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GCSE AQA Organic Chemistry Notes
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Hydrocarbons and Alkanes
Hydrocarbons are compounds containing only carbon and hydrogen atoms. The simplest family of hydrocarbons is the alkanes, which include methane (CH₄), ethane (C₂H₆), propane (C₃H₈), and butane (C₄H₁₀). All alkanes follow the general formula C₅H₂₂₊₂.
Alkanes belong to a homologous series (similar compounds with similar properties) and are saturated compounds, meaning all carbon atoms form four single bonds. As the carbon chain length increases, so do certain properties:
- Longer chains have higher melting and boiling points
- Shorter chains evaporate more easily and are more flammable
- Longer chains are thicker and stickier (more viscous)
Did you know? Alkanes make excellent fuels because they release significant energy when burned with oxygen, which is why they're widely used in vehicles and heating systems.
Crude oil, a fossil fuel formed from the remains of ancient organisms over millions of years, is our primary source of hydrocarbons. It's extracted by drilling into rocks where it has been stored for millennia. Because crude oil takes so long to form, it's considered a finite resource that will eventually run out.
To separate the different hydrocarbons in crude oil, we use fractional distillation. This process involves heating the oil until it vaporizes, then passing the vapor through a column that's hot at the bottom and cooler at the top. As the gases rise, they condense into liquids at different heights based on their boiling points.
Fractional Distillation and Cracking
In fractional distillation, compounds separate based on their boiling points. Longer chain hydrocarbons like bitumen (used for roads) and heavy fuel oils condense at the bottom of the column where it's hottest. Medium chains like diesel and petrol collect in the middle. Very short chains like propane and butane (components of LPG) may remain gaseous throughout.
Cracking is a thermal decomposition reaction that breaks longer hydrocarbon chains into shorter, more useful ones. There are two main methods:
- Catalytic cracking: The hydrocarbon vapor passes over hot powdered aluminium oxide, causing it to split into smaller molecules
- Steam cracking: The hydrocarbon vapor mixes with steam at very high temperatures to break apart
Remember this! Cracking typically produces a shorter chain alkane plus an alkene - this is how we create the unsaturated hydrocarbons industry needs.
Alkenes are unsaturated hydrocarbons with at least one carbon-carbon double bond. This double bond makes alkenes more reactive than alkanes. When bromine water is added to alkenes, it changes from orange to colorless as the bromine reacts with the double bond - this is a key test for unsaturation.
Alkenes can undergo several important reactions:
- With hydrogen (plus a catalyst) to form alkanes
- With water (plus a catalyst and heat) to form alcohols
- With halogens (no catalyst needed) to form halogenated compounds
The high reactivity of alkenes makes them extremely useful in industry, particularly for creating polymers where many alkene molecules join together in long chains.
Esters and Polymers
Esters are organic compounds with the -COO- functional group. They typically have pleasant, fruity smells and evaporate easily, making them perfect for perfumes and food flavourings. To create an ester, a carboxylic acid and an alcohol react in the presence of a catalyst like concentrated sulphuric acid, producing water as a byproduct.
Esters form the basis of important condensation polymers like polyester. These polymers form when two different monomers—typically a dicarboxylic acid and a diol —combine. During this reaction, small molecules like water are eliminated as the monomers join together through ester links.
Chemistry tip: Condensation polymers are often biodegradable because microorganisms can easily break the ester links—that's why polyester fabrics eventually break down in nature!
The natural world is full of naturally occurring polymers. These include:
- Polypeptides: Chains of amino acids joined by amide bonds (also called peptide bonds)
- DNA: Two polymer chains of nucleotides coiled in a double helix, with the four bases A, C, G, and T distinguishing each nucleotide
- Carbohydrates: Polymers made of sugar monomers, including starch, glycogen, and cellulose
Amino acids can join together because they have two functional groups: a carboxylic acid group and an amino group. When these react, water is eliminated as the carbon and nitrogen atoms join to form an amide bond. This same chemistry creates the long chains of proteins that make up much of your body's structure.
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In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
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very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
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I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
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THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
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This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
GCSE AQA Organic Chemistry Notes
S
Sophie
@sophie_fcge
Organic chemistry explores the vast world of carbon-based compounds that make up living things and many everyday materials. This branch of chemistry helps us understand everything from the fuels that power our vehicles to the polymers in our clothing and... Show more
Hydrocarbons and Alkanes
Hydrocarbons are compounds containing only carbon and hydrogen atoms. The simplest family of hydrocarbons is the alkanes, which include methane (CH₄), ethane (C₂H₆), propane (C₃H₈), and butane (C₄H₁₀). All alkanes follow the general formula C₅H₂₂₊₂.
Alkanes belong to a homologous series (similar compounds with similar properties) and are saturated compounds, meaning all carbon atoms form four single bonds. As the carbon chain length increases, so do certain properties:
- Longer chains have higher melting and boiling points
- Shorter chains evaporate more easily and are more flammable
- Longer chains are thicker and stickier (more viscous)
Did you know? Alkanes make excellent fuels because they release significant energy when burned with oxygen, which is why they're widely used in vehicles and heating systems.
Crude oil, a fossil fuel formed from the remains of ancient organisms over millions of years, is our primary source of hydrocarbons. It's extracted by drilling into rocks where it has been stored for millennia. Because crude oil takes so long to form, it's considered a finite resource that will eventually run out.
To separate the different hydrocarbons in crude oil, we use fractional distillation. This process involves heating the oil until it vaporizes, then passing the vapor through a column that's hot at the bottom and cooler at the top. As the gases rise, they condense into liquids at different heights based on their boiling points.
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Fractional Distillation and Cracking
In fractional distillation, compounds separate based on their boiling points. Longer chain hydrocarbons like bitumen (used for roads) and heavy fuel oils condense at the bottom of the column where it's hottest. Medium chains like diesel and petrol collect in the middle. Very short chains like propane and butane (components of LPG) may remain gaseous throughout.
Cracking is a thermal decomposition reaction that breaks longer hydrocarbon chains into shorter, more useful ones. There are two main methods:
- Catalytic cracking: The hydrocarbon vapor passes over hot powdered aluminium oxide, causing it to split into smaller molecules
- Steam cracking: The hydrocarbon vapor mixes with steam at very high temperatures to break apart
Remember this! Cracking typically produces a shorter chain alkane plus an alkene - this is how we create the unsaturated hydrocarbons industry needs.
Alkenes are unsaturated hydrocarbons with at least one carbon-carbon double bond. This double bond makes alkenes more reactive than alkanes. When bromine water is added to alkenes, it changes from orange to colorless as the bromine reacts with the double bond - this is a key test for unsaturation.
Alkenes can undergo several important reactions:
- With hydrogen (plus a catalyst) to form alkanes
- With water (plus a catalyst and heat) to form alcohols
- With halogens (no catalyst needed) to form halogenated compounds
The high reactivity of alkenes makes them extremely useful in industry, particularly for creating polymers where many alkene molecules join together in long chains.
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Esters and Polymers
Esters are organic compounds with the -COO- functional group. They typically have pleasant, fruity smells and evaporate easily, making them perfect for perfumes and food flavourings. To create an ester, a carboxylic acid and an alcohol react in the presence of a catalyst like concentrated sulphuric acid, producing water as a byproduct.
Esters form the basis of important condensation polymers like polyester. These polymers form when two different monomers—typically a dicarboxylic acid and a diol —combine. During this reaction, small molecules like water are eliminated as the monomers join together through ester links.
Chemistry tip: Condensation polymers are often biodegradable because microorganisms can easily break the ester links—that's why polyester fabrics eventually break down in nature!
The natural world is full of naturally occurring polymers. These include:
- Polypeptides: Chains of amino acids joined by amide bonds (also called peptide bonds)
- DNA: Two polymer chains of nucleotides coiled in a double helix, with the four bases A, C, G, and T distinguishing each nucleotide
- Carbohydrates: Polymers made of sugar monomers, including starch, glycogen, and cellulose
Amino acids can join together because they have two functional groups: a carboxylic acid group and an amino group. When these react, water is eliminated as the carbon and nitrogen atoms join to form an amide bond. This same chemistry creates the long chains of proteins that make up much of your body's structure.
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user