11 Pre-U Review Questions 2 - SHAKRA-Courses - 12 …shakra-courses.weebly.com/uploads/1/1/0/3/11037233/_… ·  · 2012-06-06What will the new volume be if the temperature remains

1

11 Pre-U Review Questions 2

Short Answer

1. Write two ionization reactions to illustrate the fact that hydrochloric acid has high conductivity and

hydrofluoric acid has low conductivity.

2. Write the ionic equation to represent the dissociation of calcium hydroxide.

3. State two differences between nitric acid and nitrous acid.

4. What is the concentration of hydrogen ions in

(a) acidic solutions

(b) basic solutions

5. State the approximate pH values for the following substances:

(a) vinegar

(b) distilled water

(c) swimming pool water

(d) normal rain

(e) seawater

6. How does dilution affect the pH of

(a) acidic solutions?

(b) basic solutions?

7. A 0.1 mol/L solution of nitric acid has a pH of about 1 and a 0.1 mol/L solution of acetic acid has a pH of

about 3.

(a) Account for this difference in pH.

(b) Explain which acid is more acidic and by how much.

8. List three empirical properties for acids and three empirical properties for bases.

9. Define acid and base according to the Bronsted-Lowry theory.

10. Identify the two acid-base conjugate pairs in the following reaction:

HF(aq) + H2O(l) H3O+

(aq) + F–(aq)

11. List three important applications of neutralization reactions.

12. Write a balanced chemical reaction for sulfuric acid dissolving iron metal.

13. Write the balanced chemical equation for the neutralization of aqueous phosphoric acid by potassium

hydroxide.

14. List three effects on the environment that are caused by acid rain.

15. If the absolute temperature of a gas is doubled and the pressure is tripled, what happens to the volume of the

gas? Assume ideal gas behaviour.

16. What are the three types of motion for particles?

17. What is the cause of the weak interaction between noble gas molecules according to the intermolecular force

theory?

18. Rank the following states of matter on their ability to be compressed, from lowest compressibility to highest.

2

(a) solid

(b) liquid

(c) gas

19. Use the kinetic molecular theory to explain why the pressure increases in a tire when it has been driven for a

long period of time on a hot afternoon.

20. Use the kinetic molecular theory to explain why gases are more compressible than solids or liquids.

21. Manipulate the following formula to isolate the variable P2.

P1V1 = P2V2

22. Explain Boyle’s law using the kinetic molecular theory.

23. Explain Charles’s law using the kinetic molecular theory.

24. Solve for the missing variable in the following chart:

P1 P2 V1 V2

101 kPa 125 kPa 7.52 L ?

25. Solve for the missing variable in the following chart:

P1 P2 V1 V2

? 125 kPa 7.52 L 12.5 L

26. Solve for the missing variable in the following chart:

P1 P2 T1 T2

101 kPa 125 kPa 450 K ?

27. What would happen to the volume of an ideal gas if the absolute temperature is doubled and the pressure is

halved?

28. State the ideal gas law in equation form and give a statement describing the different relationships between

the variables.

29. Rank the following gases from 1 (most abundant) to 5 (least abundant), in terms of their percentage

composition in dry air at sea level.

CO2 N2 Ar O2 CH4

30. Propane is used as the fuel for barbeques. What volume of oxygen would be required to completely burn 2 L

of propane, C3H8, and produce CO2 and H2O?

31. What amount of oxygen, in moles, is available for a combustion reaction in a volume of 12.5 L at STP?

32. State Avogadro's theory.

33. List the different groups of compounds that hydrocarbons can be divided into.

34. Describe and give an example of a homologous series.

35. Write the molecular formulas and draw structural formulas for the following compounds:

3

(a) butane

(b) cis-2-butene

(c) 2-butyne

36. How does the process of cracking help to meet the demands for gasoline?

37. Write the reaction for the complete combustion of hexane.

38. What are the three steps in naming branch-chain alkanes? Give an example.

39. Draw and name three isomers of an alkane containing six carbons.

40. Draw the complete structural diagram for 1-ethyl-2-methylcyclohexane.

41. Indicate how the physical properties of the alkane family change as the size of the molecule increases.

42. How can the trends in the physical properties of the alkane series be explained? For example, as the size of

the molecule increases, the melting point or boiling point increases.

43. Other than the combustion of alkanes, why are alkanes not reactive, or when they do react, they do so very

slowly?

44. What is the key characteristic that distinguishes alkenes from alkanes?

45. What is the key characteristic that distinguishes alkynes from alkanes?

46. When naming branched alkenes or alkynes, how does the numbering of carbons in the parent chain differ

from that used when naming branched alkanes?

47. Name the following alkenes:

(a)

(b)

48. Draw the structural formula for the following alkenes:

(a) 3-hexene

(b) 2,4-dimethyl-2-pentene

(c) 5-methyl-2-hexene

49. Name the following alkynes:

(a)

(b)

50. Draw comlete structural diagrams for the following alkynes:

(a) 1-butyne

(b) 4,4-dimethyl-2-pentyne

4

51. What chemical reaction can alkenes and alkynes undergo that alkanes cannot? Explain.

52. Describe a quick test to determine if a hydrocarbon is saturated or unsaturated.

53. Explain why geometric isomers exist in some alkenes. Give an example.

54. What are polymers? Give an example of a common synthetic polymer.

55. Of the four basic energy sources, describe and give an example of the two from which we obtain most of our

energy.

56. What is specific heat capacity? What units are used for specific heat capacity?

57. Describe a simple laboratory calorimeter.

58. State three assumptions that are often made when using a calorimeter to measure energy changes.

59. What type of calorimeter is used to determine the heat of combustion?

60. In a thermochemical equation, if the heat term is on the product side, what type of reaction is being analyzed?

Explain.

61. How does a thermochemical equation indicate whether a reaction is exothermic or endothermic?

62. Activation energy is an "extra boost" of energy needed to "activate" a reaction. How could this be explained

in terms of bond energy?

63. What is bond energy?

Problem

64. Calculate the pH of seawater which has a hydrogen ion concentration of 1 10–8

mol/L.

65. A swimming pool has a pH of 7.5. Calculate the hydrogen ion concentration in the pool.

66. Coffee has a pH of 5.0 and grapefruit juice has a pH of 3.0. Calculate the hydrogen ion concentration for both

drinks and determine how many times more concentrated the hydrogen ion is in the juice compared to the

coffee.

67. A titration was performed on a 10.00-mL sample of water taken from an acidic lake. If it took 8.66 mL of

0.0512 mol/L NaOH(aq) to neutralize the sulfuric acid in the lake water sample, calculate the concentration of

the sulfuric acid. What is the pH of this lake water?

68. The hydrogen ion concentration in beer is 3.12 10–5

mol/L. Calculate the pH of beer.

69. Determine the volume of a balloon at STP assuming that it occupies a volume of 7.75 L at a temperature of

0ºC and a pressure of 125 kPa.

70. What is the initial pressure of a gas if it occupied a volume of 375 mL, but now occupies a volume of 1.25 L

at a pressure of 95.5 kPa. Assume that the temperature remains constant throughout the process.

71. What pressure is required to reduce a balloon's volume to 2.25 L from a volume of 9.75 L at a pressure of

1.00 atm? Assume that the temperature remains constant throughout the process.

72. A balloon filled with helium gas has a volume of 5.80 L measured at 101.325 kPa and is placed into a

hyperbaric chamber at a pressure of 1255 mm of Hg. What will the new volume be if the temperature remains

constant throughout the process?

5

73. Determine the volume occupied by 3.45 g of carbon dioxide gas at STP.

74. What is the reading on the pressure gauge if a canister holds 0.155 mol of N2 at 23ºC and has a volume of

8.95 L?

75. Calculate the volume that 3.25 mol of He gas will occupy at a temperature of 25ºC and a pressure of 799 mm

of Hg.

76. Determine the number of moles of neon gas contained in a 5.25-L gas tank at 105 kPa and a temperature of

299 K. If the gas is nitrogen instead of neon, will the answer be the same? Explain your reasoning.

77. If 45.6 g of CO2 is contained in a 2.75-L container at 25ºC, what will the pressure be in this container

expressed in units of kPa and atm?

78. Magnesium was added to hydrochloric acid, HCl, and produced 5.25 L of H2 gas at a temperature of 325 K

and a pressure of 100 kPa. What mass of Mg was used in this single displacement reaction?

79. Calculate the % by mass of each element in .

80. Determine the empirical formula of the compound that has a percent composition of 85.7% carbon and 14.3%

hydrogen.

81. Chemical analysis of gasoline indicates that one of its constituents has a percent composition of 92.29%

carbon and 7.71% hydrogen by mass. If it is later determined that this compound has a molar mass of 78 g,

determine its molecular formula.

82. What is the molecular formula for an alkane with a molar mass of 58.14 g/mol?

83. If 150 mL of water at 10ºC is heated to 80ºC, how much heat must have been added to the system?

84. A 400-g piece of copper piping is taken from outside at 0ºC into a house at 25ºC. How much heat will be

gained by the piece of copper pipe?

85. Calculate the heat flow when the temperature of a 10-kg block of ice changes from –20.0ºC to –5.0ºC.

Essay

86. A train has derailed and there has been a chemical spill. You are the environmental chemist leading an

emergency response team to the area where this spill has occurred. Outline the steps that you would take to

handle this situation.

87. Describe and give examples of the different ways in which hydrocarbons can be expressed.

88. Explain, using examples, why the physical properties of alkenes are similar to alkanes, but the chemical

properties are quite different.

89. "Of the more than 10 million compounds known, at least 90% are molecular compounds of the element

carbon." Explain.

90. The term "global warming" has become a well-recognized term in the past few years. What is global warming

and what are the most likely causes of it? What are the predicted effects if this trend continues?

6

11 Pre-U Review Questions 2

Answer Section

SHORT ANSWER

1. ANS:

HCl(aq) H+

(aq) + Cl–

(aq) (> 99%)

HF(aq) H+

(aq) + F–

(aq) (< 50%)

PTS: 1

2. ANS:

Ca(OH)2(s) Ca2+

(aq) + 2OH–(aq)

PTS: 1

3. ANS:

Nitric acid

-strong acid

-almost 100% ions (H+ and NO3

–)

-has lower pH value than same concentration of nitrous acid

Nitrous acid

-weak acid

-less than 50% molecules of HNO2 in solution and low percent of ions(H+ and NO2

–).

-has a higher pH value than the same concentration of nitric acid

PTS: 1

4. ANS:

(a) In acidic solutions, [H+

(aq)] > 1 10–7

mol/L

(b) In basic solutions, [H+

(aq)] < 1 10–7

mol/L

PTS: 1

5. ANS:

(a) pH = 2.0

(b) pH = 7.0

(c) pH = 7.5

(d) pH = 5.5

(e) pH = 8.0

PTS: 1

6. ANS:

(a) Diluting acidic solutions decreases the hydrogen ion concentration. This increases the pH and makes these

solutions less acidic.

(b) Diluting basic solutions decreases the pH and makes these solutions less basic.

PTS: 1

7. ANS:

7

(a) Nitric acid is a strong acid and ionizes almost 100% into hydronium ions which makes it very acidic

(lower pH). Acetic acid is a weak acid and only ionizes about 1% into hydronium ions which makes less

acidic (higher pH).

(b) Nitric acid is about 100 times more acidic than acetic acid because nitric acid solution contains about 100

times the number of hydronium ions in solution than is found in acetic acid.

PTS: 1

8. ANS:

Acids

-tastes sour

-turns blue litmus red

-reacts with active metals to produce hydrogen gas

Bases

-tastes bitter

-feels slippery

-has a pH higher than 7

-neutralizes acids

PTS: 1

9. ANS:

A Bronsted acid is a proton donor. A Bronsted base is a proton acceptor.

PTS: 1

10. ANS:

HF(aq) and F–(aq) are conjugate acid-base pairs. H3O

+(aq) and H2O(l) are conjugate acid-base pairs.

PTS: 1

11. ANS:

Neutralization reactions are important in cleaning up acid spills, adjusting the pH level in swimming pools,

and in the titration of consumer products to ensure proper quality control.

PTS: 1

12. ANS:

H2SO4(aq) + Fe(s) FeSO4(aq) + H2(g)

3H2SO4(aq) + 2Fe(s) Fe2(SO4)3(aq) + 3H2(g)

Both of these single displacement reactions are possible in this situation.

PTS: 1

13. ANS:

H3PO4(aq) + 3KOH(aq) K3PO4(aq) + 3H2O(l)

PTS: 1

14. ANS:

-acidification of lakes and rivers, thus killing fish

-prevents the uptake of nutrients by plants from too acidic soils

-dissolves marble statues and buildings

8

PTS: 1

15. ANS:

P2 = 3P1

T2 = 2T1

V2 = xV1

The final volume will be that of the initial volume.

PTS: 1

16. ANS:

translational, rotational, and vibrational motions

PTS: 1

17. ANS:

london forces (dispersion forces)

PTS: 1

18. ANS:

solid, liquid, gas

PTS: 1

19. ANS:

As temperature rises, the particles move more rapidly and this increases the number of collisions with the

sides of the tire. Greater force per unit area increases the pressure.

PTS: 1

20. ANS:

Gas particles are relatively far apart compared to their size. Solids have particles that are very close to each

other, while liquids have small spaces between particles. To compress a substance, the particles must be

brought closer together. Since gas particles are far apart, their total occupied volume can be easily changed by

applying a force such as increasing the pressure or decreasing the temperature.

PTS: 1

21. ANS:

9

PTS: 1

22. ANS:

Assume that the number of particles in a gas and the temperature of the gas remains constant. As the pressure

increases on the gas, the particles will be forced to move in closer to one another, thereby decreasing the total

volume that they occupy. As the volume decreases, there will be more collisions with the sides of the

container due to the reduction of exposed surface area, but the number of particles is constant. (More particles

hitting the same spot on the sides of the wall increases the pressure.)

PTS: 1

23. ANS:

Assume that the pressure and number of molecules of a gas are constant. As the temperature increases, the

particles gain more energy, thereby increasing the distance separating the individual gas particles. As the

distance increases, so does the volume, because gases always occupy the entire volume of their containers. As

the particles lose kinetic energy (i.e., are cooled), the particles get closer together and reduce the total volume

that they occupy. The individual size of the particles do not change and are considered dimensionless points

in this theory.

PTS: 1

24. ANS:

PTS: 1

25. ANS:

PTS: 1

26. ANS:

10

PTS: 1

27. ANS:

Both are positive growth factors for the volume, hence, volume would be quadrupled (2 2 = 4).

PTS: 1

28. ANS:

PV = nRT

The product of the pressure of an ideal gas and the volume of an ideal gas is equal to the product of the

number of moles of this ideal gas times the universal gas constant, in the proper units, times the temperature

of the gas in Kelvin.

PTS: 1

29. ANS:

CO2 N2 Ar O2 CH4

4 1 3 2 5

PTS: 1

30. ANS:

C3H8 + 5O2 3CO2 + 4H2O

PTS: 1

31. ANS:

PTS: 1

32. ANS:

Equal volumes of gases at the same temperature and pressure contain an equal number of molecules.

11

PTS: 1

33. ANS:

aliphatic, aromatic

apliphatic—cyclic, acyclic

acyclic—alkanes, alkenes, alkynes

cyclic—cycloalkanes, cycloalkenes

PTS: 1

34. ANS:

A homologous series is a series of compounds that differ from the one before by the same increment (e.g.

– –)

Example: alkanes

PTS: 1

35. ANS:

(a)

(b)

(c)

PTS: 1

36. ANS:

Large molecules (15–18 carbon atoms) are "cracked" to create molecules in the gasoline component

hydrocarbons ( to ).

PTS: 1

37. ANS:

or

12

PTS: 1

38. ANS:

1. Determine the longest chain of carbon atoms (the "parent chain") and the names of each of the branches off

of the parent chain.

2. Note which end of the parent chain is closest to the first branch. The smallest sum of all the numbers must

be used to obtain the correct end of the chain from which to start numbering.

3. Write the number(s) of the branch(es) and separated by commas if there are more than one. Followed with

a dash and the name of the branch(es) and then the name of the parent chain. Different branches should be

written alphabetically.

Example: 3-ethyl-2-methylhexane

PTS: 1

39. ANS:

hexane

2-methylpentane

3-methylpentane

PTS: 1

40. ANS:

PTS: 1

41. ANS:

-The state of the molecule at SATP moves from gas to liquid to solid.

-The melting point increases.

-The boiling point increases.

-The density increases.

13

PTS: 1

42. ANS:

The trends are explained by London forces between the molecules. The larger the molecules, the larger the

number of electrons and protons and, therefore, the larger the London force between the molecules.

PTS: 1

43. ANS:

Since alkanes are saturated, for any reaction to proceed, the bonds within the molecule must be broken.

Alkanes contain only single C–C and C–H bonds; both kinds of bonds are stable and not easily broken. Thus,

a lot of energy is required for the reaction to proceed. Therefore, the reaction does not occur or occurs very

slowly.

PTS: 1

44. ANS:

Alkanes contain only single C–C bonds, while alkenes contain one or more C–C double bonds.

PTS: 1

45. ANS:

Alkanes contain only C–C single bonds, while alkynes contain one or more C–C triple bonds.

PTS: 1

46. ANS:

The numbering of the carbons in alkanes is done such that the lowest numbers are used for the branches. In

alkenes and alkynes, the location of the multiple bond takes precedence over the location of the branches.

PTS: 1

47. ANS:

(a) 2-butene

(b) 5-methyl-2-hexene

PTS: 1

48. ANS:

(a)

(b)

(c)

PTS: 1

49. ANS:

(a) 2-pentyne

(b) 2,5-dimethyl-3-hexyne

PTS: 1

14

50. ANS:

(a)

(b)

PTS: 1

51. ANS:

Alkenes and alkynes can undergo addition reactions that alkanes cannot. The addition of a small molecule

(like or ) across the multiple bond causes the molecule to become saturated. Since alkanes are already

saturated, they cannot undergo this reaction.

PTS: 1

52. ANS:

Add bromine water (orange) to the unknown hydrocarbon. If the orange colour disappears quickly, the

hydrocarbon is unsaturated. If it does not, the hydrocarbon is saturated.

PTS: 1

53. ANS:

This occurs because rotation about the double bond is not possible without breaking the bond.

cis-2-butene

trans-2-butene

PTS: 1

54. ANS:

Polymers are substances whose molecules are made up of many similar small molecules (monomers) linked

together in long chains.

Example: polyethylene, teflon

PTS: 1

55. ANS:

Chemical energy

energy derived directly from a chemical reaction (e.g., burning of hydrocarbons in a furnace)

Nuclear energy

15

energy derived from a nuclear reaction (e.g., a nuclear reactor for production of electricity)

PTS: 1

56. ANS:

Specific heat capacity is the quantity of heat required to change the temperature of a unit mass of a substance

by one degree Celsius. The unit used is J/gºC (joules per gram*degree Celsius).

PTS: 1

57. ANS:

A simple calorimeter is one in which the chemical system being studied is surrounded by a known quantity of

water so that the energy can be transferred between the system and the surroundings in a controlled manner.

PTS: 1

58. ANS:

-No heat is transferred between the calorimeter and the outside.

-Any heat absorbed or released by the calorimeter materials (container, thermometer, etc.) is negligible.

-A dilute aqueous solution is assumed to have the same density and specific heat capacity as pure water.

PTS: 1

59. ANS:

bomb calorimeter

PTS: 1

60. ANS:

The reaction is exothermic. This is because the heat is a product of the reaction. The energy is being lost by

the system and is transferred to the surroundings.

PTS: 1

61. ANS:

If the heat term is on the product side of the thermochemical equation, then the reaction is exothermic. If it is

on the reactant side, then the reaction is endothermic.

PTS: 1

62. ANS:

Once a reaction is started, the energy produced by the formation of bonds will provide energy for the breaking

of more bonds in the reactants. However, before the reaction starts there is no energy to break the bonds in the

reactants. The activation energy must provide enough energy to break the bonds in the initial reactant

molecule(s).

PTS: 1

63. ANS:

Bond energy is the energy required to break a chemical bond.

PTS: 1

PROBLEM

64. ANS:

16

Seawater has a pH of 8.0.

PTS: 1

65. ANS:

The hydrogen ion concentration of the swimming pool is 3.2 10–8

mol/L.

PTS: 1

66. ANS:

coffee grapefruit juice

The hydrogen ion concentration is 100 greater in grapefruit juice than it is in coffee.

Therefore, grapefruit juice is 100 more acidic than coffee.

PTS: 1

67. ANS:

H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l)

10.00 mL 8.66 mL

C 0.00512 mol/L

17

The sulfuric acid concentration in the lake is 2.22 10–2

mol/L.

The pH of the lake water is 1.65.

PTS: 1

68. ANS:

The pH of beer is 4.506.

PTS: 1

69. ANS:

P1 = 125 kPa

V1 = 7.75 L

P2 = 101.325 kPa

V2 = ?

The new volume of the balloon is 9.56 L.

PTS: 1

70. ANS:

V1 = 375 mL

P2 = 95.5 kPa

V2 = 1.25 L

P1 = ?

18

Convert mL to L for V1:

The pressure of the gas was 318 kPa.

PTS: 1

71. ANS:

P1 = 1.00 atm

V1 = 9.75 L

V2 = 2.25 L

P2 = ?

The pressure required is 4.33 atm.

PTS: 1

72. ANS:

P1 = 101.325 kPa

V1 = 5.80 L

P2 = 1255 mm of Hg

V2 = ?

Convert P2 to kPa unit:

19

The new volume of the balloon will be 3.51 L.

PTS: 1

73. ANS:

m = 3.45 g

T = 273 K

P = 101.325 kPa

R = 8.31 kPa L/mol K

V = ?

Convert mass to moles of CO2:

The volume occupied by the CO2 is 1.76 L.

PTS: 1

74. ANS:

n = 0.155 mol N2

V = 8.95 L

T = 23ºC + 273 = 296 K

R = 8.31 kPaL/molK

P = ?

20

The pressure gauge would read 42.6 kPa.

PTS: 1

75. ANS:

n = 3.25 mol

T = 25ºC + 273 = 298 K

R = 8.31 kPa L/mol K

P = 799 mm Hg

V = ?

Convert P into kPa from mm Hg:

The He gas will occupy a volume of 75.6 L.

PTS: 1

76. ANS:

V = 5.25 L

P = 105 kPa

T = 299 K

R = 8.31 kPa L/mol K

n = ?

21

The answer would be the same if the question asked for the number of moles of nitrogen gas. The question

assumes ideal gases and Avogadro's theory states that two gases at the same temperature, pressure, and

volume would contain the same number of molecules. If you have the same number of molecules, you have

the same number of moles; however, the masses will be different.

PTS: 1

77. ANS:

m = 45.6 g of CO2

V = 2.75 L

R = 8.31 kPa L/mol K

T = 25ºC + 273 = 298 K

P = ?

Convert mass to moles for CO2:

The pressure of the gas would be 933 kPa.

The pressure of the gas would be 9.21 atm.

PTS: 1

78. ANS:

Mg(s) + 2HCl(aq) MgCl2 (aq) + H2 (g)

22

P = 100 kPa

V = 5.25 L

R = 8.31 kPa L/mol K

T = 325 K

nH2 = ?

Therefore, 4.72 g of Mg was added to the HCl to form 5.25 L of H2.

PTS: 1

79. ANS:

1 mol of = 30.08 g contains: 2 mol of C, 24.02g

6 mol of H, 6.06 g

C2H6 is 79.9% carbon and 20.2% hydrogen by mass.

23

PTS: 1

80. ANS:

Assume 100 g of compound.

Element Mass Number of moles Ratio of moles Whole-number

ratio

C

H

85.7 g

14.3 g

1

2

The empirical formula is CH2.

PTS: 1

81. ANS:

Assume 78 g of compound.

Element Mass Number of moles Ratio of moles

C

H

92.29% of 78g = 72.0 g

7.17% of 78g = 6.0 g

6

6

The molecular formula is C6H6.

PTS: 1

82. ANS:

Since the general formula for an alkane is , the compound must have less than five carbons because

five carbons have a mass of approximately 60 g. Thus would have a molar mass of 4(12.01 g) +

10(1.01 g) = 58.14 g/mol.

PTS: 1

83. ANS:

The amount of heat that must be added to the system is 43.9 kJ.

PTS: 1

24

84. ANS:

The amount of heat gained by the copper pipe is 3.8 kJ.

PTS: 1

85. ANS:

The heat flow would be 302 kJ.

PTS: 1

ESSAY

86. ANS:

-Identify the chemical; it would be an acid if it is dissolving the metallic parts of the train.

-Confirm that the chemical is an acid by using quick pH paper test 0–6.

-Use sodium carbonate powder to spread onto the acid spill.

-Monitor the neutralization reaction by checking for carbon dioxide bubbles and pH paper readings.

-Spill is neutralized when pH reading is 7.

HX(aq) + Na2CO3(s) CO2(g) + 2NaX(aq) + H2O(l)

PTS: 1

87. ANS:

Molecular formulas (formula showing the number of carbons and hydrogens in the molecule)

Expanded molecular formulas (formula showing the clusters of carbons and hydrogens)

Structural formulas (formula showing all atoms and bonds in the hydrocarbon)

Condensed structural formula (formula showing only the carbon-carbon bonds)

25

Line structure diagram (formula where the end of each line segment represents a carbon atom)

PTS: 1

88. ANS:

Since the physical properties of both alkanes and alkenes are determined by London forces, the loss of a

couple hydrogens and their electrons have a very small effect on the overall attraction between the molecules.

Thus, they have fairly similar boiling points, melting points, densities, etc.

Examples: propane b.p. –42.1ºC

propene b.p. –47.4ºC

The double bond in alkenes has a dramatic effect on the chemical properties of the substance. For example,

hydrocarbons with double bonds react quickly at room temperature with bromine, whereas alkanes react very

slowly. Because of the fewer hydrogens in an alkene it is said to be unsaturated, which allows more atoms to

be attached to the molecule without affecting the C–C single bond. For atoms to react with the C–C double

bond it only requires rearrangement of the electrons involved in the double bond, not the single bond. For

example, cyclohexane and cyclehexene have very similar physical properties, but a diagnostic test using

bromine or aqueous potassium permanganate can quickly distinguish between the two substances.

PTS: 1

89. ANS:

-The number of compounds of carbon far exceeds the number of compounds of all other elements combined.

-This is due to the unique bonding properties of carbon.

-Carbon is a small atom that can form four bonds—more than atoms of most other elements.

-Carbon atoms have the special property of being able to bond together to form chains, rings, spheres, sheets,

and tubes of almost any size.

-Carbon can form multiple combinations of single, double, and triple covalent bonds with itself and with

atoms of other elements.

-With all of the special bonding abilities of carbon, carbon can and does form millions of different compounds

that are the basis of organic chemistry.

PTS: 1

90. ANS:

-Many scientists consider global warming to be one of the key environmental issues of the world today.

-The greenhouse effect, which causes global warming, refers to the trapping of the thermal energy in the

atmosphere. The thermal energy is trapped like the glass in a greenhouse which causes the temperature to rise.

-The main cause of the effect is the increase of "greenhouse" gases in the atmosphere.

-Two major greenhouse gases are carbon dioxide gas and water vapour.

-Main products of the combustion of hydrocarbons.

26

-The concentration of carbon dioxide in the atmosphere is steadily increasing due to the increased combustion

of fossil fuels.

-With increased carbon dioxide in the atmosphere, more thermal energy is kept in the atmosphere and causes

the overall temperature of the earth to rise.

-The effects of this could be diastrous.

-A rise of a few degrees could result in the melting of the polar caps, causing the sea levels to rise as well as

significant climate changes.

-However, much of this is not understood and the effects of the global warming may be minimal.

PTS: 1