Unit 3 Chemistry AOS 2: Production of Chemicals Using Electrolysis

This set of vocabulary flashcards covers the fundamental principles of electrolysis, commercial cell designs, rechargeable batteries, green hydrogen technology, and the application of Faraday's Laws.

Electrolysis

The passing of electrical energy through a conducting source (electrolyte) to cause non-spontaneous redox reactions to occur.

Electrolytic Cell

A device that converts electrical energy into chemical energy through a non-spontaneous redox reaction, requiring an external power supply.

PANIC

A mnemonic for electrolytic cells standing for "Positive is Anode, Negative Is Cathode."

Secondary Cells

Rechargeable cells that discharge as a galvanic cell (converting chemical to electrical energy) and recharge as an electrolytic cell (converting electrical to chemical energy).

Green Hydrogen

Hydrogen produced using renewable energy, such as solar or wind, to electrolyse water, resulting in net zero emissions.

Polymer Electrolyte Membrane (PEM)

A selectively permeable plastic polymer in an electrolyser that allows protons to pass while blocking electrons, water, and gases ($H_2$ and $O_2$).

Artificial Photosynthesis

A system using visible light-absorbing materials and catalysts to convert water and solar energy into hydrogen fuel and oxygen: $2H_2O \rightarrow 2H_2 + O_2$.

Faraday's Constant ($F$)

The magnitude of electric charge per mole of electrons, approximately equal to $96500\,C\,mol^{-1}$.

Downs Cell

A commercial electrolytic cell used to produce chlorine gas ($Cl_2$) and sodium metal ($Na$) from molten sodium chloride ($NaCl$).

Hall-Heroult Cell

An industrial cell used to produce aluminium metal ($Al$) by dissolving alumina ($Al_2O_3$) in molten cryolite ($Na_3AlF_6$).

Cryolite

A substance ($Na_3AlF_6$) added to alumina in the Hall-Heroult cell to lower its melting point from approximately $2050^{\circ}\text{C}$ to between $950\text{--}1000^{\circ}\text{C}$, saving energy.

Membrane Cell

A cell used to produce chlorine, hydrogen, and sodium hydroxide from concentrated brine, utilizing a semipermeable membrane to prevent products from mixing.

Electroplating

The process of depositing a layer of or metal onto the surface of another metal via electrolysis, where the object to be plated acts as the cathode.

Anode Mud

A sludge of solid metal impurities, such as silver ($Ag$) and gold ($Au$), that forms beneath the anode during copper refining because they are weaker reductants than copper.

Inert Electrodes

Electrodes, such as graphite or platinum, that facilitate the transfer of electrons but do not take part in the chemical reaction.

Charge Equation ($Q$)

The formula used to calculate electric charge: $Q = I \times t$, where $I$ is current in Amperes ($A$) and $t$ is time in seconds ($s$).

Electrode Polarities (Recharging)

During the recharging of a secondary cell, the anode is the positive terminal and the cathode is the negative terminal.

Strongest Oxidising Agent (Aqueous Electrolysis)

In aqueous solutions, water ($H_2O$) can act as the strongest oxidant if the dissolved metal ions are below it on the electrochemical series.

Polymer electrolyte membrane electrolysis (PEM)

$2H_2O(l)\rightarrow2H_2(g)+O_2(g)$ is Polymer electrolyte membrane electrolysis and artificial photosynthesis 2H + 2e- + H2(g)

What considerations would you make choosing an electrode material for an electrolytic cell

How would the material react at the anode, how would the material react at the cathode and are the desired products still being produced or does the material affect this?

State the rules for oxidation numbers for the following scenarios with exceptions if relevant to element, metal in a compound, H in a compound, O in a compound and F in a compound

Element = 0, Metal in a compound = its charge, H in a compound = +1 except hydrides that are minus 1, O ina. compound = -2 apart from peroxides (-1) and OF2 (+2), F in a compound = -1

Electrolysis and electrolytic cell definition and what they do

Electrolysis is a chemical process that uses electricity to drive a non-spontaneous reaction, typically used in electrolytic cells to decompose compounds into their individual elements. An electrolytic cell consists of two electrodes, an anode and a cathode, where oxidation and reduction reactions occur, respectively.

comparison of galvanic and electrolytic cells in detail

Galvanic - spontaneous reactions, two seperate half cells, portable source of energy, oxidation at anode that is negative and reduction at cathode that is positive, salt bridge or membrane needed, strongest oxidant reacts with strongest reductant, electrons flow to positive electrode.

Electrolytic- Non-spontaneous reactions, requires external energy, operates with a single cell, oxidation at anode that is positive and reduction at cathode that is negative, electrolytic solution necessary, electrons are driven by an external power source.

Electrochemical series to predict electrolytic reactions

The electrochemical series is a ranking of elements and compounds based on their standard electrode potentials, which predicts the direction of electrochemical reactions. It is used to determine which species will be oxidized or reduced during electrolysis.

Commercial electrolytic cells and the two types

1. Molten Electrolytic Cells

   • Operate with solid salts that are melted to allow ions to move freely.

   • Example: Downs Cell for chlorine and sodium production.

2. Aqueous Electrolytic Cells

   • Use liquid solutions containing dissolved ionic compounds.

   • Example: Membrane Cell for chlorine and sodium hydroxide production.

Commercial electrolytic cell are industrial systems designed for large-scale electrolysis, typically splitting compounds to isolate elements or produce compounds through electrochemical processes.

Electrodes ( Inert, Cathodes and reactive)

Inert Electrodes- do not take point in the reaction. Cathodes made of metals are always inert, since always supplied with electrons. Reactive electrodes take part in the reaction, participating in oxidation or reduction processes, influencing the overall cell reactions and output.

Cells with aqueous electrolytes

Cells with aqueous electrolytes are preferred because they operate at a much lower temperature which saves money and energy compared to molten electrolytic cells. Additionally, they allow for greater control over the reaction conditions and product formation.

Water as reductant or oxidant in electrolysis

Aqueous electrolytes contain water so water could be the strongest oxidant or reductant in electrolysis reactions, facilitating oxidation and reduction processes.

Water as a reductant - o2 (g) + 4H+ (aq) + 4e arrow 2H2o (l) E= 1.23V, could be oxidised which is backwards reaction

Water as oxidant - 2h20 (l) + 2e arrow H2 (g) + 2OH-(aq) E=-0.83V - could be reduced which is forwards reaction

Secondary Cells in Detail

Secondary cells, or rechargeable batteries, discharge electricity as galvanic cells by converting chemical energy into electrical energy and recharge as electrolytic cells by converting electrical energy back into chemical energy. Common examples include lithium-ion and nickel-metal hydride batteries. Their long cycle life and ability to store energy make them essential for portable electronics and electric vehicles.

When can secondary cell be recharged and terminal + discharging and recharging

Two conditions to be able to recharge are the cell must be connected to a power supply that provided a voltage above required voltage and the products of discharge half-reactions must remain in contact with electrode at which they react.

Terminal - negative , Discharging is producing electricity when anode goes through oxidation and recharging electric convert, cathode is going through reduction, and flipped for the positive terminal but discharging is when electrons are applied and recharging is the production of electrons

Designing cells to produce green hydrogen

Cells for green hydrogen production utilize renewable energy sources for electrolysis on water, focusing on:

• Electrolyzer Types: Like PEM or alkaline, chosen for efficiency.

• Energy Source: Must be renewable to ensure net-zero emissions.

• Materials: Durable catalysts that enhance efficiency and minimize emissions.

• Integration: Effective with solar/wind systems to ensure power consistency.

Design cell features

The electrodes are usually covered with a platinum catalyst to increase the rate of production of gases. Gas diffusion layers comrpised of gold-lined, titanium and carbon paper help to distribute the gases evenly and maintain optimal performance. Additionally, a membrane is used to separate the gases produced, preventing recombination and ensuring safety. Biopolar plates prevent the build up of current and provide unachieved support for the electrolyser.

PEM design features in electrolyser cell

PEM (Proton Exchange Membrane) electrolyzers feature a proton-conducting membrane that allows protons to pass while blocking gases. They utilize a catalyst layer, often made of platinum, to facilitate the electrochemical reactions and benefit from a compact design that enables high efficiency and rapid response to power fluctuations. This design enhances hydrogen production and improves overall performance.

Artificial photosynthesis definition and what it does

Artificial photosynthesis refers to the process of mimicking natural photosynthesis in plants to convert sunlight, water, and carbon dioxide into useful fuels, primarily hydrogen or hydrocarbons. It aims to create sustainable energy sources by harnessing solar energy to produce chemicals and fuels.

Stages of artificial photosynthesis

1. Light Absorption: Capturing sunlight using visible light-absorbing materials.

2. Charge Separation: Generating electron-hole pairs by separating charges in the absorber.

3. Catalytic Conversion: Using catalysts to convert water and carbon dioxide into fuels (like hydrogen) and oxygen.

4. Product Collection: Collecting and storing the generated fuels for use.

Advantages and disadvantages of AP

Artificial photosynthesis offers several advantages, including the ability to produce renewable energy sources, reduce greenhouse gas emissions, and utilize abundant resources like sunlight and CO₂. However, it also faces challenges such as high production costs, efficiency concerns, and the need for advanced materials and technology to optimize the process.

Define electroplating

Electroplating is a process that uses electrical current to reduce dissolved metal cations, which then form a coherent metal coating on an electrode. This technique is commonly used for providing a decorative finish, corrosion resistance, or improving wear resistance on various objects.

What is validity and purpose of a control group

Validity refers to the extent to which a concept, conclusion, or measurement accurately reflects the real-world situation it intends to represent. It is crucial in both experimental design and scientific research to ensure that results are applicable and trustworthy.

A control group serves as a benchmark to compare the results of the experimental group and isolate the effects of the independent variable. Validity is enhanced by ensuring that the control group is identical to the experimental group in all aspects except for the variable being tested.

What is the resolution in an experiment

Resolution in an experiment refers to the smallest change in a measurable quantity that can be detected by the measuring instrument or method used. High resolution is essential for accurately determining the effects of variables and ensuring reliable experimental results.

Difference between valid but unrepeatable and invalid but repeatable

The difference lies in the reliability and accuracy of the results. Valid but unrepeatable results may be accurate but cannot be consistently reproduced, limiting their scientific credibility. In contrast, invalid but repeatable results may consistently produce the same outcome, but the conclusions drawn from them are not reflective of the true underlying phenomena.

Differences between accuracy and precision

Accuracy refers to how close a measured value is to the true value, while precision indicates the consistency or repeatability of measurements, regardless of their closeness to the true value. In experimental contexts, both accuracy and precision are vital for reliable data interpretation.

Primary and secondary differences

The primary differences refer to the fundamental distinctions between two subjects, whereas secondary differences highlight less critical, additional variations. Understanding both types is essential for comprehensive analysis.

What is a systematic and random error and define independant and dependant variable

A systematic error is a consistent, repeatable error associated with faulty equipment or experimental design, while a random error is unpredictable and arises from uncontrolled variables in the measurement process.

An independent variable is the factor that is intentionally changed or manipulated in an experiment, whereas a dependent variable is the factor being measured or tested in response to changes in the independent variable.

How would you reduce the effect of random errors in an experiment

To reduce the effects of random errors in an experiment, you can increase the number of trials, use more precise measurement instruments, and control environmental conditions to eliminate variability.

Difference between aim and hypothesis

The aim of an experiment outlines the purpose or objective, while a hypothesis is a testable prediction about the expected outcome based on the aim. Both components are essential for guiding experimental design and interpretation.

What happens if we use different concentrations of CuSo4 with copper electrode for electroplating

Using different concentrations of $CuSO_4$ with copper electrodes for electroplating will affect the rate of deposition, the thickness of the copper layer, and the quality of the plating. Higher concentrations typically lead to faster deposition rates and smoother coatings.

Economic, ethical, legal, political and social considerations define each one

Economic considerations relate to the costs and financial benefits of a process or decision. Ethical considerations involve moral implications and responsibilities. Legal considerations pertain to laws and regulations governing behavior. Political considerations involve the influence of government policies and public opinion. Social considerations address how actions affect communities and societal norms.

Qualitative data, qualitative analysis, quantitative data, quantitative analysis, primary and secondary data define each one

Qualitative data refers to non-numerical information that describes characteristics or qualities, while quantitative data involves numerical measurements.

Qualitative analysis focuses on identifying the components of a mixture, whereas quantitative analysis measures the amount of those components.

Primary data is collected firsthand through experiments or observations, and secondary data is gathered from existing sources or prior research.

Safety considerations

involve identifying potential hazards, implementing protective measures, and ensuring compliance with safety regulations to prevent accidents and injuries in chemical processes. Make sure to name each of the specific risk and its specific minimisation

Writing a research question, aim and hypothesis

The research question is a specific query that guides an investigation, while the aim defines the overall goal of the research. The hypothesis is a testable statement predicting the relationship between variables.

What to do in a discussion

explain experimental data and discuss your findings, link your findings back to your experimental question and aim to explain whether or not your data supports your hypothesis, link your findings to relevant chemical concepts to see whether or not the hypothesis is supported, it is important to recognise the scientific theory that could explain the observations made and identify any errors or limitations in your data and method and suggest improvements.

Define reproducibility and repeatability

Reproducibility refers to the ability of an experiment or study to produce consistent results when repeated under different conditions or by different researchers, while repeatability involves achieving the same results when the same experiment is performed multiple times under the same conditions.

Define bias, method, methodology, an outlier, significant figures and uncertainty

Bias refers to a systematic distortion in data or results due to subjective influence, method is the specific procedure employed to conduct a study, methodology is the overarching strategy or rationale informing the choice of methods, an outlier is a data point that differs significantly from other observations, significant figures are the digits in a number that carry meaningful information about its precision, and uncertainty describes the range of values within which the true value is expected to lie.

Faradays law

Faraday's law states that the amount of substance produced at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte. It provides a quantitative relationship between current, time, and the amount of reactant transformed.

Ion movement and concentration effect

I - Cu2+ ions migrate toward cathode; so42- toward anode, explains deposition and dissolution.

C- higher cu2+ means faster plating until satuation or limiting current, shows understanding of rare-determining factors

Temperature, electrode surface area and current and voltage stability effect

C & V - fluctuates change charge passed which gives inconsistant mass a key source of error.

T - affects ion mobility and resistance which must be controlled for valid comparison

E- larger area means more sites for reduction, impacting rate and uniformity of plating

Visual evidence of experiment

Cathode appeared darker patchy copper layer which meant reduction of cu2- ions and uneven plating shows current density variation.

Beaker colour gradient means deeper blue due to higher cu2+ concentration; confirms independent variable

Colour change after electrolysis - slight fading means cu2+ ions consumed at cathode and replenished at anode.

Texture of Deposit - smooth means stable current; rough means voltage fluctuations or contamination

Anode Observation - putting or thinning means oxidation releasing cu2+ ions.

Systematic errors

Electrode cleaning error - residual oxide reduces surface area which means lower mass deposited.

Voltage fluctuations - alters current and means inconstant charge passed

Incomplete drying - residual solution adds mass and overestimation

Unequal immersion depth - different surface area exposed means inconsistent plating rate

Temperature variation - changes ion mobility which is a systematic deviation.

Random errors

Splashing or bubbles - random loss of deposit

Timing inconsistency - seconds off means random mass variation

Balance fluctuation - small random mass differences

Solution Movement - random ion distribution changes

Effect of concentration and collision theory link

Effect of C - higher cu2+ means faster plating until current becomes limiting

CT - more ions means more successful collisions which means faster reduction

Reliability, accuracy, validity and issues

Reliability is the consistency of measurements over time or across different conditions, indicating how repeatable the results are. Issues - no repeats cannot confirm trend

Validity refers to whether the experiment measures what it claims to measure, ensuring that results are applicable to the intended context. Issues - uncontrolled current means concentration wasn’t isolated.

Reliability - consistency of results, improved by repeats

about both electrodes gained mass, imperfect concentration trend and industry link

Both electrodes gained mass due to incomplete oxidation or contamination which gives false mass increase

Imperfect concentration trend = current instability masked true effect

Industry link - uniform plating requires controlled current, temperature and concentration.

the why behind my trend

Why higher concentration increases rate - more ions available for reaction, leading to greater collision frequency and faster reaction rates.

Why trend wasnt perfect - impurities and temperature fluctuations affected ion distribution and reaction efficiency.

Why mass doesnt increase forever - current becomes limiting as ions are depleted from solution.

The limiting factor shift and the mass gain at cathode vs mass loss at anode relationship

LF- at low concentration, limiting factor is ion avaliability. At high concentration, limiting factor is electron supply ( current ).

MG- If they dont match then systematic error has happened (drying, incomplete oxidation or contamination).

Why cathode was patchy and validity explanation

• uneven current density, surface impurities or localised ion depletion

V - did we isolate concentration as only variable?

( Validity was reduced because current was not controlled, meaning concentration was not the only variable affecting mass deposited.

Faradays law and electrolyte colour change

F - beacuse current was not measured theoretical mass cannot be accurately compared to experimental mass.

E - Deeper blue means higher cu2+ concentration, fading after electrolysis means ions consumed and anode replenishes cu2+

Best improvement and Industry link in sentences

BI- Use a constant current power supply to eliminate voltage fluctuation, ensuring charge passed is consistent across trials

IL- Electroplating in industry, requires controlled current, temperature, and concentration to ensure uniform coating thickness.

Why electroplating is non spontaneous and electrochemical E value meaning

why non spontaneous - Because the reaction has a negative cell potential, so it needs energy input.

E value - More positive E is strongest oxidant, more negative E is strongest reductant.

Precision and how it is relevant

precision refers to the consistency and repeatability of measurements. High precision in electrolysis experiments ensures that results are reliable and can be reproduced under the same conditions.

Precision was limited because only one trial was conducted for each concentration to insufficient data, inconsistant drying, voltage fluctuations, uneven plating and mass changes didn’t follow a perfect trend.

two improvements to help with validity and 3 r’s

Constant voltage to stop flunctuations in readings and conducting multiple trials to increase reliability, ensuring results are consistent and reproducible. Also considering temperature control to minimize environmental influences.