化学代写 Chem代写 Midterm代写 化学考试代考

Chem 1220 Midterm 3 Practice Activity Week 12

化学代写 A 20.0 mL sample of hypochlorous acid (HClO, Ka = 3.0 × 10−8) of an unknown concentration is titrated with 0.100 M of NaOH(aq).

1.

A 20.0 mL sample of hypochlorous acid (HClO, K_a = 3.0 × 10⁻⁸) of an unknown concentration is titrated with 0.100 M of NaOH(aq). What is concentration of the hypochlorous acid if 11.5 mL of NaOH(aq) is needed to reach the equivalence point?

(a) 1.15 × 10⁻³ M

(b) 3.65 × 10⁻² M

(c) 5.75 × 10⁻² M

(d) 0.134 M

2.

What is the pH at the equivalence point in the titration from previous problem?

(a) 4.48

(b) 7.00

(c) 9.52

(d) 9.62

(e) 10.08

3. 化学代写

A 25.00 mL sample of 0.100 M CH₃COOH solution (K_a = 1.8 × 10⁻⁵) is titrated with 0.100 M NaOH solution. What is the pH of the solution at the points where 24.5 and 25.5 mL of NaOH have been added?

(a) 6.44, 11.00

(b) 6.13, 11.00

(c) 6.44, 9.85

(d) 6.13, 9.85

(e) 7.00, 8.00

4.

If 15.0 mL of a 8.6 × 10⁻² M aqueous solution of Ba(OH)₂ is titrated with a 0.100 M HCl(aq) solution what is the pH after 5.00 mL of the HCl solution is added?

(a) 8.79

(b) 9.64

(c) 11.32

(d) 12.60

(e) 13.02 

5.

Determine the molar solubility of PbCl₂ (K_sp = 1.7 × 10^–5)

(a) 0.068 M

(b) 4.1 × 10^–3 M

(c) 2.9 × 10^–3 M

(d) 0.016 M

(e) 0.026 M

6. 化学代写

In which of the following would PbI₂ have the lowest solubility?

(a) Pure H₂O

(b) A 0.5 M HI solution

(c) A 0.5 M NaOH solution

(d) A 1.0 M HNO₃ solution

(e) A 0.8 M KI solution

7.

What is the concentration of free Ni²⁺, if 1.83 g of Ni(NO₃)₂ is dissolved in 1.00 L of 3.0 M NH₃ solution? The formation constant for the complex ion [Ni(NH₃)₆]²⁺ is K_f = 1.2 × 10⁹ .

(a) 2.1 × 10^–12

(b) 1.1 × 10^–10 

(c) 6.1 × 10^–14 

(d) 2.8 × 10^–12 

(e) 1.1 × 10^–14 

8.

A block of ice containing 1.00 mol of H₂O (melting point = 0 °C, ΔH_fusion = 6.01 × 10³ J/mol) is placed in a dish at 37 °C and allowed to melt. At the point where the ice has just finished melting what is the change in the entropy of the universe? Is this a reversible or irreversible process?

(a) +22.0 J/K, irreversible

(b) −22.0 J/K, reversible

(c) 2.6 J/K, irreversible

(d) 2.6 J/K, reversible

(e) −2.6 J/K, reversible

9. 化学代写

Consider the reaction shown below:

What sign would you expect for the enthalpy, entropy and Gibbs free energy? Assume all bonds are equal in strength and all molecules are gas phase molecules?

(a) ΔS < 0 (negative), ΔH < 0 (negative), ΔG < 0 (negative)

(b) ΔS > 0 (positive), ΔH < 0 (negative), ΔG < 0 (negative)

(c) ΔS > 0 (positive), ΔH > 0 (positive), ΔG > 0 (positive)

(d) ΔS < 0 (negative), ΔH > 0 (positive), ΔG > 0 (positive)

(e) ΔS < 0 (negative), ΔH < 0 (negative), but the sign of DG cannot be determined without more information

10.

Given the following thermodynamic quantities:

What is the value of DGº at 373 K for the oxidation of solid elemental sulfur .to gaseous sulfur trioxide?

2 S(s) + 3 O₂(g) → 2S O₃(g)

(a) +740.8 kJ/mol

(b) −61.3 kJ/mol

(c) −740.8 kJ/mol

(d) −728.3 kJ/mol

(e) +61.3 kJ/mol

11.

Given the fact that K_sp for CaSO₄ is 2.4 × 10⁻⁵, what is ΔG° for the following precipitation reaction

Ca²⁺(aq) + SO₄ ²⁻(aq) → CaSO₄(s)

(a) 26.4 kJ

(b) 2.21 kJ

(c) 0 kJ

(d) −2.21 kJ

(e) −26.4 kJ 

12. 化学代写

Balance the following reaction in acidic conditions and determine which side of the balanced equation H+ is located on, and its coefficient.

Cr₂O₇ ²⁻ (aq) + I⁻ (aq)  → Cr³⁺(aq)    +  IO₃⁻ (aq) 

(a) Reactant side, coefficient = 14

(b) Reactant side, coefficient = 8

(c) Reactant side, coefficient = 2

(d) Product side, coefficient = 6

(e) Product side, coefficient = 4

13.

Balance the following reaction in basic conditions and determine which side of the balanced equation H2O is located on, and its coefficient.

H₂O₂(aq) + CIO₂(aq) → CIO₂⁻(aq) + O₂(g)

(a) Reactant side, coefficient = 2

(b) Reactant side, coefficient = 4

(c) Water does not show up in the balanced equation

(d) Product side, coefficient = 1

(e) Product side, coefficient = 2

14.

If you were asked to construct a voltaic cell using one the following half reactions in the cathode compartment and another in the anode compartment, which combination would give the largest cell voltage (emf)?

Cu²⁺ (aq) + 2e^– → Cu (s)   E° = +0.34 V

Zn²⁺ (aq) + 2e^– → Zn (s)   E° = –0.76 V

Ni²⁺ (aq) + 2e^– → Ni (s)   E° = –0.28 V

a. Cathode = Zn/Zn²⁺; Anode = Cu/Cu²⁺ 

b. Cathode = Cu/Cu²⁺ ; Anode = Zn/Zn²⁺

c. Cathode = Zn/Zn²⁺; Anode = Ni/Ni²⁺

d. Cathode = Ni/Ni²⁺; Anode = Zn/Zn²⁺

e. Cathode = Cu/Cu²⁺; Anode = Ni/Ni²⁺

15. 化学代写

Consider an electrochemical cell based on the following reaction:

2H⁺ (aq) + Sn (s) → Sn²⁺ (aq) + H₂ (g)

Which of the following actions would increase the measured cell potential?

a. Increasing the size of the tin electrode

b. Adding HNO₃(aq) to the anode compartment

c. Adding HNO₃(aq) to the cathode compartment

d. Adding NaOH(aq) to the cathode compartment

e. Both (b) and (c) would increase the measured cell potential

16.

The standard cell potential (E°_cell) for the reaction below is +0.63 V.

Pb²⁺(aq) + Zn (s) → Zn²⁺ (aq) + Pb (s)

What is the cell potential when [Zn²⁺] = 1.0 M and [Pb²⁺] = 2.0 × 10⁻⁴ M?

a. +0.52 V 

b. +0.85 V

c. +0.41 V

d. +0.74 V

e. +0.63 V

17.

The voltaic cell shown below relies on the half reactions

If the measured cell voltage is 0.85 V what is the standard reduction potential for the cathode half reaction Ce⁴⁺(aq) + e⁻ → Ce3+(aq)?

a. −0.05 V

b. +0.05 V

c. 1.65 V

d. −1.65 V

e. +0.85 V

18. 化学代写

If the voltaic cell shown below puts out a voltage of 0.80 V when [Zn²⁺] = 1.00 M, the pressure of H₂(g) is 1.00 atm and the temperature is 298 K, what is the pH in the cathode compartment?

(a) pH = 0.21

(b) pH = 0.34

(c) pH = 0.68

(d) pH = 1.35

(e) pH = −0.68

更多代写：Java代写  澳大利亚宏观经济代考  英国thesis代寫  summary essay  Speeches代写 算法作业代写

合作平台：essay代写 论文代写 写手招聘 英国留学生代写