Sulfur burns in oxygen: properties of sulfur dioxide; test with acidified potassium dichromate paper

Summary

In this chemistry video, sulfur burns in oxygen to form sulfur dioxide, which is observed with a blue flame. The experiment tests sulfur dioxide's acidic and reducing properties using acidified potassium dichromate and distilled water with a universal indicator. The video explains the chemical equations behind these properties, showing sulfur dioxide's ability to form sulfurous acid and its reduction potential when reacting with oxidizing agents like potassium dichromate.

Takeaways

• 🔥 Sulfur burns in oxygen to produce sulfur dioxide, which is a colorless gas.
• 🔵 Burning sulfur in oxygen produces a bright blue flame, which can be difficult to see in air.
• 🧪 Sulfur dioxide can be tested by its reducing properties using acidified potassium dichromate; it changes color from orange to green.
• 🌡️ Sulfur dioxide is an acidic gas, as demonstrated by its reaction with water and changing the pH of the solution to acidic (pH below 4).
• 🌊 Sulfur dioxide reacts with water to form sulfurous acid, which is a weak acid.
• ⚛️ Sulfurous acid, formed from sulfur dioxide and water, demonstrates reducing properties by giving up oxygen.
• 🔋 Sulfur dioxide has an oxidation state of +4 and can be oxidized to sulfate, which has an oxidation state of +6.
• 🌡️ Sulfite ions are oxidized to sulfate ions, losing two electrons in the process.
• ⚖️ The reaction between sulfur dioxide and dichromate ions demonstrates redox chemistry, where dichromate is reduced to chromium (III) and sulfur dioxide is oxidized.
• 📊 The balanced half-equations for the reduction of dichromate and oxidation of sulfite are provided, showing electron transfer processes.

Q & A

What is the purpose of the experiment in the video?

The purpose of the experiment is to burn sulfur in oxygen and observe the properties of the resulting product, sulfur dioxide.

What is the visual indication that sulfur has started burning?

Although the flame is difficult to see in air, it becomes visible as a bright blue flame when sulfur burns in oxygen.

What chemical equation describes the burning of sulfur in oxygen?

The balanced chemical equation is: S (solid) + O₂ (gas) → SO₂ (gas), where sulfur reacts with oxygen to produce sulfur dioxide.

How is the reducing property of sulfur dioxide demonstrated in the experiment?

The reducing property of sulfur dioxide is demonstrated using acidified potassium dichromate. When exposed to sulfur dioxide, the orange potassium dichromate turns green.

What is the test for sulfur dioxide's presence using acidified potassium dichromate?

The test for sulfur dioxide involves dipping filter paper in acidified potassium dichromate. When exposed to sulfur dioxide, the paper changes color from orange to green.

How is the acidic nature of sulfur dioxide shown in the experiment?

The acidic nature of sulfur dioxide is shown by dissolving it in water containing a universal indicator. The water turns from green (neutral) to a color indicating an acidic pH, around 4 or lower.

Why is sulfur dioxide considered an acidic gas?

Sulfur dioxide is considered an acidic gas because it is a non-metallic oxide that reacts with water to form sulfurous acid (H₂SO₃), a weak acid.

What is the balanced half-reaction for the oxidation of sulfite (SO₃²⁻) to sulfate (SO₄²⁻)?

The balanced half-reaction is: SO₃²⁻ + H₂O → SO₄²⁻ + 2H⁺ + 2e⁻. Sulfite is oxidized to sulfate by losing two electrons.

What is the balanced half-reaction for the reduction of dichromate (Cr₂O₇²⁻) to chromium (Cr³⁺)?

The balanced half-reaction is: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O. Each chromium atom is reduced from an oxidation state of +6 to +3, gaining a total of 6 electrons.

Why does potassium dichromate change color during the reaction with sulfur dioxide?

Potassium dichromate changes color from orange to green because the dichromate ion (Cr₂O₇²⁻) is reduced to chromium (Cr³⁺) by the sulfur dioxide, indicating a reduction process.

Outlines

00:00

🔥 Burning Sulfur and Observing Sulfur Dioxide

In this video segment, Sergey begins by introducing the experiment where sulfur is burned in oxygen to observe the properties of sulfur dioxide. He shows a conical flask filled with oxygen and sulfur powder, explaining that sulfur melts at a low temperature, turning from a yellow powder to a clear liquid, and eventually becoming deep brown and black. He mentions that the burning of sulfur can be hard to see, but in oxygen, it produces a blue flame, following the equation for the formation of sulfur dioxide (SO₂).

05:00

🔬 Testing Reducing Properties with Potassium Dichromate

Sergey demonstrates the reducing properties of sulfur dioxide using an oxidizing agent, acidified potassium dichromate. He prepares the agent by mixing two liquids with sulfuric acid and tests it with filter paper soaked in the solution. Upon exposing the filter paper to sulfur dioxide gas, the paper changes color from orange to green, confirming the presence of sulfur dioxide. This reaction signifies sulfur dioxide's ability to reduce potassium dichromate.

🌡 Testing Acidic Properties of Sulfur Dioxide

In this part, Sergey explains how sulfur dioxide behaves as an acidic gas. He tests its acidic properties by dissolving it in water with a universal indicator. The green indicator shows that water is neutral, but upon mixing with sulfur dioxide, the pH drops significantly, likely below 4. Sergey explains that sulfur dioxide is acidic because it is a non-metallic oxide that reacts with water to form sulfurous acid (H₂SO₃), a weaker acid than sulfuric acid (H₂SO₄).

⚛️ Chemical Properties and Equation Balancing

Here, Sergey delves deeper into the chemical behavior of sulfur dioxide. He explains that sulfur in sulfur dioxide can act as a reducing agent due to its ability to gain or lose oxygen. He also balances the half-equations for the oxidation of sulfite ions (SO₃²⁻) into sulfate ions (SO₄²⁻), showing that sulfur’s oxidation state changes from +4 to +6 during this process. He emphasizes the general rule for balancing such reactions: accounting for oxygen with water and hydrogen with hydrogen ions.

🔄 Balancing the Dichromate Reduction Equation

Sergey shifts focus to potassium dichromate, an oxidizing agent, and its reduction in acidic conditions. He balances the equation for the reduction of dichromate (Cr₂O₇²⁻) into chromium ions (Cr³⁺). He explains that each chromium atom’s oxidation state decreases from +6 to +3, which means that each chromium atom gains three electrons, resulting in six electrons being involved for the two chromium atoms present. This reaction involves water and hydrogen ions, consistent with balancing rules for acidic solutions.

👍 Conclusion and Encouragement for Viewers

Sergey wraps up the video by reviewing the properties of sulfur dioxide—its acidic nature and reducing ability. He reinforces the chemical principles demonstrated in the experiment and explains how the equations and reactions illustrate these properties. Finally, Sergey encourages viewers to subscribe, like the video, and thanks them for watching.

Keywords

💡Sulfur

Sulfur is a yellow non-metallic element that is the focus of the experiment in the video. It burns in oxygen, producing sulfur dioxide. In the video, the presenter heats sulfur, which melts into a liquid before burning with a blue flame, illustrating its combustion properties.

💡Oxygen

Oxygen is a colorless, odorless gas that supports combustion. In the video, the presenter fills a conical flask with oxygen to facilitate the burning of sulfur, which highlights oxygen's role as an essential reactant in the formation of sulfur dioxide (SO2).

💡Sulfur Dioxide (SO2)

Sulfur dioxide is a colorless, toxic gas with a pungent odor that is produced when sulfur burns in oxygen. In the video, the presenter tests its properties, including its reducing and acidic behaviors, showing its transformation into sulfurous acid when dissolved in water.

💡Combustion

Combustion refers to the process of burning a substance in the presence of oxygen. In this experiment, sulfur combusts in oxygen, producing sulfur dioxide. The video showcases how sulfur burns with a bright blue flame, which is a characteristic of its combustion.

💡Potassium Dichromate

Potassium dichromate is a chemical oxidizing agent used in the video to test the reducing properties of sulfur dioxide. The orange dichromate solution turns green when exposed to sulfur dioxide, demonstrating its ability to reduce the compound and change its oxidation state.

💡Reduction

Reduction refers to the gain of electrons in a chemical reaction. In the video, sulfur dioxide reduces potassium dichromate from an orange solution to a green one. This change is part of a redox reaction, where sulfur dioxide donates electrons to the dichromate.

💡Acidic Gas

An acidic gas is a gas that can dissolve in water to form an acidic solution. Sulfur dioxide is described as an acidic gas in the video. When SO2 dissolves in water, it forms sulfurous acid, which lowers the pH, as shown with the use of a universal indicator.

💡Universal Indicator

A universal indicator is a chemical solution that changes color to indicate the pH level of a solution. In the video, the presenter uses a universal indicator to demonstrate that sulfur dioxide dissolved in water creates an acidic solution, turning the indicator from green (neutral) to red (acidic).

💡Half Equation

A half equation represents either the reduction or oxidation part of a redox reaction. In the video, the presenter discusses balancing half equations for the oxidation of sulfite ions to sulfate and the reduction of dichromate ions to chromium ions, emphasizing the electron transfer in these processes.

💡Sulfurous Acid

Sulfurous acid (H2SO3) is a weak acid formed when sulfur dioxide dissolves in water. In the video, the presenter explains how sulfur dioxide reacts with water to form this acid, showcasing the acidic properties of the gas and its ability to lower the pH of water.

Highlights

Introduction to burning sulfur in oxygen and examining sulfur dioxide properties.

Melting sulfur turns from yellow to clear liquid, then brown and black before burning.

Sulfur burns with a bright blue flame in the presence of oxygen, forming sulfur dioxide.

Balanced chemical equation for sulfur burning in oxygen to produce sulfur dioxide is shown.

Sulfur dioxide is identified as a reducing agent using acidified potassium dichromate.

Color change from orange to green confirms sulfur dioxide's reducing properties.

Test for sulfur dioxide’s acidic properties using distilled water and universal indicator.

Sulfur dioxide forms sulfurous acid when it reacts with water, lowering the pH.

Explanation of sulfur dioxide’s weak acidic properties due to its non-metallic oxide nature.

Detailed explanation of the oxidation and reduction process of sulfite ions turning into sulfate.

Sulfite ion oxidation results in the loss of two electrons, explaining the reducing property.

Balancing half-equations for oxidation and reduction processes in acidic conditions.

Chromium from potassium dichromate reacts with sulfur dioxide, reducing to chromium 3+.

Balancing half-equations for the reduction of dichromate to chromium 3+ with hydrogen ions and water.

Conclusion summarizing sulfur dioxide as an acidic and reducing gas and encouraging viewer engagement.

Transcripts

hello welcome to sergey's chemistry

today I'm just going to burn sulfur and

oxygen and check the properties of the

product of the burning sulfur dioxide

here I have conical flask filled with

oxygen

and here is sulfur yellow powder

which melts at pretty low melting point

you see it easily turns into

clear liquid which First turns brown

deep Brown and virtually black

now we probably started burning already

although the flame is difficult to see

in the air

but it will be reducible in oxygen let's

see

we observe here

clear textbook description software

Burns and oxygen with bright blue flame

for example dioxide and that's the

equation

pretty easy to balance

we write solid in standard State at

least in solid

gaseous oxygen producing glacial sulfur

dioxide

now for other properties first reducing

one

for that we need oxidizing agent which

change color on reduction this is

acidified potassium dichromate

it's prepared by mixing these two

liquids

solution and sulfuric acid here is

filter paper I deep with an acidified

potassium dichromate when I keep

as control and another output in the gas

the result of the

color changes virtually immediately

from Orange into green

that's the test for sulfur dioxide

acidic hypertension later made paper

turning from Orange to green and now for

another property

acidic properties

you say that sulfur dioxide is an acidic

gas

let's check it with water

clear distilled water with universal

indicator on it

Universal indicator is green which means

water in the beaker is neutral th7

even no need to mix it up

still we can mix it up a little bit to

make sure Peach is definitely at least

four or maybe even lower because 4 is

the limit of this particular indicator

okay here is the

group photo of the result

acidic properties and reducing

properties of sulfur dioxide

we have found out that sulfur dioxide is

acidic gas and reducing gas

now I'm just going to show you the

formulas

equations

which illustrate this property in this

particular case

where it is

acidic

well simply just for a simple fact that

it's non-metallic oxide many

non-metallic oxides are acidic the

reactive water forming acids this is not

an exception

3x with water forming sulfurous acid

almost like sulfuric but SO3 here one

oxygen less

it can take this sulfur can take one

oxygen more and this is the reason for

its reducing properties

so this is weak acid but still acidic

enough to bring pH quite low

now for reducing properties

let's take sulfide ion for Simplicity

sulfite ion

would change into sulfate

on oxidation

heading one oxygen oxidation state of

sulfur here

if you can calculate it but I'm just

telling it is plus 4 and here is plus 6.

it means two electrons are lost

you can reduce them here two electrons

to get a to get a balanced equation we

just take care of oxygens with water and

of hydrogens with hydrogen ions

that's the general rule of balancing

half equations in acidic conditions

so I have to add one water molecule here

because for oxygens and three I need

four oxygens on left oxygen on the right

and here I need to balance hydrogens

with hydrogen ions two hydrogen ions

that's the

half equation for oxidation of sulfide

ion into sulfate

for every mole of sulfide ion we have

two moles of electrons produced

and now for oxidizing engine size

potassium dichromate we used

but the iron which is interesting to us

is chromium 207 2 minus decremental

it is changing into green chromium 3

plus

orange green

well let's balance it like that

two chromiums two chronions

again the same rule

balancing for oxygens in acidic

conditions with water and with hydrogens

with hydrogen ions

and now taking care of electrons

here oxidation state is plus 6 and here

equal to the charge plus three

it means each chromium atom received

three electrons

difference between 6 and 3.

but there are two chromiums here

so we have to multiply this three by two

six electrons is received

that's the half equation for dichromate

when it's oxidizing some reducing agent

in this case it was oxidizing sulfur

dioxide or more precisely sulfide ion

thank you for being here

please subscribe to the channel and

encourage me with likes

see you next time bye