Test 1: Analytical Chemistry ✅ Flashcards
How are chemical analysis methods classified?
Classical methods:
- gravimetric methods (measure the mass of the analyte)
- titrimetric methods (measure the quantity of a reagent needed to completely react the analyte)
Instrumental methods:
- automated methods (use an instrumental technique to assay the amount of sample)
What is teh SI unit of mass?
kilogram (kg)
What is the SI unit for measuring the amount of substance?
mole (mol)
What is the SI unit for measuring the volume?
cubic meter (m^3)
What is a “chemical equivalent”?
The amount of a substance which will either:
- react with or supply 1 mole of hydrogen ions (H+) in acid-base reactions,
- react with or supply 1 mole of electrons in redox reactions.
What is the historical definition of a “chemical equivalent”?
The amount of substance that will react with:
- one gram of hydrogen,
or
- eight grams of oxygen,
and
- attatch or exchange one mole of electrons
How to calculate an elements equivalence?
E=A/n
A= elements atomic mass
n= number of bonds the atom makes in the compound
How to calculate compound equivalence?
E=M/(n * v)
M- compounds molar mass
v- valence of atoms, ions, radicals which participated in the exchange reactions
n- number of these atoms, ions, radicals
How to calculate oxidizer’s (reducer’s) equivalent?
E=M/e
E= equivalence
M= compounds molar mass
e= attatched by oxidiser or release by reducer electron number
What is the law of conservation of mass?
In an isolated or closed system, the mass of reactants in the beginning must be equal to the mass of the products in the end.
What is the mass-energy equivalence law?
e=mc^2
Neither mass or energy are conserved seperately. They can be traded one for another and the total “mass energy” will be conserved.
What is the law of definite proportions?
Every chemical compound contains a fixed and constant proportions (by weight) of its constituent elements.
What is the law of multiple proportions?
When two same elements combine to form more than one compound, the ratios of the mass of one element in the first compound to its mass in the second compound can always be expressed as ratios of whole numbers.
What is the law of combining volumes?
Under constant pressure and temperature, the ratio of the volumes of gases consumed or produced in a chemical reaction is equal to the ratio of simple whole numbers
What is avogadros law?
Equal volumes of all gasses under the same conditions of temperature and pressure will contain equal number of molecules.
22.4 liters of any gas contains 6.02 * 10^23 molecules
What is the law of equivalent proportions?
The proportions in which two elements seperately combine with a third element are also the proportions in which they combine together.
m1/m2 = E1/E2
m1,m2= mass of reactants
E1,E2= equivalents of reactants
How are volumetric methods of titrations classified?
- neutralization
- precipitation
- complexometry
- redoxometry
What is a standard solution?
A solution containing a precisely known concentration of an element or a substance.
What is a titrated solution?
A known quantity of the analyte (the unknown solution).
What is the equivalence point?
The moment when the reactants have reacted completely, with no excess or defecit of either the analyte or the titrant.
What is the mathematical expression of the equivalence point?
moles of base initial = moles of acid added
How to calculate the concentration of titrated solutions?
molarity (M) of the acid x volume (V) of the acid = molarity (M) of the base x volume (V) of the base
How to calculate the molarity of an acid or base?
the number of gram moles of reagent contained in one liter of solution.
CM=nA/V
Explain the strong acid and strong alkali titration. What colour change? What indicator is used for a strong acid and strong alkali titration?
strong acid = red
decreasing acid amount = orange
ending point (neutralization) = yellow
NaOH + HCl –> NaCl +H20
equivalence point = 7
indicator: methyl orange
Explain the strong base and strong acid titration. What colour change? What indicator is used for a strong acid and strong alkali titration?
colour change: yellow to orange
indicator: methyl orange
Explain the weak acid and strong alkali titration. What colour change? What indicator is used for a strong acid and strong alkali titration?
equivalent point: pH>7
indicator: phenolophtalein
acid= clear, neutral= light pink, base=dark pink
colour change: clear –> purple pink
How to calculate molarity?
the number of gram moles of reagent that is contained in 1L of solution.
Cm=n/V
n= number of moles
V= volume of solution
How to calculate normality?
Cn=m/(E * v)
m= solutes mass (g)
E= solutes equivalent
V= solutions volume
How to calculate percent concentration?
C%=m(substance)/m(solution) * 100%
m= mass
How to calculate the titer?
T=Cn * E / 1000 g/ml
How to calculate molar concentrations from data from a titration?
Cn1 * V1 = Cn2 * V2
Cn= concentration of equivalent (normality)
V= volumes
What is a complex compound?
A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the coordination centre, and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents.
Explain complex compound nomenclature.
- coordination number (greek): mono-, di-, tri-, etc.
- ligand
- name of metal ion with valence indicated
What is coordination?
When an orbital from a ligand with a lone pair of electrons overlaps with an empty orbital from a metal.
What is a coordination number?
The number of atoms or ions immediately surrounding a central atom in a complex or crystal.
What are Werners coordination theory points?
- the central metal atom exhibits the primary valency (oxidation state), and teh secondary valency (coordination number).
- every metal atom has a fixed number of secondary valencies (coordination numbers).
- The coordination number (secondary valencies) are always directed towards the fixed positions in space, leading to definite geometry.
- the central metal and its directly bonded ligands, make up the coordination sphere of the complex.
What is complexometry?
titrimetric method based on reactions of complex compund formation.
What is a complexone?
Any chelating agent used for the analytical determination of metals.
They form stable complex compounds with metals called complexonates.
Whta is a chelating agent?
an organic compound which complexes or sequesters metal ions.
What is EDTA and Trilion B used for in complexometric titrations?
determining water hardness
What are the two types of water hardness?
1) temporary (carbonate hardness: Ca(HCO3)2 and Mg(HCO3)2 )
2) permanent (non-carbonate hardness: Ca2+ and Mg2+)
What are the two salts causing temporary water hardness?
Ca(HCO3)2
Mg(HCO3)2
What is water softening?
The elimination of calcium and magnesium salts from water.
How can temporary water hardness be eliminated? State equations.
1) BOILING:
- Ca(HCO3)2–> CaCO3 + H2O + CO2
- Mg(HCO3)2 –> MgCO3 + H2O + CO2
2) SLACKED LIME (CALCIUM HYDROXIDE):
- Ca(HCO3)2 + Ca(OH)2 –> CaCO3+ 2H2O
- MgSO4 + Ca(OH)2 –> Mg(OH)2 + CaSO4
3) SODA:
- CaSO4 + Na2CO3 –> CaCO3 + Na2SO4
4) SODIUM PHOSPHATE:
- 3CaCl2 + 2Na2PO4 –> Ca3(PO4)2 + 6NaCl
5) BORAX:
- CaCl2 + Na2B4O7 –> CaB4O7 + 2NaCl
softened by IONITES (EXCHANGERS)
- sodium and hydrogen cationites
How is total water hardness determined? What indicator? What colour change?
direct titartion with EDTA of Ca2+ and Mg2+ together at pH=10 (NH3 buffer).
indicator: Eriochrome black T
colour change: Red to Blue
How is the temporary water hardness determined and calculated?
Temporary hardness is determined by finding the alkalinity of water before boiling and that left after boiling. This is because temporary hardness is removed on boiling.
How is the permanent water hardness determined and calculated?
The estimation of hardness is based on complexometric titration. Hardness of water is determined by titrating with a standard solution of ethylene diamine tetra acetic acid (EDTA) which is a complexing agent. Since EDTA is insoluble in water, the disodium salt of EDTA is taken for this experiment.
What are the different methods of redoximetry?
1) Half reaction method
2) Oxidation number method
how to classify the different redoximertry methods?
Qualitative analysis of irreversible reactions.
- lyophyllic colloids are reversible in nature (stable and do not precipitate easily.
- lyophobic colloids are irreversable in nature (less stable).
Qualitative analysis of analytical reactions in electrolyte solutions.
Analytical signals of irreversable reactions.
Ions in electrolyte solutions can react reversibly. All other reactions are irreverable.
Reactions of flame coloration:
- sodium
- potassium
- calcium
- strontium
- barium
- lead
- copper
sodium - bright yellow
potassium - pale violet
calcium - brick red
strontium - crimson (rich, deep red color)
barium - green
lead - blue
copper - green / blue
What is a solution?
A solution is a homogeneous mixture of one or more solutes dissolved in a solvent.
How are solutions classified?
According to:
1) PHYSICAL STATE
2) ELECTRICAL CONDUCTIVITY: electrolytes (eg. salt) vs non electrolytes (eg. sugar).
saturated
unsaturated
supersaturated
What is a true solution?
A true solution is a homogeneous mixture of two or more substances in which the particle size of the material dissolved (solute) in the solvent is less than 10-9 m or 1 nm.
particles cannot be filtered and are not visible by the naked eye
eg. sugar and water
What is the solute? What is the solvent?
solute- what is dissolved
solvent- most abundant, the dissolving agent
What is solubility?
Solubility describes the amount of solute that will dissolve in a specified amount of solvent.
completely soluble = miscible
insoluble - immiscible
What effects solubility?
- nature of solute and solvent (polarity)
- temperature (increase in temperature, increases solubility)
- pressure (as pressure increases, solubility increases (for GASES)) (little effect for liquid in liquid and solid in liquid)
polarity depends on asymmetry and the difference in electronegativity.
What factors affect the rate of solubility?
- particle size
- temperature
- concentration
- agitation (movement/stirring)
How to calculate the concentration of a solution? Units?
amounts: masses, moles or liters
dilute
concentrated
mass % of component = mass of component / total mass solution * 100%
How to calculate the molarity of a solution?
M= number of moles of solute / liter of solution = moles/liter
How to calculate the molality of a solution?
molality=concentration
m=mol of solute/kg of solvent
How to calculate the mole fraction of a solution?
Xa=na/na+nb+nc+nd+ne…+nx
the sum of all mole fractions must equal 1.
What are the physical properties of true solutions?
vapour pressure
melting point
boiling point
osmotic pressure
- mixture is homogenous
- dissolved solute is molecular or ionic in size (0.1nm-1nm)
- either coloured or colourless
- solute is uniformly distributed and will not settle with time
- solute can be seperated from solvent by purely physical means such as evaporation
What is Raolt’s law?
The vapour pressure of an ideal solution is proportional to the mole fraction of solvent.
