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4 marks

QUESTION

Hydrazine (N₂H₄) is a colourless, oily, flammable liquid. It is a toxic substance with an odour similar to ammonia. Exposure to hydrazine can cause irritation of the eyes, nose and throat, as well as dizziness, headaches and nausea. High levels of exposure can damage the liver, kidneys and central nervous system. Hydrazine is corrosive and can cause burns if skin contact occurs.

One method for synthesising hydrazine is by the ‘peroxide process’ where ammonia and hydrogen peroxide react to form hydrazine and water. There are several other ways to manufacture hydrazine, however they all generally rely on the oxidation of a nitrogen-containing compound.

Hydrazine is synthesised by a redox reaction. Write a chemical equation representing the ‘peroxide process’ and use this equation to elaborate on redox processes. Your answer should include a definition of a redox reaction, as well as identifying which species have been oxidised or reduced in this reaction by way of oxidation numbers.

ANSWER

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Tyler Dewitt - https://www.youtube.com/playlist?list=PL3hPm0ZdYhyycIQ3TiRApJRTFPPEvJ1uX
Khan Academy -
http://www.youtube.com/watch?v=wVMe8ZmCZo0&list=PL0pJUwkI0YCaDkuO3tuN4_NvQZ7ZoP5gl
Crash Course + More -
http://www.youtube.com/playlist?list=PL2zvqMtiL3JnwkWCKyKVbymdpV7z-Bs9B
BIll Wurtz -
https://youtu.be/xuCn8ux2gbs

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https://www.khanacademy.org/science/ap-chemistry/redox-reactions-and-electrochemistry-ap/skill-checks-on-redox-reactions-and-electrochemistry-ap/e/skill-check--oxidation-states-and-redox-reactions

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Creelman Chem Page 69 Chapter 8 Asids and Bases

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Creelman Chem Page 69 Chapter 8 Asids and Bases

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Creelman Chem Pg80
[6 marks]
(a) Select one basic, one acidic and one neutral salt from the list below to complete the table [3]
KCN, NH4Cl, Mg3(PO4)2, NaNO3, KHCO3, NaCH3COO, KCl
(any numbers are supposed to be subscript)
(b)Use the Bronsted-Lowery model to explain why the pH of ammonia solution is greater than 7.0 at 25 degrees celsius. Incorporate at least one appropriate equation in your answer.[3]
Answer

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REDOX - WACE STUDY GUIDE - Q11 P165 - 12 marks

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Q: A sealed vial contains a pale yellow mixture of NO2 (g) / N2O4 (g). Some colourless N2O4 (g) was then injected into the vial. The mixture soon becomes a darker brown colour. Use collision theory and reaction rates to explain how the addition of N2O4 affects the equilibrium system from just before adding the extra N2O4 until after the equilibrium is re-established. [8 marks]

A:
Before adding: the system is at equilibrium so the concentration of NO2 and N2O4 remain constant as does the pale yellow colour. Rate of forward reaction= rate of reversed.

At the point of adding extra N2O4:
_[N2o4] increases
_ The rate of collision between N2O4 molecules increase and hence increase the rate of forward reaction.
_Reversed reaction rate initially unaffected due to [NO2] has not been altered
After adding extra N2O4:
_ Overtime, [NO2] increases and [N2O4] decreases.
_Rate of forward reaction begins to fall and rate of reversed reaction begins to increase.
_Once the equilibrium is re-established, rate of forward= rate of reversed. [NO2] will be higher than it initially was, therefore brown colour is intensified.

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[7 mark]

Question:
An aqueous solution is prepared that contains 0.1 mol/L Na⁺ and 0.1 mol/L HC₂O₄⁻
a) Write the TWO possible reactions for the hydrolysis of the HC₂O₄⁻ ion.
b) The pH of the solution was measured and found to be less then seven. Based on this observation, state which of the hydrolysis equations has the higher equilibrium constant. Use your understanding of equilibrium concepts to explain your choice fully.

Answer:
Part a)
Equation ONE: HC₂O₄⁻ (aq) + H₂O(l) <-> C₂O₄ ²⁻ (aq) + H₃O⁺ (aq)
Equation TWO: HC₂O₄⁻ (aq) + H₂O(l) <-> H₂C₂O₄ (aq) + OH⁻ (aq)
Part b)
The pH was less than 7. This means the solution is acidic, indicating a relative excess of H₃O⁺ ions over OH⁻ ions. Therefore the first reaction (Equation ONE) is quite possible. Therefore, the first equation should have a higher equilibrium constant. This constant is expressed as:
K = {[C₂O₄ ²⁻][H₃O⁺] / [HC₂O₄⁻]}
HC₂O₄⁻ acts as a stronger acid compared to water.
Whether an anion shows acidic or basic properties in solution depends on the relative tendencies of these competing hydrolysis reactions. HC₂O₄⁻ is an acidic anion because it is a better proton donor than proton acceptor.

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The decomposition of carbon dioxide into carbon and oxygen is an endothermic reaction. It is also reversible.
A)  Given that the enthalpy change for the reaction as described is +394 kJ/mol, write the balanced equation for the decomposition of CO₂. Include energy in the equation
B) If the volume of the reaction vessel is decreased, how will the value of the equilibrium constant be affected? (i.e. will it increase, decrease or stay the same?)
C) If the system is heated, will the forward or reverse reaction be favoured?  Use LCP to explain your answer.

Answers
A) CO2(g) + 394 kJ <-> C(s) + O2(g)
B) Equilibrium constant will not be affected
C) Forward reaction is favoured so as to (partially) consume the added energy.

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Briefly describe the chemical principles behind an electrochemical cell and explain why different cells are able to produce different voltages. (4 marks)

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Briefly describe the chemical principles behind an electrochemical cell and explain why different cells are able to produce different voltages. (4 marks)

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1. Electrochemical cells use a redox reaction where the oxidation happens in a physically different location to the reduction.
2. The electrons are forced to divert through an external pathway to move from the reductant to the oxidant, and this creates an electrical current.
3. Different voltages are produced by different cells because oxidation and reduction half-reactions have different E voltages
4. The greater the difference in the E volts value of the two half- reactions involved,, the greater the voltage produced by the cell
5. Cells may also be connected in series to produce a larger range of voltages.

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Equilibrium
(From WACE Study Guide, no mark allocations, perhaps 6/7 marks?)

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Solid magnesium hydroxide is added to a beaker of water. The water is stirred and the contents of the beaker left to settle. A saturated solution is formed, with undissolved magnesium hydroxide at the bottom of the beaker. The system can be shown by the following equation
Mg(OH)2 -> Mg 2+(aq) + 2OH- (aq)
a) The system is allowed to come to equilibrium. Explain why the amount of solid present remains constant.
WHERE IS THE ANSWER!!!!!!!!!!!???
Here it is
Magnesium hydroxide solution is saturated. It has come to equilibrium. This means there are no further changes in the concentrations since the rate of dissolution is equal to the rate of re-crystallisation, allowing no net change in the amount of undissolved solid present.

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Creelman 2017 Chapter 9, page 84

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6. Predict whether reactions could occur in each of the following. Assume standard conditions. Show your reasoning
(a) Chlorine gas is bubbled through potassium bromide solution
(b) Iron (II)  nitrate is mixed with sodium iodide.
(c) Aluminium is added to hydrochloric acid.
(d) An iron nail is placed in a tin (II) chloride solution
(e) An iron(II) sulfate solution is placed in a nickel container
(f) Hydrogen sulfide is bubbled through an acidified potassium dichromate solution.
(g) Chlorine gas is bubbled through an acidified solution of barium nitrate
(h) Chlorine gas is bubbled through an acidified solution of iron(II) bromide.

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REDOX QUESTION
Chem Revision book

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Acids and Bases
[7 marks]

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REDOX ANSWER

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Acid Base Question

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Acid Base Answer

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Acids and Bases

Commercial hydrochloric acid, known as 'spirits of salts', is purchased as an approximately 10 mol/L solution. A procedure to determine the exact hydrochloric acid concentration in some spirits of salts [HCl(aq)] involved the following steps:
Primary standard Preparation: A carefully weighed 1.288g sample of anhydrous Na2CO3(s) was dissolved in water and made up to 250.0mL.
Dilution of the original approximately 10mol/L HCl solution: A 25.00mL sample of the acid was made up to 2.00L in a volumetric flask.
Titration of the diluted acid: 20.00mL samples of the diluted acid solution required on average, 20.62mL of the primary standard for equivalence.
a) Write an equation for the titration reaction
b) What is a suitable indicator for this titration? Explain your choice
c) Determine the concentration of the diluted acid
d) What is the concentration of the original approximately 10mol/L acid?

Answers:
a)2HCl(aq)+Na2CO3(aq)-->
2NaCl(aq)+2H2O(l)+CO2(g)
b)Methyl orange. Strong acid + weak base so reaction will reach equivalence when it is more acidic. Acidity is caused by presence of CO2(g) product.
c) 0.1002mol/L
d) 8.018mol/L

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Question 40 (14 marks)

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Question 40 (14 marks) continued

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20 Mark Question Acids + Bases

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Question 28 (12 marks)