AQA Chemistry Unit 2

Natalia  Cliff
Flashcards by , created over 2 years ago

Taken from the specification, so should be all you need to know for unit two, AQA Chemistry GCSE. Good luck =)

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Natalia  Cliff
Created by Natalia Cliff over 2 years ago
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Question Answer
Draw a sodium Ion Sodium Ions (image/gif)
Draw a water molecule Water Molecule (image/gif)
Draw a metal Metalic Bonding (image/gif)
What are compounds? Substances in which atoms of two or more elements are chemically combined
What does chemical bonding involve? Either transferring or sharing electrons in the highest occupied shells of atoms in order to achieve the electronic structure of a noble gas
How are ions formed -By the transferring of electrons -Atoms that lose electrons become positively charged -Atoms that gain electrons become negatively charged -Ions have the electronic structure of a noble gas
What do Alkali Metals react with? -Alkali Metals (group one) react with Halogens (group seven) -This forms ionic compounds -Alkali Metals have a single positive charge as they lose one electron -Halogens have a single negative charge as they gai one electron
What are ionic compounds -A giant structure of ions -Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions -These forces act in all directions in the lattice -This is called ionic bonding -Ionic bonding occurs between metals and nonmetals
Sodium Chloride structure Sodium Chloride (image/gif)
What is Covalent bonding? -Forms when atoms share electrons -Bonds between the atoms are very strong -Occurs between nonmetals -Can form simple molecules like Cl2, H2, O2, HCl, H2O, NH3, CH4 -Can also called giant covalent structures (macromolecules) like diamond and silicon dioxide
What are metals made of? -Giant structure of atoms arranged in a regular pattern -The electrons in the outermost shell of metal atoms are delocalised and so free to move about -Structure of positive ions with delocalised electrons between the ions holding them together by strong electrostatic forces of attraction
Properties of simple molecules -Relatively low melting and boiling points -Because of weak intermolecular forces despite strong covalent bonds -It's these intermolecular bonds that need to be overcome for the substance to be molten or boiled -Don't conduct electricity as they have no overall electrical charge
Properties of Ionic Compounds -Ionic compounds have regular structures (giant ionic lattices) -Strong electrostatic forces in all directions between oppositely charged ions -High melting and boiling points because of the large amount of energy needed to break the many strong bonds -When molten or dissolved in water can conduct electricity because the ions are free to move and carry the current
Properties of Covalent Structures -Also formed by covalent bonds -For example Diamond, Graphite and silicon dioxide (Silica) -All of the atoms are linked to each other by very strong covalent bonds -Very high melting points
Properties and structure of Diamond -Each carbon atom bonds with four other carbon atoms -This makes diamond very strong
Properties and structure of Graphite -Each carbon atom bonds with three other carbon atoms -The final carbon in the outer shell is delocalised -This allows graphite to conduct electricity and heat
What are fullerenes? -Carbon can also form fullerenes with different numbers of carbon atoms -Fullerenes structure is based on hexagonal rings of carbon atoms
What are fullerenes used for? -Used for drug delivery in the body (stops potentially toxic drugs affecting other parts of the body as it's covered by carbon fullerenes) -In lubricants (same sliding properties as graphite) -As catalysts (spreading a catalyst over it gives it a large surface area) -As nanotubes for reinforcing materials as it is strong -They also have the delocalised
Properties of metals -Conduct heat and electricity because the delocalised electrons are free to move throughout the structure -Layers of ions in metals can slide over each other so the metal can be bent and shaped
Structure and properties of Alloys -Usually made from two or more different metals -Different sized ions of the metals distort the layers in the structure -Makes it more hard for them to move over each other -Hence alloys are harder than pure metals -Shape memory alloys can return to their original shape after being deformed -E.g. nitinol can be used in dental braces
What do the properties of polymers depend on? -Properties of polymers depend on the conditions they were made under -E.g. Low Density and High Density poly(ethene) are made using different catalysts and reaction conditions
Types of polymers -Thermosoftening polymers consist of individual tangled polymers chains, melt when heated because of weak intermolecular forces -Thermosetting polymers consist of polymer chains with cross-links between them, so they don't melt when heated -Thermosoftening and thermosetting polymers can be high density or low density
What is Nanoscience? Refers to structures that are 1-100 nm in size, or a few hundred atoms -Have different properties to the same material in bulk and have a high surface area to volume ratio
Why is Nanoscience useful? May be used to develop: -New Computers -New Catalysts -New Coatings -Highly Selective Sensors -Stronger and Lighter Construction Materials -New Cosmetics -Deodorants
Atomic Structure Check out the C1 flashcards if you really don't know that atoms are made from neutrons protons and electrons
What is an atom's Relative Atomic Mass (Ar)? -A measurement of the mass of one atom of an element -Found by comparison with the 12C Isotope -An average value for the isotopes of the element
What is the Relative Formula Mass (Mr)? The relative formula mass of a compound is the sum of the relative atomic masses of the atoms shown in the formula
What are Moles? The relative formula mass of a substance, in grams, is one mole of that substance
If you have problems understanding moles, this explanation is by Randall Munroe, I found it helpful A mole is a unit. It’s not a typical unit, though. It’s really just a number — like “dozen” or “billion.” If you have a mole of something, it means you have 602,214,129,000,000,000,000,000 of them (usually written 6.022×1023). It’s such a big number because it’s used for counting numbers of molecules, which there are a lot of.
Instrumental Methods -Elements and compounds can be detected and identified using instrumental methods -Instrumental methods are accurate, sensitive and rapid -Particularly useful when the sample is very small
Chemical Analysis -Can be used to identify additives in foods -Artificial colours can be detected by paper chromatography
Paper Chromatography -Put ink dots on a straight pencil line at the bottom of a piece of paper -Put the bottom of the piece of paper into water
What is Gas Chromatography -An instrumental method -Allows the separation of a mixture of compounds -The time taken for a substance to travel through the column can be used to help identify substances
How does Gas Chromatography work? -Different substances are carried by a gas -Travel through a column packed with a solid material at different speeds, so they separate -The number of peaks on the output of a gas chromatograph shows the number of compounds present -The position of the peak indicates retention time
Mass Spectronomy -The output of a gas chromatography column can be linked to a mass spectrometer, which can identify the substances leaving the column -It can also give the relative atomic mass of each substance that is separated in the column -Can identify substances very quickly, accurately and from small quantities -Molecular Mass is given from the molecular ion peak
Calculating the percentage of an element in a compound Relative mass of the element in the compound over the relative formula mass of the compound
Empirical Formula -It's a ratio of the number of elements in a compound -G=mxr where G is grams, m is moles and r is relative atomic mass
Why may you not get 100% yield? Even though no atoms are gained or lost: -The reaction may be reversible and so not complete -Some product may be lost when it is separated from the reaction mixture -Some of the reactants may react in different ways to expected
What is a percentage yield? -The amount of product obtained is known as the yield -When compared to the maximum theoretical yield, it is called percentage yield
What is a reversible reaction? A reaction where the products can react to produce the original reactants E.g. ammonium chloride to ammonia and hydrogen chloride is a reversible reaction
How can you find the rate of reaction? -Either amount of reactant used over the time taken -Or the amount of product formed over the time taken
When do chemical reactions occur? When, and only when, particles collide with each other with sufficient energy
What is activation energy? The minimum amount of energy particles need to react
What factors increase the rate of reaction? -Temperature, increases energy so more and more successful collisions -Pressure, increases frequency of collisions -Concentration of reactants, increases frequency of collisions -Surface area, increases frequency of collisions -Catalysts speed up the rate of reaction without getting used up but different reactions need different catalysts, used in the industry to reduce costs
What happens when chemical reactions occur? Energy is transferred to the surroundings
What is an exothermic reaction? -A reaction that transfers energy to it's surroundings -E.g. combustion, many oxidisation reactions and neutralisation -Everyday uses include self-heating cans and hand warmers
What is an endothermic reaction? -A reaction that takes in energy from it's surroundings -E.g. thermal decomposition -Everyday uses include some sports injury packs
Energy change in reversible reactions If a reversible reaction is exothermic one way, it will be endothermic the other way. The same amount of energy is transferred in each case
Copper Sulphate reaction need to know, including colour Copper Sulphate (image/jpeg)
What are the state symbols in equations? -(s) is solid -(l) is liquid -(aq) is aqueous solution
What are the different reactions for salts? -Acid + Base -> Metal Salt + Water -Acid + Metal -> Metal Salt + Hydrogen -Soluble Salt + SOluble Salt -> Insoluble Salt
Acids and Alkalis Method -Put 10 ml of acid in beaker -Add a few drops of universal indicator -Add Alkali slowly, drop by drop, stirring whilst doing so -Stop when solution turns green -Record the volume of ALkali added -Repeat procedure with clean equipment but no universal indicator -Put solution in an evaporating basin and evaporate
Acids and Metals Method -Place 25 ml of acid in a boiling tube -Add metal and note occurring reaction -Filter the solution into an evaporating basin -Leave in a warm place to evaporate
Soluble Salts Method -Place 10 ml of a soluble salt in a beaker -Add 10 ml of another soluble salt -A precipitate will be formed -Filter the mixture with filter paper and a funnel -Rinse the precipitate in the filter with distilled water -Remove the participate from the filter paper with a spatula and place on glass to evaporate
How can you turn a salt solution into a solid salt Crystalise it
How can you remove unwanted ions from solutions? -Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed -Precipitation can be used to remove unwanted ions from solutions -E.g. treating water for drinking of treating effluent
What are bases and alkalis? -Metal oxides and hydroxides are bases -Soluble hydroxides are alkalis
What does the particular salt formed in an acid and base/alkali reaction depend on? -The acid used (hydrochloric acid produces chloride, nitric acid produces nitrates and sulfuric acid produces sulfates) -The metal in the base/alkali
What is ammonia used for? -Ammonia dissolves in water to produce an alkaline solution -It is used to produce ammonium salts -Ammonium salts are important fertilisers
The ions in acids and alkalis -Hydrogen ions H+(aq), make solutions acidic -Hydroxide ions OH-(aq) make solutions alkaline -In neutralisation reactions these ions react to form water
PH scale -Measure of acidity or alkalinity of a solution -7 is neutral -Beneath 7 is acidic -Over 7 is alkaline
What happens when ionic substances are melted or dissolved? The ions are free to move around in the liquid or solution
What does passing an electrical current through this do? -Passing an electric current through ionic substances that are molten (e.g. lead bromide) breaks them down into elements --This is called electrolysis -The substance being broken down is called the elctrolyte
What happens in electrolysis -Positively charged ions move to the negative electrode (cathode) -Negatively charged ions move to the positive electrode (anode) -At the negative electrode positively charged ions gain electrons (reduction) -At the positive electrode negatively charged ions lose electrons (oxidation) -If there is a mixture of ions, the product formed depends on the reactivity of elements involved
What is electrolysis used for? -Used to Electroplate objects -This may be for a variety of reasons and includes copper and silver plating
Half equations -Reactions at electrodes can be shown as half equations e.g. 2Cl- --> Cl2 + 2e-
Electrolysis of Aluminium -Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite -Cryolite is used as aluminium has a very high melting point, so it's dissolved in molten cryolite -Aluminium forms at the negative electrode -Oxygen forms at the positive electrode -Positive electrode is made of graphite (carbon) which reacts with oxygen to produce carbon dioxide -Hence the positive electrode needs to be replaced ever so often
Electrolysis of Aluminium Diagram Aluminium (image/gif)
Electrolysis of brine -Brine is sodium chloride solution -This process produces hydrogen and chlorine -Sodium hydroxide solution is left behind -These are important reagents for the chemical industry -E.g. sodium hydroxide is used in the production of soap and chlorine for bleach and plastics
Predicting the Products of Electrolysis At the Negative Electrode: -Metal will be produced if it is more reactive than hydrogen -Hydrogen will be produced if the metal is less reactive than hydrogen At the Positive Electrode: -Halide ion will form -If halide ion not present then oxygen will form