AP Chemistry Unit 4
What are the rules for determining oxidation numbers?
1. In free elements (elements that are not combined with or chemically bonded to other elements)(including diatomic ones) each atom has an oxidation number of zero. 2. For monatomic ions the oxidation number is equal to the charge of the ion. 3. The more electronegative element in a binary compound is assigned the oxidation number equal to the charge it would have if it were an ion. 4. Fluorine has an oxidation number of -1 in all of its compounds. Other halogens have negative oxidation numbers when they occur as halide ions in their compounds, but when combined with oxygen they have positive oxidation numbers. 5. The oxidation number of oxygen is -2 unless it is combined with fluorine (when it is +2) or in peroxides (when it is +1). 6. The oxidation number of hydrogen is +1 except when bonded to metals in binary compounds. In such cases its oxidation number is -1. 7. In compounds, the elements of groups one and two as well as aluminum have oxidation numbers of +1, +2, and +3 respectively. 8. In a neutral molecule the sum of all the oxidation numbers must be zero. 9. In a polyatomic ion the sum of all the oxidation numbers in the ion must equal the net charge of the ion. 10. Oxidation numbers do not have to be integers, though they typically are.
Al(s)→Al3+(aq)+3e− Sn2+(aq)+2e−→Sn(s) Based on the half-reactions represented above, which of the following is the balanced ionic equation for the oxidation-reduction reaction between Al(s) and Sn2+(aq) ?
2Al(s)+3Sn2+(aq)→2Al3+(aq)+3Sn(s)
Solubility Rules
Alkali ions and NH4+, are always soluble if in a compound. There are no exceptions NO3-, C2H3O2-, HCO3-, CIO4-, and CIO3- are always soluble if in a compound. There are no exceptions. Cl-, Br-, and I- are always soluble if in a compound except with Pb(2+), Hg(2+), or Ag+. SO42- is always soluble if in a compound except with Pb(2+), Ag+, Hg(2+), Ca(2+), Sr(2+), and Ba(2+). OH- is always insoluble except compounds of the alkali metals, NH4+, Sr2+, or Ba2+. If a substance does not fit one of the four rules above, assume it is insoluble and should be written as molecule (not ionized).
hypobromite
BrO -
bromite
BrO2 -
bromate
BrO3 -
perbromate
BrO4 -
acetate
C2H3O2 -
cyanide
CN -
carbonate
CO3 2-
hypochlorate
ClO -
chlorite
ClO2 -
chlorate
ClO3 -
perchlorate
ClO4 -
Zn(s)+CuSO4(aq)→Cu(s)+ZnSO4(aq) When a zinc plate is placed in an aqueous solution of copper sulfate, elemental copper forms, as represented by the equation above. Which of the following represents the reduction half-reaction of the reaction?
Cu2+(aq)+2e−→Cu(s)
fluorate
FO3 -
5Fe2+(aq)+MnO4−(aq)+8H+(aq)→5Fe3+(aq)+Mn2+(aq)+4H2O(l) Which of the following represents the oxidation half-reaction based on the balanced ionic equation shown above?
Fe2+(aq)→Fe3+(aq)+e−
bicarbonate
HCO3 -
What are the strong acids?
HCl, HBr, HI, HNO3, H2SO4, HClO3, HClO4
hypoiodite
IO -
iodite
IO2 -
iodate
IO3 -
periodate
IO4 -
What are the strong bases?
LiOH, NaOH, KOH, RbOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
permangante
MnO4 -
ammonium
NH4 +
nitrite
NO2 -
nitrate
NO3-
hydroxide
OH -
phosphite
PO3 3-
Phosphate
PO4 3-
sulfite
SO3 2-
Sulfate
SO4 2-
What are examples of physical changes?
Separations of mixtures and phase changes
What does the hypo- prefix on a polyatomic ion mean?
There are two less oxygen than in the -ate form.
What does the -ite ending on a polyatomic ion mean?
There is one less oxygen than the -ate form.
What does the per- prefix on a polyatomic ion mean?
There is one more oxygen than in the -ate form.
In the reaction between C5H5N(aq) and HCl(aq) represented on slide 12, C5H5N acts as...
a Bronsted-Lowry base
What are things that are evidence of chemical change?
heat or light being produced and formation of a precipitate
Conjugate acid-base
in an acid-base reaction every acid has a conjugate base formed by removing H+ and each base has a conjugate acid formed by adding an H+
Oxidation number rules
- atoms in their elemental form have an oxidation number of zero - Monoatomic ions have an oxidation number equal to their charge - Oxygen is a compound most often has an oxidation number of -2, one notable exception is peroxides, like H2O2, where oxygen has an oxidation number of -1 - Hydrogen usually is +1 when it is bonded to a nonmetal and -1 when it is bonded to a metal - Fluorine always has an oxidation number of -1 - the sum of all oxidation numbers in neutral compounds is zero - the sum of all oxidation numbers in a polyatomic ion equal the charge
Al(s)→Al3+(aq)+3e− Zn2+(aq)+2e−→Zn(s) 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?
2
C3H8(g) + 4Cl2(g) ---> C3H4Cl4(g) + 4HCl(g) A 6.0 mol sample of C3H8(g) and a 20. mol sample of Cl2(g) are placed in a previously evacuated vessel, where they react according to the equation above. After one of the reactants has been totally consumed, how many moles of HCl(g) have been produced?
20. mol
Ni(s)→Ni2+(aq)+2e− Ag+(aq)+e−→Ag(s) What 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)
When the equation below is balanced and all coefficients are reduced to lowest whole-number terms, what is the coefficient for H3PO4(l)? Ca3(PO4)2(s) + H3PO4(l) ---> Ca(H2PO4)2(s)
4
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 A cube of metal was changed into a flat sheet of metal. B When two liquids at room temperature were combined in a beaker, the beaker became hot. C When two clear liquids were combined, the resulting mixture was cloudy. D When a colorless liquid was added to a blue liquid, the resulting solution was yellow.
A A cube of metal was changed into a flat sheet of metal.
Na2CO3(aq)+2HCl(aq)→2NaCl(aq)+H2O(l)+CO2(g) A student combined two colorless aqueous solutions. One of the solutions contained Na2CO3 as the solute, and the other contained HCl. The chemical reaction that took place is represented by the equation above. What experimental result would be evidence that a chemical reaction took place when the solutions were combined? A Bubbles formed when the two solutions were combined. B The total volume of the mixture is close to the sum of the initial volumes. C The resulting solution is colorless. D The resulting solution conducts electricity.
A Bubbles formed when the two solutions were combined.
Based on the Brønsted-Lowry theory of acids and bases, which of the following species can act as both a conjugate acid and a conjugate base? A HS− B CH3COO− C H3O+ D NH4+
A HS−
2Mg(s)+SiCl4(l)→2MgCl2(s)+Si(s) Which of the following statements about the reaction represented above is correct? A It is an oxidation-reduction reaction, and Mg is oxidized. B It is an oxidation-reduction reaction, and electrons are transferred from SiCl4 to Mg C It is an oxidation-reduction reaction, and the oxidation number of Cl changes from +4 to +2. D It is not an oxidation-reduction reaction because none of the oxidation numbers change.
A It is an oxidation-reduction reaction, and Mg is oxidized.
HC2H3O2(aq)+OH−(aq)→C2H3O2−(aq)+H2O(l) A student carried out a titration using HC2H3O2(aq) and NaOH(aq). The net ionic equation for the neutralization reaction that occurs during the titration is represented above. The NaOH(aq) was added from a buret to the HC2H3O2(aq) in a flask. The equivalence point was reached when a total of 20.0mL of NaOH(aq) had been added to the flask. How does the amount of HC2H3O2(aq) in the flask after the addition of 5.0mL of NaOH(aq) compare to the amount of HC2H3O2(aq) in the flask after the addition of 1.0mL of NaOH(aq), and what is the reason for this result? A It is less because more HC2H3O2(aq) reacted with the base. B It is the same because the equivalence point has not been reached. C It is the same because all of the coefficients in the neutralization equation are 1. D It is greater because HC2H3O2(aq) is a proton donor.
A It is less because more HC2H3O2(aq) reacted with the base.
A student was given two clear liquids; a colorless liquid and a dark-blue liquid. The student was asked to combine the liquids in a beaker and record observations. Which of the following results, if true, would provide the best evidence that a chemical change took place when the liquids were combined? A The resulting mixture was cloudy. B The total volume of the mixture was equal to the sum of the initial volumes. C The resulting liquid was light blue. D The liquids formed two separate layers in the beaker.
A The resulting mixture was cloudy.
Is the following reaction classified as an acid-base reaction, redox reaction, or precipitation reaction? C2H3O2-(aq) + H3O+(aq) ---> HC2H3O2(aq) + H2O(l)
Acid-Base
Is the following reaction classified as an acid-base reaction, redox reaction, or precipitation reaction? NH3(aq) + HCl(aq) ---> NH4+(aq) + Cl-(aq)
Acid-Base
C6H5COOH(aq)+NaOH(aq)→C6H5COONa(aq)+H2O(l) What are the conjugate acid-base pair in the reaction represented above?
Acid: C5H5COOH Conjugate Base: C6H5COO-
A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. What is the balanced net ionic equation for the formation of the precipitate?
Ag+(aq)+Cl−(aq)→AgCl(s)
The color of AgI(s), a salt of silver, is yellow. A student adds a solution of Nal to a test tube containing a small amount of solid, cream-colored AgBr. After stirring the contents of the test tube, the student observes that the solid in the test tube changes color from cream to yellow. Write the net ionic equation for the reaction that occurred in the test tube.
AgBr(s) + I-(aq) ---> AgI(s) + Br-(aq)
Slide 11: Which of the following best describes the process represented above that takes place when NH3 is added to water? A It is a single replacement reaction in which an electron pair on N is replaced with an H atom. B It is an acid-base reaction in which a proton is exchanged from H2O to NH3. C It is a precipitation reaction in which NH4OH, an insoluble solid, is produced. D It is an oxidation-reduction reaction in which the oxidation number of N changes from −3 to −4.
B It is an acid-base reaction in which a proton is exchanged from H2O to NH3.
A student places a sample of a pure metal in a crucible and heats it strongly in air. The mass of the empty crucible is 12.0g. The mass of the crucible and sample before heating was 14.4g. The mass of crucible and sample after heating was 16.0g. The final mass was determined after the sample was cooled to room temperature. Which of the following statements related to the experiment is correct? A The mass of the sample decreased, so physical changes occurred as the metal first melted and then boiled out of the crucible. B The mass of the sample increased, so a chemical change occurred when bonds formed between the metal and another substance. C There was nothing for the metal to react with, so only a physical change could have occurred. D The sample was only heated, so neither a physical nor a chemical change occurred.
B The mass of the sample increased, so a chemical change occurred when bonds formed between the metal and another substance.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) 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? A The resulting solution is colorless. B The temperature of the reaction mixture increases. C The total volume of the mixture is approximately equal to the sum of the initial volumes. D The resulting solution conducts electricity.
B The temperature of the reaction mixture increases.
Which of the particulate diagrams on slide 2 best shows the formation of water vapor from hydrogen gas and oxygen gas in a rigid container at 125*C?
C
Mass of NaI crystals: 2.0 g Color of NaI crystals: white Color of solid recovered: yellow Color of filtered solution: colorless Mass of dry solid recovered: 3.0g When students added 2.0g of NaI crystals to 100.mL of Pb(NO3)2(aq), a yellow precipitate formed. After the solution was filtered, the yellow solid was dried and weighed. Data from the experiment are shown in the table above. Which of the following claims is best supported by the observations? A A physical change occurred when a new yellow compound was formed. B A physical change occurred when the color of the NaI solid added changed to yellow when mixed with water. C A chemical change occurred when a yellow, insoluble compound with a larger mass than the original NaI formed. D A chemical change occurred when covalent bonds between the yellow solid and water were broken during drying.
C A chemical change occurred when a yellow, insoluble compound with a larger mass than the original NaI formed.
A chemistry teacher carried out several demonstrations, and students recorded their observations. For one of the demonstrations, a student concluded that a physical change took place, but not a chemical change. Which of the following observations could the student have made of the results of the demonstration? A Two colorless solutions were combined, and the resulting solution was pink. B When a solid was added to a liquid, sparks were produced. C One piece of solid substance was changed into small pieces. D When two solutions were combined, a precipitate formed.
C One piece of solid substance was changed into small pieces.
A student combines a solution of NaCl(aq)NaCl(aq) with a solution of AgNO3(aq)AgNO3(aq), and a precipitate forms. Which of the following is evidence that ionic bonds formed during the precipitation? A The resulting solution is colorless. B The resulting solution conducts electricity. C The precipitate has a high melting point. D The temperature of the solution did not change significantly during the precipitation.
C The precipitate has a high melting point.
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? A The volume of the resulting solution will be equal to the sum of the volumes of the original solutions. B The mass of the resulting solution will be equal to the sum of the masses of the original solutions. C The resulting solution would contain a precipitate. D The resulting solution will be clear.
C The resulting solution would contain a precipitate.
K2SO3(aq)+2HNO3(aq)→2KNO3(aq)+SO2(g)+H2O(l) According to the balanced chemical equation above, when 100.0mL of 0.100MK2SO3(aq) is mixed with 100.0mL of 0.200MHNO3(aq) at 30°C and 1 atm, the volume of SO2 gas produced is 0.24 L. If it is assumed that the reaction goes to completion, which of the following changes would double the volume of SO2 produced at the same temperature and pressure, and why? (For each change, assume that the other solutions and volumes remain the same.) A Using 200.0mL of the 0.100MK2SO3(aq), because it then becomes the reactant in excess B Using 200.0mL of the 0.200MHNO3(aq), because the volume of SO2 produced is inversely proportional to the number of moles at constant temperature and pressure C Using 200.0mL of 0.100MK2SO3(aq) and 200.0mL of 0.200MHNO3(aq), because this provides double the number of moles with the correct stoichiometric ratio D Using 400.0mL of 0.100MK2SO3(aq) and 200.0mL of 0.200MHNO3(aq), because this provides the same number of moles of each reactant
C Using 200.0mL of 0.100MK2SO3(aq) and 200.0mL of 0.200MHNO3(aq), because this provides double the number of moles with the correct stoichiometric ratio
The diagrams on slide 8 represent solutes present in two different dilute aqueous solutions before they were mixed. Water molecules are not shown. When the solutions were combined, a precipitation reaction took place. Which of the diagrams on slide 9 is the best particle representation of the mixture after the precipitation reaction occurred?
D
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? A The solution does not change color after stirring. B The KCl crystals are no longer visible after mixing with water. C There is a temperature change in the solution during the dissolving process. D After the water has evaporated, the white crystals in the beaker have a mass of 20.0g.
D After the water has evaporated, the white crystals in the beaker have a mass of 20.0g.
A beaker was half filled with freshly distilled H2O and placed on a hot plate. As the temperature of the water reached 100°C, vigorous bubbling was observed in the beaker. The gaseous contents of the bubbles were analyzed. The presence of which of the following substances would support the claim that the observed phenomenon was a physical change? A H2(g) B O2(g) C CO2(g) D H2O(g)
D H2O(g)
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) When the reaction represented above proceeds, heat is produced. Which of the following best describes the reaction? A It is a combustion reaction because heat is produced by the reaction. B It is a double replacement reaction because 2Cl atoms are added to Zn. C It is an acid-base reaction because HCl is an acid that is capable of exchanging H+. D It is an oxidation-reduction reaction because zinc is oxidized and hydrogen is reduced.
D It is an oxidation-reduction reaction because zinc is oxidized and hydrogen is reduced.
The table on slide 7 summarizes data given to a student to evaluate the type of change that took place when substance X was mixed with water. The student claimed that the data did not provide enough evidence to determine whether a chemical or physical change took place and that additional tests were needed. Which of the following identifies the best way to gather evidence to support the type of change that occurred when water and X were mixed? A Measuring the melting point of the mixture of water and X B Adding another substance to the mixture of water and X to see whether a solid forms C Measuring and comparing the masses of the water, X, and the mixture of water and X D Measuring the electrical conductivities of X and the mixture of water and X
D Measuring the electrical conductivities of X and the mixture of water and X
A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Assume that 50.0mL of 1.0MNaCl(aq) and 50.0mL of 1.0MAgNO3(aq) were combined. According to the balanced equation, if 50.0mL of 2.0MNaCl(aq) and 50.0mL of 1.0MAgNO3(aq) were combined, the amount of precipitate formed would A double, because all of the coefficients are 1 B double, because the amount of one of the reactants was doubled C not change, because all of the coefficients are 1 D not change, because the amount of AgNO3(aq) did not change
D not change, because the amount of AgNO3(aq) did not change
The diagram on slide 5 represents H2(g) and N2(g) in a closed container. Which of the diagrams on slide 5 would represent the results if the reaction shown were to proceed as far as possible? N2(g) + 2H2(g) ---> 2NH2(g)
E
HNO3(aq) + H2O(l) ---> NO3-(aq) + H3O+(aq) For the dissolution of HNO3 in water represented above, which species are Bronsted-Lowry bases?
H2O(l) and NO3-(aq)
What is the correct net ionic equation of the neutralization reaction between hydrofluoric acid and sodium hydroxide in aqueous solution?
HF(aq) + OH-(aq) --> H2O(l) + F-(aq)
HNO3(aq) + H2O(l) ---> NO3-(aq) + H3O+(aq) For the dissolution of HNO3 in water represented above, which species are Bronsted-Lowry acids?
HNO3(aq) and H3O+(aq)
HNO3(aq) + H2O(l) ---> NO3-(aq) + H3O+(aq) For the dissolution of HNO3 in water represented above, what are the two sets of conjugate acid-base pairs?
HNO3(aq) and NO3-(aq) are a conjugate acid-base pair and H2O(l) and H3O+(aq) are a conjugate acid-base pair
HNO3(aq) + H2O(l) ---> NO3-(aq) + H3O+(aq) For the dissolution of HNO3 in water represented above, what occurs during the reaction that identifies it as an acid-base reaction?
HNO3(aq) donates a proton and becomes NO3-(aq) and H2O(l) accepts a proton and becomes H3O+(aq)
A student is carrying out various experiments in a lab. In one experiment, the student mixes two clear, colorless solutions together, and a yellow precipitate is formed. The student determines that this is evidence of a chemical reaction. Do you agree with the student? Justify your answer.
I agree with the student. This is an example of a chemical reaction because a precipitate is formed. We can conclude that a new product was made after the solutions were mixed that has different chemical properties than the original solutions.
LEO the lion says GER
Loss of electrons is oxidized; gain of electrons is reduced
NH3(aq) + HCl(aq) <--- ---> NH4+(aq) + Cl-(aq) What are the Bronsted-Lowry bases in the reaction represented above?
NH3(aq) and Cl-(aq)
What is the correct net ionic equation of the reaction that occurs when aqueous solutions of ammonia and hydrochloric acid are combined?
NH3(aq)+H+(aq)→NH4+(aq)
Cu(s)+2AgNO3(aq)→Cu(NO3)2(aq)+2Ag(s) The reaction between solid copper and aqueous silver nitrate produces solid silver and a blue solution, as represented by the balanced equation shown above. Based on the balanced equation, what are the oxidation and reduction half-reactions?
Oxidation Half-reaction: Cu(s) ---> Cu(2+)(aq) + 2e- Reduction Half-reaction: Ag+(aq) + e- ---> Ag(s)
I2(aq)+C6H8O6(aq)→C6H6O6(aq)+2I−(aq)+2H+(aq) The compound C6H8O6 reacts with I2 according to the reaction represented by the equation above. What type of reaction is this?
Oxidation-reduction
Slide 10: When C2H4(g) reacts with H2(g), the compound C2H6(g) is produced, as represented by the equation above. What type of reaction is this?
Oxidation-reduction
Equal volumes of 0.2M solutions of lead(II) nitrate and potassium bromide are combined to form lead(II) bromide as a yellow precipitate. What is the net ionic equation for the reaction?
Pb2+(aq)+2Br−(aq)→PbBr2(s)
Is the following reaction classified as an acid-base reaction, redox reaction, or precipitation reaction? Ca(2+)(aq) + SO4(2-)(aq) ---> CaSO4(s)
Precipitation
Is the following reaction classified as an acid-base reaction, redox reaction, or precipitation reaction? Ca2+(aq) + SO4(2-)(aq) ---> CaSO4(s)
Precipitation
Is the following reaction classified as an acid-base reaction, redox reaction, or precipitation reaction? 2C6H6(l) + 15O2(g) ---> 12CO2(g) + 5H2O(l)
Redox
Is the following reaction classified as an acid-base reaction, redox reaction, or precipitation reaction? 3Br2(aq) + 6OH-(aq) ---> 5Br-(aq) BrO3-(aq) + 3H2O(l)
Redox
The reaction between aqueous strontium chloride (SrCl2) and aqueous potassium sulfate (K2SO4) forms a precipitate of strontium sulfate (SrSO4). What is the net ionic equation for the reaction?
Sr2+(aq)+SO42−(aq)→SrSO4(s)
A student sands the surface of a 6 cm strip of Mg metal and places it into a crucible. The crucible and Mg are massed, placed over a Bunsen burner, and heated strongly in air for 10 minutes. After cooling, the final mass of the crucible and combustion product are taken. The mass of the crucible and Mg before heating if 35.6439 g. The mass of the crucible and combustion product after heating is 37.8901 g. What experimental evidence would best help the student confirm that a new compound has been made and that a chemical change occurred?
The data indicates that the combustion product has a greater mass that the reactant, Mg. The Mg must have reacted with another substance to form a compound with a greater mass.
In aqueous acid-base reactions what can water do?
Water can behave like an acid and donate a proton or like a base and accept a proton.
Physical change
When a substance undergoes a physical process in which the composition of the substance does not change; physical properties may change; involves a change in intermolecular attractions but bonds are generally not broken and/or formed and the substance's chemical composition is unchanged
A student is given a small mass of baking soda and a sample of vinegar. The student is asked to predict what will happen when the two substances are added together, as well as whether a physical or a chemical process will occur. What prediction should the student make, and how could she provide evidence to justify her answer?
When baking soda and vinegar react together, a gas forming reaction occurs. The formation of carbon dioxide will result in new bonds being made and an endothermic reaction. It takes energy to break apart the baking soda and vinegar, and energy is released when carbon dioxide, water, and sodium acetate are formed. The production of heat from the reaction as well as the observation of gas evolution are evidence of a chemical change.
What happens when solutions of an acid and a base are mixed?
a neutralization reaction occurs
Titrant
a solution of known concentration
Potassium sorbate, KC6H7O2 (molar mass 150. g/mol) is commonly added to diet soft drinks as a preservative. A stock solution of KC6H7O2(aq) of known concentration must be prepared. A student titrates 45.00 mL of the stock solution with 1.25 M HCl(aq) a. Write the net-ionic equation for the reaction between KC6H7O2(aq) and HCl(aq). b. A total of 29.95 mL of 1.25 M HCl(aq) is required to reach the equivalence point. Calculate [KC6H7O2] in the stock solution.
a. C6H7O2- + H+ ---> HC6H7O2 b. 0.832 M KC6H7O2
A student titrates 10.0 mL of a 2.000 M HC2H3O2(aq) with an NaOH(aq) solution of unknown concentration. The student monitors the pH during the titration. The titration curve on slide 6 was created using the experimental data presented in the table. a. Write the balanced net ionic equation for the reaction that occurs when HC2H3O2(aq) and NaOH(aq) are combined. b. Calculate the molar concentration of the NaOH(aq) solution.
a. HC2H3O2 + OH- ---> C2H3O2- + H2O b. 1.43 M NaOH
A student learns that ionic compounds have significant covalent character when a cation has a polarizing effect on a large anion. As a result, the student hypothesizes that salts composed of small cations and large anions should have relatively low melting points. a. Select two compounds from the table on slide 1 and explain how the data supports the student's hypothesis. b. When fluoride compounds are dissolved in water, hydroxide ions are produced. Write the net ionic equation for the reaction that occurs when one of the fluorides in the table is combined with water. (Hint: HF doesn't dissociate appreciably in water.)
a. LiI and KI: LiI has a small cation and a large anion, and KI has a large cation and the same large anion. The melting point of LiI (with its smaller cation) is lower than that of KI OR LiI and LiF: Lil has a small cation and a large anion, and LiF has the same small cation and small anion. The melting point of LiI (with its larger anion) is lower than that of LiF. OR LiI and NaF: LiI has a small cation and a large anion, and NaF has a relatively small cation and a small anion. The melting point of LiI (with its larger anion) is lower than that of NaF. b. Either LiF or NaF is acceptable. F- + H2O <---- ----> HF + OH-
Zn(s) + 2HCl(aq) ---> ZnCl2(aq) + H2(g) When a student adds 50.0 mL of 1.00 M HCl to 2.35 g of Zn, a reaction occurs according to the equation above. a.) When the reaction is complete at 273 K and 1.0 atm, what volume of H2(g) is produced? b.) Which of the following changes would increase the volume of H2(g) produced in a? i. doubling the mass of Zn ii. doubling the volume of HCl iii. doubling the concentration of HCl
a.) 0.560 L H2 b.) i. no effect ii. increases iii. increases
6H+ (aq) + 2MnO4-(aq) + 5H2C2O4(aq) ---> 10CO2(g) + 8H2O(l) + 2Mn2+(aq) A student dissolved a 0.139 g sample of oxalic acid, H2C2O4 in water in an Erlenmeyer flask. Then the student titrated the H2C2O4 solution in the flask with a solution of KMnO4 which has a dark purple color. The balanced chemical equation for the reaction that occurred during the titration is shown above. a.) The student used a 50.0 mL buret to add the KMnO4(aq) to the H2C2O4(aq) until a faint lavender color was observed in the flask, an indication that the end point of the titration had been reached. the initial and final volume readings of the solution in the buret are shown on slide 6. Write down the initial reading and the final reading and use them to determine the volume of KMnO4(aq) that was added during the titration. b.) Given that the concentration of KMnO4(aq) was 0.0235 M, calculate the number of moles of MnO4- ions that completely reacted with the H2C2O4. d.) The student proposes to perform another titration using a 0.139 g sample of H2C2O4 but this time using 0.00143 M KMnO4(aq) in the buret. Would this titrant concentration be a reasonable choice to use if the student followed the same procedure and used the same equipment as before? justify your response?
a.) 26.20 mL of KM nO4 added b.)6.16x10^-4 mol MnO4- c.) No, the titrant is so dilute that volume of titrant needed would exceed the capacity of the 50 mL buret.
2MnO4-(aq) + 5H2O2(aq) + 6H+(aq) ---> 2Mn2+(aq) + 5O2(g) + 8H2O(l) A student was given the task of determining the molarity of an unkown concentration of H2O2(aq). She analyzed a 10.0mL sample of H2O2(aq) by titrating it with 0.0330 M KMnO4 which has a dark purple color. The balanced chemical equation for the reaction that occurred during the titration is shown above. A total of 10.69 mL of 0.0330 M KMnO4 was required to reach the equivalence point. a.) Calculate the number of moles of MnO4- that reacted completely with the H2O2. b.) Calculate the {H2O2] in the solution.
a.) 3.53x10^-4 mol MnO4- b.) 0.0882 M H2O2
C3H8(g) + 5O2(g) ---> 3CO2(g) + 4H2O(g) Propane burns in air to produce carbon dioxide and water according to the above equation. 44.1 g of propane and 44.1 g of oxygen are added to a rigid vessel. The reaction is parked and goes to completion. a.) When the reaction is complete at 273 K and 1.0 atm, what mass of CO2(g) is produced? b.) What effect would each of the following changes have on the mass of CO2(g) produced in a? i. doubling the mass of C2H8(g) ii. doubling the mass of O2(g)
a.) 36.4 g CO2 b.) i. no effect ii. increases
Co(s) ---> Co(2+)(aq) + 2e- Ag(1+)(aq) + e- ---> Ag(s) The half-reactions for the oxidation-reduction between Co(s) and Ag(1+)(aq) are represented above. a.) Which substance is being oxidized and which substance is being reduced? b.) Write the balanced net ionic equation for the oxidation-reduction reaction based on the half-reactions above.
a.) Co is being oxidized and Ag is being reduced b.) Co(s) + 2Ag(1+)(aq) ---> Co(2+)(aq) + 2Ag(s)
Cr(s) ---> Cr(3+)(aq) + 3e- Ag(1+)(aq) + e- ---> Ag(s) The half-reactions for the oxidation-reduction between Cr(s) and Ag(1+)(aq) are represented above. a.) Which substance is being oxidized and which substance is being reduced? b.) Write the balanced net ionic equation for the oxidation-reduction reaction based on the half-reactions above.
a.) Cr is being oxidized and Ag is being reduced b.) Cr(s) + 3Ag(1+)(aq) + 3e- ---> Cr(3+)(aq) + 3e- + 3 Ag(s)
HC2H3O2(aq) + OH-(aq) ---> C2H3O2-(aq) + H2O(l) A student performed a titration of HC2H3O2(aq) with KOH(aq). The net ionic equation for the neutralization reaction that occurs during the titration is shown above. a.) Identify both of the Bronsted-Lowry conjugate acid-base pairs in the neutralization reaction above. For each pair, label the acid and the base. b.) In terms of the species in the reaction, explain what occurs during the reaction that identifies it as an acid-base reaction.
a.) HC2H3O2(aq) and C2H3O2-(aq) are a conjugate acid-base pair and OH-(aq) and H2O(l) are a conjugate acid-base pair. b.) HC2H3O2(aq) donates a proton and becomes C2H3O2-(aq)
Al(s) + Ni(NO3)2(aq) ---> Al(NO3)3(aq) + Ni(s) The reaction between solid aluminum and aqueous nickel (II) nitrate is represented by the equation shown above. Based on the equation, answer the following: a.) Write the oxidation half-reaction and reduction half-reaction. b.) Write the balanced net ionic equation for the oxidation-reduction reaction shown above.
a.) Oxidation Half-Reaction: Al(s) ---> Al(3+)(aq) + 3e- Reduction Half-Reaction: Ni(2+)(aq) + 2e- ---> Ni(s) b.) 2Al(s) + 3Ni(2+)(aq) ---> 2Al(3+)(aq) + 3Ni(s)
The oxidation of one substance is always...
accompanied by the reduction of another substance
What are the three important types of chemical reactions?
acid-base reactions, oxidation-reduction (redox) reactions, and precipitation reactions
Titration
an experimental technique where a solution of known concentration (standard solution) is combined with a solution of unknown concentration to determine the amount of moles in the unknown
In a redox reaction, electrons...
are transferred from one species to another
What should you look for to determine if a reaction is an oxidation-reduction (redox) reaction?
assign oxidation numbers to each element and look for atoms that have oxidation numbers that change
Which of the following describes the changes in forces of attraction that occur as H2O changes phase from a liquid to a vapor? a. H - O bonds break as H - H and O - O bonds form. b. Hydrogen bonds between H2O molecules are broken. c. Covalent bonds between H2O molecules are borken. d. Ionic bonds between H+ ions and OH- ions are broken. e. Covalent bonds between H+ and H2O molecules becomes more effective.
b. Hydrogen bonds between H2O molecules are broken.
A student is asked to formulate a hypothesis about what would happen to sodium metal when it is placed in water. Which of the following hypotheses indicates that the student thinks a chemical change will occur? a. If sodium is added to water, it will dissolve. b. If sodium is added to water, heat and light will be released. c. If sodium is added to water, the total mass will be the same. d. If sodium is added to water, the water will remain a clear, colorless liquid.
b. If sodium is added to water, heat and light will be released.
Redox Titrations
can be used to determine the concentration of an unknown solution; may not require the use of an indicator
Processes that involve the breaking and/or formation of chemical bonds are generally referred to as...
chemical reactions
Fe(s) + 2HCl (aq) ---> FeCl2 (aq) + H2(g) When a student adds 30.0 mL of 1.00 M HCl to 0.56 g of powdered Fe, a reaction occurs according to the equation above. When the reaction is complete at 273 K and 1.0 atm, which of the following is true? a. HCl is in excess, and 0.100 mol of HCl remains unreacted. b. HCl is in excess, and 0.020 mol of HCl remains unreacted. c. 0.015 mol of FeCl2 has been produced. d. 0.22 L of H2 has been produced.
d. 0.22 L of H2 has been produced.
Net Ionic equations
do not include spectator ions; useful to represent only the substance undergoing a chemical change
Bronsted-Lowry acid-base reactions
involve a transfer of one or more protons (H+) from the acid to the base; the acid is proton donor and the base is a proton acceptor; products are often water and an ionic compound (salt)
Oxidation-Reduction (Redox) Reaction
involve the transfer of one or more electrons between reactants
Oxidation numbers
may be assigned to each of the atoms in the reactants and products; this is often an effective way to identify the oxidized and reduced species in a redox reaction
Chemical changes
occur when a substance undergoes a reaction and a new substance is formed; chemical properties change in this type of reaction
In an Oxidation-Reduction (Redox) Reaction, the substance that loses electrons is _______.
oxidized
Precipitation Reactions
precipitation reacts frequently involve mixing ions in aqueous solution to produce an insoluble ionic compound called a precipitate
Titration curve
produce during an acid-base titration when a pH meter is used to monitor the progress of the titration; can be used to determine the equivalence point of titration; the point on the curve where the pH change is the greatest indicates the volume of the titrant needed to react with the analyte in stoichiometric ratios
Equivalence point
reached when the amount of titrant added from the buret has completely reacted with all the analyte in the flask in stoichiometric ratios
In an Oxidation-Reduction (Redox) Reaction, the substance that gains electrons is _______.
reduced
2H2O2(aq) ---> 2H2O(l) + O2(g) Hydrogen peroxide, H2O2, decomposes according to the equation above. This reaction is thermodynamically favorable at room temperature. A particulate representation of the reactants is shown on slide 3. Draw the particulate representation of all the molecules that would be produced from these four reactant molecules.
see slide 4
Balanced molecular equations
show all species participating in a reaction; these equations indicate that mass is being conserved
Complete ionic equations
show ions in aqueous solution as separate charged particles; this type of equation can be used to easily identify spectator ions
In titration, the titrant is in _____ and the analyte is in ______.
the buret; the flask
What should you look for to determine if a reaction is an precipitation reaction?
the formation of an insoluble ionic compound from two aqueous solutions (sodium potassium, ammonium, and nitrate salts are soluble in water)
End Point
the point at which the indicator changes color; often an indicator is added to the analyte that shows a color change very near the equivalence point
Analyte
the solution with unknown concentration
What should you look for to determine if a reaction is an acid-base reaction?
two sets of conjugate acid-base pairs
Acid-Base Reactions
when solutions of an acid and a base are mixed, a neutralization reaction occurs
