Mod 7.2 - Hydrocarbons Flashcards
What are single bonds?
One shared pair of electrons; C-C
What are double bonds?
Two shared pairs of electrons; C=C
What are triple bonds?
Three shared pairs of electrons; C☰C
What are the angles between bonds of a tetrahedral?
109.5 degrees
What are the angles between bonds of a Planar?
120 decrees
What are the angles between bonds of a linear?
180 degrees
What is the geometrical arrangement of bonds and angle between bonds for ‘four single bonds around the carbon atom’
Tetrahedral - 109.5 degrees
What is the geometrical arrangement of bonds and angle between bonds for ‘One double and two single bonds around the carbon atom’
Planar - 120 degrees
What is the geometrical arrangement of bonds and angle between bonds for ‘two double bonds around the carbon atom’
Linear - 180 degrees
What is the geometrical arrangement of bonds and angle between bonds for ‘One triple and one single bond around the carbon atom’
Linear - 180 degrees
What is the general formula of alkanes?
C(n)H(2n+2)
What is the general formula of alkenes?
C(n)H(2n)
What is the general formula of alkynes?
C(n)H(2n-2)
What is the procedure required to safely handle and dispose of organic substances?
There is the use of a safety data sheet as a document which is prepared by the manufacturer or importer of a hazardouz chemical
This provides info on the chemical and how to handle it safely including storage and disposal
How can organic substances enter the body? (3)
Inhalation through the lungs
Absorption through the skin
Ingestion (swallowing)
What are the consequences of organic substances entering the body?
It can cause varying degrees of damage depending on the chemical
What substances can be poured down the sink as a safe disposable of organic substance after being diluted?
Organic substances that are water miscible(A miscible liquid can be mixed with another liquid ) - includes short chained alcohols and short chained ketones.
These substances are readily consumed by microorganisms in the sewer but are highly flammable
Are different types of waste kept in the same place?
No, they are often kept separate and disposed of differently
What is used for water-immiscible organig wastes?
A waste container, as it shouldnt be washed down the sink.
What are the two types of water immiscible organic wastes?
Non-halogenated organic waste
Halogenated organic waste
Why shouldnt non halogenated organic waste by washed down the sink?
Non halogenated organic waste includes hydrocarbons, floats on top of water and can form an explosive vapour
Why shouldnt halogenated organic waste by washed down the sink?
Halogenated organic wastes (contains halogen in the compound) are also flammable, can form toxic halogenated compounds during combustion and many are highly toxic to aquatic life
What are our primary source of hydrocarbons?
Fossil fuels - they are non renewable resources, formed from the remains of prehistoric animals and plants.
Three types of fossil fuels include; coal, crude oil and natural gas
What are the environmental implications of obtaining and using hydrocarbons from the Earth?
The combustion of hydrocarbon fuels releases carbon dioxide (CO2), as well as other greenhouse gases that contribute to atmospheric pollution and climate change.
Materials produced by the chemical industry using components of crude oil as the raw materials are non-biodegradable. Therefore, their disposal poses an environmental concern, particularly in the long-term as the amount of non-biodegradable materials being used accumulate
Oil spills impose significant damage to the environment especially aquatic ecosystems. Oils spills are also difficult to clean up.
What are the economic implications of obtaining and using hydrocarbons from the Earth?
Significant economic growth for countries that have access to oil reservoirs as crude oil forms a major party of their export.
The exponential use of petroleum led to dwindling supplies and high costs of this non-renewable fossil fuel and by the late 1900s it became evident that traditional materials needed to be supplemented or replaced by others derived from renewable resources.
Electrical energy, once largely provided by the burning of fossil fuels such as coal in power stations, is now supplemented by the use of batteries and the development of the renewable energy industry. Renewable energy production is not only environmentally but also more economically viable in the long-term.
What are the sociocultural implications of obtaining and using hydrocarbons from the Earth?
During the twentieth century, the world population increased significantly. With this increase in population came increased demands for materials such as fuels for transport, industry and heating, materials for construction to replace and supplement timber and iron, fibres for clothing and household goods and chemicals to improve medical care. For a large part of that century, the demands were satisfied by hydrocarbons in fossil fuels.
As the demands for liquid fuels for transport increased, crude oil refining increased, and crude oil provided not only petrol, diesel and aviation fuel but also chemicals such as ethylene, which is an essential raw material for polymer production.
Chemical industries based around fossil fuels developed. These included manufactures of polymers, such as polyethylene, PVC and polystyrene, as well as synthetically produced materials including esters, acids, alcohols, nylon, polyesters, synthetic rubber. These chemicals, based on the petroleum industry, changed the lifestyles of society.
How do you deal with the handling of organic substances? (5)
Store “like material with like” – so that flammable materials should be stored together and away (in a different cabinet) from materials that are corrosive, toxic, etc to prevent hazardous reactions.
Oxidising agents must be stored separately from organic substances as they can ignite organic solvents or acids.
Organic nitrates and peroxidies are shock-sensitive and should be handled with care as shock can result them in generating large volume of gases in a short period of time, resulting in a high increasing pressure. This would result in an explosion.
Some organic acids such as acetic and propanoic acid are corrosive which can cause burns upon contact with skin where severity depends on concentration of the acid. TO minimise the risk, lab coat, safety gloves and goggles should be used. Enclosed leather shoes also needed
Ensure that a well-ventilated area such as a fume hood is used when handling flammable, volatile organic substances (e.g. alcohols). This is because the inhalation of alcohol can cause dizziness and could result in brain damage depending on duration of exposure.
What precaution should you use before leaving the lab?
Wash your hands before leaving the laboratory, even if gloves are worn as a safety precaution especially after cleaning up a spill. This is because organic solvents can strip off your skin’s natural oil layer resulting in skin irritation whereby your skin would be more susceptible to absorbing toxic chemicals.
What are intermolecular forces?
It is an attractive force that can be found between molecules?
WHat are the 3 types of intermolecular forces?
Dispersion forces
Dipole-Dipole forces
Hydrogen bonding
What are dispersion forces? Where do they occur? What are there strengths?
Dispersion forces are a type of intermolecular force between non-polar and polar molecules (it is present between all molecules).
It describes a temporary attractive force due to the formation of temporary dipoles in a nonpolar molecule (i.e. one side may become temporarily more polar due to more electrons being on that side etc, thereby allowing for bonds between other molecules)
Dispersion forces are the weakest IMF. The strength of it is determined by the number of electrons, which is proportional to the molecular mass of the substance
What happens to dispersion forces as the molecular mass increases?
The larger the molecule, the more electrons it will have, with more electrons held loosely further away from the nucleus. Hence, the electrons can form larger partial charges and dispersion forces will be stronger
The longer the hydrocarbon chain, the stronger the attractive dispersion forces
What are dipole-dipole forces?
These are a type of intermolecular force that exists between polar molecules (with permanent dipoles). I.e. in unsymmetrical molecules, such as F-H, where F would be permanentnly negative, and H is permanently positive, thereby allowing them to bond with their opposite charge molecule
How does the strength of dipole-dipole forces change? What is the strength of this IMF?
The strength of dipole dipole forces increases with increasing bond polarity, which can be determined by finding the difference in electronegativity of two atoms in the bond
Dipole-dipole forces are moderate in strength (higher than dispersion forces but lower than hydrogen bonding)
What is hydrogen bonding?
It is a type of IMF that exists between a hydrogen and a molecule that has either F, O or N.
What is the strength of hydrogen bonding? What is it affected by?
Hydrogen bonds are the strongest type of IMF (stronger than dispersion and dipole dipole)
It is affected by;
- The difference in electronegativity of the two atoms in the bond; N < O < F in terms of electronegativity
- The number of hydrogen bonds which can form. The number of hydrogen bonds which can form is limited by the number of available bond donors and acceptors as well as the molecular shape
What are 3 main factors of STRUCTURAL ARRANGEMENT which influence the intermolecular forces?
Symmetry
Surface area
Packing
What is symmetry as a structural arrangement which influences the IMF?
All hydrocarbons exhibit dispersion forces, while dipole-dipole and hydrogen bonding is dependent on functional groups.
If a molecule is symmetrical, it is non-polar. This will mean that there is zero net dipole movements –> only dispersion forces exist (dominant IMF is dispersion) -> less IMF than other molecules which will be polar based on their unsymmetrical nature
What is surface area as a structural arrangement which influences the IMF?
A higher molecular surface area allows for more points of contact for dispersion forces to exist between molecules. Thus, the greater the surface area, the stronger the IMF
This is especially seen when comparing linear to highly branched organic compounds. Highly branched organic compounds with different alkyl groups will have a smaller surface area than if it was just linear –> lower IMF for highly branched organic compounds as there are less opportunities for dispersion forces
Thus, a linear compound > branched organic compound in terms of dispersion forces because of greater Surface area for dispersion to occur
For example, pentane > 2-methylbutane > 2,2-dimethylpropane in terms of surface areas
What is packing? Compare packing for unbranched vs branched organic compounds
Packing refers to the way molecules fit together in 3D space, and it is dependent on their structural arrangement.
Unbranched organic compounds are able to pack closely together
Branched organic compounds have a lower packing efficiency
What is packing as a structural arrangement which influences the IMF?
The closer the molecules pack, the stronger the IMF between them.
Unbranched organic compounds are able to pack closely –> forms stronger intermolecular forces
Branched organic compounds have lower packing efficiency –> weaker IMF
What is the order of the strength of dispersion forces for alkanes, alkenes and alkynes? Explain why. (NEED TO DOUBLE CHECK - NOT CONFIRMED, IT MIGHT JUST BE ALKANES > ALKENES > ALKYNES)
Strongest to weakest
1. Alkynes
2. Alkanes
3. Alkenes
In these compounds, there are only dispersion forces as they are non=polar molecules. The difference in strnegth of dispersion is due to the interplay between molecular mass and packing:
Alkynes - lowest molecular mass and highest packing
Alkanes - Highest molecular mass and lowest packing
Alkenes - Middle molecular mass and middle packing
For alkynes, even though they have the lowest molecular mass, they have a linear geometry, which increases packing efficiency. A higher electron density from the triple bonds can form larger partial charges –> stronger intermolecular forces
For alkenes, even though they have the decent molecular mass and packing, we would assume that it is between alkanes and alkynes. However, effect of increased packing efficiency in alkenes compared to alkanes is not as significant because of the lower mass –> weaker dispersion forces than alkanes
NOTE: APPARENTLY, ALTOUGH THE ABOVE IS TRUE, FOR HSC CHEM PURPOSES, THE TREND IS THAT ALKANE > ALKENE > ALKYNE IN TERMS OF MP AND BP AND EXPLAIN IT IN TERMS OF STRENGTH OF DISPERSION FORCES BUT IDK SO DOUBLE CHECK
What are the dominant IMF forces present in an alcohol?
Dispersion forces in the non-polar region, and hydrogen bonding in the polar region (O-H bond).
Alcohols can form hydrogen bonds between its molecules because of the presence of the O - H
The strength of dispersion forces increases with chain length and surface area of contact and packing
What is the order of strength of hydrogen bonds between primary, seocndary and tertiary alcohols?
Weakest –> strongest:
Tertiary < Secondary < Primary
This is because, in secondary and tertiary alcohols, there are alkyl groups adjacent to the hydroxyl group which hinder the hydroxyl groups from getting close to each other –> restricting formation of strong hydrogen bonds with other alcohol molecules .
What are the dominant IMF forces in carboxylic acid groups?
They can form two hydrogen bonds with each other forming a ‘dimer’. Thus carboxylic acids have stronger IMFs compared to other functional groups(except for amides) due to hydrogen bonds
What are the dominant IMF forces in amines?
They can form one hydrogen bond with another amine molecule. Since oxygen is more electronegative than nitrogen the N-H bond is less polar than an O-H bond, thus hydrogen bonds between amines are comparatively weaker compared to alcohols and carboxylic acids
What are the dominant IMF forces in amides?
Amide molecules can form a network of hydrogen bonds between O and H and also N and H. Thus, they have the strongest IMF forces due to dipole dipole forces and hydrogen bonding
What is the order of the strength of hydrogen bonds between amines, amides, carboxylic acids and alcohols
Amines < Alcohols < Carboxylic Acids < Amides
What are the dominant IMF forces in ketones?
The main intermolecular force that determines the melting & boiling point of ketone molecules are dipole-dipole forces
Ketones have a higher boiling point than aldehydes because ketones have two alkyl (R) groups attached a central carbon atom where each alkyl group has a greater electron density than a hydrogen atom. Comparatively, aldehyde only has one alkyl (R) group and one hydrogen atom attached to a central carbon atom.
WHat are the dominant IMF forces in aldehydes?
The main intermolecular force between aldehyde molecules are dipole-dipole forces, followed by dispersion forces.
(dont make the mistake of putting that it can form hydrogen bonds, bc although it can, for hsc chem, it only needs to mention dipole dipole and dispersion
WHat are the dominant IMF forces in aldehydes?
The main intermolecular force between aldehyde molecules are dipole-dipole forces, followed by dispersion forces.
(dont make the mistake of putting that it can form hydrogen bonds, bc although it can, for hsc chem, it only needs to mention dipole dipole and dispersion)
What is the order of number of hydrogen bonds between amines and amides?
Tertiary < secondary < primary
WHat are the dominant IMF forces in haloalkanes?
The electronegativity difference between the halogen and the carbon atoms makes the C-X bond polar, where X represents a halogen atom. Due to this, there are dipole-dipole forces between haloalkane molecules as well as dispersion forces compared to only dispersion forces present between molecules in the three hydrocarbon homologous series (alkane, alkenes and alkynes).
How does IMF link to MP and BP?
A stronger IMF will mean that more heat energy is required to break apart the bonds –> greater MP and BP. Thus a stronger IMF –> higher MP and BP. Weaker IMF –> weaker MP and BP
What is the general trend of MP and BP?
Amides > Carboxylic acid > Alcohol > ketone >aldehyde > Amine > haloalkane > Alkane > Alkene >Alkyne
Note; the trend should actually be alkyne > alkane >alkene, but for HSC chem, should just use alkane > alkene > alkyne and explain it in terms of strength of dispersion forces
What happens to Mp and Bp as chain length increases?
There is an increased likelihood of dispersion forces. –> becoming major intermolecular forces
When asked about the properties within the homologous series, what should we discuss?
Differences in Mp, BP, solubility and miscibility
What is a solute?
A solute is a substance, usually a solid, that is dissolved in a solution, which is usually a liquid.
What is a solvent?
the liquid in which a solute is dissolved to form a solution.
What is the condition for solubility?
A solute will dissolve in a solvent if the IMF between the solute and solvent are stronger than both the intermolecular forces within the solute and within the solvent
What is the solubility of ketones?
Although the ketones with one to three carbons (C1 to C3) are very soluble in water, as the molecular mass increases (i.e. moving into C4 and beyond), the length of the non-polar hydrocarbon chain increases. This results in ketone molecules experiencing a gradual decrease in water solubility as molecular mass increases, resulting in the non-polar alkyl chain/group increasing in length.
What is the solubility of aldehydes?
Although the aldehydes with one to three carbons are very soluble in water, as the molecular mass increases (i.e. moving into C4 and beyond), the length of the non-polar hydrocarbon chain increases. This results in aldehydes experiencing a gradual decrease in water solubility as molecular mass increases, resulting in the non-polar alkyl chain/group increasing in length.
What is the solubility of alcohols
Although the alcohol molecules with one to three carbons (C1 to C3) are soluble in water, as the molecular mass increases (i.e. moving into C4 and beyond), the length of the non-polar hydrocarbon chain increases. This results in alcohols experiencing a gradual decrease in water solubility as molecular mass increases due to the increasing non-polar alkyl chain/group.
WHat is the solubility of amides?
In terms of solubility, this is similar to other cases we have talked about. As the molecular mass increases, the non-polar alkyl group will increase resulting in a gradual decline in solubility in polar substances.
What is the solubility of amines?
Similar to alcohols, as the molecular mass of the amine molecules increases, the length of the non-polar alkyl chain increases. Thus, the solubility of amines molecules in polar substances (or solvents) such as water decreases with increasing molecular size.
What is the solubility of carboxylic acid groups?
That being said, when comparing carboxylic acid to their corresponding alcohol with the same number of carbon, the carboxylic acid is more soluble in water due to the capacity to form two hydrogen bonds compared to only one for alcohol.
How do you assess solubility in non-polar solvents?
Identify types of IMF within solute, solvent and between the solute and solvent.
If the solute-solvent forces are enough to disrupt the solvent-solvent and solute-solute forces –> mixing at molecular level –> solubility
WHat is the solubility of carboxylic acids, amines and amides (in non polar solvents)
Solubility in non-polar solvents is low for short chained carboxylic acids, amines and amides, but increases with increasing chain length
What is the solubility of alcohols in non polar solvents?
The solubility of alcohols in non polar solvents increases as the length of the carbon chain increases
What is density?
Mass/volume
Explain the intramolecular and intermolecular bonds present between alkanes
Intramolecular: covalent bonding
Intermolecular: dispersion forces
What is the effect of branching on the Bp of an alkane?
As an alkane chain branch, the surface area of the molecule decreases. The intermolecular force reduces as a result of this.
Therefore, as the branching increases, the boiling point of an alkane chain decreases.
How do you format an answer to a question which gives you a graph with different Bp and Mp and asks you to explain the differences with a trend
Initially establish the trend. I.e. initially, the BP of A is lower than B, however as the carbon chain lengthens, the gap between A and B shortens, however A continues to be above B
The strength of intermolecular forces directly link to how much energy is needed to break apart bonds, with stronger bonds needing more energy, hence higher BP/MP.
Establish initial types of IMF in both, and explain why one is lower than the other. Use exact values from graph
Include a diagram of the types of IMF of each functional group
After that, state that the gap closes as the carbon chain lengthens due to the increased dominance of dispersion forces as the prominent IMF compared to polar/hydrogen bonds –> smaller gap in BP
As chain length increases –> greater dispersion forces because of greater electron density and stronger temporary dipoles
Concluding sentence
What is the general characteristics of hydrocarbons? (5)
Low MP and BP (that increases as chain length increases)
are less dense than water
are insoluble in water and soluble in non-polar solvents
are colourless
Dont conduct electricity
What happens to dispersion forces as chain length increases?
As chain length increases –> greater dispersion forces because of greater electron density and stronger temporary dipoles
