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Spring 2018 > Chem final 4, 5, 6, + 2 questions from others > Flashcards

Chem final 4, 5, 6, + 2 questions from others Flashcards

1
Q

Which element is oxidized in this reaction?

FeO+CO→Fe+CO2

A

remember this..
.. reduction means “reduction in charge”
.. “agents” are opposites

from which 
.. reduction means reduction in charge 
.. oxidation means increase in charge 
.. species reduced = oxidizing agent 
.. species oxidized = reducing agent

this problem

O in FeO is in the -2 state.. why? it has the higher electronegativity value and takes as
.. .. .. . ….many electrons as it needs from Fe to fill it’s outer orbital.
Fe in FeO is in the +2 state.. why? O is in the -2 state.. the overall molecule has zero net
.. . .. … ..charge (see any + or - after that FeO?) so Fe must be +2 to balance
.. .. .. .. …or better yet…. 1xFe + 1x(-2) = 0 =====> Fe = +2

C in CO is +2… same reasoning as above
O in CO is -2

Fe in Fe(s) is 0….. why? see any charge after that “Fe”?

C in CO2 is +4.. why? each O is -2… overall molecule = 0
.. .. . .. . … . . .1xC + 2x(-2) = 0 ===> C = +4

so..
.. .Fe went from +2 to 0 and was “reduced” (charge was reduced) and is the oxidizing agent
.. C went from +2 to +4 and was “oxidized”… . (charge increased).. and is the reducing agent

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2
Q

Strong acids

A 
Some chemists say that there are six strong acids while others include chloric acid as a strong acid, making seven strong acids as listed below. All other acids are classified as weak acids.
Strong acid	Chemical formula
Hydrochloric acid	HCl
Hydrobromic acid	HBr
Hydroiodic acid	HI
Chloric acid	HClO3
Perchloric acid	HClO4
Nitric acid	HNO3
Sulfuric acid	H2SO4
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3
Q

acids vs bases

A

As a general rule, acid leads with H, bases contain OH.

Many exceptions though

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4
Q

There are eight strong bases. All bases other than those found on this list are classified as weak bases.

A 
Strong base	Chemical formula
Lithium hydroxide	LiOH
Sodium hydroxide	NaOH
Potassium hydroxide	KOH
Rubidium hydroxide	RbOH
Cesium hydroxide	CsOH
Calcium hydroxide	Ca(OH)2
Strontium hydroxide	Sr(OH)2
Barium hydroxide	Ba(OH)2
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5
Q 
Each of the following reactions shows a solute dissolved in water. Classify each solute as a strong electrolyte, a weak electrolyte, or a nonelectrolyte.
A(l)→A(aq)
BC(aq)⇌B+(aq)+C−(aq)
DE(aq)→D+(aq)+E−(aq)
XY(s)→X+(aq)+Y−(aq)
Z(s)→Z(aq)
A

Drag the appropriate items to their respective bins.
View Available Hint(s)

Strong electrolyte
DE, XY
Weak electrolyte
BC
Nonelectrolyte
Z, A
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6
Q

nonelectrolytes
strong electrolytes
weak electrolytes
1. Ionic salts, strong acids, and strong bases are classified as .
2. Molecular compounds other than strong acids, strong bases, weak acids, or weak bases are classified as .
3. Weak acids and weak bases are classified as .

A
  1. Ionic salts, strong acids, and strong bases are classified as strong electrolytes.
  2. Molecular compounds other than strong acids, strong bases, weak acids, or weak bases are classified as nonelectrolytes.
  3. Weak acids and weak bases are classified as weak electrolytes
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7
Q

The following five beakers, each containing a solution of sodium chloride (NaCl, also known as table salt), were found on a lab shelf:
Beaker Contents
1 200. mL of 1.50 M NaCl solution
2 100. mL of 3.00 M NaCl solution
3 150. mL of solution containing 19.5 g of NaCl
4 100. mL of solution containing 19.5 g of NaCl
5 300. mL of solution containing 0.450 mol NaCl
Arrange the solutions in order of decreasing concentration.

A

4 > 2 > 3 > 1&5

#1 and 2 the concentrations are given: 1.50 M and 3.00 M respectively. 
#3 is (19.5 g / 58.44 g/mol) / 0.150 L = 2.22 mol/L = 2.22 M 
#4 is (19.5 g / 58.44 g/mol) / 0.100 L = 3.34 M 
#5 is 0.450 mol / 0.300 L = 1.50 M
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8
Q

*
According to the following reaction, what volume of 0.244 M KCl solution is required to react exactly with 50.0 mL of 0.210 M Pb(NO3)2 solution?

        2 KCl(aq) + Pb(NO3)2(aq)  →  PbCl2(s) + 2 KNO3(aq)
A

I’ll show you the process, let me know if you encounter any difficulties.

This is solved by using the formula ‘n=CV’, where n=number of moles, C = concentration of solution in moles per Litre, and V is volume in Litres.

So n=CV for Pb(NO3)2 is
0.050L x 0.210M = 0.0105 moles in solution.

Now since the stochiometry of KCl to Pb(NO3)2 is 2:1, there are 2 times the moles of KCl, so 0.0105x2=0.021 moles KCl.

To find the Volume of 0.244M concentration KCl required to react, just rearrange the formula and plug in the units:

n=CV so, V=n/c

0.021 moles /0.244M =0.086L

Which is 86.1mL

(to 3 significant figures)

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9
Q

*

Determine the percent yield of a reaction that produces 28.65 g of Fe when 50.00 g of Fe2O3 react with excess Al according to the following reaction.

Fe2O3(s) + 2 Al(s) → Al2O3(s) + 2 Fe(s)

A

Correct Answer:
Correct
81.93%

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10
Q
  • Lithium and nitrogen react in a combination reaction to produce lithium nitride:
        6 Li(s) + (g)  →  2 Li3N(s)

How many moles of lithium are needed to produce 0.31 mol of N when the reaction is carried out in the presence of excess nitrogen?

A

Correct Answer:
Correct
0.93

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11
Q

*

Identify the polyprotic acid.

A

Correct Answer:
Correct
H2SO4

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12
Q

*

What element is undergoing oxidation (if any) in the following reaction?

        Zn(s) + 2 AgNO3(aq)  →  Zn(NO3)2(aq) + 2 Ag(s)
A

Correct Answer:
Correct
Zn

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13
Q

*

Identify the reducing agent.

        2 Al3+(aq) + 2 Fe(s)  →  2 Al(s) + 3 Fe2+(aq)
A

Fe

not Fe2+

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14
Q

*
What are the coefficients in front of NO3-(aq) and Ni(s) when the following redox equation is balanced in an acidic solution?

        \_\_\_\_ NO3-(aq) + \_\_\_\_ Ni(s)  →  \_\_\_\_ NO(g) + \_\_\_\_ Ni2+(aq)
A

Correct Answer:
Correct
2, 3

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15
Q 
*
What mass (in g) of AgCl is formed from the reaction of 75.0 mL of a 0.078 M AgC2H3O2 solution with 55.0 mL of 0.109 M MgCl2 solution?
        2 AgC2H3O2(aq) + MgCl2(aq)  →  2 AgCl(s) + Mg(C2H3O2)2(aq)
A

Selected Answer:
Correct
0.838 g

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16
Q

*

Which one of the following compounds is insoluble in water?

A

Correct Answer:
Correct
Ag2SO4

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17
Q

*
According to the following reaction, what volume of 0.244 M KCl solution is required to react exactly with 50.0 mL of 0.210 M Pb(NO3)2 solution?

        2 KCl(aq) + Pb(NO3)2(aq)  →  PbCl2(s) + 2 KNO3(aq)
A

Correct Answer:
Correct
86.1 mL

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18
Q

*

A 12.39 g sample of phosphorus reacts with 42.54 g of chlorine to form only phosphorus trichloride (PCl3). If it is the only product, what mass of PCl3 is formed?

A

Selected Answer:
Correct
54.93 g

19
Q

Enter the net ionic equation for the reaction that occurs when aqueous hydroiodic acid and aqueous ammonium sulfite are mixed.
Express your answer as a net ionic equation. Identify all of the phases in your answer.

A

2H+(aq)+SO32−(aq)→H2O(l)+SO2(g)

20
Q

When 15.0 g of zinc metal reacts with excess HCl, how many liters of H2 gas are produced at STP?

  1. 3 L
  2. 14 L
  3. 229 L
  4. 458 L
A

Balanced equation: Zn+2HCl–>H2+ZnCl2

Find moles of Zn first, then convert to moles of H2, using balanced equation. From this, plug into PV=nRT to find the volume of H2 gas at STP.

Moles of Zn: [15.0 g Zn] x [1 mol Zn/65.4 g Zn] (according to periodic table, atomic weight of Zn is 65.4) =0.23 mol Zn
Moles of H2: [0.23 mol Zn] x [1 mol H2/1 mol Zn] (according to equation, mole-mole ratio of Zn to H2 is 1 to 1)=0.23 mol H2
Volume of H2: PV=nRT —> rearrange equation to become V=nRT/P, where R is the gas constant (0.082 Latm/Kmol)

Plug in moles of H2, and STP values: n (moles of H2)= 0.23 mol, P=1atm, R=0.082 Latm/Kmol, and T=273K.

This becomes V= [(0.23 mol) x (0.082 Latm/Kmol) x (273K)]/[1atm] = 5.14L

21
Q

What is ΔH∘rxn for the following chemical reaction?
CS2(g)+2H2O(l)→CO2(g)+2H2S(g)
You can use the following table of standard heats of formation (ΔH∘f) to calculate the enthalpy of the given reaction.
Element/ Compound Standard Heat of Formation (kJ/mol) Element/ Compound Standard Heat of Formation (kJ/mol)
H(g) 218 N(g) 473
H2(g) 0 O2(g) 0
H2O(l) −285.8 O(g) 249
CS2(g) 116.7 H2S(g) −20.60kJ
C(g) 71 CO2(g) −393.5kJ
C(s) 0 HNO3(aq) −206.6

A

All in kJ:

(-393.5) + (2 x -20.60) - (116.7) - (2 x -285.8) = +20.2 kJ

22
Q

The atmospheric pressure is 715 mm Hg. What is the pressure in torr?

A

715 torr

23
Q

When 15.0 g of zinc metal reacts with excess HCl, how many liters of H2 gas are produced at STP?

A

5.14 L

24
Q

The density of nitric oxide (NO) gas at 1.35 atm and 29.8°C is ________ g/L.

A

1.63

25
Q

To what volume will a 2.33 L sample of gas expand if it is heated from 30.0°C to 300.0°C?

A

4.41 L

26
Q

The volume of a gas is inversely proportional to the pressure of a gas is known as

A

Boyle’s Law.

27
Q

What pressure (in atm) will 0.44 moles of Br2 exert in a 2.6 L container at 25°C?

A

4.1 atm

28
Q

A syringe initially holds a sample of gas with a volume of 285 mL at 355 K and 1.88 atm. To what temperature must the gas in the syringe be heated/cooled in order to have a volume of 435 mL at 2.50 atm?

A

721 K

29
Q

An instrument used to measure the pressure of a gas in a laboratory is called a

A

manometer.

30
Q

Place the following gases in order of increasing density at STP.

        N2             NH3          N2O4        Kr
A

NH3 < N2 < Kr < N2O4

31
Q

What mass of NO2 is contained in a 13.0 L tank at 4.58 atm and 385 K?

A

86.7 g

32
Q 
Calculate the enthalpy of the reaction
2NO(g)+O2(g)→2NO2(g)
given the following reactions and enthalpies of formation:
1/2N2(g)+O2(g)→NO2(g),   ΔH∘A=33.2 kJ
1/2N2(g)+12O2(g)→NO(g),  ΔH∘B=90.2 kJ
A

Express your answer with the appropriate units.
View Available Hint(s)
ΔH∘ = -114.0 kJ
SubmitPrevious Answers
Correct
Thus for the overall reaction one obtains
N2(g)+2O2(g)2NO(g)2NO(g)+O2(g)→→→2NO2(g),N2(g)+O2(g),2NO2(g)
,ΔH∘A=66.4 kJ
ΔH∘B=−180.4 kJ
ΔH∘=−114 kJ

33
Q

Part complete
Calculate the enthalpy of the reaction
4B(s)+3O2(g)→2B2O3(s)
given the following pertinent information:
B2O3(s)+3H2O(g)→3O2(g)+B2H6(g), ΔH∘A=+2035 kJ
2B(s)+3H2(g)→B2H6(g), ΔH∘B=+36 kJ
H2(g)+12O2(g)→H2O(l), ΔH∘C=−285 kJ
H2O(l)→H2O(g), ΔH∘D=+44 kJ

A

Express your answer with the appropriate units.
View Available Hint(s)
ΔH∘ = -2552 kJ
SubmitPrevious Answers
Correct
Significant Figures Feedback: Your answer −2557kJ was either rounded differently or used a different number of significant figures than required for this part.

34
Q

Define specific heat capacity.

The quantity of heat required to raise the temperature of 1 mole of a substance by 1°C.

The quantity of heat required to raise the temperature of 1 gram of a substance by 1°C.

The quantity of heat required to change a system’s temperature by 1°C.

The quantity of heat required to raise the temperature of 1 kilogram of a substance by 1°F.

A

Correct Answer:
Correct
The quantity of heat required to raise the temperature of 1 gram of a substance by 1°C.

35
Q

An endothermic reaction has

a negative ΔH, gives off heat to the surroundings, and feels warm to the touch.

a positive ΔH, absorbs heat from the surroundings, and feels cold to the touch.

a positive ΔH, gives off heat to the surroundings, and feels warm to the touch.

a negative ΔH, absorbs heat from the surroundings, and feels cold to the touch.

A

Correct Answer:
Correct
a positive ΔH, absorbs heat from the surroundings, and feels cold to the touch.

36
Q

Use the standard reaction enthalpies given below to determine ΔH°rxn for the following reaction:

        2 NO(g) + O2(g)  →  2 NO2(g)         ΔH°rxn =  ?

Given:

        N2(g) + O2(g)  →  2 NO(g)               ΔH°rxn = +183 kJ                                                          

        1/2 N2(g) + O2(g)  →  NO2(g)          ΔH°rxn = +33 kJ

-333 kJ

+115 kJ

  • 117 kJ
    1. kJ
A

You need to reverse N2(g) + O2(g) → 2 NO(g) DH°rxn = +183 kJ to get NO(g) on the left
Doing so you need to reverse the sign of DHº giving DH°rxn = -183 kJ

To this equation 1/2 N2(g) + O2(g) → NO2(g) DH°rxn = +33 kJ you need to double it to get 2NO2
Doing so you need to double the DHº giving DH°rxn = +66 kJ

If you add the two changed formulas together it will reduce to 2 NO(g) + O2(g) → 2 NO2(g)
so then DH°rxn = -183 kJ + 66kJ
DH°rxn = -117kJ

Correct Answer:
Correct
-117 kJ

37
Q

Identify what a bomb calorimeter measures.

Measures ΔH for combustion solutions.

Measures ΔE for reduction reactions.

Measures ΔE for combustion reactions.

Measures ΔH for oxidation solutions.

A

Correct Answer:
Correct
Measures ΔE for combustion reactions.

38
Q

Using the following equation for the combustion of octane, calculate the heat of reaction for 50.00 g of octane. The molar mass of octane is 114.33 g/mole.

        2 C8H18 + 25 O2  →  16 CO2 + 18 H2O            ΔH°rxn = -11018 kJ
  • 4820 kJ
  • 2410 kJ
  • 2.410 kJ
  • 6300 kJ
A

Correct Answer:
Correct
-2410 kJ

39
Q

Calculate the amount of heat (in kJ) required to raise the temperature of a 88.0 g sample of ethanol from 298.0 K to 405.0 K. The specific heat capacity of ethanol is 2.42 J/g°C.

  1. 0 kJ
  2. 9 kJ
  3. 6 kJ
  4. 8 kJ
A

Correct Answer:
Correct
22.8 kJ

40
Q

Use the information provided to determine ΔH°rxn for the following reaction:

CH4(g) + 4 Cl2(g) → CCl4(g) + 4 HCl(g) ΔH°rxn = ?

ΔH°f (kJ/mol)

CH4(g) -75

CCl4(g) -96

HCl(g) -92

+113 kJ

+79 kJ

  • 113 kJ
  • 389 kJ
A

Correct Answer:
Correct
-389 kJ

41
Q

How much energy is required to form 141.8 g of Cl2, according to the reaction below?

        4 PCl3(g)  →  P4(s) + 6 Cl2(g)    ΔH°rxn = +1207 kJ
  1. 444 × 103 kJ
  2. 010 × 103 kJ
  3. 460 × 103 kJ
  4. 02 × 102 kJ
A

Correct Answer:
Correct
4.02 × 102 kJ

42
Q

How much energy is evolved during the formation of 816 g of Al2O3, according to the reaction below?

        Fe2O3(s) + 2 Al(s)  →  Al2O3(s) + 2 Fe(s)            ΔH°rxn = -852 kJ
  1. 60 × 102 kJ
  2. 90 × 103 kJ
  3. 60 × 103 kJ
  4. 82 × 103 kJ
A

Correct Answer:
Correct
6.82 × 103 kJ

43
Q

For a process at constant pressure, 5350 joules are released. This quantity is equivalent to

A

Correct Answer:
Correct
1.279 × 103 cal.

Spring 2018 (13 decks)

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