AS CHEMISTRY 9701

Why is ice less dense than liquid water?

!This is due to hydrogen bonding. Ice is less dencse than liquid water because the molecules are held further apart in a lattice of hydrogen bonds (some of these break on melting).

What happens to a weak acid as it dissolves in water?

A weak acid only partially dissoiciates into ions when it dissolves in water.

How do you tell Chloride, bromide and iodide apart?!

By adding acidified AgNO2(aq). This forms a precipate. The faster the precipitate forms the faster the rate of reaction. Chloride = white bromide = cream iodide = yellow

How would you show that ammonia gas was given off?

It turns damp litmus paper blue, and can also be recognized by its pungent smell.

What instrument is used to measure relative atomic mass?

Mass spectrometer.

Mole

One mole is the amount of substance that contains the same number of particles as there are atoms in 12.0 g of carbon-12.

Metal oxide + acid -> ?

metal oxide + acid -> salt + water MgO(s) + 2HCl(aq) -> MgCl2(aq) + H2O(l)

Define: the standard enthalphy of neutralisation.

∆H⊖neutThe standard enthalpy of neutralisation is the enthalpy change when an acid and a base react to form one mole of water under standard conditions.

Group 2 metals with water: state key points.!*

Be and Mg do not react (though Mg does with steam). *Metals form hydrogen and a metal hydroxide. *rate of reaction increases down the group. - as ionisation energy decreases. *pH increases during reaction.

What are i.m.f.s?!

Intermolecular forces are attractions (very weak bonding) between simple covalent molecules.

What is the volume of one mole of gas at r.t.p.?!

It turns damp litmus paper blue, and can also be recognized by its pungent smell.

empirical formula

The empirical formula is the simplest whole-number ratio of the number of atoms of each element in a compound.

state standard conditions.!usually

usually 100kPa and 298K.

Compare a strong acid with a weak acid.

* A strong acid completely dissociates into ions when dissolved in water (weak acids only partially). *Strong acids have higher electrical conductivity than weak acids. * Strong acids have a low pH (1 or 2) and weak have a higher pH (3-6). * Strong acids are very corrosive (weak acids are less corrosive). * Strong acids react more quickly than weak acids.

How does a mass spectrometer work?!

* Ionisation: the gaseous atoms are bombarded with electrons - which knock out an electron per atom - forming postively charged ions. *Acceleration - accelerated by an electric field. *Deflection - deflected by a magnetic field - lightest ions are the most deflected. *Detection: the detector detects ions and their masses. *info is printed out (graph).

What are three factors that affect ionisation energy?

* atomic radius * nuclear charge * electron shielding

What are the colors of Chlorine, Bromine, and Iodine?!

*Chlorine = green *Bromine = orange volatile liquid *Iodine = grey/purple solid.

What are/were CFCs used for and why?!

*Refrigerants *Propellants *Solvents etc. They seemed ideal due to their unreactive, non-flammable, boiling point being about room temperature and non-toxic (and dont cause corrosion) properties.

What are properties of induced dipole forces!

*The bigger the atoms the more electrons (bigger electron cloud) thus the stronger the force (and more easily it can be polarised). *They are the weakest type of i.m.f. (Note: Induced ,temporary and instantaneous dipole all mean the same thing.) *

List the three types of i.m.f.s?!

*induced dipole - induced dipole (aka Van der Waals) *permanent dipole-permanent dipole *hydrogen bonding (the strongest type of i.m.f.)

Properties of polar molecules?!

*permanent dipole foces happen between polar molecules. *higher boiling points Happens due to large difference in electronegativity between elements in the molecule. - electrons get pulled toward the more electronegative element.

Group 2 metals with oxygen: list key points.!

*tarnish in air *burn vigorously when heated in air *all form ionic metal oxides when they react with oxygen.

If the electronic configuration of an element is 1s^2 what is meant by 1, s and 2?

1 is the principal quantum number; s is the subshell; and 1 is the number of electrons in the subshell.

What is the order of repulsion with regard to electrons?!

1. lone pair-lone pair (greatest repulsion) 2. bonding pair-lone pair 3. bonding pair-bonding pair (least repulsion - but still quite a bit of repulsion)

What is the maximum amount of electrons in a "d" subshell?!

10

What is the maximum amount of electrons in a "f" subshell?!

14

What is the maximum amount of electrons in a "s" subshell?!

2

What is the maximum amount of electrons in a "p" subshell?!

6

Define: cation.

A cation is a positive ion formed from the loss of electon(s).

What happens to a strong acid as it dissolves in water?

A strong acid completely dissociates into ions when it dissolves in water.

If an acid reaches equilibrium does that mean it is a weak acid or a strong acid?

A weak acid, as it is able to reach equilibrium because the acid does not dissociate into ions completely (so there is always leftover reactant). ethanoic acid:CH3COOH(aq) <=> H+(aq) + CH3COO-(aq)

An acid does what when it reacts? Therefore an acid is...?

Acids give up H+ ions when they react. Therefore acids are proton donors.

How can you tell there is a double bond present?!

Add bromine water (aqueous bromine). The solution will turn from orange to colorless if a double bond is present. (addition reaction)

What is an alkali?

Alkali's are soluble bases.

Define: anion.

An anion is a negative ion formed by the gain of electron(s).

Define: electrophile.

An electrophile is an electron pair acceptor.

Define: ionic bond.

An ionic bond is the electrostatic attraction between positive and negative ions.

Define: isotope.

An isotope is an atom of the same element (with the same atomic number thus) that has a different mass. Isotopes have the same number of protons but different number of neutrons.

Define: molecular orbital.

An orbital is the area of space where an electron is most likely to be found.

Define: Bond enthalpy.

Bond enthalpy (E) is the energy required to break one mole of a particluar type of bond in gaseous molecules under standard conditions. Standard conditions being 298K, 100kPa.

How can you tell the difference between the halogens?!

Chlorine is a pale green solution. Bromine and iodine are both brown ,however, so: Use a few drops of hexane. *Bromine = orange/red layer *Iodine = purple layer

concentration = ?

Concentration = (mass in grams) / (volume in dm^3) or concentration = (# of moles) / (volume in dm^3)

What is cracking and what are two different types of cracking?!

Cracking splits longer chain molecules into more useful shorter chain molecules. *Thermal cracking - uses heat to split *Catalytic cracking - uses a catalyst to split

Define: electronegativity.

Electronegivity is the power of an atom to attract electrons towards itself in a covalent bond.

What is equilibrium? And what do you see?!

Equilibrium is the state of balance where the concentrations (or pressures) of reactants and products remain constant. There is both a forward and backward reaction going on continuously. At a microscopic scale the equilibrium is dynamic (constantly changing). Macroscopically nothing can be seen as the forward and backward reaction are happening at the same rate so no overall change can be seen. Pressure/concentration stay constant.

What is the most electronegative element?

Flourine (4.0)

What is the structure of polymers or silicon dioxide? List the properties of this structure and state why these properties exist.!

Giant Molecular (Covalent) - covalent bonding. *generally do not conduct electricity *can be very hard - they have strong covalent bonds *high melting/boiling points - due to these strong covalent bonds. *

What structure does diamond have, list diamond's properties and state why it has these properties.!

Giant molecular (covalent) structure. *Diamond is an allotrope of carbon. *has very high melting/boiling points - due to very strong covalent bonding. *insoluble in water - no charges to interact with polar water molecules. *very hard - each atom is strongly bonded to 4 others. *does not conduct electricity - complete covalent bonding and thus no charge movement.

What is the structure of graphite. List graphite's properties and state why it has these properties.!

Giant molecular (covalent) structure. *allotrope of carbon *conducts electricity - due to delocalised electrons between layers. *covalent bonding within layers and thus strong there, but only weak i.m.f.s between layers (induced dipole-induced dipole) so layers break off easily.

What is the ionic equation for neutralisation?

H+(aq) + OH-(aq) -> H2O(l)

Define: Hess's law.

Hess's law states the total enthalpy change for a reaction is the same for any reaction route, provided that the starting and finishing conditons are the same.

Which of the following is a strong acid, and which is a weak acid? *Hydrochloric acid *Ethanoic acid

Hydrochloric acid is a strong acid. Ethanoic acid is a weak acid.

Name the structure of NaCl and list the properties and state why it has these properties.!

Ionic structure / ionic bonding. -Giant 3D lattice. *high melting poins & boiling points - due to strong electrostatic attraction between positive and negative ions. *often soluble in water - ions interact with H2O dipoles. *Conduct electricity in molten + aqueous state (not as solids!) - ions can move and carry charge in these states.

Le Chatelier's Principle

It states that if a closed system at equilibrium is subject to a change, the system adjusts itself and so minimises the effects of the change.

Hess's Law

It states the enthalpy change in making given products from given reactants is the same whatever route is taken, provided that the conditions do not change. ∆Hfθ = ∆H1 - ∆H2 ∆H1 = ∆H2 + ∆H3

What is used to test for CO2? Give equation. What happens if too much CO2 is added?!

Lime water: calcium hydroxide. Ca(OH)2(aq) + CO2(g) -> CaCO3(s) + H2O(l) (turns cloudy as CaCO3 is formed) If too much CO2 is added then the the precipitate redissolves. CaCO3(s) + CO2(g) + H2O(l) -> Ca(HCO3)2(aq)

Shapes: 2 bonds (no lone pairs)!

Linear (thus planar)

Name the structure and list the properties of a metal and state why it has these properties.!

Metallic bonding. *High melting point -strong bonding due to delocalised electrons. *can be worked into different shapes - layers of metal ions can move over eachother. *high densitites - metal ions are packed close together. *good electrical conductors - electrons are delocalised and can flow.

List trends in electron configuration across a period and state why they exist.!*

Number of protons and electrons increase * newest electrons all enter the smame shell: so there is an increase in positive charge but no increase in electron shielding as there are no new shells. (thus also not new inner shells) *Atomic radius decreases *First ionisation energy increases *electronegativity increases (more nuclear charge - no extra shielding).

Define: Mole.

One mole is the amount of substance that contains as many particles as there are atoms in exactly 12g of carbon-12.The number of particles in one mole is 6x10^23 (Avogadro's constant.)Note: the relative atomic mass in grams of any element contains one mole of atoms.

What is the structure of I2 (Iodine), what are the properties of the structure, and state why it has these properties.!

Simple molecular structure - covalent bonding. *very low boil/melting points - due to weak intermolecular forces. *does not conduct electricity - bonding involves shared electrons (thus no charged particles) *very low densities - they are usually gases or liquids due to weak I.M.F.s

Define: Actual yield.

The Actual Yield is the amount of product that is actually made/measured at the end of the reaction.percentage yield = ( actual yield / theorectical yield ) x 100

Define: atomic number.

The atomic (proton number) is the number of protons in the nucleus.

Define: empirical formula.

The emperical formula is the simplest whole-number ratio of the number of atoms of each element in a compound.

First electron affinity

The first electron affinity is the energy released on adding one mole of electrons to one mole of gaseous atoms to make one mole of gaseous negative ions. X(g) + e- -> X-(g)

Define: First Ionisation energy.

The first ionisation energy is the energy needed to remove one mole of electrons from one mole of gaseous atoms to form one mole of ions wih a single positive charge.

Define: relative atomic mass.

The relative atomic mass (Ar) of an element is the average relative mass of its atoms -taking into account its isotopes and their abundances - compared to one atom of C-12. Its the mass of 1 mole of atoms of an element.

Define: Relative molecular mass.

The relative molecular mass of a compound is the mass of its fomula unit - relative to 1/12 the mass of an atom of carbon-12.

Define: Second electron affinity.

The second electron affinity is the energy needed to be taken in (its endothermic thus) in order to add a second electron to an atom.

What is the difference between the strength of an acid and its concentration?

The strength refers to the type of acid: and each type of acid can be diluted to different concentrations. Therefore a strong acid can be of lesser concentration than a weak acid, and yet it is still a strong acid.(Note: However to compare the types of acids fairly it is best to use the same concentration.)

Define: theoretical yield.

Theoretical yield is the maximum amount of product that can be made from the available reactancts. (This is calculated from the amounts of the reactants using the balanced equation.)percentage yield = ( actual yield / theorectical yield ) x 100

Change of state: when do i.m.f.s break?!*

They partially break when in liquid state - molecules are allowed to move over eachother in liquid state. *In gase state the i.m.f.s are broken completely as molecules seperate to form gas. (That's why boiling takes a lot of energy input.)

Define: isotopes

atoms of the same element with different numbers of neutrons, and so different nucleon numbers. Isotopes have the same number of protons but different number of neutrons.

What is the formuala for the enthalpy change of water? What is the specific heat capacity of water?!

enthalpy change (q) = m x c x ∆T m = mass c = specific heat capacity of water which is 4.2 J/gK ∆T = change in temperature

Why are CFCs bad?!T

hey are responcible for the depletion of ozone in the stratosphere. Because they are unreactive they reach the stratosphere rather than breaking up in the lower atmosphere. (They are so unreactive due to the C-F bond being extremely strong.) The UV radiation finally does break the bond and this produces Cl* free radicals. These catalyse the breakdown of the ozone. Cl* + O3 → ClO* + O2 ClO* + O3 → Cl* + 2 O2 etc. Takes a very long time before the termination reaction takes place. more saturated molecules are more reactive and thus somewhat better (used as replacements) such as HFCs and HCFCs.

Electrophile

is an electron deficient species that can form a new covalent bond by accepting an electron pair and is attracted to areas of negative charge.

Nucleophile

is an electron rich species with a lone pair of electrons that can form a new covelant bond by donating a pair of electrons to the electron deficient carbon atom, and is attracted to areas of positive charge.

Relative atomic mass

is the average mass of one atom compared to 1/12 the mass of the carbon-12 isotope.

ionic bond

is the electrostatic attraction between the oppositely charged ions formed by transfer of one or more electrons from one atom to another.

First Ionisation Energy

is the energy required to remove one electron from each atom in one mole of gaseous atoms to make one mole of gaseous ions with one positive charge. example: X(g) -> X+(g) + e-

Relative isotopic mass

is the mass of an isotope of an element compared to 1/12 the mass of the carbon-12 isotope.

atomic number or proton number

is the number of protons in the nucleus of an atom

Electronegativity

is the power of an atom to attract bonding electrons towards itself in a covalent bond.

mass number or nucleon number

is the total number of protons and neutrons in the nucleus of an atom

Heterolytic fission

is when a covalent bond is broken, the shared pair of electrons are taken by one of the atoms.

Metal + acid -> ?

metal + acid -> salt + hydrogen Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)

Why? Metal oxides are basic and bases neutralise acids ^^.metal carbonate + acid -> ?

metal carbonate + acid -> salt + water + carbon dioxide. MgCO3(s) + 2HCl(aq) -> MgCl2(aq) + H2O(l) + CO2(g)

metal hydroxide + acid -> ?

metal hydroxide + acid -> salt + water NaOH(aq) + HCl(aq) -> NaCl(aq) + H2O(l)

List trends in electron configuration down a group and state why they exist.!*

number of protons and electrons increase - thus increase in atomic radius. * more inner electron shells - thus more shielding of the nucleus -thus less attractive force between outer electrons and the nucleus so: > first ionisation decreases > electronegativity decreases

What is the formula for the ideal gas law?!

p x V = n x R x T p = pressure (Pa) V = volume (m^3) n = # of gas moles R = gas constant = 8.31 J/K mol T = temperature (K) assuming its an ideal gas.

Bond energy

the energy required to break 1 mole of those bonds under standard conditions in the gas state. Bond energy values are endothermic.

Define: nucleon (mass) number.

the sum of the numbers of protons and neutrons

Standard enthalpy change of combustion

∆H⊖c is the enthalpy change when 1 mole of a substance is completely burnt in oxygen at 298K and 1 atm pressure.

Define: the standard enthalpy change of combustion.

∆H⊖cThe standard enthalpy change of combustion is the enthalpy change when one mole of a substance burns completely in oxygen under standard conditions.

Standard enthalpy change of formation

∆H⊖f is the enthalpy change when 1 mole of a substance forms from its elements in their standard states at 298K and 1 atm pressure.

Define: the standard enthalphy change of formation.

∆H⊖fThe standard enthalpy of change of formation is the enthalpy change when one mole of a compound is formed from its elements under standard conditions.

Standard enthalpy of neutralisation

∆H⊖neut is the enthalpy change when 1 mole of water is formed from the reaction between an acid and a base at 298K and 1 atm pressure.