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What is the electronic structure of noble gas?
Atoms of noble gases have stable electronic structures, they have full outer shells and are unreactive.
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What is a compound?
They are substances formed when atoms from two or more elements are chemically combined.
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What is an element?
A substance made up of one type of atom.
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What is an ion?
A charged particle produced by the loss or gain of electon/s
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What do the two types of chemical bonding involve?
It involves either the transferring for sharing of electrons in the outer shells of atoms in order to achieve the electronic structure of a noble gas.
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What is covalent bonding?
When atoms from non-metallic elements join together by sharing electrons. They form strong covalent bonds. Simple covalent structures form molecules
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How many electrons are there in a covalent bond?
2
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What is ionic bonding?
When atoms form chemical bonds by transferring electrons. Atoms that lose electrons gain a +ve and vice versa. Ions have the electronic structure of a noble gas
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What charge to group 1 metals have when they react with halogen on-metals?
A single positive charge
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What charge to group 7 metals have when they react with alkali metals?
A single negative charge called a halide/
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How do we represent atoms and ions involved in ionic bonds?
We use dot cross diagrams
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. What are the main points about noble gases?
They have a full outer shell, they are unreactive/stable
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Why are ionic compounds neutral?
Because the charges on the ions in an ionic compound always cancel each other out.
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Describe the structure of an ionic lattice(in past paper 3).
It is a giant structure of ions that forms a giant lattice that are held together by electrostatic forces of attraction between oppositely charged ions. Which act in all directions.
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Explain how ionic bonds are formed in magnesium oxide (4) (in exam)
Mg donates 2 electrons to oxygen in order to get a full outer shell and a noble gas configuration there are electrostatic forces of attraction between the negative and positive ions.
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Explain why silicon dioxide has a giant structure?
Silicon atoms form 4 covalent bonds. The covalent bonds are strong and each silicon atom can join onto 4 other atoms this continues so that the structure is formed. Silicon dioxide is used in glass
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Explain how atoms form a piece of sodium are held together?
The outer electrons delocalise leaving a lattice of positive ions the delocalised electrons attract the positive ions. These electrostatic forces are strong. And they hold the ions in position.
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What are the properties of simple covalent molecules?
They are gases at room temperature, low boiling/melting point, electrical & thermal insulators
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Why do simple covalent structures have low boiling/melting points?
While the covalent bonds are strong, there are weak intermolecular forces between the molecules so they break easily.
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Why are ionic compounds solid at room temperature?
Because they have strong electrostatic forces that hold them together. So a lot of energy is needed to overcome the ionic bonds to melt the solids
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Why can ionic substances conduct electricity when molten or dissolved in water (in past paper)?
When the ionic compound is melted the ions are free to move which gives them the ability to carry current.
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Why are ionic compounds unable to conduct electricity when they are solid?
In a solid particles they are in a fixed position so the charge is unable to move through the solid
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Why can’t simple molecules conduct electricity?
Because the molecules have not overall electrical charge so can’t carry electrical charge
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Why do simple molecules have low boiling points and melting points?
Because although the bonds between the atoms in the molecules are strong the bonds between molecules are weak. They have weak intermolecular force which are easily overcome when the substance is heated. diagr
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What are intermolecular forces?
Attraction between individual molecules in a covalently bonded substance.
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Why are substances with large molecules more likely to be liquids or solids at room temp?
The intermolecular forces are stronger for large molecules.
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Why do substances with giant covalent structures have very high melting points?
Every atom is joined to several other atoms many strong covalent bonds. In order for to break down the lattice large amounts of energy is need.
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What is diamond?
Diamond is a form of carbon atoms form four covalent bonds. It is a 3D giant structure that is hard and transparent.
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What is graphite?
It is a form of carbon in which the carbons atoms are joined to 3 other carbon atoms in giant flat 2D layers.
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What are the properties silicon dioxide?
High melting point-because the atoms form strong convent bonds, doesn’t conduct electricity it is giant covalent structures.
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Name two similarities of diamond and graphite.
They are both forms of carbon. And they are both giant covenant structures.
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Name two differences between diamond and graphite.
In diamond the carbon atoms are bonded to 4 others, graphite: carbon atoms are bonded to 3 others. Diamond: 3D, Graphite: 2D layers. Graphite is a good conductor of heat/electricity. Diamond is a poor conductor.
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Why is graphite soft/slippery?
Because each carbon atom bonds to 3 others forming layers, the layers are free to slide over each other because there are no covalent bonds between the layers. There are only very weak intermolecular forces between the layers.
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Why graphite is good insulator/conductor(in past paper)?
Because it has delocalised electrons (one electron from each carbon atom) that are free to move around charging charge as they do so .
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What are fullerenes? And how can they be used?
They are a form of carbon that can form large cage/ football like structures based on hexagonal rings of carbon atoms. They can be used in lubricants, catalysts and delivering drugs into the body and in nanotubes for reinforcing materials
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Why can fullerenes be used in lubricants (in exam)?
Because of their spherical shape. Also the intermolecular forces of attraction between the carbon hexagonal rings are weak thus making it easy for the layers of carbon to slide past each other.
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Why is diamond hard?
Because each carbon forms 4 strong covalent bonds with 4 other carbon atoms in a giant covalent structure.
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Name the 4 properties of metals.
Malleable-ability to deform under stress, ductile-it can be deformed without fracture, conducts electricity/heat, high melting/boiling points.
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Why are metals malleable and ductile?
The atoms are arranged in layers. When a force is applied on the layers of atoms they can slide past each other.
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Why are metals useful for making wires and rods?
Because they can be moved into a new position without breaking apart
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Why can metals conduct electricity?
The electrons in the outer shell of metals are delocalized electrons move freely around the structure and transfer energy quickly.
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Why do metals have high melting and boiling points?
Electrostatic forces of attraction between the ions and electrons are very strong, lots of energy is needed to break them.
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What is an alloy?
They are substances made from two or more different metals
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Why are alloys stronger than pure metals?
The different sized atoms of the metals distort the layers in the structure making it more difficult for them to slide past each other.
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Give 2 reasons why alloys can be more useful than pure metals.
They are harder than pure metals. They can be designed to have specific properties or special properties e.g shape memory alloys.
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What is a shape memory alloy?
It is an alloy that can return to it original shape after being deformed nitinol (nickel, titanium) is used in dental braces, they don’t have to be frequently adjusted or replaced.
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What do the properties of a polymer depend on?
What monomer it is made from and the conditions under which they were made.
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What conditions would have to be met in order to make low density poly(Ethene)?
High pressure (2000atm), high temperature (200oC) molecules, tiny traces of oxygen
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What are the properties of low density poly (Ethene)?
Low melting point, soft, flexible because the chains are highly branched and less close together, this means that the force of attraction are weaker.
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What conditions would have to be met in order to make high density poly (Ethene)?
Low temperature (60oC), low pressure (2atm).
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What are the properties of high density poly (Ethene)?
Higher melting point, and harder because the polymers are more close together so the forces of attraction are stronger.
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What are the properties of a thermo softening polymer?
They are made up of individual tanged polymer chains (not joined together making them easy to separate) e.g poly(ethene), plastic bottles.
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Why can thermo softening polymers be easily melted
There are weak intermolecular forces between the polymer chains and there are no crosslinks so they can be easily separated by heat at low temperatures-less heat is needed to separate the polymer chains-makes them ideal for recycling.
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What are the properties of thermosetting polymers?
It consist of polymer chains with strong cross links which are strong covalent bonds that hold them together. This makes the thermosetting polymer strong and not melt-they burn when they are heated. E.g cooking spatulas.
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What is nanoscience?
It is the study of small particles that are between 1 and 100 nanometres in size. One nanometre is 10-9
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Why are nanoparticles different from the bulk materials they are made of?
They have a high surface area to volume ratio which can make them useful materials
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What can nanoparticles be used for?
Gold particles -Catalysts, new coatings, titanium oxide-sunscreens and deodorants, lubricators silver can kill bacteria
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What is the risk of nanoparticles?
They is a risk of them finding their way into the body. This could have unpredictable consequences for our health and the environment.
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What are the relative masses of protons, neutrons and electrons?
P=1+, E=1-, N=0.
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What is an atoms mass number?
Mass no. = Protons + Neutrons
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What is an isotope?
A different version of the same element it has the same number of protons and electrons but different numbers of neutrons.
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How do you work out relative formula mass (Mr)?
By adding the atomic masses of each element together.
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What is a mole of a substance?
The amount of a substance
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What is the unit for mass?
Grams
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What is the mass of one mole of a sodium atoms?
23g- the relative atomic mas of an element in grams is called one mole of atoms of the element.
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Why is the relative mass of chlorine not a whole number?
It has two main isotopes and the relative mass is an average value of the 2.
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Calculate the Mr of calcium chloride
CaCl2 Ar of Ca = 40, Ar of Cl =35.5 so Mr = 40 + (35 x 2) = 111
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How do you work out the percentage of an element in a compound e.g % of oxygen in H2O?
Total relative mass of element in compound/Relative mass of compound * 100. E.g Answer= Total relative mass of 0 in h20/Relative mass of h20 * 100 = ((16/18)*100) =89%.
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What is the formula for calculating the amount of moles in a substance?
Moles = Mass/Mr
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Calculate the amount of mole in 72g of Mg.
Moles = Mass/Mr, Ar of Mg=24, Mass = 72g, Moles = 72/24 Answer = 3 moles.
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How do you calculate the mass of chemicals involved in reactions?
1) Write a balanced formula, 2) use the equation Moles = Mass/Mr to work out the amount of moles in the ‘known’ compound, 3) Work out the moles of the known compound, 4) Work out the unknown mass using the same formula.
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What is the equation for percentage yield?
Percentage yield= actual yield/theroretical yield * 100
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What is molecular formulae?
How many of each atom are in a compound e.g ethene C2H4 C=2, H=4.
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What is empirical formula?
The simplest ratio of atoms in compund e.g ethene CH2 it has to be whole numbers. You can only round up if it is within 0.1 of a whole number.
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Find the simplest whole number ratio for each of the following… a. 1.50: 1 b. 1:198 c. 4.97:1 d.1:2.52 e. 1:33 f. 166: 1 f.1:1.74.
See phone Picture
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Why is it not possible to collect the amounts calculated from the chemcial reactions?
Reactions may not go to completion because it is reversible, other reactions may happen that are not expected, some product may be lost when it is separated or collected from the appartus.
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why should manufacturers use reactions with high yields?
To help conserve resources, reduce wastse and/ or pollution.
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What is a reversible reaction?
When the produces can react to produce the orignal reactants e.g ammonium chloride = ammonia + hydrogen chloride
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What is paper chromatography used to identify?
Adetives in food – artifical colours
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Why is paper chromatograghy used?
To analyse coloured substances. Chromatography different dyes or pigments in a coloured substance.
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Why shouldn’t you put the whole paper into the sovlent?
The sample would be washed away into the solvent
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Why do you put a lid on the beaker?
To prevent evaporation
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Why was the line drawn in pencil(in past paper)?
Because pencil is not souble in water
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What information can be obtained from the molecular ion peak in a mass spectrum?
The relative molecular mass.
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What is the retention time?
The amount of time they spend in the column (the time it takes for them to come out of the column)
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What is the efect of adding a mass spectrometer in gas chromatography?
It would identifiy the suubstance for you instead of you having to compare the substance rentention time to known substances.
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What an you work out from a mass spectrum
You can work out the molecular mass by looking at the molecular ion peak which is for an indivaul compund the peak with the largest mass.
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What is the benefit of using a mass spectrometer?
It can identify chemical quickly, accuratly and it can detect very small quanitites (sensitive)
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What is a pull factor to using a mass spctrometer?
The eqiupment is usually very expensive and it requires training to use.
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What does the postion of the peaks indicate?
The retenion time
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What does the number of peaks on a gas chromatograph show
It shows the number of compunds present.
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What is the main purpose of the gas chromatograpghy column in GC-MS anaylsis?
To separature the ompunds in the mixture.
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What are the 2 ways through which the rate of reaction can be found?
Rate of reaction = amount of reactant used/Time OR Rate of reaction = amount of product formed/time.
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What has to happen for chemicals to react?
Particles need to collide with each other, they must collide in the correct orientation and with sufficint energy.
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What is activation energy?
The minimum amount of energy particles must have to react.
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What shows the rate of reaction on a graph?
The gradient or the slope of the line on a graph of the amount of reactant against time.
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What factors could increase the chance of collisons?
Temperature, concentration of soltions, pressure of gases, surface area of soilds, using a catalyst.
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Why does and increase in surface area increase the rate of reaction?
Braking large pieces of solid into smaller pieces exposes new surfaces . this increases the frequency of successful collisons thus increasing the react of reaction.
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Why does and increase in temperture increase the rate of reaction?
An ^ temp ^ the average speed of the particles as they have more energy-they can collide more frequently with enough activation energy. This increases the ROR . Also more particles have the activation energy when the temperature is increased.
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Why does an increase in presure increase the rate of reaction?
When the presure is increased there are more gas in the same volume this means that particles are closer. This increases the frequency of successful collisons.
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Why does an increase in concentration increase the rate of reaction(in exam)?
Increasing the concentration of reactants in a solution means that there are more particles dissolved in the same volume. This emans that the particles are closer together so this increase sthe frequency of succesful collisons.
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Why do catalysts increase the rate of reaction?
They lower the activation energy of the reaction-meaning more paricles have the enrgy required to react- so there is a higher frequency of successful collisons.
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Why can catalysts be used over and over again?
They are not used up in the reaction.
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Why do different reactions need different catalysts?
Because cataylsts often only work with one type of reaction.
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What are the benefits of using catalysts in industrial procceses?
They reduce the energy needed and the time needed and so reduce costs. They may reduce the amount of fossil fuel used and so conserve resources and reduce polution
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Give one disadvantage of transition metal catalysts>.
They may be toxic or expensive
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What 2 areas of reasearch offer possinlities for new or better catalysts?
Nanoscience and enzymes.
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What is an exothermic reaction?
A reaction that transfers energy in the surroundings. E.g combustion, oxidation reactions and neutralisation involving acids and bases.
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What is an endothermic reaction (in exam)?
Takes in energy from the surroundings e.g thermal decompositions
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What are the two ways that show if a reaction is endothermic ?
Either it cools the surroundings or it needs to be heated to keep it going.
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What happens in a reversible reaction in regards to exothermic and endothermic?
If a reversible reaction is exothermic in one direction, it is endothermic in the other direction. The same amount of energy is transferred in each case.
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Give an example of an everyday use of exothermic reactions?
Hand warmers, self-heating cans (for coffee).
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Suggest on advantage and one disadvantage of using a re-usable hand warmer in comparison to a single use hand warmer?
A-less waste, save resources D-it needs energy so it can be heated again, it has to be heated, smaller temperature rise.
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Give an example of an everyday use of endothermic reactions?
Sports injury ice packs, to cool drinks.
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Suggest one advantage and disadvantage of using a chemical cold pack in comparison to using an ice pack.
A-Can be used anywhere, can be stored easily. D-Can only be used once, more waste, more likely than ice to be hazardous.
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What is the opposite of an acid?
A base
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What type of reaction occurs between acids and alkalis?
Neutralisation
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What element do all acids contain?
Hydrogen
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When does HCl become an acid?
It becomes and acid once water is added to it. When it is dissolved in water it releases hydrogen ions.
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What is a neutralisation reaction?
The chemical reaction of an acid with a base in which they cancel each other out forming a salt and water –it is an exothermic reaction. The hydrogen ions react with the hydroxide ions to form water. H+ + OH- = H2O
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Give 3 examples of acids?
Nitric acid, hydrochloric acid and sulphuric acid
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What is a base?
All bases are ionic compounds apart from ammonia. They can be oxide, hydroxide(mainly soluble alkalis) or carbonate of a metal (mainly insoluble) that will react with an acid to form a salt- they release OH- ions (aq) (they are H+ ion acceptors.)
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What is an alkali?
A base that can dissolve in water
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How can we identify if a substance is an acid or an alka
Adding a universal indicator and using the pH scale.
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What is an acid?
A substance that when dissolved in water, its solution has a pH less than 7. Acids release H+ ions (aq) (they are H+ donors).
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What is a salt?
An acid that has had its H+ ion replaced with a metal ion.
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What are the 4 state symbols in reactions?
S,l,g,aq
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Explain the neutralisation of Ammonium hydroxide and nitric acid?
Ammonium hydroxide + nitric acid = ammonium nitrate + water. When you evaporate and crystallise the solution you get ammonium salt which is a good fertiliser (because it contains nitrogen which is require for growth (to make protein).
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Explain the process of forming soluble salts?
By reacting them with some metals-some metals are too reactive or not above H. Insoluble bases-added to acid until no more will react-filter off excess. Alkalis-indicators can be used 2 show when has been completely reacted to form a salt.
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Explain the process of forming insoluble salts?
React 2 soluble salts, they react to make 1 soluble and 1 insoluble salt, filter the solution to separate the solid. Wash any residue or insoluble salt, you now have an insoluble salt and water so you need to evaporate the solution to remove the wate
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What are the 3 stages involved in producing an insoluble salt?
Neutralisation, filtration, evaporation
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What can you add to a salt to make it insoluble?
Sodium and nitrates e.g you can add nitrates (METALS) and sodium (NON-METALS) to barium sulphate to make it insoluble – barium sulphate – barium nitrate + sodium sulphate.
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What is precipitate?
An insoluble solid formed by a reaction taking place in a solution.
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What can precipitation be used for?
It can be used to remove unwanted ions from solutions. E.g. treating water for drinking or in treating effluent.
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How can insoluble salts be made?
By mixing appropriate solutions of ions so that a precipitate is formed.
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What does the salt produced in a reaction between a salt and a base depend on?
The acid used, and the metal in the base
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What is produced when an acid reacts with a metal?
Acid + Metal = Salt + hydrogen
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What is produced when a metal reacts with a base?
Acid + base = salt + water
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How is the neutralisation between any acid and any alkali represented?
H+(aq) + OH-(aq) = H2O(l)
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Why do we need to add excess of the base when making a salt?
To insure that all the acid is neutralised.
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Why potassium would not be used by students(in Exam)
It is a strong oxidising agent it can explode with contact with organic matter
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What is the formula for sodium sulphate(in past paper)?
NA2SO4
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What is electrolysis?
The process that uses electricity to break down ionic compounds.
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What is an electrolyte?
The substance that is broken down.
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What must be done to ionic compounds before they can be electrolysed and why?
They must be melted or dissolved so the ions are free to move around within the liquid or solution.
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