Chemistry Unit 2

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  • Created by: elliesp
  • Created on: 12-06-16 14:06
what is a compound?
a substance where the atoms of 2 or more elements are chemically combined (chemical bonds between atoms)
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explain ionic bonding?
an atom with 1 too many electrons will donate its electron to an atom with 1 less electron of a full outer shell. Therefore, both atoms will have full outer shells & become ions.
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how do you draw an atom when it has gained or lost 1 electron to get a full outer shell.
it is now an ion so you put brackets around it and a plus sign outside the brackets if it's lost an electron, or a minus sign if it's gained an electron
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what is an ionic compound?
a giant structure of ions held together by strong forces of attraction between oppositely charged ions. These forces act in all directions & this is called ionic bonding.
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what must the charge of an ionic compound equal?
zero
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how is heat conducted through an ionic compound?
If heat is applied to an ionic compound, the ions inside of it near the heat supply would start to more around more vigorously than they were before. The ions would eventually then break away from the electrostatic forces of attraction
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what is covalent bonding?
when 2 atoms are both missing an electron to gain a full outer shell they make a covalent bond and share their electrons between them so they both have a full outer shell. When atoms form a covalent bond they become molecules.
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how many electrons are being shared in a single covalent bond?
2
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how many electrons are being shared in a double covalent bond?
4
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in what case is a double bond formed?
if both atoms are missing 2 electrons instead of one
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what is chemical bonding?
transferring or sharing electrons in the outer shells of atoms in order to achieve a full outer shell
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why do simple molecules have low boiling and melting points?
covalent bonds binding the atoms are v strong but there are only weak forces (intermolecular forces) holding the molecules to eachother so a low temp is needed to melt/boil it as little energy is necessary to break the intermolecular bonds
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why is a metal structure sturdy?
Metals have delocalised electrons which are negative, and the ions in the metal are positive, so there is a strong electrostatic attraction between the atoms and electrons, so everything is held in place and the structure is strong.
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what are the features of simple molecules?
all have low boiling and melting points, no overall electric charge so don't conduct electricity
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what do covalent bonds hold together? what do intermolecular forces hold together.
1) atoms 2) molecules
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what are macromolecules?
when atoms share electrons to form giant structures
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why do macromolecules have very high melting points?
because all the atoms in them are linked by strong covalent bonds which take a lot of energy to break
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list all the types of macromolecules?
graphite, diamond, silica
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explain the structure and features of graphite.
made of carbon layers, which slide over eachother bc there's no covalent bonds between just intermolecular forces = v soft. But covalent bonds between it's atoms =high bp. conducts electricity as each atom only joined to 3 others = free electrons.
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explain the structure and features of a diamond
a form of carbon in which each carbon atom is joined to four others, meaning that the diamond is very hard. Has a high melting point because of covalent bonds between atoms. Doesn't conduct electricity as no free electrons.
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explain the structure and features of silica
made of silicon and carbon atoms- each atom is linked to 4 others, making it hard. also has a high melting point bc of covalent bonds between atoms.
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what are fullerenes used for?
drug delivery in the body because the drug can be locked inside them so they don't damage other cells, used for lubricants, catalysts, and in nanotubes as reinforcing materials (e,g tennis rackets.
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what are reinforcing materials?
very light but very strong materials
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why do metals conduct heat so well?
when a metal is heated the atoms vibrate more vigorously and bump into neighbouring atoms, delocalised electrons speed up this process as they can move freely and bump into random atoms in the metal and pass the heat energy on.
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why do metals conduct electricity so well?
because if a positive charge is applied to the metal then the negative electrons will drift towards the positive charge as they're attracted to it, causing a flow of charge.
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why can metals be shaped/bent so easily?
the layers of atoms in metals are able to slide over each other so they can change shape easily
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why might alloying a metal make it harder?
by combining the atoms of 2 different metals, the atoms are different sizes and this distorts the layers in the structure, so the layers can't move over each other as easily, making them less malleable.
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advs and disadvs of steel?
advs: hard, tough and strong DISADVS: high density so heavy, corrodes in contact with perspiration
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what are shape memory alloys?
metals that can be returned to their original shape after being deformed
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what is nitinol used for and what is it made from? why is this useful?
nitinol is made from nickel and titanium and can be used for braces, broken bones, glasses frames
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advs and disadvs of nitinol?
advs: low density so light weight, can return to original shape, strong and resists corrosion DISADVS: expensive
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what are polymers?
long chains of monomers joined together
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what is a low density polymer?
a polymer that has a low melting point, and is softer as it has weaker forces of attraction as the polymer chains are further apart (set out in a branch like structure)
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what is a high density polymer?
a polymer that has a high melting point, and is harder as it has stronger forces of attraction as the polymer chains are closer together.
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what is a thermosoftening polymer? used for?
consist of individual tangled polymer chains, and have low melting points because the weak intermolecular forces between the polymer chains can be overcome easily. Used for plastic bottles etc.
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what is a thermosetting polymer? used for?
consist of polymer chains with cross links made up of covalent bonds between them so they don't melt easily when heated, the covalent bonds also stop the polymer chains from being flexible. Used for cooking utensils and plug sockets etc.
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what are nano particles?
very very small particles with a very large surface area to volume ratio, so are often able to react quickly. Their uses are catalysts, suntanning creams (absorb more UV light), construction materials (strong but light), computers.
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how good is a giant ionic compound at conduct electricity when it's solid? when it's molten?
when it's solid it doesn't conduct electricity, but when it's molten it is a good conductor.
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how good is a metallic compound at conducting electricity when it's solid? when it's molten?
when solid it is a good conductor of electricity, and when it's molten.
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what is the number of protons always equal to?
number of electrons
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which is the mass number? what does it tell you?
the big one, the number of protons + neutrons
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what does the atomic number tell you?
the number of protons
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what is an isotope?
when two atoms are of the same element but have different number of neutrons & mass number & physical properties (density, boiling & freezing point). But isotopes have same chemical properties & their electronic structures are same so react same.
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what is relative atomic mass?
a measure of the max of one atom of the element
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who do you calculate relative atomic mass?
write the formula of the compound, write the numbers of each atom in the formula, insert the relative atomic mass for each atom type, calculate total mass for each element, add up total mass for compound.
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how do you calculate relative Formula mass? what is it called?
add up all the relative atomic masses present in the compound, the relative formula mass of a substance is called one mole.
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how do you calculate the number of moles?
mass of substance divided by the relative formula mass.
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what can elements and compounds be detected by? when are they used and why?
intrumental methods, they are accurate, sensitive and rapid and are useful for small samples.
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what is the instrumental method spectroscopy used for?
identification of illegal drugs and explosives.
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what is chemical analysis used for? what are the disadvs of this method?
to identify additives in food, the disadvs of it is that its slow and labourous.
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paper chromatography
check notes
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gas chromatography
check notes
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how do you work out the percentage of an element in a compound?
relative atomic mass of the element divided by the relative formula mass of the compound.
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how do you work out the empirical formula?
divide the mass by the relative atomic mass for each, divide each of the previous answers for the atoms by the smallest answer to get a simplified ratio for the atoms in the molecule, using the ratio you can now write the formula
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P51 double check
dkwlc
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why is it not always possible to obtain the calculated amount of a product even though no atoms are gained or lost in a chemical reaction?
the reaction may be reversible, reactants may react in ways which are different from what you expect, product may be lost when separated from the reaction mixture.
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what is the amount of product obtained called?
the yield
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how do you calculate a percentage yield?
actual mass of product/ theoretical mass of product x100%
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what are reversible reactions?
the products of the reaction can react to produce the original reactants.
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how can a rate of reaction be calculated?
amount of reactant used/time OR amount of product produced/time
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what is the collision theory?
chemical reaction scan only occur when reacting particles collide with each other with sufficient energy
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what is the minimum amount of energy particles must have to react called?
activation energy
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what increases the rate of reaction?
temp, concentration, pressure, surface area
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what does increased temperature do in the reaction?
increases speed of particles so they collide more frequently and with more energy so the rate of reaction goes up
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what does increased concentration do in the reaction?
it increases the rate of collision of particles as theres more of them and so increases the rate of reaction
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what does increased pressure do in the reaction?
it increases the frequency of collisions and this increases the rate of reaction
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what does increased surface area do?
increases the frequency of collisions and this increases the rate of reactions
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why is using a catalyst to speed up reactions more efficient than increasing certain features in the reaction?
increasing the temp of the reaction etc costs a lot, whereas catalysts may initially cost a lot of money but can be used over and over again.
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advs and diadvs of catalysts.
advs: speeds up reaction, reduces energy costs, reduces labour costs involved, can be done at lower temp which is safer & cheaper, can be reused DISADVS: expensive, can be difficult to remove product
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what is an exothermic reaction? such as?
when energy is transferred to the surroundings, i.e combustion or neutralisation
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what is an endothermic reaction? such as?
takes energy from the surroundings i.e thermal decomposition
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if a reversible reaction is exothermic in one direction, it must be...in the other direction
endothermic
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explain the test for water.
to see whether a liquid contains water or not you can add a drop of it to anhydrous copper sulphate powder, and if water is present it will go blue.
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what kind of ions are in acid solutions?
hydrogen ions
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what kind of ions are in alkali solutions?
hydroxide ions
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what is produced in neutralisation (acid and alkalis added together)? why?
water is produced as hydrogen and hydroxide atoms react
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how can soluble salts be made from acids?
by reacting them with metals, insoluble bases or alkalis
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what kind of insoluble bases are used? how?
copper oxide may be added to the acid until no more will react, this is when there is unreacted solid at the bottom of the mixture which is then filtered off
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how can alkalis produce a soluble salt?
an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution
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how are salt solutions crystallised to produce solid salts?
a little alkali solution at a time is added to acid & stirred together, then the Ph is tested after each addition on indicator paper, when acid is neutralised the salt solution is evaporated to crystallising point & set aside to cool & crystallise.
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what are the general equations for acids to produce salt?
acid + metal --> salt + hydrogen acid + base --> salt + water acid +alkali --> salt + water
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which metals are used to make insoluble salts? why?
nitrates, as they are soluble
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what is precipitation used for? what is the precipitate?
to remove unwanted ions from solutions, the precipitate is the insoluble compound and can be removed from the mixture
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what happens when an insoluble compound is made?
the ions that were free to move in the separate solutions become locked up in the giant structure, as they have been removed from the solution.
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name some ammonium salts and how they're useful.
ammonium nitrate and ammonium phosphate, these are important as fertilisers as they are soluble in water and can be taken up by the plants to increase growth
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what is the pH for most acidic?
0
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what is the pH for neutral?
7
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what is the pH for alkali?
14
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what is used to show if a substance is acidic or alkaline? name types of them.
indicators: e.g litmus (only shows if the substance contains acid or alkali) or universal indicator (more specific and measures pH)
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what colours indicate certain pHs when using universal indicator?
pH 1 is shown as red, pH 7 is shown as green, pH 14 is very dark blue
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what are the equations for neutralisation reactions?
acid +alkali --> salt + water Acid + base --> salt + water
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what is electrolysis?
the conduction of an electric current through ionic substances & breaking them down into elements
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in what circumstances will ionic substances conduct electricity? why?
when molten or dissolved in water, because it is only when they're melted or dissolved that their ions are free to move
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what is the substance that is broken down in electrolysis called?
electrolyte
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explain electrolysis
+charged ions move to -electrode & - ions to +electrode. At the - electrode +ions gain electrons (reduction) & at + electrode -ions lose electrons (oxidation). Metals &hydrogen formed at cathode, oxygen &halogens formed at anode
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does oxidation or reduction have to involve oxygen?
No
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what would be the product if there is a number of metal ions present in a solution?
the element with the lowest reactivity
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describe how you electroplate a fork with silver using electrolysis?
make fork a cathode & silver an anode. As current flows, silver atoms from anode dissolve to form silver ions. Electrolyte already has silver ions & as more made, the same number change to silver atoms at cathode, coating fork in silver.
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electrolysis p 64
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Other cards in this set

Card 2

Front

explain ionic bonding?

Back

an atom with 1 too many electrons will donate its electron to an atom with 1 less electron of a full outer shell. Therefore, both atoms will have full outer shells & become ions.

Card 3

Front

how do you draw an atom when it has gained or lost 1 electron to get a full outer shell.

Back

Preview of the front of card 3

Card 4

Front

what is an ionic compound?

Back

Preview of the front of card 4

Card 5

Front

what must the charge of an ionic compound equal?

Back

Preview of the front of card 5
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