Studied by 10 people
TRIPLE : Triple content only EXTRAS: extra Information that I think is useful to know
The process requires heat energy which transforms into kinetic energy, allowing the particles to move
It occurs at a specific temperature known as the melting point which is unique to each pure solid
Boiling is when a liquid changes into a gas
This requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and from within the liquid
It occurs at a specific temperature known as the boiling point which is unique to each pure liquid
Freezing is when a liquid changes into a solid
This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same
Water for example freezes and melts at 0 ºC
It requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature which is unique for each pure substance
When a liquid changes into a gas
Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquids surface at low temperatures, below the boiling point of the liquid
The larger the surface area and the warmer the liquid/surface, the more quickly a liquid can evaporate
Evaporation occurs over a range of temperatures, but heating will speed up the process as particles need energy to escape from the surface
When a gas changes into a liquid, usually on cooling
When a gas is cooled its particles lose energy and when they bump into each other, they lack energy to bounce away again, instead grouping together to form a liquid
When a solid changes directly into a gas
This happens to only a few solids, such as iodine or solid carbon dioxide
The reverse reaction also happens and is called desublimation or deposition
Description:
When potassium magnate (VII) crystals are dissolved in water, the solution can be diluted several times
The colour fades but does not disappear until a lot of dilutions have been done
Explanation:
This indicates that there are a lot of particles in a small amount of potassium manganate (VII) and therefore the particles must be very small
Description:
Here, we see the diffusion of bromine gas from one gas jar to another
After 5 minutes the bromine gas has diffused from the bottom jar to the top jar
Explanation:
The air and bromine particles are moving randomly and there are large gaps between particles
The particles can therefore easily mix together
Solubility is a measurement of how much of a substance will dissolve in a given volume of a liquid
Different substances have different solubilities
Solubility can be expressed in g per 100 g of solvent
Solubility of solids is affected by temperature
As temperature increases, solids usually become more soluble
Solubility graphs or curves represent solubility in g per 100 g of water plotted against temperature
To plot a solubility curve, the maximum mass of solvent that can be dissolved in 100 g of water before a saturated solution is formed, is determined at a series of different temperatures
Solubility curve for three salts. While the solubility of most salts increases with temperature, sodium chloride, or common salt, hardly changes at all
Prepare a two beakers, one as a hot water bath and one as an ice bath
Using a small measuring cylinder, measure out 4 cm3 of distilled water into a boiling tube.
On a balance weigh out 2.6 g of ammonium chloride and add it to the boiling tube
Place the boiling tube into the hot water bath and stir until the solid dissolves
Transfer the boiling tube to the ice bath and allow it to cool while stirring
Note the temperature at which crystals first appear and record it in a table of results
Add 1 cm3 of distilled water then warm the solution again to dissolve the crystals
Repeat the cooling process again noting the temperature at which crystals first appear.
Continue the steps until a total of 10 cm3 of water has been added
Pure substances melt and boil at specific and sharp temperatures e.g. pure water has a boiling point of 100 °C and a melting point of 0 °C
Mixtures have a range of melting and boiling points as they consist of different substances that tend to lower the melting point and broaden the melting point range
The closer the measured value is to the actual melting or boiling point then the purer the sample is
This is used to separate a liquid and soluble solid from a solution (e.g., water from a solution of salt water) or a pure liquid from a mixture of liquids
The solution is heated, and pure water evaporates producing a vapour which rises through the neck of the round bottomed flask
The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker
After all the water is evaporated from the solution, only the solid solute will be left behind
This is used to separate two or more liquids that are miscible with one another (e.g., ethanol and water from a mixture of the two)
The solution is heated to the temperature of the substance with the lowest boiling point
This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
For water and ethanol
Ethanol has a boiling point of 78 ºC and water of 100 ºC
The mixture is heated until it reaches 78 ºC, at which point the ethanol boils and distills out of the mixture and condenses into the beaker
When the temperature starts to increase to 100 ºC heating should be stopped. Water and ethanol are now separated
Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g., sand from a mixture of sand and water)
Centrifugation can also be used for this mixture
A piece of filter paper is placed in a filter funnel above a beaker
A mixture of insoluble solid and liquid is poured into the filter funnel
The filter paper will only allow small liquid particles to pass through as filtrate
Solid particles are too large to pass through the filter paper so will stay behind as a residue
Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g., copper sulphate from a solution of copper (II) sulphate in water)
The solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind
Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution
If the solution is saturated, crystals will form on the glass rod
The saturated solution is allowed to cool slowly
Crystals begin to grow as solids will come out of solution due to decreasing solubility
The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry
This technique is used to separate substances that have different solubilities in a given solvent (e.g., different coloured inks that have been mixed to make black ink)
A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples
The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent, so the samples don’t wash into the solvent container
The paper is called the stationary phase
The solvent travels up the paper by capillary action, taking some of the coloured substances with it; it is called the mobile phase
Different substances have different solubilities so will travel at different rates, causing the substances to spread apart
Those substances with higher solubility will travel further than the others
This will show the different components of the ink / dye
If two or more substances are the same, they will produce identical chromatograms
If the substance is a mixture, it will separate on the paper to show all the different components as separate spots
An impure substance will show up with more than one spot, a pure substance should only show up with one spot
Pure substances will produce only one spot on the chromatogram
If two or more substances are the same, they will produce identical chromatograms
If the substance is a mixture, it will separate on the paper to show all the different components as separate spots
An impure substance therefore will produce a chromatogram with more than one spot
These values are used to identify the components of mixtures
The Rf value of a particular compound is always the same but it is dependent, however, on the solvent used
If the solvent is changed then the value changes
Calculating the Rf value allows chemists to identify unknown substances because it can be compared with Rf values of known substances under the same conditions
These values are known as reference values
Calculation
The Retention factor is found using the following calculation:
Rf = distance travelled by substance ÷ distance travelled by solvent
The Rf value will always lie between 0 and 1; the closer it is to 1, the more soluble is that component in the solvent
The Rf value is a ratio and therefore has no units
The electron configuration of an element describes how electrons are distributed in its atomic orbitals.
Electrons orbit the nucleus in shells and each shell has a different amount of energy associated with it
The further away from the nucleus, the more energy a shell has
Elements in the same group in the periodic table will have similar chemical properties
This is because they have the same number of outer electrons so will react and bond similarly
We can use the group number to predict how elements will react as the number of valence shell electrons in an element influences how the element reacts.
Therefore, elements in the same group react similarly
By observing the reaction of one element from a group, you can predict how the other elements in that group will react
The group 1 metals become more reactive as you move down the group while the group 7 metals show a decrease in reactivity moving down the group
They are all non-metal, monatomic (exist as single atoms), colourless, non-flammable gases at room temperature
The group 0 elements all have full outer shells of electrons; this electronic configuration is extremely stable
Elements participate in reactions to complete their outer shells by losing, gaining, or sharing electrons
The Group 0 elements do not need to do this, because of their full outer shells which makes them unreactive and inert
Other than helium which has 2 electrons in its outer shell, the noble gases have eight valence electrons (which is why you may see this group labelled “group 8”
The reactants are those substances on the left-hand side of the arrow and can be thought of as the chemical ingredients of the reaction
They react with each other and form new substances
The products are the new substances which are on the right-hand side of the arrow
The arrow (which is spoken as “goes to” or “produces”) implies the conversion of reactants into products
Reaction conditions or the name of a catalyst (a substance added to make a reaction go faster) can be written above the arrow
An example is the reaction of sodium hydroxide (a base) and hydrochloric acid produces sodium chloride (common table salt) and water:
sodium hydroxide + hydrochloric acid ⟶ sodium chloride + water
Chemical equations use the chemical symbols of each reactant and product
When balancing equations, there has to be the same number of atoms of each element on either side of the equation in accordance with the Law of Conservation of Mass
A symbol equation uses the formulae of the reactants and products to show what happens in a chemical reaction
A symbol equation must be balanced to give the correct ratio of reactants and products:
S + O2 → SO2
This equation shows that one atom of sulfur (S) reacts with one molecule of oxygen (O2) to make one molecule of sulfur dioxide (SO2)
The following non-metals must be written as molecules: H2, N2, O2, F2, Cl2, Br2 and I2
To balance an equation you work across the equation from left to right, checking one element after another
If there is a group of atoms, for example a nitrate group (NO3–) that has not changed from one side to the other, then count the whole group as one entity rather than counting the individual atoms
Examples of chemical equations:
Acid-base neutralisation reaction:
NaOH (aq) + HCl (aq) ⟶ NaCl (aq) + H2O (l)
Redox reaction:
2Fe2O3 (aq) + 3C (s) ⟶ 4Fe (s) + 3CO2 (g)
In each equation there are equal numbers of each atom on either side of the reaction arrow so the equations are balanced
Don't forget to add state symbols when writing balanced equations:
(s) solid
(l) liquid
(g) gas
(aq) aqueous
The best approach is to practice lot of examples of balancing equations
By trial and error change the coefficients (multipliers) in front of the formulae, one by one checking the result on the other side
Balance elements that appear on their own, last in the process
We have seen previously that the symbol for the relative atomic mass is Ar
To calculate the Mr of a substance, you have to add up the relative atomic masses of all the atoms present in the formula
n = little number after Chemical symbol symbol
(n x Chemical symbol Ar ) + (n x chemical symbol Ar) = Mr
Chemical equations can be used to calculate the moles or masses of reactants and products
To do this, information given in the question is used to find the amount in moles of the substances being considered
Then, the ratio between the substances is identified using the balanced chemical equation
Once the moles have been determined they can then be converted into grams using the relative atomic or relative formula masses
percentage yield = (actual yield/theoretical yield) x 100
The actual yield is the recorded amount of product obtained
The theoretical yield is the amount of product that would be obtained under perfect practical and chemical conditions
Aim:
To determine the formula of hydrated copper sulfate, CuSO4. xH2O
Measure the mass of evaporating dish
Add a known mass of hydrated salt
Heat over a Bunsen burner, gently stirring, until the blue salt turns completely white, indicating that all the water has been lost
Record the mass of the evaporating dish and its contents
Mass of the white anhydrous salt:
Measure the mass of white anhydrous salt remaining
Mass of water:
Subtract the mass of the white anhydrous salt remaining from the mass of known hydrated salt
Step 1 – Divide the mass of the copper sulfate and the water by their respective molar masses
Step 2 – Simplify the ratio of water to copper sulfate:
Step 3 – Represent the ratio in the form ‘salt.xH2O’
Divide the relative formula mass of the molecular formula by the relative formula mass of the empirical formula
Multiply the number of each element present in the empirical formula by this number to find the molecular formula
At room temperature and pressure, the volume occupied by one mole of any gas was found to be 24 dm3 or 24,000 cm3
This is known as the molar gas volume at RTP
RTP stands for “room temperature and pressure” and the conditions are 20 ºC and 1 atmosphere (atm)
amount of gas (moles) = volume (dm3)/24 (dm3 mol -1)
amount of gas (moles) = volume (cm3)/24 ,000 (cm3 mol -1)
to determine the empirical formula of magnesium oxide by combustion of magnesium
Method:
Measure mass of crucible with lid
Add sample of magnesium into crucible and measure mass with lid (calculate the mass of the metal by subtracting the mass of empty crucible)
Strongly heat the crucible over a Bunsen burner for several minutes
Lift the lid frequently to allow sufficient air into the crucible for the magnesium to fully oxidise without letting magnesium oxide smoke escape
Continue heating until the mass of crucible remains constant (maximum mass), indicating that the reaction is complete
Measure the mass of crucible and contents (calculate the mass of metal oxide by subtracting the mass of empty crucible)
Working out the empirical formula:
Mass of metal:
Subtract mass of crucible from magnesium and the mass of the empty crucibleMass of oxygen:
Subtract mass of the magnesium used from the mass of magnesium oxide
Step 1 – Divide each of the two masses by the relative atomic masses of the elements
Step 2 – Simplify the ratio
magnesium oxygen
Mass a b
Mole a / Ar b / Ar
= x = y
Ratio x : y
Step 3 – Represent the ratio into the form ‘MxOy‘ E.g, MgO
An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons
This loss or gain of electrons takes place to obtain a full outer shell of electrons
The electronic structure of ions of elements in groups 1, 2, 3, 5, 6 and 7 will be the same as that of a noble gas - such as helium, neon, and argon
Negative ions are called anions and form when atoms gain electrons, meaning they have more electrons than protons
Positive ions are called cations and form when atoms lose electrons, meaning they have more protons than electrons
All metals lose electrons to other atoms to become positively charged ions
All non-metals gain electrons from other atoms to become negatively charged ions
Example: what is the formula of aluminium sulfate?
Write out the formulae of each ion, including their charges
Al3+ SO42-
Balance the charges by multiplying them out:
Al3+ x 2 = +6 and SO42- x 3 = -6; so +6 – 6 = 0
So the formula is Al2(SO4)3
Another method that also works is to 'swap the numbers'. In the example above the numbers in front of the charges of the ions (3 and 2) are swapped over and become the multipliers in the formula (2 and 3). Easy when you know how!
Ionic compounds are made of charged particles called ions which form a giant lattice structure
Ionic substances have high melting and boiling points due to the presence of strong electrostatic forces acting between the oppositely charged ions
These forces act in all directions and a lot of energy is required to overcome them
For electrical current to flow there must be present freely moving charged particles such as electrons or ions
Ionic compounds can conduct electricity in the molten state or in solution as they have ions that can move and carry charge
They cannot conduct electricity in the solid state as the ions are in fixed positions within the lattice and are unable to mov
Non-metal atoms can share electrons with other non-metal atoms to obtain a full outer shell of electrons
When atoms share pairs of electrons, they form covalent bonds
Covalent bonds between atoms are very strong
When two or more atoms are covalently bonded together, they form ‘molecules’
Covalently bonded substances may consist of small molecules or giant molecules
Weak intermolecular forces exist between individual molecules
E.g. Each liquid water molecule consists of two hydrogen atoms covalently bonded to an oxygen atom, and in between two individual water molecules there are weak intermolecular forces
Shared electrons are called bonding electrons and occur in pairs
Electrons on the outer shell which are not involved in the covalent bond(s) are called non-bonding electrons
Simple covalent molecules do not conduct electricity as they do not contain free electrons
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In a normal covalent bond, each atom provides one of the electrons in the bond
A covalent bond is represented by a short straight line between the two atoms, H-H
Covalent bonds should not be regarded as shared electron pairs in a fixed position; the electrons are in a state of constant motion and are best regarded as charge clouds
Sharing electrons in the covalent bond allows each of the 2 atoms to achieve an electron configuration similar to a noble gas
This makes each atom more stable
Simple molecular structures have covalent bonds joining the atoms together, but intermolecular forces that act between neighbouring molecules
They have low melting and boiling points as there are only weak intermolecular forces acting between the molecules
These forces are very weak when compared to the covalent bonds and so most small molecules are either gases or liquids at room temperature
Often the liquids are volatile
As the molecules increase in size the intermolecular forces also increase as there are more electrons available
This causes the melting and boiling points to increase
the term intermolecular forces of attraction can be used to represent all forces between molecules
As the relative molecular mass of a substance increases, the melting and boiling point will increase as well
An increase in the relative molecular mass of a substance means that there are more electrons in the structure, so there are more intermolecular forces of attraction that need to be overcome when a substance changes state
So larger amounts of heat energy are needed to overcome these forces, causing the compound to have a higher melting and boiling point
The family of organic molecules called alkanes show a clear increase in boiling point as the size of the molecule increases
Diamond and graphite are allotropes of carbon
Both substances contain only carbon atoms but due to the differences in bonding arrangements they are physically completely different
In diamond, each carbon atom bonds with four other carbons, forming a tetrahedron
All the covalent bonds are identical, very strong and there are no intermolecular forces
Diamond has the following physical properties:
It does not conduct electricity
It has a very high melting point
It is extremely hard and has a density of 3.51 g / cm3 – a little higher than that of aluminium
All the outer shell electrons in carbon are held in the four covalent bonds around each carbon atom, so there are no freely moving charged particles to the current
The four covalent bonds are very strong and extend in a giant lattice, so a very large amount of heat energy is needed to break the lattice
Diamond ́s hardness makes it very useful for purposes where extremely tough material is required
Diamond is used in jewellery and for coating blades in cutting tools
The cutting edges of discs used to cut bricks and concrete are tipped with diamonds
Heavy-duty drill bits and tooling equipment are also diamond tipped
Each carbon atom in graphite is bonded to three others forming layers of hexagons, leaving one free electron per carbon atom
These free electrons migrate along the layers and are free to move and carry charge, hence graphite can conduct electricity
The covalent bonds within the layers are very strong, but the layers are attracted to each other by weak intermolecular forces, so the layers can slide over each other making graphite soft and slippery
Properties of Graphite
Graphite has the following physical properties:
It conducts electricity and heat
It has a very high melting point
It is soft and slippery and less dense than diamond (2.25 g / cm3)
The weak intermolecular forces make it a useful material
It is used in pencils and as an industrial lubricant, in engines and in locks
It is also used to make inert electrodes for electrolysis, which is particularly important in the extraction of metals such as aluminium
Fullerenes are a group of carbon allotropes which consist of molecules that form hollow tubes or spheres
Fullerenes can be used to trap other molecules by forming around the target molecule and capturing it, making them useful for targeted drug delivery systems
They also have a huge surface area and are useful for trapping catalyst molecules onto their surfaces making them easily accessible to reactants so catalysis can take place
Some fullerenes are excellent lubricants and are starting to be used in many industrial processes
The first fullerene to be discovered was buckminsterfullerene which is affectionately referred to as a “buckyball”
In this fullerene, 60 carbon atoms are joined together forming 20 hexagons and 12 pentagons which produce a hollow sphere that is the exact shape of a soccer ball
Metals have high melting and boiling points
There are many strong metallic bonds in giant metallic structures
A lot of heat energy is needed to overcome forces and break these bonds
Metals conduct electricity
There are free electrons available to move and carry charge
Electrons entering one end of the metal cause a delocalised electron to displace itself from the other end
Hence electrons can flow so electricity is conducted
Metals are malleable and ductile
Layers of positive ions can slide over one another and take up different positions
Metallic bonding is not disrupted as the valence electrons do not belong to any particular metal atom so the delocalised electrons will move with them
Metallic bonds are thus not broken and as a result metals are strong but flexible
They can be hammered and bent into different shapes without breaking
Ionic compounds can conduct electricity in the molten state or in solution as they have ions that can move and carry charge
They cannot conduct electricity in the solid state as the ions are in fixed positions within the lattice and are unable to move
Note 
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