GCSE Chemistry - Electrolysis Part 3 - Aqueous Solutions #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
⚡ 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.
🧪 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
💡Electrolyte
💡Cathode
💡Anode
💡Aqueous solution
💡Reactivity series
💡Copper sulfate
💡Hydroxide ions
💡Sodium chloride
💡Discharge of ions
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.
Transcripts
we've seen in our last couple of videos
that electrolysis is a technique that we
use to split compounds into their
elements
which we do by passing an electric
current through an electrolyte
for this process to work though the ions
in our electrolyte have to be free to
move around
so for insoluble compounds like most
metal oxides this means that we'd have
to melt them to make them a molten
liquid
however for soluble compounds like
copper sulfate and sodium chloride we
can just dissolve them in water to make
our electrolyte
so in today's video we're going to see
how the electrolysis of these aqueous
solutions works
whenever you do an electrolysis
experiment you're going to need a beaker
full of electrolyte
your two electrodes with a positive
anode on the right
and a negative cathode on the left
a wire joining the two electrodes
and a power supply in the middle
now the main difficulty with the
electrolysis of aqueous solutions is
figuring out which ions will go to each
electrode
this is because in aqueous solutions as
well as the ions from the ionic compound
like copper and sulfate ions there will
also be hydrogen ions and hydroxide ions
from the water itself
because water in solutions splits up
into its ions
to work out which of the ions will react
with each electrode you need to know a
couple of basic rules
the cathode which is negative will
attract the positive ions
so the metal ion from the compound
and the hydrogen ion from the water
but importantly it will only discharge
one of these ions and we have to tell
which one it is
the rule is that the ion of the least
reactive element will be the one they
guessed is charged
so if we take a look at our reactivity
series
we can see that if the ions of any of
these metals were present then the
hydrogen ions would be discharged
because hydrogen is less reactive than
these metals
whereas if we had copper ions then the
copper ions would be the ones discharged
because copper is even less reactive
than hydrogen
over the anode which has a positive
charge we have a similar problem
as well as a negative ion from our
compound which could be something like a
nitrate ion or a bromide ion would also
have hydroxide ions
this time though the rule to decide
which will be discharged is a bit easier
if a halide is present so fluoride
chloride bromide and so on then they'll
be the one that gets discharged
but if a halide isn't present
then it's always the hydroxide that gets
discharged
to see how all of this works let's see
what would happen if our electrolyte was
an aqueous solution of copper sulfate
the first step is to work out which ions
would have in the solution
from the copper sulfate we'd have copper
2 plus ions
and so4 two minus ions
then from the water because remember
it's an aqueous solution we'd have h
plus and o h minus ions
if you think about the negative cathode
first
it could either discharge the hydrogen
ions or the copper ions
so all we need to do is check our
reactivity series
and because copper is lower down on the
list and so less reactive the copper
ions will be the ones that get
discharged
so they'll gain two electrons from the
cathode
and form pure copper
and because all of this is done at
normal temperatures the copper will be
solid so it actually accumulates around
the cathode
meanwhile for the positive anode it
could either discharge the hydroxide
ions or the sulfate ions
so it would discharge the hydroxide
because our rule remember was that it
will always do the hydroxide ions unless
halides are present
so the hydroxide ions will give up the
extra electron to the anode
and they actually go to form oxygen and
water
the equation for this is that four oh
ions
could form two h2o
one o2 molecule
and four electrons
before we finish let's try one more
example where our electrolyte is aqueous
sodium chloride
in this electrolyte we'll have sodium
ions chloride ions hydrogen ions and
hydroxide ions
so just like before to find which of our
positive ions the negative cathode will
discharge we look at our reactivity
series
and can see that hydrogen is less
reactive than sodium
so the hydrogen ions will be the ones
that get discharged
by gaining electrons
and forming hydrogen gas
meanwhile at the anode we have to pick
between chloride and hydroxide ions
and because chloride is a halide that
would be the one that gets discharged
so or lose electrons and form chlorine
gas
anyway that's all for today so hope you
enjoyed this video if you did give us a
like and subscribe and we'll see you
next time
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