AP chem unit 4 reactions

Oxidation Number Rules

- An atom existing as element, have oxidation number is zero - Hydrogen in compounds has oxidation number of +1 (except in hydrogen hydrides) - Oxygen in compounds has oxidation number of -2, but H2O2 has oxidation number of -1 - Sum of oxidation numbers equals the charge on the species

Acid base reactions

-acid & base react resulting in formation of conjugate base of acid & conjugate acid of base -The reaction proceeds as long as the reactants are stronger (more reactive) than the products they form

Rules for balancing using the redox method (not in an acid or base)

1) Assign Oxidation Numbers 2) Write Oxidation and Reduction half reactions. a. Balance Half Reactions for ATOMS b. Balance Half Reactions for CHARGE by adding electrons. 3) Make electrons lost equal to the electrons gained by multiplying the entire half reactions 4) Put the coefficients into the reaction; then balance the remaining atoms. Do not change the coefficients for the species involved in the redox. 5) Check to make sure that the total charge is the same on both side of the equation

Rules for balancing in an acidic solution

1) Assign Oxidation Numbers 2) Write Oxidation and Reduction half reactions. a. Balance Half Reactions for ATOMS b. Balance Oxygen by adding H2O as needed. c. Balanced Hydrogen by adding H+ as needed. d. Balance Half Reactions for CHARGE by adding electrons. 3) Make electrons lost equal to the electrons gained by multiplying the entire half reactions 4) Put the coefficients into the reaction; then balance the remaining atoms. Do not change the coefficients for the species involved in the redox. 5) Check to make sure that the total charge is the same on both side of the equation.

Rules for balancing in a basic solution

1)Complete the balancing process as if it is an acid. Then add OH- to both sides of the equation to form water with all of the hydrogen ions. 2) Cancel as many water molecules as possible.

evidence of chemical change

1. Color Change from within 2. Production of gas or odor 3. Release or absorption of heat 4. Production of light or sound 5. Total loss of identity 6. Formation of a precipitate 7. Formation of a new substance with new properties

The half-reactions for the oxidation-reduction reaction between Al(s) and Zn2+(aq) are represented above. Based on the half-reactions, what is the coefficient for Al(s) if the equation for the oxidation-reduction reaction is balanced with the smallest whole-number coefficients? (Write out oxidation and reduction to solve)

2

Which of the following is the balanced net ionic equation for an oxidation-reduction reaction between Ag+(aq) and Ni(s) based on the half-reactions represented above?

2Ag+(aq) + Ni(s) -> 2Ag(s) + Ni2+(aq)

A student was studying physical and chemical changes. The student carried out some procedures in the laboratory and recorded observations. For one of the procedures, the student concluded that a physical change took place, but not a chemical change. Which of the following could have been the results of the procedure?

A cube of metal was changed into a flat sheet of metal.

heterogeneous mixture

A mixture in which different materials can be distinguished easily

conjugate acid

A molecule that can be described as a base that has gained one proton.

Conjugate base

A molecule that can be described as an acid that has lost one proton

A student mixes 20.0g of white KCl crystals with distilled water in a beaker. After the mixture was stirred, no crystals are visible and the solution is clear. After several days, all of the water evaporates and white crystals are found in the beaker. Which of following pieces of experimental evidence would best help the student to confirm that a new compound had not been made and that only a physical change occurred?

After the water has evaporated, the white crystals in the beaker have a mass of 20.0g.

Matter

Anything that has mass and takes up space

Bronsted Lowry

Common definition of acids as proton donors and bases as proton acceptors.

What is the percent yield in the reaction between 46.1 g of cesium and 13.4 g of oxygen if 28.3 g of cesium oxide (Cs2O) are collected?

Compare 236 grams with 48.9 grams, 48.9 grams are the smaller amount. Therefore, Cs is the limiting reagent, O2 is excess and 48.9 g Cs2O is the theoretical yield. % yield = 57.9%

Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid

F−(aq)+H+(aq)→HF(aq)

Diatomic elements are

H2, N2, O2, F2, Cl2, Br2, I2

Strong acids are

HCl, HBr, HI, HNO3, HCLO3, H2SO4, HClO4

redox reaction

In some chemical reactions there is a transfer of electrons between two of the substances. When this occurs the reaction is considered a "RedOx" reaction.

Strong bases are

LiOH, NaOH, KOH, RbOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

pure substance

Matter that always has exactly the same composition

When C2H4(g) reacts with H2(g), the compound C2H6(g) is produced, as represented by the equation above. The reaction is correctly classified as which of the following types?

Oxidation-reduction, because H2(g) is oxidized.

The compound C6H8O6 reacts with I2 according to the reaction represented by the equation above. The reaction is correctly classified as which of the following types?

Oxidation-reduction, because I2 is reduced.

The reaction between solid copper and aqueous silver nitrate produces solid silver and a blue solution. Based on the balanced equation, which of the following identifies the oxidation and reduction half-reactions?

Oxidation: Cu(s) -> Cu2+(aq) + 2e- Reduction: Ag+(aq) + e- -> Ag(s)

Equal volumes of 0.2 M solutions of lead(II) nitrate and potassium bromide are combined to form lead(II) bromide as a yellow precipitate. Which of the following is the correct net ionic equation for the reaction?

Pb2+(aq) + 2Br-(aq) -> PbBr2(s)

oxidation number

Positive or negative number that indicates how many electrons an atom has gained, lost, or shared to become stable

Ions soluble in water

Sodium, potassium, ammonium, and nitrate salts are soluble in water

The reaction between aqueous strontium chloride (SrCl2) and aqueous potassium sulfate (K2SO4) forms a precipitate of strontium sulfate (SrSO4). Which of the following represents the net ionic equation for the reaction?

Sr2+(aq)+SO42−(aq)→SrSO4(s)

A 2 mol sample of F2(g) reacts with excess NaOH(aq) according to the equation above. If the reaction is repeated with excess but with of , which of the following is correct?

The amount of OF2(g) produced is halved

A student places a sample of a pure metal in a crucible and heats it strongly in air. Data from the experiment are given in the table above. The final mass was determined after the sample was cooled to room temperature. Which of the following statements related to the experiment is correct?

The mass of the sample increased, so a chemical change occurred when bonds formed between the metal and another substance.

A student was asked to formulate a hypothesis about what would happen if 100.mL of 0.1MNaOH(aq) at 25°C was combined with 100.mL of 0.1MMgCl2(aq) at 25°C. Which of the following hypotheses indicates that the student thought a chemical change would occur?

The resulting solution would contain a precipitate.

A student had two dilute, colorless solutions, HCl(aq) and NaOH(aq), which were at the same temperature. The student combined the solutions, and the reaction represented above occurred. Which of the following results would be evidence that a chemical reaction took place?

The temperature of the reaction mixture increases.

A 100 mL sample of 0.1M MgCl2(aq) and a 100mL sample of 0.2M NaOH(aq) were combined, and Mg(OH)2(s) precipitated, as shown by the equation above. If the experiment is repeated using solutions of the same molarity, which of the following changes in volume will double the amount of Mg(OH)2(s) produced?

Using twice the volume of MgCl2(aq) and twice the volume of NaOH(aq)

homogeneous mixture

a mixture in which the composition is uniform throughout

Precipitation reactions

a reaction that occurs between substances in solution in which one of the products is insoluble

amphoteric substance

a substance that can behave either as an acid or as a base

Compound

a substance with constant composition that can be broken down into elements by chemical process

Physical process

a transformation of a sample of matter, such as a change in its physical state or mixture separation, that does not alter the chemical identity of any substance in the sample

Percent yield

actual yield/theoretical yield x 100

net ionic equation

an equation for a reaction in solution showing only those particles that are directly involved in the chemical change, include charge and state

ionic equation

an equation in which substances that primarily exist as ions in solution are shown as ions (solids and liquids stay together typically) - must include charge and state

strong acids and bases

completely dissociate in solution and separate into its ions

physical change examples

distillation, filtration, melting ice, evaporating water, making solutions

redox titration

during these reactions, a color change is produced when the oxidation state of a metal ion in the reaction changes.

acid-base titration

either the acid or the base can be the titrant. An acid-base indicator which changes color at a pH close to 7 is added to determine the end point of a strong acid/base reaction. Sometimes pH meters are used to determine equivalence point.

Reduction

gain of electrons, loss of charge

oxidation-reduction reaction

involvetransfer of one or more electronsbetween chemical species, as indicated by changes in oxidation numbers of the involved species. Ex: combustion

Oxidation

loss of electrons, gain of charge

Can oxidation occur without reduction?

no because when electrons are lost by one atom, they must be gained by another element. these processes are complementary, one cannot occur without the other

chemical process

occurs when a substance is transformed into a new substance with a different composition. During a chemical process bonds are broken/formed. ex: 2 elements bond together to form a compound

physical change

physical property of a substance changes without changing the composition

physical vs chemical forces

physical/intermolecular chemical/intramolecular

sublimation/deposition

solid to gas and gas to solid

Elements

substance that cannot be decomposed into simpler substances by chemical or physical means

weak acids and bases

substance will only partially separate into its ions

Chemical reactions

the making and breaking of chemical bonds

equivalence point

the point at which the two solutions used in a titration are present in chemically equivalent amounts

pH meter

used to monitor an acid/base titration, it's common for pH and volume of titrant to be plotted on a graph

Stronger acid will form a _____ conjugate base, a weaker acid will form a _____ conjugate base

weaker, stronger

Precipitation titration

when the titrant reacts with ions in the analyte, a precipitation can occur. The formation of a precipitate or its color change can signal the end point.

Data needed to be recorded in a titration

x molarity of titrant x initial volume of titrant x final volume of titrant x volume or mass of analyte