A-Level Chemistry Unit 1

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Relative charge of a proton?
+1
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Relative charge of a neutron?
0
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Relative charge of an electron?
-1
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Relative mass of a proton?
1
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Relative mass of a neutron?
1
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Relative mass of an electron?
Negligable
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Where are protons and neutrons found?
In the nucleus
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Where are electrons found?
Atomic shells orbiting the nucleus
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How do you deduce the number of protons, neutrons and electrons?
The number of protons are equal to the atomic number as is the number of electrons. The number of neutrons are found by taking the atomic number away from the mass
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Define an isotope
An atom of the same element with the same number of protons and electrons but a different number of neutrons
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Define relative isotopic mass
Mass of an atom of an isotope compared to 1/12 of the mass of an atom of carbon-12
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Define relative atomic mass
Average weighted mass if an atom of an element compared with 1/12 of of the mass of an atom of carbon-12
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Define amount of substance
A quantity whose unit is the mole, used as means of counting of the number of atoms
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What is Avogadro's constant?
6.02 x 10(23) mol-1
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Define molar mass
Mass per mole of a substance
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Define empirical formula
the simplist whole number ratio of atoms of each element present in a compound
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Define molecular formula
The actual number of of atoms in each element in a molecule
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What is the empircal formula equation?
(Mass / % of composition) / Molar mass : (Mass / % of composition) / Molar mass ; then divide by the the smallest number of moles to find the ratio
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What is special about group 7, oxygen, and nitrogen?
They're diatomic
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How do you work out the number of moles?
Mass / Molar mass
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How do you work out the number of moles in a gas
Volume (dm3) / 24
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How else can you work out the number of moles
Concentration x volume (dm3)
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What does the stoichiometric value determine?
The ratio between the number of moles of a substance
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Define concentration
The amount of solute, in mole, per 1dm3 of solution
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Define concentrated
A high amount of solute per dm3 of solution
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Define dilute
A low amount of solute per dm3 of solution
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What is the fomula of hydrochloric acid?
HCl
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What is the formula of sulphuric acid?
H2SO4
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What is the formula of nitric acid?
HNO3
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Name two common metal oxides
MgO (magnesium oxide) and CuO (copper oxide)
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Name two common metal hydroxides
NaOH (sodium hydroxide) and Mg(OH)2 (magnesium hydroxide)
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What is the formula of ammonia?
NH3
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What is the formula of amines?
CH3NH2
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What are bases and what do they do?
They are proton acceptors and neutralise acids
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What are alkali's and what do they do?
They are special bases that dissolve in water forming aqeuous hydroxide ions
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How is a salt produced?
When the H+ ion of an acid is replaced by a metal ion or NH4+
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What is the product of acid + carbonate?
Salt + carbon dioxide + water
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What is the product of acid + base?
Salt + water
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What is the product of acid + alkali?
Salt + water
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What is the product of acid + aqueous ammonia?
Ammonium salt
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Define anhydrous
A substance containing no water molecules
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Define hydrated
Crystalline compound containing water molecules
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Define water of crystallisation
Water molecules that form an essential part of the crystalline structure of a compound
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What is the oxidation number of an uncombined element?
0
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What is the oxidation number of combined oxygen?
-2
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What is the oxidation number of combined hydrogen?
+1
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What is the oxidation number of a simple ion?
The charge on the ion
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What is the oxidation number of combined fluorine?
-1
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When does reduction occur (in terms of electron transfer)?
If the number of electrons increases
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When does oxidation occur (in terms of electron transfer)?
If the number of electrons decreases
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When does reduction occur (in terms of oxidation number)?
If the oxidation number of an element decreases
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When does oxidation occur (in terms of oxidation number)?
If the oxidation number of an element increases
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How do metals generally form ions?
By losing electrons with an increase in oxidation number to form positive ions
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How do non-metals generally react?
By gaining electrons with a decrease in oxidation number to form negative ions
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Define first ionisation energy
Energy required to remove one electron from each atom in one mole of gaseous atoms
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Define successive ionisation energy
Energy required to remove each electron in turn
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What is nuclear charge and its trend?
The greater the nuclear charge, the greater the attractive force of the outer electrons; therefore the more energy needed to remove an electron from the outer shell. This increases across a period
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What is electron shielidng and its trend?
More inner electron shells shield the nuclear charge from the outer electron so the electron is easier to remove. Shielding increases down a group
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What is atomic radius and its trend?
In larger atoms, the outer electrons are further from the nucleus due to the number of shells, this means that nuclear attraction is lower so the energy needed to remove an electron is lower. This increases down a group
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How many electrons can fill the first shell?
2
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How many electrons can fill the second shell?
8
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How many electrons can fill the third shell?
18
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How many electrons can fill the fourth shell?
32
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Define orbital
A region that can hold up to two electrons of opposite spins
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How many electrons can an s orbital hold and what's its shape?
2 in total and spherical
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How many electrons can a p orbital hold and what's its shape?
2 in each orbital of which there is 3 so 6 in total and dumb-bell shaped
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State how many orbitals each subshell has
S- 1, P- 3, D- 5, F- 7
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State in which order the subshells fill
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 4d, 4f
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Which groups are in the s-block of the periodic table?
Groups 1 and 2 plus hydrogen and helium
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Which groups are in the p-block of the periodic table?
Groups 3-8 minus helium
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Which group is in the d-block periodic table?
Transition metals
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Define ionic bonding
Electrostattic attraction between oppositely charged ions
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What is the formula for nitrate?
NO3-
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What is the formula for sulphate?
SO4 (2-)
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What is the formula for carbonate?
CO3 (2-)
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What is the formula for ammonium?
NH4+
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Define covalent bonding
A shared pair of electrons
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Define dative covalent bond
The two electrons derive from the same atom
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What is the shape of a molecule determined by?
The repulsion of between electron pairs surrounding a central atom
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Which repels more: lone pairs or bonded pairs?
Lone pairs
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What is the shape and bond angle of BF3 ?
Trigonal Planar and 120 degrees
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What is the shape and bond angle of CH4 and NH4+?
Tetrahedral and 109.5 degrees
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What is the shape and bond angle of SF6
Octahedral and 90 degrees
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What is the shape and bond angle of NH3?
Pyramidal and 107 degrees
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What is the shape and bond angle of H2O?
Non-linear and 104.5 degrees
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What is the shape and bond angle of CO2?
Linear and 180 degrees
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Define electronegativity
The ability of an atom to attract the bonding electrons in a covalent bond
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How might a permenant dipole arise and what bond does it form?
It may arise when covalently-bonded atoms have different electronegativities which results in a polar bond
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Describe permenant dipoles
The permenant dipole of one molecule attracts another peremenant dipole to form a weak peremnant dipole-dipole force
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How are london dispersion forces created (first two steps)?
1. The movement of electrons in shells unbalances the distribution of charge in the electron shells. 2. An instantaneous dipole is formed due to the unbalanced distribution of electrons
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How are london dispersion forces created (last two steps)?
3. The instantaneous dipole induces a dipole in neighbouring molecules, which then in turn induces further molecules. 4. The induced dipoles attract each other, forming weak intermolecular forces
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Define hydrogen bonding
A strong dipole-dipole interaction between an electron defficient hydrogen atom and a lone pair on a highly electronegative atom (usually oxygen or nitrogen)
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Which two bonds are polar with permanent dipoles
O-H and N-H
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Name two properties of water
Ice floats and it has a high freezing and boiling point
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Explain these
Ice floats becuase it has an open lattice structure which holds the water molecules apart(this distance causes ice to be less desnse than water). It has a high freezing and boiling point becuase the hydrogen bonds need more energy to break
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Define metallic bonding
The attraction of positive ions to delocalised electrons
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Describe the structure of giant ionic lattices
They have strong ionic bonding, they are formed by the attraction of oppositley charged ions, oppositely charged ions attract each other to form lattice
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Describe the structue of giant covalent lattices
3D structure with atoms bonded together by strong intramolecular covalent bonds
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Describe the structure of giant metallic lattices
Contain ionised atoms, positive ions are fixed in the lattice, delocalised electrons spread through out structure, charge balances over whole structure
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Describe the structure of simple molecular lattices
3D structure of molecules bonded together by intermolecular forces, weak forces between them, atoms within molecules are covalently bonded
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What bonds are broken when a simple molecular lattice is broken?
The london dispersion forces (NOT the covalent bonds
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Name the 3 properties of metallic structures
1. High melting and boiling point, 2. Good electrical conductivity, 3. Malleable and ductile
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Name the 4 properties of giant ionic compounds
1. High melting and boiling point, 2. Doesn't conduct when solid, 3.. Conducts when molten, 4. Can dissolve in polar solvents
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Name the 3 properties of simple molecular structures
1. Low melting and boiling point, 2. Non conductors of energy, 3. Soluable in non polar solvents
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Name the 3 properties of giant covalent structures
1. High melting and boiling point, 2. Non conductors of energy, 3. Insoluable in both polar and non-polar solvents
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Name 2 properties of diamond
1. Poor conductivity due to no delocalised electrons, 2. Strong because tetrahedral shape allows for external forces to be spread across the lattice
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Name 2 properties of graphite
1. Good electrical conductivity due to delocalised electrons between the layers, 2. Soft becuase the LDF's allows layers to slide over each other
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Describe the periodic table in terms of element arrangement
1. Increasing atomic number, 2. In periods showing repeating trends, 3. In groups having similar physical and chemical properties
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Define periodicity
A repeating pattern across different periods
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What is similar in atoms of elements in groups
Similar electron configuration which results in similar properties
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What happens as you go across a period?
1. The number of protons increases so there is more attraction towards the electrons, 2. Electrons are added to the outer shell so it is drawn inwards slighly but the shielding hardly changes
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What happens you go down a group?
1. Atomic radius increases so the nucleus-electron attraction is less, 2. Shielding increases so nucleus-electron attraction is less, 3. Nuclear charge increases
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What happens when goup 2 elements react with oxygen?
They react vigorously. A redox reaction happens where an ionic oxide is produced with the formula MO
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What happens when group 2 elements react with water?
The reaction produces hydroxides with the general formula M(OH)2. Hydrogen gas is also formed
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What are group 2 carbonates decomposed by and what is produced?
Decomposed by heat and produces an metal oxide and CO2
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What is calcium hydroxide used for?
Used as "lime" by farmers and gardeners to neutralise acidic soil
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What is magensium hydoxide used for?
Used as "milk of magnesia" to relive indigestion as it neutralises excess stomach acid
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Why does the boiling point increase down group 7?
The number of electrons increases leading to more LDF's so more energy is required to break the bonds
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Why do group 7 elements become less reactive as you go down the group?
1. Atomic radius increases, 2. Shielding increases, 3. Nucleus-electron attraction increases so it's harder to gain an electron into the p-subshell
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Define disproportination
A reaction in which an element is simultaneously oxidised and reduced
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What is an example reaction showing disproportionation?
Cl2 + 2NaOH = NaCl + NaClO + H2O
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What are halides used in (3 examples)
1. Salts (NaCl), 2. Toothpaste to prevent decay (NaF and SnF2), 3. Lenses to focus infrared light (CaF2(fluorite))
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What is the benefit of having chlorine in water?
Makes water safer to drink by killing bacteria
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What are the cons of having chlorine in water?
1. Reacts with organic matter to form chlorinated hydrocarbons which can cause cancer, 2. Chlorine is toxic
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What is the method for finding out an unknown halide?
1. An unknown halide is dissolved in water, 2. AgNO3 is added, 3. The Ag+ ions react with halide ions to form coloured precipitates (if unsure about colour add NH3)
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What does the NH3 do?
Distinguishes halides as the precipitates have different soluability in ammonia
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State the equation for chloride
Ag+ + Cl- = AgCl (white precipitate and soluable in dilute NH3)
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State the equation for bromide
Ag+ + Br- = AgBr (cream precipitate and soluable in concentrated NH3)
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State the equation for iodide
Ag+ + I- = AgI (yellow precipitate and insoluable in concentrated NH3)
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What types of reactions are these?
Precipitate reactions and they take place in aqueous solutions when aqueous ions react together to form a solid precipitate
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Relative charge of a neutron?

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Relative charge of an electron?

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Relative mass of a proton?

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Relative mass of a neutron?

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