|
Hint
|
Answer
|
|
what is an impure substance
|
a substance that melts or boils over a range of temperatures.
|
|
what does pure water melt at
|
0°C
|
|
what does pure water boil at
|
100°C
|
|
what is simple distillation
|
process that separates out a liquid from a solution
|
|
what is fractional distillation
|
process that separates out a mixture of different liquids with different boiling points
|
|
explain the process of simple distillation in separating water from saltwater
|
first the saltwater is boiled, water vapourises, forming water vapour which condenses back into a liquid when passed through the condenser, then it's collected in a beaker, salt is left behind in flask. Cold water is passed through the bottom of the condenser and out through the top so the water is constantly cold and running and completely full of cold water at all times.
|
|
explain the process of fractional distillation in separating alcohol from a mixture of alcohol and water
|
first know that water boils at 100°C and our alcohol boils at 78°C. Use a thermometer to carefully measure the temperature of the fractionating column, controlling it. Keep it at 78°C, this ensures only the alcohol turns into vapour and only the alcohol will pass through the column. This vapour reaches the condenser, condensing back into a liquid.
|
|
what is filtration
|
the process that separates an insoluble solid from a liquid
|
|
what is crystallisation
|
the process that separates a soluble solid from a solution
|
|
explain the process of filtration in separating sand from sand water
|
mixture is poured into a funnel lined with filter paper, sand doesn't pass through the paper and is left behind, it's called the residue. The water does pass through and collects into the flask beneath, this is called the filtrate.
|
|
explain the process of crystallisation
|
gently heat solution in an evaporating basin to evaporate off some water. Once the point of crystallisation is reached ( crystals begin to form), remove the basin from the heat and leave it to cool so it can crystallise, once hydrated crystals form, filter the crystals out and leave them in a warm place to dry so all water evaporates off and we form anhydrous crystals. If we left the solution on the first step, so gentle heat, and let all the water evaporate then we wouldn't form anhydrous crystals we would form anhydrous powder, and we want crystals.
|
|
explain the process of paper chromatography
|
First, we obtain chromatography paper, then we draw a pencil line near the bottom of the paper, this is called the baseline. Get your mixtures and dot them onto the baseline at regular intervals. Pour a shallow amount of solvent into a beaker and place the paper in this beaker so the baseline is just above the top of the solvent. Put a lid onto the container to stop any solvent evaporating. The solvent is absorbed into the paper and rises up it, taking the mixtures with it. Each dye moves up the paper at different rates, depending on how strongly they adhere to the paper and how soluble they are in the solvent.
|
|
what is paper chromatography
|
it's the process that separates parts of mixtures into their constituents
|
|
what is the Rf value
|
the ratio of how far the solute travels compared to the solvent
|
|
how do we calculate Rf value
|
distance travelled by solute ────────────────── distance travelled by solvent |
|
what are SRM's
|
standard reference materals
|
|
what is a chromatogram
|
end results of spots in paper chromatography
|
|
why do we draw the baseline in pencil
|
because if we used pen then the ink in the pen would dissolve in the solvent and ruin our experiment
|
|
why does the baseline have to be above the solvent
|
so the dyes on the baseline don't dissolve in the solvent and ruin our experiment
|
|
what two things change our chromatogram
|
solvent used and paper used
|
|
how do we pick the appropriate solvent for our dye
|
determine the solubility of the dye, if the dye doesn't stick to the paper or doesn't dissolve in the solvent then our chromatogram isn't right. If our dye doesn't dissolve in water then we can use ethanol.
|
|
how do we use SRM's to determine the composition of a mixture using paper chromatography
|
baseline is drawn, unknown mixture is dotted on baseline and the known mixtures (SRM's) are dotted alongside it too. Paper is put in the shallow solvent just above the baseline and the solvent seeps up the paper, through spots taking most if not all of the dyes with it. Different dyes travel heights up the paper, the resulting pattern of dyes is our chromatogram. If the unknown mixture contains a dye that has travelled the same distance up the paper as one of the SRM's then we know that our mixture contains that dye.
|
|
describe things relating to Rf values
|
For each dye their Rf value is calculated, if the Rf value of one of the components of the unknown mixture equals the Rf value of one of the SRM's then that component is that SRM.
As solvent must travel higher than the highest dye the Rf value is always between 0 and 1.
More soluble dyes have higher Rf values - as they are more soluble in the solvent so will be able to travel further - than less soluble ones
the Rf value is 0 if the dye doesn't travel at all and stays on the baseline |
|
what determines how far the dye travels up the paper
|
how well it sticks to the paper
|
|
describe a paper chromatography experiment with inks/dyes in 6 steps
|
1: baseline is drawn 1cm above bottom of paper. pencil won't dissolve in solvent, but pen will as it contains ink, this ruins out chromatogram
2: a spot of each dye is dropped at regular intervals along the baseline
3:Paper is placed in a beaker in a shallow solvent. Baseline with dyes are placed just above the solvent, so around 1cm is submerged in the solvent. This ensures the dyes don't directly dissolve into the solvent.
4: Lid is placed on top of beaker to stop solvent evaporating from the surface of the paper, this also allows the atmosphere to become saturated with solvent.
5:when the solvent has travelled near the top of the paper, remove it and a line in pencil is drawn where the solvent is reached, this is the level of the solvent that has reached the paper, it's known as the solvent front
6: chromatogram is left to dry so all solvent evaporates |
|
what are the 2 most common solvents to use in paper chromatography
|
ethanol and water
|
|
what are ions
|
electrically charged particles formed when atoms lose or gain electrons
|
|
what ions do metals form and why
|
positive ions because they lose electrons
|
|
what ions do non-metals form and why
|
negative ions because they gain electrons
|
|
what is a cation
|
positive ion
|
|
what is an anion
|
negative ion
|
|
what is the full outer shell also known as
|
noble gas configuration
|
|
what charge do ionic compounds have
|
neutral
|
|
do ions have a full outer shell and explain your answer
|
yes, because they have gained or lost the amount of electrons it took for them to become stable
|
|
why do atoms long for a full outer shell
|
full outer shell provides stability, so every unstable ( without full outer shell ) atom wants to become stable
|
|
what is an ionic bond formed between
|
metal and non-metal
|
|
what is a carbonate ion
|
CO₃ ²⁻
|
|
what is a hydroxide ion
|
OH ⁻
|
|
what is an ammonium ion
|
NH₄ ⁺
|
|
what is a nitrate ion
|
NO₃ ⁻
|
|
what is a sulfate ion
|
SO₄ ²⁻
|
|
what is a silver ion
|
Ag⁺
|
|
what is a hydrogen ion
|
H⁺
|
|
what is a copper (ii) ion
|
Cu ²⁺
|
|
what is an iron (ii) ion
|
Fe ²⁺
|
|
what is a lead (ii) ion
|
Pb ²⁺
|
|
what is a zinc (ii) ion
|
Zn ²⁺
|
|
what is an iron (iii) ion
|
Fe ³⁺
|
|
what is ionic bonding
|
the strong electrostatic attraction between oppositely charged ions
|
|
why have ionic compounds got high melting and boiling points
|
because they have a giant structure with strong electrostatic forces between oppositely charged ions which requires lots of energy to break.
|
|
why do ionic compounds not conduct electricity when solid
|
no delocalised anions
|
|
why do ionic compound conduct electricity when molten or in aqueous solution
|
there are delocalised anions present, so the giant ionic lattice is broken meaning it's ions are free to move which can conduct electricity
|
|
how many elements do ionic compounds ending in -ide contain?
|
2
|
|
how many elements do ionic compounds ending in -ate contain?
|
3 or more where at least 1 is oxygen
|
|
what is a covalent bond formed between
|
non-metal and non-metal
|
|
what is a covalent bond
|
the strong attraction between a shared pair of electrons and 2 nuclei
|
|
what is the displayed formula of oxygen
|
O=O
|
|
what is the displayed formula of nitrogen
|
N≡N
|
|
what is the displayed formula of carbon dioxide
|
O=C=O
|
|
why do 2 non metal atoms share pairs of electrons
|
to get a full outer shell becoming stable
|
|
if 2 non metals share one pair of electrons what sign and name is it
|
|
|
if 2 non metals share two pair of electrons what sign and name is it
|
|
|
if 2 non metals share three pair of electrons what sign and name is it
|
|
|
what is the displayed formula of hydrogen chloride
|
H─Cl
|
|
what is the displayed formula of hydrogen
|
H─H
|
|
what is the displayed formula of water
|
H─O─H
|
|
what is the displayed formula of chlorine
|
Cl─Cl
|
|
what is the displayed formula of hydrochloric acid
|
H─Cl
|
|
what type of structure does carbon dioxide have
|
simple molecular structure
|
|
what is a simple molecular structure
|
structure made only of molecules
|
|
describe the structure of a simple molecular substance, like how they are broken, what are the forces, what type of bonds, boiling points, etc
|
in each molecule, atoms are covalently bonded, these covalent bonds in the molecules are strong. Between these molecules are weak forces of attraction called intermolecular forces which aren't covalent bonds, they are easily broken so require little energy to break. So simple molecular substances have low boiling points, the covalent bonds aren't broken, it's the weak intermolecular forces that're broken.
|
|
why does a simple molecular substance's melting and boiling point increase with size
|
larger molecules have more molecules so more intermolecular forces. These intermolecular forces are weak when isolated but when there are loads of them they are very strong. These forces have to be broken in order for the substance to melt or boil, so large molecules have loads of intermolecular forces which makes them strong so large molecules have high melting and boiling points
|
|
what's graphene
|
a single layer of graphite
|
|
can giant covalent structures conduct electricity when solid, aqueous or molten
|
no, except graphite
|
|
are giant covalent structures usually soluble in water
|
no
|
|
why is diamond so strong and has got a very high melting point
|
giant covalent structure with lots of strong covalent bonds, this require lots of energy to break. 1 giant molecule, meaning it's very strong because there are no intermolecular forces, there are just really strong covalent bonds made of a giant 3D lattice where each carbon atom is bonded to 4 other carbon atoms via strong, covalent bonds every one of carbon's outer electrons is involved in a strong covalent bond, this means it's extremely strong |
|
what is diamond used in because of it's hardness
|
fast cutting tools like diamond tipped saws
|
|
what are the 4 allotropes of carbon
|
C₆₀ fullerenes Diamond Graphite Graphene |
|
what's an allotrope
|
different forms of the same element
|
|
what is diamond made of
|
carbon atoms
|
|
what is graphite made of
|
carbon atoms
|
|
what are C₆₀ fullerenes made of
|
carbon atoms
|
|
what type of structure is graphite
|
giant covalent structure
|
|
how can graphite conduct electricity
|
It has layers where each carbon atom is covalently bonded to 3 other carbon atoms. Carbon atoms can bond to 4 atoms so 1 electron from every carbon atom isn't involved in any bond, so it is a delocalised electron. These electrons form a sea of delocalised electrons between the layers. So even though graphite is a non-metal, it can still conduct electricity because it has these delocalised electrons between it's layers that can move freely and conduct electtricity.
|
|
why is graphite soft and slippery
|
each layer is a giant structure, with weak forces of attraction between the layers, this means the layers can slide over each other easily.
|
|
why is graphite used in pencils and lubricants
|
it's soft and slippery
|
|
how many carbon atoms is C₆₀ fullerene made of
|
60
|
|
what type of structure has C₆₀ fullerene got
|
simple molecular structure
|
|
are C₆₀ fullerenes considered molecules, elements, compounds or mixtures
|
molecules
|
|
why are C₆₀ fullerenes soft and easy to break
|
weak intermolecular forces between the molecules which requires a small amount of energy to break
|
|
why can't C₆₀ fullerenes conduct electricity even though they have 1 delocalised electron
|
in each molecule every carbon atom is bonded to 3 other carbon atoms, so there is 1 free electron, but these electrons cannot jump between different molecules so C₆₀ fullerenes cannot conduct electricity and they have a low melting point.
|
|
what are metallic bonds
|
the strong electrostatic attraction between the metal cations and the sea of delocalised electrons
|
|
how can metals conduct electricity
|
when metal atoms join together their outer electrons become delocalised, meaning they're free to move throughout the entire structure. So metals have a massive, regular structure of positive ions and a sea of delocalised electrons. So metals are good conductors of electricity because they have delocalised electrons that can move freely.
|
|
why are metals malleable
|
they have layers of ions that can slide over each other easily
|
|
what is electric current
|
the flow of ions or electrons
|
|
how is electricity and heat created using ions and electrons
|
when ions or electrons move in a material, energy can be transferred quickly
|
|
what is electrical conductivity
|
movement of charged particles
|
|
what are charged particles referring to
|
ions and electrons
|
|
Bobby says that his material has delocalised electrons in it, so it automatically is considered conductive. Is Bobby correct or incorrect and explain your answer
|
Bobby is incorrect, this is because the delocalised electrons have to be able to move freely throughout a substance, look at C₆₀ fullerenes, they have delocalised electrons but they can't conduct electricity because they're immobile. So in order to be considered conductive they need to be able to move freely.
|
|
can covalent compounds conduct electricity and explain why
|
no because usually they don't have any charged particles that're free to move, graphite is an exception.
|
|
can ionic compounds conduct electricity and explain why
|
yes and no. They can't conduct electricity when in solid form because they're ions aren't free to move. But when molten or in aqueous solution they can conduct electricity because their ions break free from their lattice and become free to move so can conduct electricity.
|
|
define electrolysis
|
the breaking down of an ionic compound that's molten or in aqueous solution into it's constituents using an electric current to form new substances
|
|
what are electrolytes
|
molten or aqueous solutions of an ionic compound that can conduct electricity
|
|
what is the cathode
|
negative electrode
|
|
what is the anode
|
positive electrode
|
|
what does the cathode attract
|
cations
|
|
what does the anode attract
|
anions
|
|
why is the anode called the anode
|
because it attracts cations
|
|
why is the anode called the anode
|
because it attracts anions
|
|
how are new substances made during electrolysis
|
When a voltage is applied to an electrolyte, the charged ions are attracted to the electrode with the charge opposite to it. When the ions touches the electrode, electrons are transferred, forming new substances.
|
describe the electrolysis of molten lead (ii) bromide (PbBr₂)
include the equation, what is formed at the anode and cathode, etc |
first, lead (ii) bromide is heated to become molten because it's insoluble, now the ions are free and it can conduct electricity. Electrodes attached to a power supply are placed into the molten lead (ii) bromide. Bromine (Br₂) gas forms at the anode and is released, this is because bromide ions are attracted to the anode. At the anode, bromide anions lose an electron to form bromine gas. Molten lead which is a shiny substance is formed at the cathode. At the cathode, lead cations gain electrons becoming lead atoms.
lead bromide ─> lead + bromine PbBr₂ ─> Pb + Br₂ |
|
if the ionic compound is insoluble how can we make it conduct electricity
|
melt it
|
|
if the ionic compound is soluble how can we make it conduct electricity
|
dissolve it in water
|
|
what are electrodes made of and what are their properties and why
|
usually made of graphite or platinum. These are inert, but can still conduct electricity, if they were reactive they would react with the substances and ruin the procedure. When we take the power supply away, the electrodes are just inert sticks, the power gives them their charge.
|
|
why do electrodes need to be inert
|
so they don't interfere with the reaction, all they do is supply the surface area for the reaction to take place on
|
|
where do electrons flow in electrolysis
|
from the anode to the cathode
|
|
why are the products of the electrolysis of aqueous solutions hard to predict
|
because the water molecules split up to form hydroxide ions and hydrogen ions.
|
|
in the electrolysis of aqueous solutions, what does the product formed at the cathode depend on
|
depends on how reactive the metal is
if the metal is more reactive than hydrogen then hydrogen gas is produced if the metal is less reactive than hydrogen then the metal is produced |
|
in the electrolysis of aqueous solutions, what does the product formed at the anode depend on
|
depends on if there are halide ions present
if there are then the halogen forms if there aren't then oxygen gas forms |
|
why do metal ions and hydrogen form at the cathode
|
because they are both cations and the cathode attracts cations
|
|
why do halide ions and oxygen form at the anode
|
because they are both anions and the anode attracts anions
|
describe the electrolysis of aqueous sodium chloride solution (NaCl)
include half equations, what is formed at the anode and cathode, other equations, etc |
solid sodium chloride is dissolved in water, making the sodium and chloride ions free to move. This solution also contains hydroxide and hydrogen ions because the water has slightly ionised as it's a very weak electrolyte.
H₂O ⇌ H⁺ + OH⁻
Sodium and hydrogen ions are attracted to the cathode and chloride and hydroxide ions are attracted to the anode. At the anode, green chlorine gas is formed. This is because at the anode chloride ions lose an electron forming chlorine molecules through oxidation. Chloride ions react at the anode instead of hydroxide ions because they are more chloride ions. The chlorine gas produced might be lower than expected because chlorine is slightly soluble in water. The half equation is:
2Cl⁻ ─> Cl₂ + 2e⁻
At the cathode, colourless hydrogen gas is produced. This is because hydrogen ions gain electrons through reduction forming hydrogen molecules. The hydrogen ions react at the cathode instead of the sodium ions because sodium is higher up in the reactivity series. The half equation is:
2H⁺ + 2e⁻ ─> H₂
The solution at the end of this is sodium hydroxide. |
describe the electrolysis of aqueous copper sulfate solution
including half equations, what's formed at the cathode and anode, etc |
first, we know our solution is made of hydroxide, hydrogen, copper and sulfate ions. At the cathode, a brown layer of copper forms around the cathode. This is because copper ions gain electron through reduction to form copper atoms. Copper is below hydrogen in the reactivity series this is why it forms on the cathode. The electron half equation is:
Cu²⁺ + 2e⁻ ─> Cu
At the anode, bubbles of oxygen gas are released. Hydroxide ions lose electrons to form oxygen and water. The hydroxide ions react at the anode instead of the sulfate ions because hydroxide ions are more unstable. The electon half equation is:
4OH⁻ ─> O₂ + 2H₂O + 4e⁻ |
|
describe the electrolysis of sulfuric acid
|
sulfuric acid is made of hydrogen ions, hydroxide ions and sulfate ions. At the cathode, bubbles of hydrogen gas are released. Hydrogen ions gain electrons through reduction, forming hydrogen molecules. The electron half equation is:
2H⁺ + 2e⁻ ─> H₂
at the anode, bubbles of oxygen are released. Hydroxide ions lose electrons through oxidation to form molecules of oxygen and water. The hydroxide ions react at the anode instead of sulfate ions because they're more reactive. The electron half equation is:
4OH⁻ ─> O₂ + 2H₂O + 4e⁻
In this equation : 2H₂O ─> 2H₂ + O₂ there are 2 times the amount of hydrogen molecules than oxygen, meaning there are twice as many moles, so more hydrogen gas is released. |
|
reduction
|
gain of electrons or loss of oxygen
|
|
oxidation
|
gain of oxygen or loss of electrons
|
|
where does reduction happen in electrolysis
|
cathode
|
|
where does oxidation happen in electrolysis
|
anode
|
