Module 2 - chapters 2 and 3 Flashcards
What is valency?
Valency is just the number of electrons the atom loses or gains (if ionic) or the number of bonds it can form (if covalent).
What are two isotopes of hydrogen?
Deuterium and Tritium
How do the compounds of hydrogen’s isotopes with oxygen compare with water?
Deuterium oxide (heavy water) cannot sustain life. Tritiated water is a radioisotope used to detect how much fluid a patient passes.
What is the difference between relative molecular mass and relative formula mass?
Relative molecular mass is used for simple molecules, relative formula mass is used for giant structures.
How do you calculate relative atomic mass of an element from relative abundances of its isotopes?
1) Calculate the total mass of each isotope in the sample. (total mass of isotope = relative isotopic mass x abundance)
2) Add together all the masses to give the sum of the isotopic masses.
3) Add together the abundances to give the sum of the abundances.
4) Relative atomic mass = sum of isotopic masses/sum of abundances.
How many particles are there in 1 mole?
6.02 x 10 ^23
What is Avogadro’s constant?
6.02 x 10^23, the number of particles per mole.
What is molar mass?
Molar mass is the mass per mole of a substance.
What are the units for molar mass?
g mol-1
How many moles is it if there is exactly the same amount of an atom or molecule as its atomic mass?
1 mole
e.g. 16g of an oxygen atom = 1 mole
and 32g of an oxygen molecule is 1 mole.
32g of oxygen ATOMS would be 2 moles.
How do you calculate molecular formula?
1) Work out the Mr of the molecule with the empirical formula you have calculated.
2) Divide this Mr into the molecular mass (mass for one mole) value given in the question
3) This gives you a value of how many times bigger the actual molecule is – multiply all of the atoms in the empirical formula by this figure.
what is a hydrated salt?
a crystalline compound containing water molecules
What is an anhydrous salt?
a salt containing no water molecules
what is water of crystallisation?
water molecules that are bonded into a crystalline structure of a compound
what is an example of an investigation investigating water of crystallisation?
blue copper sulphate heated to white copper sulphate and steam - this is a reversible reaction
how do you calculate the formula of a hydrated salt?
1) Find the mass of water in the crystals driven off by heating by minusing the mass of the anhydrous salt from the hydrated salt.
2) Work out the moles of water
3) Work out the moles of the anhydrous salt
4) Calculate the ratio of moles of salt to water
5) Convert the ratio to a whole number (divide by the smallest number)
6) Devise the formula of the hydrated salt (including the water of crystallisation) using the ratio
what volume does 1 mole of any gas occupy at room temperature and pressure (RTP?)
24dm^3
what is the molar gas value at RTP?
24dm^3mol^-1
What apparatus can be used to measure volume of gas?
gas syringe or upturned measuring cylinder
What are the factors which may affect pressure?
volume and temperature
what is the ideal gas equation?
PV = nRT (n= PV/RT)
What units must pressure be in for the ideal gas equation?
Pa
What units must volume be in for the ideal gas equation?
m^3
What units must temperature be in for the ideal gas equation?
K (kelvin)
What units must R be in for the ideal gas equation?
jmol^-1 K^-1
What are the assumptions for the molecules making up an ideal gas?
- random motion
- elastic collisions
- negligible size
- no intermolecular forces
how do you convert from cm^3 to m^3?
x10^-6
how do you convert from dm^3 to m^3?
x10^-3
how do you convert from C to K?
+273
how do you convert from KPa to Pa?
x10^3
What is the equation for percentage uncertainty?
number of critical measurements taken x uncertainty / mass of salt (for example for mass balance)
x 100
what is the uncertainty of the mass balance?
+- 0.01
what is the uncertainty of the gas syringe?
1cm^3
what is the equation for percentage error?
(difference in Mr / actual Mr) x 100
What is atom economy a measure of?
How much of the products are useful
How do you calculate atom economy?
(Mr of desired product/ sum total of Mr for all products) x 100
What is meant by a reaction having a low atom economy?
Few atoms in the reactants have been converted into the desired product
Why is a high atom economy desirable?
- reduces the production of unwanted products
- makes the process more sustainable
With what type of reaction is 100% atom economy not possible?
Substitution reactions
How do you calculate percentage yield?
Actual yield (amount of product made) / theoretical yield
x100
What is the difference between percentage yield and atom economy?
% yield is the amount of product you actually make as a % of the amount you should theoretically make, atom economy is the mass of the product you want as a % of the mass of all the products made.
What does molarity mean? What are its units?
An alternative term for concentration, units for molarity = M (1moldm^-3 = 1 M)
How do you calculate the concentration of a diluted solution?
- divide the volume of stock solution used (the solution before solution) by the final volume of diluted solution made
- multiply this value by the concentration of the stock solution used
Why might we have an unknown concentration of solution to titrate?
The solute used to make the solution may absorb water or carbon dioxide from the atmosphere
What makes a standard solution of a primary standard?
Made from a pure and anhydrous solid which is stable in storage and does not decompose when dissolved in water
What is another way of saying titration?
Volumetric analysis
Which results from a titration should be used to calculate the mean titre?
The two most concordant results - values within 0.1 of each other
How do you construct ionic equations?
1) write all soluble ionic compounds with the ions separated
2) write all insoluble ionic compounds and all covalent compounds in the usual manner
3) cross out ions which appear on both sides of the equation - these are spectator ions.
State symbols must be included
What are spectator ions?
Ions which are not changed during the reaction (don’t change state or bond with anything)
What are two points which question the accuracy of the experiment with hydrated salts?
- assumed that all of the water has been lost, only see the surface of the crystals, water may remain inside the crystals, heat to a constant mass to reduce this
- assumes that there is no further decomposition, many salts decompose further with heating - if heated strongly copper (II) sulphate decomposes to form copper (II) oxide.
What is a standard solution?
A solution of a known concentration
What is atmospheric pressure?
110KPa (1atm)
What is room temperature regarded as for the ideal gas equation?
20C (different to standard conditions temperature)
Why is theoretical yield difficult to achieve?
- reaction may not have been complete
- other reactions (side reactions) may have taken place alongside the main reaction
- purification of the product may result in loss of some product
How do you convert atm to Pa?
x100,000
how does the mass of an electron compare to the mass of a proton?
1/1836th of the mass of a proton
alternative name for mass number
nucleon number
what is the mass defect?
the small amount of mass lost due to the strong nuclear force holding together protons and neutrons
what is a binary compound?
a compound containing only two elements
the name is the first element and then the second element but with the second element’s name ending in “ide”, the metal ion always comes first in ionic compounds. e.g. sodium oxide
what are polyatomic ions?
an ion containing atoms of more than one element bonded together, e.g. ammonium ion
what is the formula of a phosphate ion?
PO₄³⁻
what is the formula of a nitrite ion?
NO₂⁻
what is the formula of a sulfite ion?
SO₃²⁻
what is the formula of a hydrogencarbonate ion?
HCO₃⁻
what is the formula of a dichromate (VI) ion?
Cr₂O₇²⁻
what is the formula of a manganate (VII) (permanganate) ion?
MnO₄⁻
what are diatomic molecules?
molecules containing two atoms bonded together e.g. H₂, P₄, S₈
how do you take the limiting reagent into consideration in calculations?
calculate the moles of each reactant and compare to the equation,
e.g. if one reactant (hydrogen) requires 2 moles in the equation and another reactant requires 1 mole in the equation (oxygen) but you have the same amount of moles of both reactants then hydrogen is the limiting reagent and so equations must be based on hydrogen as only half of the oxygen will react
state the key points for making a standard solution
- dissolve solute in small amount of solvent
- transfer to volumetric flask and rinse all apparatus adding to flask
- make up solution to calibration (volume graduation) mark (bottom of meniscus on line)
- add stopper and invert to make miscible
key points for diluting a concentrated solution
- transfer required volume of stock solution to volumetric flask using glass pipette
- add solvent to flask to calibration (volume graduation) mark on flask
- stopper and invert
how to improve the accuracy of measuring the volume of gas produced by a reaction
- prevent gas escaping before the bung is in place (use a bung with two capillary tubes for a closed system)
- prevent gas dissolving in water of upturned measuring cylinder (use gas syringe)
solubility of all common sodium, potassium and ammonium salts
soluble in water
solubility of all nitrates
soluble in water
solubility of chlorides
most soluble in water except silver and lead chlorides
solubility of sulfates
soluble except lead, barium and calcium sulfates
solubility of carbonates
most insoluble except sodium, potassium and ammonium carbonates
solubility of hydroxides
most insoluble except sodium, potassium and ammonium hydroxides
why are neutrons required in the nucleus?
to prevent the positive neutrons from repelling each other
do isotopes of an element have different chemical/physical properties?
same chemical properties because have the same number of electrons, higher mass isotopes may have higher mpt/bpts and densities
