclei together to form a heavier nucleus. Produces even more energy than nuclear fission. Stars produce their energy this way.

Nuclear Fission

Splitting a heavy nucleus into two nuclei with smaller mass numbers. In addition to the product nuclides, neutrons are produced. Each of these neutrons can then collide with other nuclides and cause another reaction event, thus making the process self-sustaining. However, critical mass is the exact mass of material needed to make a process self-sustaining. If too much mass is there, the process can escalate too fast and cause an explosion. If there is not enough, the process stops.

Nuclear Reactors

Nuclear fission has been developed as an energy source to produce electricity in reactors. The resulting energy is used to heat water to produce steam that runs turbine generators. Breeder reactors are used to make fissionable material.