Chemistry (Unit 1) R#2 Flashcards
Describe the intermolecular forces, arrangement, motion, and compressibility of a solid
High intermolecular forces of attraction, tightly packed and regularly arranged, vibrate in fixed positions, incompressible
Describe the intermolecular forces, arrangement, motion, and compressibility of a liquid
Intermediate intermolecular forces of attraction, closely packed and irregularly arranged, slide past each other, incompressible
Describe the intermolecular forces, arrangement, motion, and compressibility of a gas
Very weak/non-existent intermolecular forces of attraction, far apart and irregularly arranged, quickly, randomly, freely moving in all directions, compressible
Describe the 4 main changes in state
Melting: solid to liquid
Freezing: liquid to solid
Boiling/evaporation: liquid to gas
Condensation: gas to liquid
What is sublimation
The direct change of a substance from solid to gas
Explain how changes of state occur
As particles of a substance are heated, they gain kinetic energy move more and overcome attractive forces; when they are cooled, they lose kinetic energy and form attractive forces. When a certain temp. is reached the substance changes state
What are melting and boiling points?
They are the temps. at which changes of state occur
What is the difference between the melting and boiling points of pure and impure substances?
Pure substances: have sharp defined melting and boiling points
Impure substances: have a range of melting and boiling points (usually lower melting point and higher boiling point)
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What is diffusion?
The spreading out of particles in a gas or liquid from an area of high to lower concentration until evenly spread.
Diffusion cannot happen in a solid; it must dissolve before diffusing.
What factors affect diffusion?
Temperature and the molecular weight (Mr) of the compound.
As temperature increases, the diffusion rate increases; as molecular weight increases, the diffusion rate decreases.
What happens in the white ring experiment?
Vapours from soaked cotton diffuse and move towards the center of the tube, forming a white ring of ammonium chloride (NH4Cl) nearer to the HCl cotton.
NH3 (Mr = 17) moves faster than HCl (Mr = 36.5) due to its lower molecular weight.
What type of reaction occurs between HCl and NH3 in the white ring experiment?
Neutralization reaction.
This reaction can be reversed by heating ammonium chloride.
What occurs during the thermal decomposition of ammonium chloride?
Ammonium chloride is thermally decomposed, releasing a mixture of hydrogen chloride and ammonia gas.
The chemicals react again to form ammonium chloride at the exit of the test tube.
What is the mixture of gases in the center of the test tube during the experiment?
Hydrogen chloride and ammonia.
These gases react to form ammonium chloride.
Why does the experiment take a few minutes despite gases traveling rapidly?
Because gases do not travel in straight lines and collide with particles already in the test tube.
What is the chemical name for HCl when in liquid form?
Hydrochloric acid.
In gas form, it is referred to as hydrogen chloride.
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What is solubility?
The amount of solute that can dissolve in a solvent at a certain volume and temperature
By definition, it is the maximum mass (g) that can dissolve in 100g of solvent.
How does temperature affect solubility?
Solubility increases with temperature
As temperature increases, there are wider intermolecular spaces, allowing more solid to dissolve.
How does pressure affect the solubility of gases?
Solubility of gases increases with pressure
As pressure increases, gases become more soluble.
Define solute.
A substance that dissolves in a solvent.
Define solvent.
What the solute dissolves in.
What is a solution?
A mixture of the solute dissolved in solvent.
What is a saturated solution?
When the maximum amount of solute has been dissolved in a solvent at a certain volume and temperature.
What does a solubility curve show?
Solubility in g of solute/100g of water over temperature.
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What is an element?
A pure substance made of only one type of atom
Elements are the simplest form of matter and cannot be broken down into simpler substances.
Define compounds.
Two or more different elements chemically bonded in a fixed composition
Compounds have unique properties that differ from the individual elements that compose them.
What are mixtures?
Two or more different substances physically bonded not in a fixed composition
Mixtures can be separated by physical means.
How can you separate an iron/sulfur mixture?
Use a magnet as iron is magnetic
This method exploits the magnetic property of iron.
What is the method to separate a sand/salt mixture?
Dissolve the mixture in water, filter to remove sand, and evaporate the water to get salt
This uses solubility and filtration techniques.
What is the process to separate a solid insoluble in a liquid?
Filter to obtain solid (filtration)
Filtration is effective for separating solids from liquids.
What is the method for separating a solid soluble in a liquid if the liquid is needed?
Simple distillation
Simple distillation involves heating the solution to vaporize the liquid and then condensing it back to liquid.
What are the steps in crystallization?
- Heat till point of crystallisation to evaporate water
- Leave to cool to form crystals
- Filter the solution to remove crystals as residue
- Dry between 2 filter papers
Crystallization allows for the formation of pure solid crystals from a solution.
How do you separate immiscible liquids?
Using a filtering funnel
Immiscible liquids do not mix and can be separated based on density.
What method is used for separating miscible liquids?
Fractional distillation to separate based on different boiling points
Fractional distillation is useful for separating mixtures of liquids with close boiling points.
What is the setup for chromatography?
- Place a small amount of the solvent into a beaker
- Draw a baseline using pencil on chromatography paper
- Place drops of dyes on the baseline and place the paper into the beaker
Chromatography is a technique for separating mixtures based on the movement of substances across a medium.
What does it mean if one mark is left from a dye in chromatography?
It indicates a pure substance
A single mark shows that the dye has not mixed with any other substances.
What does it indicate if a dye doesn’t move off the baseline?
The dye is insoluble in the solvent
This means the dye cannot dissolve in the solvent used.
What does more than one mark left from a dye suggest?
Each mark is a different substance in the mixture of the dye
Multiple marks indicate the presence of various components in the dye.
What is the formula for calculating the Rf value in chromatography?
Rf value = distance travelled by solute from baseline / distance moved by solvent from baseline
The Rf value helps in identifying substances based on their movement in the solvent.
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What is an atom?
Smallest form of element that carries its properties
Atoms are the fundamental building blocks of matter.
What are subatomic particles?
What an atom is composed of
Subatomic particles include protons, neutrons, and electrons.
What is a proton?
+ve SAP with 1 amu
Protons are positively charged particles found in the nucleus of an atom.
What is an electron?
-ve SAP with negligible mass
Electrons are negatively charged particles that orbit the nucleus of an atom.
What is a neutron?
0 charge SAP with 1 amu
Neutrons are neutral particles found in the nucleus of an atom.
What is mass number?
Total mass of atom | no. protons + no. neutrons (larger no. in PT)
Mass number represents the total number of protons and neutrons in an atom.
What is atomic number?
Total no. of protons (smaller no. in PT)
Atomic number defines the identity of an element and its position in the periodic table.
What happens when an atom loses electrons?
Atom has P > e- so it’s positively charged (X+)
This process is known as ionization, resulting in a cation.
What happens when an atom gains electrons?
Atom has P < e- so it’s negatively charged (X-)
This process results in an anion.
What is the electronic configuration of the first shell?
2 e-
The first shell can hold a maximum of 2 electrons.
What is the electronic configuration of subsequent shells?
8 e-/shell
Each shell after the first can hold up to 8 electrons.
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What are isotopes?
Atoms of the same element with the same number of protons but different number of neutrons.
They have the same chemical properties due to having the same electronic configuration.
How do you calculate the relative atomic mass (RAM) using isotopes?
Use the formula: (M1 x P1) + (M2 x P2) … / 100.
Where M is mass and P is the percentage of each isotope.
What is the RAM of chlorine given the percentages of Cl-35 (75%) and Cl-37 (25%)?
35.5
Calculation: (35 x 75) + (37 x 25) / 100.
What is the method for calculating percentages of isotopes when the mass and RAM are given?
Find the ratio of differences between masses and RAM, then cross-multiply with total and 100 to get percentages.
Example: For Ca-39 and Ca-42 with RAM = 40.12, the ratios are used to find percentages.
If the RAM of calcium is 40.12, what are the calculated percentages for Ca-39 and Ca-42?
Ca-39 = 37.3%, Ca-42 = 63.7%.
Calculated using the ratios 1.12 : 1.88 : 3.
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What increases from left to right in the periodic table as proton numbers increase?
Metallic character increases
This refers to the tendency of elements to exhibit physical and chemical properties characteristic of metals.
What is the state of most elements in the periodic table?
Most elements are solids
Exceptions include hydrogen (H), oxygen (O), nitrogen (N), group 7 gases, and the liquids mercury (Hg) and bromine (Br).
How many groups are in the periodic table?
8 groups
Each group has specific characteristics based on the number of outer electrons.
What does the group number represent in the periodic table?
Number of outer electrons
This is crucial for understanding an element’s reactivity and bonding behavior.
What are the elements in Group 1 called?
Alkali metals
These metals are highly reactive and include lithium, sodium, and potassium.
What are the elements in Group 7 known as?
Halogens
Halogens are reactive nonmetals, including fluorine, chlorine, bromine, iodine, and astatine.
What is the name of Group 0 elements?
Noble gases
These gases are characterized by having a full outer shell of electrons, making them largely unreactive.
What does the period number represent in the periodic table?
Number of shells
This indicates the energy levels of electrons in an atom.
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How should symbols be written in formulas?
Write as is in the Periodic Table. If an ion is present, add the charge.
How are covalent compounds written?
Write as is given and check for any prefixes.
Example:
Carbon monoxide = CO
Dinitrogen pentoxide = N₂O₅
How to write ionic compounds?
- Write the symbols of each of the elements.
- Write the valences of each element above the equation.
- Simplify where possible.
What is the valency of ammonium?
+1 (NH₄⁺)
What are examples of radicals with a valency of -1?
- Nitrate (NO₃⁻)
- Nitrite (NO₂⁻)
- Hydroxide (OH⁻)
What are examples of radicals with a valency of -2?
- Sulphite (SO₃²⁻)
- Sulphate (SO₄²⁻)
- Carbonate (CO₃²⁻)
What are word equations?
Equations that use only words, not symbols.
Example: Carbon dioxide + water → glucose + oxygen
How to write chemical equations?
- Write full formulas for all reactants and products.
- Balance the equation so all reactants = all products.
Example:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
What are the solubility rules for liquids?
Only water, bromine, and mercury are liquids at room temperature and pressure (rtp).
What are the solubility rules for gases?
Only O₂
N₂ H₂
Cl₂ F₂
CO CO₂
SO₂ NO₂
NH₃
are gases
What are the solubility rules for solids?
All other elements not mentioned as liquids or gases.
What are the solubility rules for aqueous solutions?
- All group 1, ammonium, and nitrate compounds are aqueous. All acids are aqueous.
- All sulfate and sulfite compounds are aqueous except: Silver (Ag), Calcium (Ca), Barium (Ba), Lead (Pb).
- All halide (Group 7) compounds are aqueous except: Silver (Ag), Lead (Pb).
- All silver compounds are solid except Silver Nitrate (AgNO₃, aqueous).
- All metal oxides, hydroxides, and carbonates are solid except if they contain group 1 metals or ammonium.
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What happens during oxidation?
- Oxidation involves the gain of oxygen.
- Oxidation is the loss of electrons. (OIL: Oxidation Is Loss).
What is a redox reaction?
A redox reaction is a reaction that involves both oxidation and reduction.
What is an oxidizing agent?
An oxidizing agent is the substance that causes oxidation by gaining electrons (and, therefore, getting reduced).
What is a reducing agent?
A reducing agent is a substance that causes reduction by losing electrons (and, therefore, getting oxidized).
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What is the reactivity series and how are groups organized?
The reactivity series ranks metals by their reactivity, with Group 1 being the most reactive and Group 3 being the least reactive.
- Group 1: Potassium (K), Sodium (Na), Lithium (Li), Calcium (Ca), Magnesium (Mg), etc.
- Group 2: Magnesium (Mg), Aluminium (Al), Zinc (Zn), Iron (Fe), Tin (Sn), Lead (Pb), etc.
- Group 3: Hydrogen (H+), Copper (Cu), Silver (Ag), Gold (Au), Platinum (Pt), etc.
How do metals in Group 1 react?
Metals in Group 1 (e.g., Potassium, Sodium, Lithium) react with cold water and below (steam, acid).
- With cold water: metal hydroxide + hydrogen
- With acid: salt + hydrogen
How do metals in Group 2 react?
Metals in Group 2 (e.g., Magnesium, Calcium) react with steam and below (acid).
- With steam: metal oxide + hydroxide
- With acid: salt + hydrogen
How do metals in Group 3 react?
Metals in Group 3 (e.g., Copper, Silver, Gold) have very low reactivity and do not react under normal conditions.
What is precision in terms of measurements?
Precision refers to the number of decimal places a value is accurate to. The more decimal places, the more precise the measurement.
What does it mean for an experiment to be reliable?
An experiment is reliable when it is repeated more than once and consistently yields similar results.
What is accuracy in terms of measurements?
Accuracy refers to using the correct apparatus for measurements to ensure the values are correct and close to the true value.
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How are Group 1 metals extracted?
Group 1 based on reactivity series
Group 1 metals are extracted by electrolysis because they are more reactive than carbon.
How are Group 2 metals extracted?
Group 2 based on reactivity series
Group 2 metals are extracted by reduction with carbon because they are less reactive than carbon.
How are Group 3 metals extracted?
Group 3 based on reactivity series
Group 3 metals are mostly found free in nature because they have very low reactivity and do not react with their surroundings.
What are the raw materials needed for the extraction of aluminium?
- Bauxite ore (Al₂O₃): Pure source of aluminium oxide.
- Cryolite: Lowers the melting point of aluminium oxide.
- Graphite (carbon): Used to make electrodes for electrolysis.
What happens at the cathode during aluminium extraction?
At the cathode (-ve terminal), aluminium metal is produced.
- Half equation: Al³⁺ + 3e⁻ → Al.
What happens at the anode during aluminium extraction?
At the anode (+ve terminal), oxygen gas (O₂) is produced.
- Half equation: 2O²⁻ → O₂ + 4e⁻
- The oxygen reacts with the carbon in the graphite electrode, forming CO₂: C + O₂ → CO₂.
What are some uses of aluminium?
- Body of aeroplanes: Low density.
- Cooking pans: Good conductor of heat, non-toxic, resistant to corrosion.
What are the raw materials needed for the extraction of iron?
- Coke (carbon): Acts as a reducing agent and source of heat.
- Haematite ore (Fe₂O₃): Main source of iron oxide.
- Water: Acts as a cooling agent.
- Hot air: For combustion.
- Limestone (CaCO₃): Purifies iron from sand.
How is iron extracted in a blast furnace?
Iron (II) oxide (FeO) is reduced by coke and carbon monoxide in the blast furnace to produce iron.
How is steel made from iron?
- Iron from the blast furnace is purified by blowing hot oxygen over it to remove impurities.
- Carbon is added to form steel (an alloy).
What are alloys?
Alloys are mixtures of a metal and one or more other elements (usually carbon). They have improved properties, such as increased hardness due to the distorted arrangement of atoms.
What are the types of steel and their uses?
- Low % carbon steel / Mild steel (0.25%): Easily shaped, used for car bodies.
- High % carbon steel (2.5%): Harder, used for cutting tools.
- Stainless steel (Fe/Cr/Ni): Resistant to corrosion, used for cutlery and sinks. Expensive.
What are the uses of iron?
- Railway tracks: High strength.
- Car bodies: Strong, malleable.
What are the uses of copper?
- Electric wiring: Ductile and good conductor of electricity.
- Sauce pans: Malleable, good conductor of heat, unreactive.
How does iron rust?
Iron rusts in the presence of water and oxygen, forming iron (III) oxide.
What are barrier methods for preventing rusting?
- Painting: Used for steel bridges and railings.
- Oiling/Greasing: Used for tools, machine parts, and bicycle chains.
These methods prevent water and oxygen from reaching the iron. If scratched, they no longer prevent rust.
What is the sacrificial method for preventing rusting?
Galvanizing: Iron is coated with zinc. Zinc acts as a barrier and is more reactive than iron. When scratched, zinc oxidizes instead of the iron, protecting it.
- Zinc equation: Zn → Zn²⁺ + 2e⁻
- Iron equation: Fe → Fe²⁺ + 2e⁻
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What do all acids contain when dissolved in water?
All acids contain the H⁺ ion (proton donor) when released in water (aqueous).
What are the characteristics of strong acids?
- Completely ionized in water.
- Large number of H⁺ ions released when added to water.
- pH = 0-3.
What are the characteristics of weak acids?
- Incompletely ionized in water.
- Low number of H⁺ ions released when added to water.
- pH = 4-6.
What is the difference between dilute and concentrated acids?
- Dilute acid: Acid with a lot of water added.
- Concentrated acid: Acid with little or no water added.
Which acids are generally weak?
All acids are strong except those with carbon (C) or sulfite (SO₃²⁻).
What do all bases and alkalis contain when dissolved in water?
All bases and alkalis contain the OH⁻ ion (proton acceptor) when released in water.
What is the difference between bases and alkalis?
- Alkalis are soluble bases (e.g., Group 1 oxides, hydroxides, ammonium hydroxide).
- Bases can be insoluble or soluble in water.
What are the characteristics of strong bases?
- Contain Group 1 metals.
- pH = 11-13.
What are the characteristics of weak bases?
- Do not contain Group 1 metals.
- pH = 8-11.
What happens in a neutralization reaction?
Acid + Base → Salt + Water (Neutralization).
This reaction involves a proton donor (acid) and a proton acceptor (base) to produce water.
What is produced when an acid reacts with a carbonate?
Acid + Carbonate → Salt + Water + Carbon Dioxide.
What is the definition of pH?
pH is the measure of the number of H⁺ or OH⁻ ions given by one molecule of a substance.
What are indicators, and how do they work?
Indicators change color based on the pH of the solution.
- Litmus solution: Red in acid, purple in neutral, blue in base.
- Phenolphthalein: Colorless in acid, pink in base.
- Methyl orange: Red in acid, orange in neutral, yellow in base.
- Universal indicator: Dark red in strong acid, green in neutral, purple in strong base.
How is a soluble salt prepared using titration?
Only for Group 1 metal and ammonium compounds.
1. Use a pipette to measure exact volumes and a burette for accurate variable volumes.
2. Mix the acid and base, and crystallize the solution to obtain dry crystals.
3. Example: Prepare NaCl crystals from NaOH and HCl.
* Titrate HCl into NaOH until the indicator changes color.
* Crystallize the solution to obtain NaCl.
What is the difference between titration and dissolving when preparing salts?
- Titration: Used for Group 1 metal and ammonium salts.
- Dissolving: Used for making salts that do not contain Group 1 metals or ammonium; add solid base until the acid is used up, then filter to remove excess base.
How is an insoluble salt prepared using precipitation?
- Add two aqueous solutions to a beaker.
- Stir until a solid forms.
- Filter to obtain the solid as residue.
- Wash with distilled water.
- Leave to dry in a warm place.
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How is the number of moles calculated using mass and molar mass (Ar or Mr)?
Moles (mol) = Mass (g) / Molar mass (Ar or Mr).
How is the number of moles calculated using concentration and volume?
Moles (mol) = Concentration (mol/dm³) × Volume (dm³).
Convert volume from cm³ to dm³ (1 dm³ = 1000 cm³).
How is the number of moles calculated using the volume of gas at r.t.p.?
Moles (mol) = Volume (dm³) / 24.
Only use this if the gas is at room temperature and pressure (r.t.p.), or if it’s stated that 1 mole of gas occupies 24 dm³.
How is the number of moles calculated using particles (atoms, molecules)?
Moles (mol) = Number of particles / Avogadro’s constant (6.02 × 10²³).
What are mole ratios and how are they used?
Mole ratios are the ratios between the coefficients of reactants and products in a balanced chemical equation. These ratios can be used to calculate the moles of substances involved in the reaction.
What is an empirical formula?
An empirical formula is the simplest whole number ratio of elements in a compound.
Steps to find it:
- Divide the mass of each element by its atomic mass (Ar).
- Divide the ratios by the smallest ratio.
- Approximate if necessary, but avoid ratios like 0.5, 0.33, or 0.25.
Example of finding an empirical formula. If the mass of C is 80% and H is 20%, and Mr = 45
(80 / 12) : (20 / 1)
80% C = 6.67
20% H = 20
Divide by the smallest value (6.67):
1 : 3
Empirical formula = CH₃.
How is the molecular formula related to the empirical formula?
Molecular formula = n × Empirical formula.
To find “n”:
- Calculate the Mr of the empirical formula.
- Divide the given Mr by the empirical formula’s Mr.
- Multiply the empirical formula by “n” to get the molecular formula.
How do you calculate percentage yield?
Percentage yield = (Actual yield / Theoretical yield) × 100.
How do you calculate the percentage of an atom in a compound?
Percentage of atom = (Ar of atom / Mr of compound) × 100.
How do you calculate the X value of water in a hydrate (example problem)?
- Find the mass of substance and water:
- Write the ratio:
- Calculate moles of each:
- Find the ratio:
- Conclusion: The X value is 10, so the formula is FeSO₄·10H₂O.
Workout:
* Mass of FeSO₄ = 16g - 10g = 6g
* Mass of water = 20g - 16g = 4g
* FeSO₄ : Water = 6g : 4g
* Moles of FeSO₄ = 6 / 152 = 0.04 mol
* Moles of H₂O = 4 / 18 = 0.22 mol
* Divide by the smallest value:
* FeSO₄: 0.04/0.04 = 1
* Water: 0.4/0.04 = 10
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What are the sequences of processes that occur in any reaction?
- Add reactants together.
- Reactants take in required energy from surroundings to break their bonds (activation energy, endothermic part).
- Free electrons collide together to form new bonds, releasing energy (exothermic part).
- Enthalpy change (ΔH) = Energy of reactants – Energy of products.
What is activation energy in a reaction?
Activation energy is the energy required to break the bonds in the reactants. It is the endothermic part of the reaction.
What is enthalpy change in a reaction?
Enthalpy change = Energy of reactants – Energy of products.
- A negative value indicates an exothermic reaction.
- A positive value indicates an endothermic reaction.
Define exothermic and endothermic reactions.
- Exothermic: A reaction that releases energy to its surroundings.
- Endothermic: A reaction that absorbs energy from its surroundings.
How do you explain whether a reaction is exothermic or endothermic in terms of bonds?
- Exothermic: Energy released during bond making is greater than energy absorbed during bond breaking.
- Endothermic: Energy released during bond making is less than energy absorbed during bond breaking.
What are some reasons why experimental data might differ from theoretical values?
Back:
- Heat is lost to surroundings.
- Impure substances are used.
- Incomplete combustion.
How do you draw an exothermic or endothermic reaction diagram?
- Identify if the reaction is exothermic or endothermic.
- Label reactants and products.
* For exothermic: Products have lower energy than reactants.
* For endothermic: Products have higher energy than reactants.
How do you calculate the total energy produced in a reaction?
Use the equation:
Q = mcΔT
- m: Mass or volume of water or solutions used in the experiment.
- c: Specific heat capacity (4.2 J/g°C for water).
- ΔT: Rise in temperature.
This gives energy in joules (J).
How do you calculate enthalpy change (ΔH)?
Method 1: ΔH = Energy of reactants – Energy of products.
* If ΔH is negative, the reaction is exothermic.
Method 2: Molar enthalpy change = Energy in kJ / Number of moles.
* ΔH = Q (kJ) / Moles.
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What are organic compounds?
Compounds that contain carbon and hydrogen. There are an infinite number of organic compounds.
What is a homologous series?
A group of organic compounds with:
* The same functional group
* The same general formula
* Similar chemical properties
* A gradual change in physical properties
* A difference of CH2 between consecutive members
What is a functional group?
An atom or group of atoms bonded in a specific arrangement that determines the chemical properties of a homologous series.
How do you name organic compounds?
Prefix: Based on the number of carbon atoms (Meth-1, Eth-2, Prop-3, But-4, etc.)
Suffix:
* Alkane: -ane
* Alkene: -ene
* Alcohol: -anol
* Carboxylic Acid: -anoic acid
* Ester: -yl…anoate
How does the number of carbons affect the volatility of organic compounds? (state)
- 1-4 carbons: Gas
- 5-15 carbons: Liquid
- > 15 carbons: Solid
What are hydrocarbons?
Compounds made up of only hydrogen and carbon.
What are isomers?
Compounds with the same molecular formula but different displayed structures.
What is the general formula for alkanes?
CnH2n+2
What is an example of an alkane?
Pentane (C5H12)
How to get isomers of alkanes?
قص و الظق في النوص
What are the three reactions of alkanes?
Substitution: in the presence of halogens and UV light
* Example: CH4 + Br2 → CH3Br + HBr
Combustion: complete and incomplete
* Complete: Produces CO2 + H2O
* Incomplete: Produces CO + H2O (or soot if oxygen is very low)
Cracking: Breaking down large hydrocarbons into smaller, more useful alkanes and alkenes
What is the general formula for alkenes?
CnH2n
What makes alkenes unsaturated?
The presence of a C=C double bond.
How can you identify isomers of alkenes?
By moving the position of the double bond.
Example:
* But(1)ene → C=C-C-C
* But(2)ene → C-C=C-C
Why are double bonds reactive?
The unstable repulsion force between the two bonds makes them highly reactive.
What reactions do alkenes undergo?
Combustion (same as alkanes)
Addition reactions (breaking the double bond to add atoms):
* Hydrogenation: (+H2) → Forms an alkane (Requires Ni catalyst)
* Hydration: (+H2O) → Forms an alcohol (Requires H3PO4, 300°C, 65 atm, steam)
* Bromination: (+Br2) → Forms dibromo compounds (Orange bromine water turns colorless)
What is crude oil?
A mixture of different alkanes.
How is crude oil refined?
By fractional distillation, separating hydrocarbons based on boiling points.
What are the fractions of crude oil (from most to least volatile)?
- Refinery Gas
- Gasoline (Petrol)
- Kerosene (Paraffin)
- Diesel
- Fuel Oil
- Bitumen
What happens as you go down the fraction list?
- Higher boiling point
- More viscous
- Darker color
- Less flammable
- Less volatile
- Lower market demand and price
What is cracking, and why is it important?
- Definition: The breakdown of large hydrocarbons into smaller, more useful alkanes and alkenes.
- Conditions: 600-700°C with a silica/alumina catalyst.
How are alkenes made?
- Cracking of crude oil
- Dehydration of alcohols (Using H3PO4, 300°C, 65 atm)
