GCSE Chemistry - Electrolysis Part 3 - Aqueous Solutions #42

Cognito

24 Mar 201905:42

Summary

TLDRThis video explains the process of electrolysis, focusing on how it works in aqueous solutions. Electrolysis involves splitting compounds into elements by passing an electric current through an electrolyte, where ions must be free to move. For soluble compounds like copper sulfate and sodium chloride, dissolving them in water creates the electrolyte. The video details how ions react at the positive anode and negative cathode, explaining the rules for which ions are discharged based on reactivity. Examples include copper sulfate, where copper and hydroxide ions are discharged, and sodium chloride, where hydrogen and chloride ions are released.

Takeaways

⚡ Electrolysis splits compounds into their elements by passing an electric current through an electrolyte.
💧 Ions in an electrolyte must be free to move, meaning insoluble compounds need to be molten, while soluble compounds can dissolve in water.
📋 In electrolysis experiments, a beaker with electrolyte, two electrodes (anode and cathode), and a power supply are required.
🧲 Positive ions move to the negative cathode, while negative ions move to the positive anode.
⚖️ At the cathode, the ion of the least reactive element is discharged. Hydrogen will be discharged if it's more reactive than the metal ion present.
🔬 In aqueous solutions, ions from both the dissolved compound and water are present, including hydrogen and hydroxide ions.
🔋 At the anode, halide ions (if present) are discharged; otherwise, hydroxide ions are discharged, forming oxygen and water.
🔧 In the electrolysis of copper sulfate solution, copper ions are discharged at the cathode, forming solid copper, while hydroxide ions discharge at the anode, forming oxygen and water.
🌡️ The process at normal temperatures causes solid copper to accumulate around the cathode.
🧪 In the electrolysis of aqueous sodium chloride, hydrogen ions discharge at the cathode to form hydrogen gas, while chloride ions discharge at the anode to form chlorine gas.

Q & A

What is the purpose of electrolysis in chemistry?
-Electrolysis is used to split compounds into their constituent elements by passing an electric current through an electrolyte.
Why is it necessary for the ions in an electrolyte to be free to move during electrolysis?
-For electrolysis to work, ions must be free to move so they can migrate to the respective electrodes, allowing the process of electrolysis to occur.
What must be done to metal oxides for them to participate in electrolysis?
-Most metal oxides are insoluble, so they need to be melted into a molten liquid to allow their ions to move freely and participate in electrolysis.
How are soluble compounds like copper sulfate prepared for electrolysis?
-Soluble compounds like copper sulfate can be dissolved in water to create an electrolyte for the electrolysis process.
What components are required to set up an electrolysis experiment?
-An electrolysis setup requires a beaker with electrolyte, two electrodes (a positive anode and a negative cathode), a wire connecting the electrodes, and a power supply.
How do you determine which ions will be discharged at the cathode in an aqueous solution?
-At the cathode, the ion of the least reactive element will be discharged. This can be determined by referring to the reactivity series.
What happens at the anode during the electrolysis of aqueous solutions?
-At the anode, negative ions from the electrolyte are attracted. If a halide ion is present, it will be discharged. If no halides are present, hydroxide ions from water will be discharged.
Why are copper ions discharged instead of hydrogen ions during the electrolysis of copper sulfate solution?
-Copper ions are discharged at the cathode because copper is less reactive than hydrogen, according to the reactivity series.
What are the products formed at the cathode and anode during the electrolysis of copper sulfate solution?
-At the cathode, pure copper is deposited as copper ions gain electrons. At the anode, hydroxide ions are discharged, producing oxygen and water.
What happens at the anode and cathode during the electrolysis of sodium chloride solution?
-In the electrolysis of sodium chloride solution, hydrogen ions are discharged at the cathode, forming hydrogen gas. Chloride ions are discharged at the anode, producing chlorine gas.

Outlines

00:00

⚡ Electrolysis Overview

This paragraph introduces the concept of electrolysis, which is a technique used to split compounds into their elemental components by passing an electric current through an electrolyte. It explains that ions must be free to move for electrolysis to work, which can be achieved by either melting insoluble compounds like metal oxides or dissolving soluble compounds like copper sulfate and sodium chloride in water.

05:01

🧪 Setup for Electrolysis

Here, the necessary setup for an electrolysis experiment is described. The equipment includes a beaker filled with an electrolyte, two electrodes (a positive anode on the right and a negative cathode on the left), a wire connecting them, and a power supply. The challenge in aqueous electrolysis lies in determining which ions will move to which electrode, as both ions from the ionic compound and those from water are present in the solution.

🔋 Rules for Ion Discharge at the Cathode

This paragraph explains the basic rules for determining which ions are discharged at the cathode (negative electrode). Both metal ions from the compound and hydrogen ions from water are attracted to the cathode. However, only one type of ion is discharged, and this is determined by the element’s reactivity. The ion of the less reactive element will be discharged. For example, hydrogen ions are discharged if the metal ions are more reactive, but copper ions will be discharged because copper is less reactive than hydrogen.

⚙️ Rules for Ion Discharge at the Anode

The discharge rules for the anode (positive electrode) are discussed. Both negative ions from the ionic compound and hydroxide ions from water are attracted to the anode. The discharge rule is simpler here: if halide ions (e.g., chloride, bromide) are present, they will be discharged. If no halide is present, the hydroxide ions are discharged, which then form oxygen and water.

🧪 Example: Electrolysis of Copper Sulfate Solution

This paragraph uses copper sulfate as an example to illustrate the process of electrolysis in aqueous solutions. Copper sulfate breaks down into copper (Cu2+) and sulfate (SO42-) ions, while water provides hydrogen (H+) and hydroxide (OH-) ions. At the cathode, copper ions are discharged due to their lower reactivity compared to hydrogen. These ions gain electrons and form solid copper on the cathode. At the anode, hydroxide ions are discharged and form oxygen, water, and release electrons.

🌊 Example: Electrolysis of Sodium Chloride Solution

In this example of aqueous sodium chloride electrolysis, the solution contains sodium (Na+), chloride (Cl-), hydrogen (H+), and hydroxide (OH-) ions. At the cathode, hydrogen ions are discharged, forming hydrogen gas due to sodium being more reactive than hydrogen. At the anode, chloride ions are discharged instead of hydroxide ions because chloride is a halide. This results in the formation of chlorine gas. The paragraph concludes by inviting viewers to like and subscribe to the video.

Mindmap

Keywords

💡Electrolysis

Electrolysis is a technique used to split compounds into their elemental forms by passing an electric current through an electrolyte. In the video, this process is central to demonstrating how solutions of copper sulfate and sodium chloride break down into their respective elements. Electrolysis works by causing ions in the electrolyte to move to electrodes of opposite charge.

💡Electrolyte

An electrolyte is a substance that contains free ions and can conduct electricity, which is necessary for the process of electrolysis. In the video, copper sulfate and sodium chloride solutions act as electrolytes. For insoluble compounds, such as metal oxides, the electrolyte must be melted, while soluble compounds can simply be dissolved in water.

💡Cathode

The cathode is the negatively charged electrode in an electrolysis setup, where positive ions are attracted. In the video, it is explained that the cathode can either discharge metal ions or hydrogen ions from water, depending on their reactivity. The video provides an example with copper ions, which are less reactive than hydrogen ions, so they get discharged and form solid copper.

💡Anode

The anode is the positively charged electrode where negative ions are attracted. The video explains how the anode discharges hydroxide ions from water unless a halide (like chloride) is present. For example, in copper sulfate electrolysis, hydroxide ions are discharged, producing oxygen gas.

💡Aqueous solution

An aqueous solution is one where the solvent is water. In the video, aqueous solutions of copper sulfate and sodium chloride are used as electrolytes. Water adds hydrogen and hydroxide ions to the solution, which participate in the electrolysis process alongside the ions from the dissolved compounds.

💡Reactivity series

The reactivity series is a ranking of elements by their reactivity, used in the video to determine which ions will be discharged at the electrodes during electrolysis. The video explains that ions of less reactive elements will be discharged first, such as copper ions being discharged over hydrogen ions because copper is less reactive.

💡Copper sulfate

Copper sulfate (CuSO4) is a soluble compound used in one of the electrolysis examples in the video. When dissolved in water, it forms copper ions (Cu²⁺) and sulfate ions (SO₄²⁻). The video demonstrates that during electrolysis, copper ions are discharged at the cathode to form solid copper.

💡Hydroxide ions

Hydroxide ions (OH⁻) are produced when water splits into ions in an aqueous solution. In the video, hydroxide ions can be discharged at the anode, releasing oxygen gas unless a halide like chloride is present. For example, during copper sulfate electrolysis, hydroxide ions are discharged instead of sulfate ions.

💡Sodium chloride

Sodium chloride (NaCl), also known as table salt, is used in the second electrolysis example in the video. In an aqueous solution, it produces sodium ions (Na⁺) and chloride ions (Cl⁻). The video shows that during electrolysis, chloride ions are discharged at the anode to produce chlorine gas, while hydrogen ions are discharged at the cathode to form hydrogen gas.

💡Discharge of ions

Discharge of ions refers to the process by which ions gain or lose electrons at the electrodes during electrolysis. The video explains that the ion discharged depends on its reactivity or the presence of halides. For example, copper ions are discharged at the cathode in a copper sulfate solution because copper is less reactive than hydrogen.

Highlights

Electrolysis splits compounds into elements by passing an electric current through an electrolyte.

For insoluble compounds like most metal oxides, melting them to a molten liquid is required to create an electrolyte.

Soluble compounds like copper sulfate and sodium chloride can be dissolved in water to create the electrolyte.

Electrolysis setup requires a beaker of electrolyte, two electrodes (positive anode on the right and negative cathode on the left), and a power supply.

In aqueous solutions, the electrolyte contains ions from both the ionic compound and water itself, such as hydrogen and hydroxide ions.

The negative cathode attracts positive ions, such as metal ions from the compound or hydrogen ions from water.

The ion of the least reactive element will be discharged at the cathode.

In cases where hydrogen ions are present, they will be discharged if the metal ions in the solution are more reactive than hydrogen.

If copper ions are present, they will be discharged over hydrogen ions due to copper's lower reactivity.

At the positive anode, either the negative ion from the compound or hydroxide ions will be discharged.

Halide ions (such as chloride or bromide) will always be discharged over hydroxide ions if present.

When copper sulfate is electrolyzed, copper ions are discharged at the cathode, forming solid copper.

At the anode during copper sulfate electrolysis, hydroxide ions are discharged, forming oxygen and water.

During electrolysis of sodium chloride, hydrogen ions are discharged at the cathode, forming hydrogen gas.

At the anode in sodium chloride electrolysis, chloride ions are discharged, forming chlorine gas.