Chapter 1: Stoichiometry Flashcards
What is relative atomic mass
Average mass of one atom of an element compared to 1/12 of the mass of a Carbon 12 atom
What is relative molecular mass
Average mass of one molecule compared to 1/12 the mass KF one atom of carbon 12 isotope
How is relative atomic/molecular mass determined from mass spectroscopy
Charged particles of different masses are separated and masses are measured. It also measure relative abundance of the masses.
A neutral atom gets charged by losing/gaining an electron.
Charged particles are deflected in electric or magnetic fields. The heaver the mass the smaller the deflection. The greater the charge the greater the deflection.
Particles of different charges and masses are deflected to follow different paths
What is instrument used in mass spectroscopy
Mad spectrometer
How does the mass spectrometer work (detail)
- substance is vaporized by heating
- vapour goes into ionization chamber. high energy electrons from cathode attract to opp anode and collide with vapor and knock off electrons to form ions
- positive ions are attracted and accelerated by electric field to magnetic field.
- in the magnetic field they deflect according to mass to charge ratio m/e
- changing magnetic field strength brings different masses onto detector eg heavy ones defect less need strong field
- detector collects the species of masses and the collected charges constitute an electric current, which are of different amounts and proportional to abundance of each mass.
- percebtage abundance is amplified and a spectrum is drawn against mass
How does the mass spectrometer work (summary)
Separates species of different masses by electrical methods
- vaporization
- ionization +ve ions
- +ions attracted and accelerated by electric field
- accelerated ions deflected by magnetic field
- focused on detector and then a chart recorder draws spectrum
How to calculate relative atomic mass from a mass spectrum?
Weighted average mass = Total mass (sum of mass×abundance) / Number of atoms (100 as of % ratio)
Why is it better to use the relative mass rather than mass number?
They yield a more accurate rather than approximate result of Ar
How is mass spectroscopy used to find relative molecular mass
- Compound is ionised to lose 1e and form +ve ion
- This ion had mass equal to Mr of the compound ie called molecular ion (highest peak)
- Other ions of lower mass/charge ratios are fragment ions
What is the Avogadro constant
6.02×10^23
Definition of mole
Any amount of substance which contain as many particles as there are carbon atoms in 12g of carbon. The number of carbon atoms in 12g of carbon are 6.02×10^23
Mass of one mole of an atom is
Number of nucleons hence mass
As molecules for compounds, what is the term for ions
Formula units
Relationship between N, L and n
N= n × L
Number of particles= Avogadro constant × number of moles
What is molar mass
Mass of one mole of any substance
Molar mass =
Ar or Mr in grams/mole
Formula for moles in terms of mass
n=m/M
Stoichiometry describes the relationship between
Amount of reactants and products during a chemical reaction and how they combine in fixed ratios
Gas volume is determined by _
No of particles at temperature and pressure.
What is Avogadro law regarding gas volume
Equal no of particles of all gases under same conditions occupy same volume irrespective of molecule size
1litre=
1dm3=1000cm3
What is the molar volume
24dm3
Formula of moles regarding volume
n=V/Mv (24)
How many dm3 in a m3
1000
How many cm3 in a dm3
1000
How are liquid amounts expressed
Concentration in g/dm3 or mol/dm3
What is a solution
Homogeneous (uniform) mixture of 2 or more substances. Solute dissolved in solvent
What is a solution
Homogeneous (uniform) mixture of 2 or more substances. Solute dissolved in solvent
What is Formula for concentration
C=n/V
What is standard solution
Solution of known concentration
As a solution is diluted with distilled water what remains the same, explain, and what changes?
Then relate this in form of a equation
No of moles remains constant; they spread through a larger volume, and thus concentration decreases
n= CV so C1V2=C2V2 (1 is initial 2 is final)
What is molarity and the symbol
Concentration expressed in mol per dm3
Ie M
What is basic titration
Concentration of a solution can be determined by volumetric analysis. This is done by reacting one solution with a standard one and determine the exact volumes that react. This is called standardizing
What is back titration and how is it done
It is done in reverse as the end point is passed and hard to identify, or one reactant is impure.
A known excess of one reactant is added and the interacted excess is determined by titrating againsts a standard solution. Subtract interacted amount from original to find amount reacted
What is theoretical yield
Maximum yield in grams/moles of a product obtained, assuming 100% of the reactants are converted to products
What is a limiting reagent
Reactant that determines the quantity of the product
so other would be in excess if not equal to make this one limiting
Formula for % yield
Experimental(actual)/theoretical ×100
Which factors make the actual yield different from theoretical?
Amount lost during preparation
Impurities in reactant
Incomplete reaction
Formula for % purity
Mass of pure substance/ mass of impure substance ×100
What is empirical formula of a compound
Simplest formula which gives the smallest whole number ratio of atoms in one molecule or formula units of a compound
What is molecular formula
Formula who’ve gives the actual number and kind of atoms in one molecule or formula unit of a compound
What is formula for molecular formula
Molecular formula = q × empirical formula
q= relative molecular mass (Mr) /relative empirical formula mass
Which is number of empirical formula units (no of multiples of empirical formula)
What is the general formula for combustion/explosion of hydrocarbons?
CxHy + x + y/4 O2 —> XCO2 + y/2 H2O
V of CO2 made= x × V of hydrocarbon used
V of O2 used= x + y/4 × V of hydrocarbon used
