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Questions and Answers
In the reaction: $2CuO(s) + C(s) \rightarrow 2Cu(s) + CO_2(g)$, what is the oxidation number of the carbon in $CO_2$?
In the reaction: $2CuO(s) + C(s) \rightarrow 2Cu(s) + CO_2(g)$, what is the oxidation number of the carbon in $CO_2$?
What is the oxidation state of $Cu$ in $CuO$?
What is the oxidation state of $Cu$ in $CuO$?
In the reaction: $Mg(s) + CuSO_4(aq) \rightarrow Cu(s) + MgSO_4(aq)$, which species undergoes reduction?
In the reaction: $Mg(s) + CuSO_4(aq) \rightarrow Cu(s) + MgSO_4(aq)$, which species undergoes reduction?
Which of the following is NOT a use of electrolysis?
Which of the following is NOT a use of electrolysis?
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In the reaction: $2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)$, which species is being oxidized?
In the reaction: $2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)$, which species is being oxidized?
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What is the oxidation state of manganese in the $MnO_4^−$ ion?
What is the oxidation state of manganese in the $MnO_4^−$ ion?
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Which of the following statements about redox reactions is FALSE?
Which of the following statements about redox reactions is FALSE?
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What is the oxidation state of iron in the compound $Fe_2O_3$?
What is the oxidation state of iron in the compound $Fe_2O_3$?
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During the electrolysis of copper sulfate using graphite electrodes, what is the product formed at the anode?
During the electrolysis of copper sulfate using graphite electrodes, what is the product formed at the anode?
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What is the primary reason for the use of copper electrodes in the electrolysis of copper sulfate for copper refining?
What is the primary reason for the use of copper electrodes in the electrolysis of copper sulfate for copper refining?
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During the electrolysis of a diluted aqueous sodium chloride solution, the primary product formed at the anode is?
During the electrolysis of a diluted aqueous sodium chloride solution, the primary product formed at the anode is?
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Which of the following is NOT a common application of electrolysis?
Which of the following is NOT a common application of electrolysis?
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In the electrochemical series, a higher position indicates that the element has a greater tendency to be:
In the electrochemical series, a higher position indicates that the element has a greater tendency to be:
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What change occurs in the oxidation state during oxidation?
What change occurs in the oxidation state during oxidation?
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In the reaction 2I- → I2, what is happening to the iodine ions?
In the reaction 2I- → I2, what is happening to the iodine ions?
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Which equation shows the reduction process in the example provided?
Which equation shows the reduction process in the example provided?
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Which of the following correctly defines an oxidising agent?
Which of the following correctly defines an oxidising agent?
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In the half-equation Cu2+ + 2e- → Cu, what does Cu2+ represent?
In the half-equation Cu2+ + 2e- → Cu, what does Cu2+ represent?
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During the electrolysis of an ionic compound, which species move towards the cathode?
During the electrolysis of an ionic compound, which species move towards the cathode?
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Which of the following is NOT a requirement for a substance to act as an electrolyte in an electrolytic cell?
Which of the following is NOT a requirement for a substance to act as an electrolyte in an electrolytic cell?
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In the reaction between potassium manganate (VII) and potassium iodide, what is the oxidizing agent?
In the reaction between potassium manganate (VII) and potassium iodide, what is the oxidizing agent?
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What is the main reason why carbon and platinum are often used as electrodes in electrolysis?
What is the main reason why carbon and platinum are often used as electrodes in electrolysis?
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In the reaction CuO + C → Cu + CO2, which species is being reduced?
In the reaction CuO + C → Cu + CO2, which species is being reduced?
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Which ion is attracted to the anode during the electrolysis of brine?
Which ion is attracted to the anode during the electrolysis of brine?
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What observable change occurs at the cathode during the electrolysis of concentrated aqueous sodium chloride?
What observable change occurs at the cathode during the electrolysis of concentrated aqueous sodium chloride?
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During the electrolysis of molten lead(II) bromine, what is formed at the anode?
During the electrolysis of molten lead(II) bromine, what is formed at the anode?
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In the reactivity series, which of the following cations will form at the cathode if present during electrolysis?
In the reactivity series, which of the following cations will form at the cathode if present during electrolysis?
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What is the main product formed at the cathode during the electrolysis of concentrated aqueous sodium chloride?
What is the main product formed at the cathode during the electrolysis of concentrated aqueous sodium chloride?
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What common mistake might lead one to think that Na+ ions are oxidized during electrolysis of brine?
What common mistake might lead one to think that Na+ ions are oxidized during electrolysis of brine?
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Which statement about the direction of electron flow during electrolysis is true?
Which statement about the direction of electron flow during electrolysis is true?
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What happens to OH- ions during the electrolysis of brine compared to Cl- ions?
What happens to OH- ions during the electrolysis of brine compared to Cl- ions?
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Which gas is produced at the anode during the electrolysis of dilute sulfuric acid?
Which gas is produced at the anode during the electrolysis of dilute sulfuric acid?
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In the electrolysis of molten electrolytes, which substance is typically produced at the cathode?
In the electrolysis of molten electrolytes, which substance is typically produced at the cathode?
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What is the purpose of the anode in electroplating?
What is the purpose of the anode in electroplating?
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What happens to the anode during the electrolysis of concentrated sodium chloride solution?
What happens to the anode during the electrolysis of concentrated sodium chloride solution?
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Which of the following statements is TRUE regarding copper refining?
Which of the following statements is TRUE regarding copper refining?
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Why is chromium plating used on steel car bumpers?
Why is chromium plating used on steel car bumpers?
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Which of the following is NOT a use for chlorine?
Which of the following is NOT a use for chlorine?
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Which of the following describes the purpose of electroplating?
Which of the following describes the purpose of electroplating?
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What is the role of the electrolyte solution in electroplating?
What is the role of the electrolyte solution in electroplating?
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Which of the following statements is TRUE regarding the electrolysis of concentrated sodium chloride solution?
Which of the following statements is TRUE regarding the electrolysis of concentrated sodium chloride solution?
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Study Notes
Redox and Electrolysis
- Redox is short for reduction-oxidation.
- An electrolytic cell converts electrical energy to chemical energy.
- Electrolysis is used to extract reactive metals from ores, electroplate metals, and refine metals like copper.
- Electrolysis involves breaking down compounds.
- Redox reactions involve simultaneous oxidation and reduction.
- Oxidation is the gain of oxygen or loss of electrons.
- Reduction is the loss of oxygen or gain of electrons.
- Roman numerals indicate oxidation numbers (e.g., copper(II)).
- Not all redox reactions involve oxygen gain/loss. Reactions like the displacement of copper by magnesium involve electron transfer.
- Oxidation involves loss of electrons.
- Reduction involves gain of electrons.
- Oxidation state: a number assigned to show the number of electrons gained or lost in ions; positive oxidation state indicates oxidation, and negative indicates reduction.).
- Oxidation causes an increase in the oxidation state.
- Reduction causes a decrease in the oxidation state.
Working with Oxidation States
- Elements have an oxidation state of 0.
- The sum of oxidation states in a compound is 0.
- The oxidation number of a monatomic ion is the same as its charge.
- Example: In CuO, oxygen has an oxidation state of -2 and copper has an oxidation state of +2.
Harder Work Example
- Manganese(VII), ion (MnO4^−) has an oxidation state of +7 for the manganese ion.
- Calculating the oxidation states requires understanding the charges on the other elements involved.
During a Reaction
- Oxidation causes an increase in oxidation state.
- Reduction causes a decrease in oxidation state.
- Example: MnO4^− → Mn^2+ (oxidation state of +7 changes to +2, meaning reduction)
Writing Redox Half-Equations
- Identify the oxidised and reduced substances.
- Write a simple equation showing the change in them.
- Balance the equations for the atoms.
- Balance the charge equation by using electrons.
Reduction and Oxidising Agents
- An oxidizing agent oxidises another substance during a redox reaction and itself is reduced.
- A reducing agent reduces another substance during a redox reaction and itself is oxidised.
- An example: in the reaction copper oxide + carbon → copper + carbon dioxide, copper oxide is the oxidising agent, and carbon is the reducing agent.
Electrolysis
- Electrolysis is the breakdown of an ionic compound by passing electricity through it (molten or in aqueous solution).
- Electrolysis occurs in an electrolytic cell.
- An electrolytic cell has a battery, two electrodes, and an electrolyte.
- The cathode is the negative electrode.
- The anode is the positive electrode.
- The electrolyte is the substance being broken down (usually an ionic compound), it must be molten or in aqueous solution for the ions to move.
Electrodes
- Electrodes are often made of graphite or platinum (inert).
Main Stages of Electrolysis
- The electrolyte is melted or dissolved in water to make an aqueous solution.
- Electrical current is passed through the electrolyte.
- Cations move to the cathode (negative electrode).
- Anions move to the anode (positive electrode).
- Reactions involving ions at the electrodes will occur.
Reactions at Electrodes (Redox)
- Electrons flow from the anode to the cathode.
- At the cathode, cations gain electrons (reduction).
- At the anode, anions lose electrons (oxidation).
Electrolysis of Molten Electrolytes
- Products produced depend on the electrolyte.
- Examples include producing lead from molten lead(II) bromide and chlorine from molten sodium chloride.
Electrolysis of Aqueous Electrolytes
- Electrolysis in aqueous solutions is more complex because water itself can be decomposed.
- The ions that are released are more easily oxidised or reduced than the water.
- This means the products are sometimes different to what you'd expect from solely focusing on the ions of the original substance.
Predicting Products
- Products formed at the cathode depend on the reactivity series.
- Products formed at the anode depend on the electrochemical series.
- Any halide(Cl, Br, I) will be preferentially oxidised over water.
- If no halide ions are present, the hydroxide ion is then oxidised to form oxygen.
Copper Refining and Purification
- Impure copper serves as the anode, pure copper is used at the cathode.
- Ions of copper leave the anode and deposit as pure copper metal at the cathode.
Application of Electrolysis (Electroplating)
- Coating one metal with another (e.g., nickel, gold, chromium).
- Electrolyte: solution of metal ion to provide the metal for plating.
- Object to be coated is the cathode.
Copper Electrolysis
- Copper electrodes can be used to refine copper. Products depend on the electrode used.
- Effect of dilution of solution will affect the products (e.g., aqueous sodium chloride).
Electrolysis Products
- The electrolysis of concentrated aqueous sodium chloride produces hydrogen, chlorine, and sodium hydroxide.
- The specific products produced at each electrode.
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Description
Test your knowledge on redox reactions and electrolysis! This quiz covers the principles of oxidation and reduction, how electrolytic cells function, and the applications of electrolysis in extracting and refining metals. It's a great way to reinforce your understanding of these key chemical concepts.
