A Level Chemistry - Blog Posts

Structural Isomerism

In one boring history lesson, you and your friend (who both love chemistry) are doodling displayed formulas in the back of your textbook. You both decide to draw C5H12 - however, when you come to name what you’ve drawn, your friend has something completely different. You know what you’ve drawn is pentane and your friend knows what they’ve drawn is 2,3-dimethylpropane. So which one is C5H12?

The answer is both! What you and your friend have hypothetically drawn are structural isomers of C5H12 (another is 2-methylbutane). These are compounds which have the same molecular formula but different structural formulas.

Isomers are two or more compounds with the same formula but a different arrangement of atoms in the molecule and often different properties. 

There are several different kinds of structural isomers: chain, positional and functional group. 

Chain isomerism happens when there is more than one way of arranging carbon atoms in the longest chain. If we continue with the example C5H12, it exists as the three chain isomers shown above. Chain isomers have similar chemical properties but different physical properties because more branched isomers have weaker Van der Waals and therefore lower boiling points.

Positional isomers have the same carbon chain and the same functional group but it is attached at different points along the chain. 

This is a halogenoalkane. The locant “1″ describes where the chlorine is on the chain. For more on naming organic compounds, check out my nomenclature post.

The final type of isomer you need to know is a functional group isomer. This is a compound with the same molecular formula but a different functional group. For example, C2H6O could be ethanol or methoxymethane.

And surprisingly, that is all you need to know for the AS exam. There are also things called stereoisomers but those will be covered next year. Just make sure you know how to name and draw the three different kinds of structural isomers for the exam. Practice makes perfect!

SUMMARY

Structural isomers are compounds which have the same molecular formula but different structural formulas.

Isomers are two or more compounds with the same formula but a different arrangement of atoms in the molecule and often different properties.

There are several different kinds of structural isomers: chain, positional and functional group.

Chain isomerism happens when there is more than one way of arranging carbon atoms in the longest chain. Chain isomers have similar chemical properties but different physical properties because more branched isomers have weaker Van der Waals and therefore lower boiling points.

Positional isomers have the same carbon chain and the same functional group but it is attached at different points along the chain.

A functional group isomer is a compound with the same molecular formula but a different functional group.

Happy studying!

Combusting Alkanes

If you follow this blog, by now you must be thinking, when will we be done with the alkane chemistry? Well, the answer is never. There is still one more topic to touch on - burning alkanes and the environmental effects. Study up chums!

Alkanes are used as fuels due to how they can combust easily to release large amounts of heat energy. Combustion is essentially burning something in the presence of oxygen. There are two types of combustion: complete and incomplete. 

Complete combustion occurs when there is a plentiful supply of air. When an alkane is burned in sufficient oxygen, it produces carbon dioxide and water. How much depends on what is being burnt. For example:

butane + oxygen -> carbon dioxide + water

2C4H10 (g) + 13O2 (g) -> 8CO2 (g) + 10H2O (g)

Remember state symbols in combustion reactions. In addition, this reaction can be halved to balance for 1 mole of butane by using fractions when dealing with the numbers.

C4H10 (g) + 6 ½ O2 (g) -> 4CO2 (g) + 5H2O (g)

Incomplete combustion on the other hand occurs when there is a limited supply of air. There are two kinds of incomplete combustion. The first type produces water and carbon monoxide. 

butane + limited oxygen -> carbon monoxide + water

C4H10 (g) + 4 ½ O2 (g) -> 4CO (g) + 5H2O (g)

Carbon monoxide is dangerous because it is toxic and undetectable due to being smell-free and colourless. It reacts with haemoglobin in your blood to reduce their oxygen-carrying ability and can cause drowsiness, nausea, respiratory failure or death. Applicances therefore must be maintained to prevent the formation of the monoxide.

The other kind of incomplete combustion occurs in even less oxygen. It produces water and soot (carbon).

butane + very limited oxygen -> carbon + water

C4H10 (g) + 2 ½ O2 (g) -> 4C (g) + 5H2O (g)

Internal combustion engines work by changing chemical energy to kinetic energy, fuelled by the combustion of alkane fuels in oxygen. When this reaction is undergone, so do other unwanted side reactions due to the high pressure and temperature, e.g. the production of nitrogen oxides.

Nitrogen is regularly unreactive but when combined with oxygen, it produces NO and NO2 molecules:

nitrogen + oxygen -> nitrogen (II) oxide

N2 (g) + O2 (g) -> 2NO (g)

and

nitrogen + oxygen -> nitrogen (II) oxide

N2 (g) + 2O2 (g) -> 2NO2 (g)

Sulfur dioxide (SO2) is sometimes present in the exhaust mixture as impurities from crude oil. It is produced when sulfur reacts with oxygen. Nitrogen oxides, carbon dioxide, carbon monoxide, carbon particles, unburnt hydrocarbons, water vapour and sulfur dioxide are all produced in exhaust fumes and are also pollutants that cause problems you need to be aware of for the exam as well as how to get rid of them.

Greenhouse gases contribute to global warming, an important process where infrared radiation from the sun is prevented from escaping back into space by atmospheric gases. On the one hand, some greenhouse gases need to continue this so that the earth can sustain life as it traps heat, however, we do not want the earth’s temperature to increase that much. Global warming is the term given to the increasing average temperature of the earth, which has seen an increase in the last few years due to human activity - burning fossil fuels like alkanes has produced more gases which trap more heat. Examples of greenhouse gases include carbon dioxide, methane and water vapour.

Another pollution problem the earth faces is acid rain. Rain water is already slightly acidic due to the CO2 present in the atmosphere but acid rain is more acidic than this. Nitrogen oxides contribute to acid rain although sulfur dioxide is the main cause. The equation for sulfur dioxide reacting with water in the air to produce oxidised sulfurous acid and therefore sulphuric acid is:

SO2 (g) + H2O (g) + ½ O2 (g) -> H2SO4 (aq)

Acid rain is a problem because it destroys lakes, buildings and vegetation. It is also a global problem because it can fall far from the original source of the pollution.

Photochemical smog is formed from nitrogen oxides, sulfur dioxide and unburnt hydrocarbons that react with sunlight. It mostly forms in industralised cities and causes health problems such as emphysema.

So what can we do about the pollutants?

A good method of stopping pollution is preventing it in the first place, therefore cars have catalytic converters which reduce the amount of carbon monoxide, nitrogen oxides and unburnt hydrocarbons come into the atmosphere by converting them into less toxic gases. Shaped like a honeycomb for increased SA and therefore rate of conversion, platinum and rhodium coat ceramic and act as catalysts for the reactions that take place in an internal combustion engine.

As they pass over the catalyst, they react with each other to form less pollution:

octane + nitrogen (II) oxide -> carbon dioxide + nitrogen + water

C8H18 (g) + 25NO -> 8CO2 (g) + 12 ½ N2 (g) + 9H2O (g)

nitrogen (II) oxide + carbon monoxide  -> carbon dioxide + nitrogen

2NO (g) + 2CO (g) -> 2CO2 (g) + N2 (g)

Finally, sulfur dioxide must be dealt with. The first way it is dealt with is by removing it from petrol before it can be burnt, however, this is often not economically favourable for fuels used in power stations. A process called flue gas desulfurisation is used instead.

In this, gases are passed through a wet semi-solid called a slurry that contains calcium oxide or calcium carbonate. These neutralise the acid, due to being bases, to form calcium sulfate which has little commercial value but can be oxidised to produce a more valuable construction material.

calcium oxide + sulfur dioxide -> calcium sulfite

CaO (s) + SO2 (g) -> CaSO3 (s)

calcium carbonate + sulfur dioxide -> calcium sulfite + carbon dioxide

CaCO3 (s) + SO2 (g) -> CaSO3 (s) + CO2 (g)

calcium sulfite + oxygen -> calcium sulfate

CaSO3 (s) + O -> CaSO4 (s)

SUMMARY

Alkanes are used as fuels due to how they can combust easily to release large amounts of heat energy. Combustion is essentially burning something in the presence of oxygen.

Complete combustion occurs when there is a plentiful supply of air. When an alkane is burned in sufficient oxygen, it produces carbon dioxide and water

Remember state symbols in combustion reactions. In addition, reactions can be halved to balance for 1 mole of compounds by using fractions when dealing with the numbers.

Incomplete combustion occurs when there is a limited supply of air. There are two kinds of incomplete combustion. 

The first type produces water and carbon monoxide.

Carbon monoxide is dangerous because it is toxic and undetectable due to being smell-free and colourless. It reacts with haemoglobin in your blood to reduce their oxygen-carrying ability and can cause drowsiness, nausea, respiratory failure or death. 

The other kind of incomplete combustion occurs in even less oxygen. It produces water and soot (carbon).

Internal combustion engines work by changing chemical energy to kinetic energy, fuelled by the combustion of alkane fuels in oxygen. When this reaction is undergone, so do other unwanted side reactions due to the high pressure and temperature, e.g. the production of nitrogen oxides.

Nitrogen is regularly unreactive but when combined with oxygen, it produces NO and NO2 molecules:

Sulfur dioxide (SO2) is sometimes present in the exhaust mixture as impurities from crude oil. It is produced when sulfur reacts with oxygen.

Nitrogen oxides, carbon dioxide, carbon monoxide, carbon particles, unburnt hydrocarbons, water vapour and sulfur dioxide are all produced in exhaust fumes and are also pollutants that cause problems you need to be aware of for the exam as well as how to get rid of them.

Greenhouse gases contribute to global warming, an important process where infrared radiation from the sun is prevented from escaping back into space by atmospheric gases. Some greenhouse gases need to continue this so that the earth can sustain life as it traps heat, however, we do not want the earth’s temperature to increase that much. Global warming is the term given to the increasing average temperature of the earth, which has seen an increase in the last few years due to human activity - burning fossil fuels like alkanes has produced more gases which trap more heat. 

Another pollution problem the earth faces is acid rain. Nitrogen oxides contribute to acid rain although sulfur dioxide is the main cause. 

Acid rain is a problem because it destroys lakes, buildings and vegetation. It is also a global problem because it can fall far from the original source of the pollution.

Photochemical smog is formed from nitrogen oxides, sulfur dioxide and unburnt hydrocarbons that react with sunlight. It mostly forms in industralised cities and causes health problems such as emphysema.

A good method of stopping pollution is preventing it in the first place, therefore cars have catalytic converters which reduce the amount of carbon monoxide, nitrogen oxides and unburnt hydrocarbons come into the atmosphere by converting them into less toxic gases. Shaped like a honeycomb for increased SA and therefore rate of conversion, platinum and rhodium coat ceramic and act as catalysts for the reactions that take place in an internal combustion engine.

As they pass over the catalyst, they react with each other to form less pollution.

octane + nitrogen (II) oxide -> carbon dioxide + nitrogen + water

C8H18 (g) + 25NO -> 8CO2 (g) + 12 ½ N2 (g) + 9H2O (g)

nitrogen (II) oxide + carbon monoxide  -> carbon dioxide + nitrogen

2NO (g) + 2CO (g) -> 2CO2 (g) + N2 (g)

Finally, sulfur dioxide must be dealt with. The first way it is dealt with is by removing it from petrol before it can be burnt, however, this is often not economically favourable for fuels used in power stations. A process called flue gas desulfurisation is used instead.

In this, gases are passed through a wet semi-solid called a slurry that contains calcium oxide or calcium carbonate. Since they are bases, these neutralise the acid to form calcium sulfate which has little commercial value but can be oxidised to produce a more valuable construction material.

Happy studying!

Breaking Down Alkanes - isn’t it cracking?

Unfortunately, if you’re sitting your A Level chemistry exam, you need to know a little more than the basic properties of alkanes outlined in my last post. Luckily though, this post takes you through fractional distillation and the two types of cracking - isn’t that convenient?

Crude oil contains carbon compounds formed by the effects of pressure and high temperature on plant and animal remnants. It is viscious, black and found in rocks beneath the earth’s surface. It is a mixture of mainly alkane hydrocarbons which are separated by a process called fractional distillation. Crude oil is essential because it is burned as a fuel and each fraction has different properties e.g. diesel, petrol, jet fuel.

Fractional distillation is the continual evaporation and condensation of a mixture which causes fractions to split due to a difference in boiling point. It is important to note that fractional distillation does not separate crude oil into pure compounds but rather less complex mixtures. Fractions are groups of compounds that have similar boiling points and are removed at the same level of a fractionating column.

The first step in this process is to heat crude oil in a furnace until some changes state from a liquid to a vapour. This mixture goes up a fractionating tower or column which is hotter at the bottom than the top and reaches a layer which is cool enough to condense and be collected. Shorter chain molecules are collected at the top where it is cooler since they have lower boiling points.

As you go down the fractionating column, bear in mind that: the column temperature increases, the boiling point increases, the number of carbon atoms increases and the strength of the Van der Waals’ between molecules increases.

Different fractions have different usefulnesses and often, it is the fractions with lower boiling points and shorter chains which are much more purposeful. Therefore there needs to be a process to getting shorter chains because they are the least abundant in crude oil samples. To meet demand, long chain molecules that are less useful are broken down into shorter chain molecules. This is done by cracking.

Cracking is a process where long chain hydrocarbon molecules are broken down into shorter chain molecules which are in high demand. This can be done one of two ways - thermal or catalytic.

Thermal cracking involves heating long chain alkanes to high temperatures - usually between 1000 - 1200K. It also uses high pressures up to 70atm and takes just one second. It only needs a second because the conditions could decompose the molecule completely to produce carbon and hydrogen instead. The conditions produce shorter chain alkanes and mostly alkenes.

A typical equation for this:

Decane -> octane + ethene

C10H22 -> C8H18 + C2H4

Catalytic cracking also breaks down long alkanes by heat under pressure using the presence of a zeolite catalyst. Temperature used is approx. 800-1000K and the pressure is often between 1-2 atm. Zeolite is an acidic mineral with a honeycomb structure, made from aluminium oxide and silicion dioxide. The honeycomb structure gives the catalyst a larger surface area which increases ROR. Factories which catalytically crack are often operated continuously for around 3 years at a time and produce branched alkanes, cycloalkanes and aromatic compounds.

You need to be able to compare the conditions of catalytic and thermal cracking for the A Level exam. Know that thermal cracking has a high temperature and pressure, a short duration, no catalyst and produces a high percentage of alkenes and some short chain alkanes. Catalytic uses a catalyst, a high temperature, a low pressure and produces aromatic hydrocarbons and motor fuels.

SUMMARY

Crude oil contains carbon compounds formed by the effects of pressure and high temperature on plant and animal remnants. I It is a mixture of mainly alkane hydrocarbons which are separated by a process called fractional distillation.

Fractional distillation is the continual evaporation and condensation of a mixture which causes fractions to split due to a difference in boiling point. 

It is important to note that fractional distillation does not separate crude oil into pure compounds but rather less complex mixtures.

Fractions are groups of compounds that have similar boiling points and are removed at the same level of a fractionating column.

The first step in this process is to heat crude oil in a furnace until some changes state from a liquid to a vapour. This mixture goes up a fractionating tower or column which is hotter at the bottom than the top and reaches a layer which is cool enough to condense and be collected. Shorter chain molecules are collected at the top where it is cooler since they have lower boiling points.

As you go down the fractionating column, bear in mind that: the column temperature increases, the boiling point increases, the number of carbon atoms increases and the strength of the Van der Waals’ between molecules increases.

Fractions with lower boiling points and shorter chains are much more purposeful but are the least abundant in crude oil samples. To meet demand, long chain molecules that are less useful are broken down into shorter chain molecules. 

Cracking is a process where long chain hydrocarbon molecules are broken down into shorter chain molecules which are in high demand. 

Thermal cracking involves heating long chain alkanes to high temperatures - usually between 1000 - 1200K. It also uses high pressures up to 70atm and takes just one second. It only needs a second because the conditions could decompose the molecule completely to produce carbon and hydrogen instead. The conditions produce shorter chain alkanes and mostly alkenes.

Catalytic cracking also breaks down long alkanes by heat under pressure using the presence of a zeolite catalyst. Temperature used is approx. 800-1000K and the pressure is often between 1-2 atm. Zeolite is an acidic mineral with a honeycomb structure, made from aluminium oxide and silicion dioxide. The honeycomb structure gives the catalyst a larger surface area which increases ROR. 

You need to be able to compare the conditions of catalytic and thermal cracking for the A Level exam. Know that thermal cracking has a high temperature and pressure, a short duration, no catalyst and produces a high percentage of alkenes and some short chain alkanes. Catalytic uses a catalyst, a high temperature, a low pressure and produces aromatic hydrocarbons and motor fuels.

Happy studying!

🎓A-level Results!🎓

I didn’t update yesterday because I was so busy and overwhelmed and ahhh.

But, I got…

A*AA!

I’m so unbelievably happy! I’ve got into medical school!

The breakdown:

Biology - A

Chemistry - A

Physics - A*

I can’t believe I got an A* in physics. I cried so much in that exam and afterwards I genuinely thought I wouldn’t scrape an A.

I’m so so so happy!

How did you do?

And to anyone with GCSE results next week, best of luck! Remember, wherever you end up is where you were meant to be!

🍳19.07.2022🍳

Hello everyone!

It’s been a little while since I did a normal post. Since exams have been over I’ve been really enjoying just having a lovely little break and not having any studying to do!

However, it’s time I start getting ready for university (which is in less than two months 😳). So, I’m going to start giving updates on the little productive tasks I get done to help me learn how to adult a bit more than I do now.

Today, I fried an egg for breakfast. I know it doesn’t seem like an amazing achievement, but I don’t cook at all so it felt like a very big first step into learning how to actually look after myself independently. Plus, it tasted good!

How’s your summer going? The UK has just had a massive heatwave, it was FAR too warm. ☀️☺️

🧬Exam Diary - Biology Paper 3🧬

On Friday I had my last exam, biology. Honestly, I was so pleased with it. The questions were alright, but the essay was phenomenal, and I’m so glad I finished on a high!

Well that’s it, A-levels are over. It’s a very strange sensation, but a wonderful one nonetheless.

Well done for everyone getting through exams. They were so difficult and I’m so proud of you all! ☺️💛🌷

🌿24.06.2004🌿

Just doing some last minute studying for my last exam!

I can’t believe how fast it has all gone, but I’m so excited to have a break. It’s a really strange feeling if I’m honest. ☺️

Well, let’s go smash this last biology exam! 🥳🌷🌸🌻

🧪Exam Diary - Chemistry Paper 3🧪

I’m so happy! That paper was so so SO lovely!! Honestly, that’s the best exam I’ve done so far, I never thought I’d say that!

Only one more to go, wow! Hope you’re all having a wonderful day! ☺️🌻

🧪Exam Diary - Chemistry Paper 2🧪

I mean it was just fine?

Yesterday I sat my second chemistry paper, and yeah it felt pretty good. Nowhere near like paper 1, but that’s been my best paper yet. So, I guess I’m happy!

Good luck to anyone else with A-levels!! We’re on the home stretch now! ☺️🪷

🧬Exam Diary - Biology Paper 2🧬

I honestly loved that exam! It felt like a mock? Thank goodness for those questions. I enjoyed it even more than paper one! 😳

How did everyone else find it?? ☺️🌷

(also the heat in the UK is killing me wow)

🧲Exam Diary - Physics Paper 3🧲

That was so much nicer than paper 2!! I feel quite good about it. I can’t believe my physics a level is over! ☺️🪐

🪵16.06.2022🪵

I have my very last physics exam today! I’m honestly quite excited to know that this is the end of me taking the subject. It’s been so interesting but draining at the same time, and I’m excited to prove myself one last time!

I was originally really scared of paper 3, but after yesterday I’m feeling oddly confident.

Good luck to anyone else taking exams! 😚🌺

🧪Exam Diary - Chemistry Paper 1🧪

I honestly loved that paper! It’s been by far my favourite paper so far, I’m so happy! ☺️🌷

🧲Exam Diary - Physics Paper 2🧲

I won’t lie, I didn’t enjoy the paper. In fact I got quite upset. So much stuff was on capacitors and other really weird questions. In hindsight it wasn’t as bad as I thought and I think I’ve actually done pretty well, so fingers crossed! 🤞🏻🫠

🧬Exam Diary - Biology Paper 1🧬

I’ve just had my first A-level Biology exam! I love biology paper 1 so I was quite excited for this one.

The paper was alright, but the questions were just a bit… weird? I’ve never had a past paper that felt like that one, but the last three questions were wonderful!

Fingers crossed for physics tomorrow! 🤭🤞🏻

🥑08.06.2022🥑

Good morning!

To Do List:

2019 Biology Paper 1

2020 Biology Paper 1

Predicted Biology Paper 1

My biology exam is tomorrow! I’m feeling really confident because biology is my best subject, and all the practice papers are going well! 🤭

Have you got any exams coming up? 🤔

🪸07.06.2022🪸

Good morning!

I’ve woken up early today. I find that waking up any time before 7 always means I have a more productive day. Whilst my days haven’t been too unproductive, they haven’t been as good as they can be, hopefully today this will finally be rectified as I feel quite good. 🤭

To Do List

2018 Physics Paper 2

2019 Physics Paper 2

2018 Biology Paper 1

2019 Biology Paper 1

2020 Biology Paper 1

Later today I’m spending some time with my friends which should be really lovely. 💕

Also, I’m planning on writing some tips on how to do well in Biology, Chemistry and Physics as I feel now I’m doing quite good at them. I hope that incoming posts are useful! 💌

Have a wonderful day! 🫶🏻🤗

🌳06.06.2022🌳

Good morning! ☺️

I’m back in college today as the half term is over. These are the papers I’m hoping to get done:

2017 Physics Paper 2

2018 Physics Paper 2

2017 Biology Paper 1

2018 Biology Paper 1

2019 Biology Paper 1

I’ve finished 2017 Bio Paper 1 and got an A* so I’m very happy.

Being back inside school is definitely helping me stay focused, and I really like that I can go and talk to my teachers whenever I need (I’m going to make use of that later today!).

Have a good day! 🌞

🌷05.06.2022🌷

“I always get to where I am going by walking away from where I have been” - A. A. Milne

If I’m honest, I’m really struggling to find motivation. I don’t know why, I’m just not doing well. I’ve been feeling so distant and tired (if anyone maybe has an idea why please say). Today, I’m going to try to change that.

The quote above is really useful when I need motivation, as it reminds me starting and making any progress is still getting me to my goals.

Here is a list of things I would like to get done:

A-level Physics Specimen Paper 2

A-level Physics 2017 Paper 2

A-level Physics 2018 Paper 2

A-level Biology 2017 Paper 1

A-level Biology 2018 Paper 1

Obviously, this is quite a lot, but as long as I get ~3 done I’ll be happy.

I’m going to go get some breakfast, and I’ll update later on how I’m getting on. Wish me luck!

💛31/05/2022💛

🌻To-Do List:🌻

Inorganic chemistry reactions flashcards

Chemical tests flashcards

2017 A-Level Chemistry Paper 1

2018 A-Level Chemistry Paper 1

Fill out booklet

Online courses

I’m hoping to get all this done today, and have a really productive day! 📚

I’m feeling quite confident about chemistry at the moment, so I’m hoping these should go okay. 🧪

I’ll update later, have a productive day! ☺️🫶🏻

Welcome!

Hi there!

🌻My name is Hunny (she/her) and welcome to my study blog!

🌻I’m studying A-levels in Biology, Chemistry and Physics, and am in year 13.

Follow me for study content! ☺️