Amount Of Substance Flashcards
Define relative atomic mass (Ar)?
RAM is the average mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12
What is the formula for calculating Ar?
Ar= Average mass of an element
————————————————
1/12 the mass of 1 atom of carbon-12
Define relative formula mass (Mr)?
Mr is the sum of the Ar’s of all the atoms in a molecule
What is the formula to calculate Mr?
Add up all the Ar in the compound
What is 1/12 the mass of 1 carbon-12 atom?
1
One mole of carbon-12 atoms has a mass of?
12.000g
State Avogadro’s constant?
6.023 x 10 23( the power)
State the ideal gas equation
PV=nRT
P=pressure
V=volume
n=moles
R=gas constant
T=temperature
State the gas constant
8.31JK-1mol-1
Why can gas be liquified ( under the right conditions)?
In ideal gas there are no intermolecular forces so particles are not attracted to each other whereas in real gas attractive intermolecular forces divert the paths of particles.
What is Boyle’s law?
At constant temperature (T) the volume (V) of a fixed mass of gas is said to be inversely proportional to the pressure (p) applied to it
P x V= constant
State Charles law?
At constant pressure the volume of a fixed mass of gas is proportional to its temperature
V= constant x T
What is the absolute zero temperature and how was it proved?
-273.15*C
FOUND by plotting volumes of most gases against temp and extrapolating which shows that they all reach zero volume at the same temperature
You must always convert to Kelvin (K) when doing idea gas equations, how do you do that?
+273 to anything with a degrees Celsius
Define empirical formula?
The simplest whole number ratio of atoms of each element that are in a compound
What is theoretical yield?
The expected quantity of a product from a perfect chemical reaction
Define Actual yield ?
The actual amount of product produced after a reaction
What is the formula to calculate percentage yield?
Percentage yield = (actual yield/ theoretical yield ) x 100
What is percentage atom economy?
A way to compare the maximum mass of a product that can be obtained with the mass of the reactants
What is the formula for percentage atom economy?
PAC= (molecular mass of desired product/ sum of molecular masses for all reactants) x 100
Define spectator ions?
Ions that appear unchanged on both sides of the ionic equations
How do you calculate conc with moles and volume?
Conc= moles/vol
What is a volumetric solution and how do you make it?
A solution where the precise conc is known.
Calculate the Mf then dissolve a known volume of the solution which will be the conc
How to calculate the molecular formula?
Find the moles of each element in the compound then divide them all by the smallest mole then put those values into a molar ratio
What type of bonding is the in sodium azide? Why does it have a high melting point?
Ionic bonding
It has a high melting point because oppositely charged ions require lots of energy to overcome strong attractions between ions
What is the correct formula for magnesium azide?
MgN6
Give a formula for a molecule that has the same number of electrons as the azide ions
CO2
Write an equation for the therm decomposition of zinc carbonate to zinc oxide
ZnCO3 —> ZnO +CO2
A green solution, X, is thought to contain [Fe(H2O)6]2+ ions.
(a) The presence of these ions can be confirmed by reacting separate samples of
solution X with aqueous ammonia and with aqueous sodium carbonate.
Write equations for each of these reactions and describe what you would observe.
[Fe(H2O)6]2+ + 2NH3 →Fe(H2O)4(OH)2 + 2NH4+
Green precipitate
[Fe(H2O)6]2+ + CO3
2− → FeCO3 + 6H2O
Green precipitate
A 50.0 cm3 sample of solution X was added to 50 cm3 of dilute sulfuric acid and
made up to 250 cm3 of solution in a volumetric flask.
A 25.0 cm3 sample of this solution from the volumetric flask was titrated with a
0.0205 mol dm−3 solution of KMnO4
At the end point of the reaction, the volume of KMnO4 solution added was 18.70
cm3
.
(i) State the colour change that occurs at the end point of this titration and give a
reason for the colour change.
Colourless / (pale) green changes to pink / purple (solution)
Just after the end−point MnO4
− is in excess / present
Write an equation for the reaction between iron(II) ions and manganate(VII) ions. Use the equation and the information given to calculate the concentration of iron(II) ions in the original solution X.
MnO4
− + 8H+ + 5Fe2+
→ Mn2+ + 4H2O + 5Fe3+
Moles KMnO4 = 18.7 × 0.0205 / 1000 = (3.8335 × 10−4)
Process mark
1
Moles Fe2+ = 5 × 3.8335 × 10−4 = 1.91675 × 10−3
Mark for M2 × 5
1
Moles Fe2+ in 250 cm3 = 10 × 1.91675 × 10−3 = 0.0191675 moles in 50
cm3
Process mark for moles of iron in titration (M3) × 10
1
Original conc Fe2+ = 0.0191675 × 1000 / 50 = 0.383 mol dm−
Outline the method that the student should use for recrystallisation
Dissolve the product in the minimum volume of hot solvent
Allow solution to cool and allow crystals to form
Filter off the pure product under reduced pressure
How you would carry out a sample laboratory process to show that the recrystallised product is a pure sample
Measure the melting point
Use of melting point apparatus
Sharp melting point
Suggest two reasons as to why the percentage yield for this reaction may not be 100%
1.Sample was still wet
2.Product left in beaker or glassware
Explain why the student might prefer to use Ethanoic anhydride, even though it has a slower rate of reaction
An identified hazard of ethanoyl chloride
HCL not released when Ethanoic anhydride used
As a droplet from the funnel could enter the burette
Air bubble in jet or witte
Ensures all reagents are able to react / mix / come into contact
Accept no reagent is left unreacted on sides of flask
The added water does not affect the mols / amount of reagents / reactants / solution Z
