化学考试代写 Chem代写 Midterm代写

Chem 1220 Midterm 2 

化学考试代写 1.If 1.00 mole of HF(g), 0.500 mole of H2(g), and 0.750 mol of F2(g) are mixed in a 5.00 L flask, what is the reaction quotient and

1.

If 1.00 mole of HF(g), 0.500 mole of H₂(g), and 0.750 mol of F₂(g) are mixed in a 5.00 L flask, what is the reaction quotient and the net direction to reach equilibrium

H₂(g) + F₂(g) ⇌ 2 HF(g)           K_c = 100

(a) Q = 2.66, the system is at equilibrium

(b) Q = 0.375, the equilibrium shifts to the right

(c) Q = 2.66, the equilibrium shifts to the left

(d) Q = 0.375, the equilibrium shifts to the left

(e) Q = 2.66, the equilibrium shifts to the right

 

2.

Given the following equilibrium

CO(g) + 2 H₂(g) ⇌ CH₃OH(g)

A chemist introduces 0.42 mol of CO and 0.42 mol of H2 into a 1.00 L reaction vessel. Once the mixture comes to equilibrium there are 0.29 mol of CO remaining. What is the equilibrium constant, K_c  at this temperature?

(a) 2.80

(b) 0.357

(c) 14.5

(d) 17.5

(e) None of the above

 

3.

The reaction

PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)     ΔH° = 88 kJ

Is at equilibrium. Which of the following changes will shift the equilibrium to the right?

(1) removing Cl₂
(2) decreasing the temperature
(3) increasing the volume of the reaction vessel

(a) 1 only

(b) 2 only

(c) 3 only

(d) 1 and 3

(e) 1 and 2

 

4.  化学考试代写

Consider the following molecules CH₃NH₂, CH₃CH₂OH, CH₃CH₂CO₂H. Amongst these three _______ is a weak acid, _______ is a weak base, and _______ is neither an acid nor a base in aqueous solution.

(a) CH₃CH₂CO₂H, CH₃NH₂ , CH₃CH₂OH

(b) CH₃CH₂CO₂H, CH₃CH₂OH, CH₃NH₂

(c) CH₃NH₂ , CH₃CH₂OH, CH₃CH₂CO₂H

(d) CH₃CH₂OH, CH₃NH₂ , CH₃CH₂CO₂H

(e) CH₃NH₂ , CH₃CH₂CO₂H, CH₃CH₂OH

 

5.

Given the following K_a values determine which species is the strongest base

HF, K_a = 6.8 × 10^–4     HNO₂, K_a = 4.5 × 10^–4     HCNO, K_a= 2.2 × 10^–4

(a) F^–

(b) NO₂^–

(c) CNO^–

(d) HF

(e) HCNO

 

6.

If 0.500 mol of H₂(g) and 0.500 mol of I₂(g) are placed in a 2.00 L container at a temperature where the following equilibrium exists:

H₂(g) + I₂(g) ⇌ 2 HI(g)       K_c = 125

What concentration of HI(g) is present once the system comes to equilibrium?

(a) 0.424 M

(b) 0.0405 M

(c) 0.380 M

(d) 0.230 M

(e) 0.212 M

 

7.

What is the % ionization of a 0.015 M solution of hypochlorous acid, HClO (K_a = 3.0 × 10^-8 )?

(a) 2.1 × 10-5 %

(b) 0.0014 %

(c) 0.14 %

(d) 1.5 %

(e) 14 %

 

8.  化学考试代写

What is the pH of a 0.050 M solution of H₂SO₄ (K_a2 = 0.012)?

(a) 1.01

(b) 1.23

(c) 1.30

(d) 1.28

(e) 2.07

 

9.

Arrange the following molecules/ions from the weakest to strongest base: Cl^– , OH^– , O^2–, NH₃ .

(a) Weakest base Cl^– < NH₃ < O^2– < OH^– Strongest base

(b) Weakest base O^2– < Cl^– < NH₃< OH^– Strongest base

(c) Weakest base Cl^– < NH₃ < OH^– < O^2– Strongest base

(d) Weakest base Cl^– < O^2–< NH₃ < OH^– Strongest base

(e) Weakest base NH₃ < Cl^– < OH^– < O^2– Strongest base

 

10.

An solution of Ca(OH)₂ is determined to have a pH of 11.24. What is the concentration of Ca(OH)₂ in this solution?

(a) 5.75 × 10^-11 M

(b) 1.74 × 10^-3 M

(c) 8.69 × 10^-4 M

(d) 3.47 × 10^-3 M

(e) 2.76 × 10^-1 M

11.

Both bromous acid (HBrO₂) and hypobromous acid (HBrO) are weak acids. In both molecules the hydrogen atom is bound to _______ , yet the bond is more polar in ______ which makes it a stronger acid (larger K_a).

(a) bromine, HBrO

(b) bromine, HBrO₂

(c) oxygen, HBrO

(d) oxygen, HBrO₂

 

12.  化学考试代写

What is the pH of a 0.50 M solution of NaBrO? The K_a of HBrO is 2.5 × 10^-9 .

(a) 2.85

(b) 3.20

(c) 9.67

(d) 10.80

(e) 11.15

 

13.

How many of the following salts will form acidic solutions when dissolved in water?

AlCl₃             NaBr           NaClO            Na₂SO₃                 CH₃NH₃NO₃

(a) 0

(b) 1

(c) 2

(d) 3

 

14.

A buffer is prepared by adding 10.0 g of NH₄Cl (molar mass = 53.5 g/mol) to 250.0 mL of 1.00 M NH₃ (K_b  = 1.8 × 10^-5 ) solution. What is the pH of this buffer? Ignore any changes in volume that occur on mixing.

(a) 10.14

(b) 9.98

(c) 9.38

(d) 9.13

(e) 4.87

 

15.  化学考试代写

If 8.00 mL of 2.00 M HNO₃(aq) solution are added to the buffer from the previous problem what is the new pH?

(a) 10.01

(b) 9.44

(c) 9.31

(d) 4.93

(e) 4.81

 

Physical Constants

R = 8.314 J∙mol^-1∙K^-1
R = 0.0821 L∙atm∙mol^-1 ∙K^-1
1 F = 96,500 C∙mol^-1
1 F = 96,500 J∙V-1∙mol^-1
NA = 6.022 x 10²³ mol^-1
h = 6.626 x 10^-34 J∙s
c = 2.998 x 10⁸ m∙s^-1
0° C = 273.15 K
KW = 1.00 x 10^-14 at 25° C

 

 

 

 

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