C2 Flashcards
What is relative atomic mass?
The mean mass of an atom compared to 1/12 the mass of a (carbon 12 atom)
-a carbon 12 atom has a relative atomic mass of 12.0 exactly
-this means that an atom with less mass mass than a carbon 12 atom has a relative atomic mass less than 12.0
-this means that an atom with more mass mass than a carbon 12 atom has a relative atomic mass higher than 12.0
Al2(SO4)3. How many of each atom is there?
Aluminium = 2
Sulfur = (1x3)=3
Oxygen =(3x4)=12
What is an empirical formula?
The simplest whole number ratio of the atoms of each element
Eg
C4H10 = C2H5
What is a pure substance?
Consists of just one element or compound
What happens when a substance dissolves?
When a substance dissolves it’s particles separate and become completely mixed with the particles of the solvent.
What does filtration do?
Separates an insoluble substance from substances in the liquid state
What are the components of filtration?
-filter paper
-funnel
-residue
-Conical flask
-filtrate
How does evaporation work?
If you heat a solution the solvent evaporates leaving the solute behind. If you heat the solution too strongly, you get a powder, but if you allow the solvent to evaporate slowly, you get regularly shaped crystals.
How do you get the crystals from crystallisation?
A solution is saturated when no more solute can be dissolved at that temperature. Crystals will start forming at this point. You let the crystals cool down slowly. As it cools the solubility of the solute decreases So more crystals form. You can separate them from the remaining solution by filtration.
What components are needed for crystallisation?
-Evaporating basin
-solution
-boiling water
-water bath
How does simple distillation work?
Simple distillation separates a solvent from a solution. It relies on the solvent having a much lower boiling point than the solute.
How does fractional distillation work?
Fractional distillation separates two or more substances from a mixture in the liquid state. It relies on each substance having a different boiling point and uses a special piece of equipment called a fractionating column.
What does simple distillation use?
-thermometer
-condenser
-heat
-test tube/collecting container
-flask
-solution
-bung-so no gas can escape
What does fractional distillation use?
-thermometer
-condenser
-heat
-test tube/collecting container
-water mixture
-fractionating column
-Bung-so no gas can escape
-flask
How does chromatography work?
Chromatography relies on two different chemical phases:
A stationery phase-that does not move
A mobile phase-that does move
In paper chromatography what are the phases?
The stationery phase is: absorbent paper
The mobile phase is: a solvent in the liquid state, such as water or propanone
What is thin layer chromatography?
Thin layer chromatography works in the same way as paper chromatography but the stationery phase is a thin layer of silica or alumina powder spread over a plate of glass or plastic
What can you use thin layer chromatography for?
To separate a sample into its components for identification or analysis.
What is needed in thin layer chromatography?
-Lid
-tank
-TLC plate
-solvent
-sample
How does gas chromatography work?
The stationery phase is: silica or alumina powder packed into a metal column
The mobile phase is: an unreactive carrier gas such as nitrogen, which does not react with the sample
What does gas chromatography do?
Gas chromatography separates the components of a mixture and also measures their amounts
What apparatus is used in gas chromatography?
-Carrier gas cylinder
-oven
-detector
-vent
-flow meter
-column packed with particles of stationery phase
-chromatogram
Advantages of using thin layer chromatography over paper chromatography:
-it is quicker
-it is more sensitive, so a smaller sample can be used
-there is a larger range of stationary phases and solvents to choose from
What separation method should I use if there are two ore more substances in the liquid state
Fractional distillation
What separation method should I use if there are coloured soluble substances?
Paper chromatography or thin-layer chromatography
What separation method should I use if there are insoluble and soluble substances
Dissolving followed by filtration
What separation method should I use if there is a solute dissolved in a solvent(a solution)
Crystallisation to obtain the solute, simple distillation to obtain the solvent.
What is the appearance of a metal
Shiny
What is the melting point and boiling point of a metal
Usually high
What is the state of a metal at room temperature?
Solid
Is a metal malleable or brittle when solid?
Malleable
Is a metal ductile or non-ductile when solid?
Ductile (they can be pulled into wires)
What is a metals thermal and electrical conductivity like?
Good conductors
What are non-metals appearance like?
Dull
What are the melting and boiling point of non-metals like?
Usually low
What is a non metals state at room temperature?
About half are solid
And
About half are gas
Are non metals malleable or brittle when solid?
Brittle
Are non metals ductile or non-ductile when solid?
Non-ductile (they snap when pulled)
What are non-metals thermal and electrical conductivity like?
They are poor conductors (they are insulators)
What is a chemical property?
A chemical property is a characteristic of a substance that can only be determined by studying its chemical reactions
What is a period?
A period is a horizontal row
What is a group?
A group is a vertical column
What do the number of electrons in an elements outermost shell indicate?
What group the element is in
What is special about the electronic structure of group 0 elements?
They all have full outer shells
What are ions?
An ion is an electrically charged particle formed when an atom,or group of atoms, loses or gains electrons
What ions do metals make?
Metal atoms lose electrons to form positive ions
What ions do non-metals make?
Non-metal atoms gain electrons to form negative ions
What happens to protons and neutrons when an ion is formed?
The number of protons and neutrons do not change when an atoms forms an ion.
How does Na turn into Na+ ?
Atom loses its outer electron
How does Mg turn into Mg^2+
Atom loses its two outer electrons.
How does Cl turn into Cl-?
Atom gains one electron to complete its outer shell
How does O turn into O^2-
Atom gains 2 electrons to complete its outer shell
How do ionic compounds form
When a metal reacts with a non-metal, electrons are transferred from the metal atoms to the non-metal atoms so both achieve more stable electronic structures.
What is the structure and bonding of ionic compounds?
Ionic compounds in their solid state contain positive and negative ions arranged in a regular way. This arrangement is a called a giant ionic lattice. The ions are held in place by ionic bonds,which act in all directions.
What are ionic bonds?
Ionic bonds are strong electrostatic forces of attraction between oppositely charged ions.
What are covalent bonds
A covalent bond is a shared pair of electrons.
How do covalent bonds form?
Covalent bonds form between two non-metal atoms when the atoms get close enough to share atoms in their outer shells. By sharing electrons,the atoms complete their outer shells.
How can covalent bonds be modelled?
Covalent bonds can be modelled using dot and cross diagrams.
The electrons from one of the bonded atoms are shown as shown as dots and the electrons from the other bonded atom are shown as crosses. Each pair of electrons in the shared area between the overlapping circles shows a covalent bond. Only the outer shells are usually shown.
What are simple molecules?
Hydrogen,oxygen,water,and carbon dioxide all exist as simple molecules.
A simple molecule is a molecule that only contains a few atoms. These substances can all be modelled using a dot and cross diagram.
What is a molecule? (Covalent bonds)
A molecule is a particle in which non-metal atoms are joined to each other by covalent bonds.
What is the structure and bonding in simple molecules like?
Covalent bonds involve electrostatic forces of attraction , just like ionic bonds do. However for a covalent bond, the forces are between the nucleus of each bonded atom and the shared electrons.
What are the covalent bonds between atoms in a simple molecule like?
The covalent bonds between atoms in a simple molecule are strong, but the intermolecular forces between the molecules are weak.
What are giant covalent structures?
A giant covalent structure consists of very many non-metal atoms joined by covalent bonds and arranged in a repeating regular pattern called a giant lattice. These structures are also called giant covalent lattices.
What are the chemical formulae of giant molecules?
Just like in ionic compounds, where very many ions are involved, giant covalent structures have very many atoms. It would make little sense for you to try to write a chemical formula with these huge numbers in it. Instead, you use the empirical formula for the substance. You will remember that this formula shows the simplest whole number ratio of atoms of each element .
What are polymers?
All polymers, whether they are artificial or natural, are made from many smaller molecules called monomers. These monomers are able to join end to end in chemical reactions, producing longer polymer molecules.
How are polymer molecules modelled
Dot and cross diagrams, ball and stick diagarams
Are monomers simple molecules?
Yes
How are polymers modelled
Polymers are modelled with ball and stick models as well as dot and cross diagrams
What do monomers consist of?
-monomers consist of a few non metals
- a molecule that can be bonded to other identical molecules to form a polymer
What are monomers?
Simple molecules
What is the structure of metals like?
All metals apart from mercury, are in solid state at room temperature.
Their atoms are packed together in a regular way, forming a giant metallic lattice.
How is the structure of metals modelled?
By drawing circles or spheres arranged in a regular pattern, touching eachother
What are metallic bonds like?
Electrons leave the outer shells of the metal atoms forming a “sea” of electrons around positively charged metals ions.these electrons are free to move through the structure of the metal a, so they are called delocalised electrons.
What does localised mean?
Something that is restricted to a particular place
What does delocalised mean?
Something that is free to move from its usual place.
What did Mendeleev do?
-arranged elements in order of increasing atomic weight and grouped elements with similar chemical properties.
-He left spaces for elements he thought would exist but not yet discovered, and predicted their properties from nearby elements
What are the patterns of chemical properties?
-elements are arranged in order of increasing atomic number
-the atomic number is the number of protons in an atom
-the number of electrons is equal to the number of protons
-electronic structure is determined by the number of electrons
-the electronic structure of an element determines its chemical properties
Why can carbon form many different compounds?
Carbon is in group 4 so it’s atoms have 4 electrons in their outer shell and can form four covalent bonds. A carbon atom can join with other carbon atoms to form chains and rings. Carbon atoms in these structures can also form covalent bonds with other elements, such as hydrogen and oxygen, producing many different compounds.
What do delocalised electrons mean in terms of conducting?
It means that the substance can conduct electricity as the electrons are free to move.
What is graphene?
Graphene is a carbon allotrope that resembles a single layer of graphite.
It is almost transparent, but extremely strong, and conducts electricity.
What happens when substances change state?
When a substance melts or boils, forces of attraction between its particles are overcome. In other words, some or all of the bonds between its particles break:
-some bonds break going from the solid to the liquid state
-all remaining bonds scram going from the liquid to the gas state
Particle Bonds form when:
A substance condenses or freezes:
-Some bonds form going from the gas to the liquid state
-many bonds form going from the liquid to the solid state.
What happens to stored chemical energy during changes in state?
Stored chemical energy is transferred to the surroundings, usually by heating, when chemical bonds form.
(Energy is needed to break and form bonds)
Bonds and relative strength in metal:
Metals have Metallic bonds
Metals have a Strong relative strength
Bonds and relative strength in ionic compound:
Ionic compounds have Ionic bonds
Ionic compounds’ Relative strength is strong
Bonds and relative strength in giant covalent structure:
-Giant covalent structures have covalent bonds
-Giant covalent bonds have a Relative strength that is strong
Bonds and relative strength in simple molecules:
-Simple molecules have Intermolecular forces
-Simple molecule’s Relative strength is weak
What substances are usually solid state at room temperature
Metals
Ionic compounds
Giant covalent structures
Why are some substances brittle?
Depends on how easily the particle in the substance can change their positions in the lattice structure.
What is special about ions in metals
Layers of ions in metals can slide over each other
(This is why metals are malleable)
What is a nano particle
A nano particle is a particle between 1 and 100 nm across and consists of just a few hundred atoms
What is the formulae for the ion ammonium?
NH4^+
What is the formulae for the ion hydrogen?
H^+
What is the formulae for the ion lithium?
Li^+
What is the formulae for the ion sodium.
Na^+
What is the formulae for the ion potassium?
K^+
What is the formulae for the ion silver?
Ag^+
What is the formulae for the ion Barium?
Ba^2+
What is the formulae for the ion calcium?
Ca^2+
What is the formulae for the ion copper(II)
Cu^2+
What is the formulae for the ion Iron(II)?
Fe^2+
What is the formulae for the ion lead(II)?
Pb^2+
What is the formulae for the ion magnesium?
Mg^2+
What is the formulae for the ion zinc?
Zn^2+
What is the formulae for the ion aluminium?
Al^3+
What is the formulae for the ion Iron(III)?
Fe^3+
What is the formulae for the ion chloride?
Cl^-
What is the formulae for the ion Bromide?
Br^-
What is the formulae for the ion Iodide?
I^-
What is the formulae for the ion hydroxide?
OH^-
What is the formulae for the ion nitrate?
NO3^-
What is the formulae for the ion oxide?
O^2-
What is the formulae for the ion carbonate?
CO3^2-
What is the formulae for the ion sulfate?
SO4^2-
How do you write the formulae for ionic compounds?
In any ionic compound the total number of positive charges must equal the total number of negative charges.
How do I balance compound ions?
Magnesium hydroxide
Mg^2+ =magnesium
OH^- =hydroxide
You need 2 hydroxides to get two negative charges to balance magnesium’s positive charge.
Mg(OH)2
What is the law of conservation of mass?
Atoms cannot be created or destroyed by chemical reactions. The same atoms are present at the start and end of a reaction. They are just joined in a different way, so the total mass stays the same during the chemical reaction.
Example of conversation if mass:
C + OO —> OCO
How can you investigate conservation if mass?
You can investigate conservation if mass by carrying out a reaction in a closed system.This is a container in which no substances can enter or escape during the reaction.
Examples:
-A beaker of reactants in solution where the products are not gases
-A flask attached to a gas syringe to stop products in the gas state escaping
Why does the mass seem to change during some reactions?
Substances can leave or enter the reaction mixture in a non-enclosed system. This usually happens when a gas is involved as the gas can leave the reaction or join if it is already airborne.
What is (s) ?
Solid
What is (l) ?
Liquid
What is (g) ?
Gas
What is (aq) ?
Aqueous solution
What are half equations?
A half equation is a model for the change that happens to one reactant in a chemical equation.
Example:
2Na (s) + Cl2 (g) —> 2Nacl (s)
Sodium ions form when sodium atoms lose electrons. This equation models the change:
Na —> Na^+ + e^-
Chloride ions form when chlorine atoms gain electrons. However chlorine atoms are joined together by covalent bonds to make diatomic chlorine molecules, so this is the half equation the models the change:
Cl2 + 2e^- —> 2Cl^-
Notice you must balance the charges in half equations, not just the number of atoms and the ions they form.
What are ionic equations?
A complete ionic equation shows the ions present in a reaction mixture l. It usually also includes the formulae of any molecular substances present, or substances in their solid state.
Example:
HCl (aq) + NaOH (aq) —> NaCl (aq) + H2O (l)
The ionic equation:
H^+(aq) + Cl^- (aq) + Na^+ (aq) + OH^- (aq) —> Na^+ (aq) + Cl^- (aq) + H2O (l)
H2O is modelled as H2O as water is a molecular substance (l)
Any ions that appear on both sides are spectator II s because they are in the reaction but don’t take part in the reaction. A net ionic equation leaves out the spectator ions.
H^+ (aq) + OH^- (aq) —> H2O (l)
What is a mole?
The mole is the unit for an amount of substance. One mole of something contains the same number of sheets as the number of carbon atoms. This number is huge. If you could stack a mole of sheets of paper on top of each other, they would reach a quarter size of the way to the centre of our galaxy. It makes little sense to use the mole in everyday life, but it is useful for tiny particles like atoms, molecules l, ions, or electrons.
How is the mole defined
1 mole is defined as the amount of any substance that contains the same number of entities as there are atoms in 12.0 g of carbon-12 (Mass number 12)
Mole is abbreviated to mol in calculations. Eg 1 mol of water contains 1 mol of water molecules. It would also contain 3 mols of atoms because each H2O molecule contains 3 atoms ( 2 hydrogen atoms, 1 oxygen atom.
How do you calculate masses of reactants and products?
The mass of a substance is related to its molar mass and amount by this expression:
Mass(g) = molar mass (g/mol) x amount (mol)
What is a stationery phase
The substance that the molecules can’t move in
-eg paper in paper chromatography
What is a mobile phase?
The substance that the molecules can move in
E.g solvent/water in paper chromatography
How do you calculate the rf value (paper chromatography)
Distance travelled by the substance / distance travelled by the solvent
Why does the melting point get higher as you go down a group?
The atoms are larger so they have stronger intermolecular forces
Why are ionic bonds so strong
They are made from oppositely charged ions that are attracted by electrostatic forces
What is a condenser?
A piece of equipment that has a water jacket with cold water surrounding it to cool down a vapour and turn it into liquid form
What components are needed for evaporation?
-evaporating dish
-solution
-tripod
-Bunsen burner
Why is evaporation not good for separating a solute from a solution?
The heat from the Bunsen burner will cause thermal decomposition on some of the solute
What happens to solutes at colder temperatures?
They become less soluble
What is reactivity?
How easily atoms lose or gain electrons and thus react with other atoms
