21-23 Flashcards
Qualitative Analysis
Identification of a specific substance present
Quantitative analysis
The determination of the quantity of substance present
Colorimetry
Analysis by color, light emitted, absorbed or transmitted by chemical used
Gravimetric analysis
Uses stoichiometric calculations from the mass of a reagent
Titration analysis
Uses stoichiometric calculations from the volume of a reagent
Flame test
Some ions impart specific colours when subjected to flame, detect the presence of several metal ions
Solution color
Some ions create specific colours when in solution, most aqueous solutions are colourless. Solutions containing monatomic and polyatomic ions of the transition elements have a visible colour (due to ions interference with light)
Ions absorb specific wavelengths of light, % of light that is absorbed depends on concentration of that ion
Precipitates
Understanding the solubility table, we can determine what ions are in solution by whether or not a precipitate is formed
Atomic absorption spectrophotometer
Used to analyze the light absorbed by a sample vaporized in a flame, can detect minute quantities of substances
Precipitation reaction
Is a reaction where a slightly soluble product (precipitate) is formed
Limiting reagent
Reactant whose entities are completely consumed in a reaction, reaction stops when all of this reactant is used up and none remains
Excess reagent
Other reactant must be present in greater quantity, some will remain when limiting reagent has completely reacted
Titration analysis
Used to determine the amount concentration of substances in solution, the process of carefully measuring and controlling the addition of a solution (titrant) from a burette into a measured volume of another solution(sample) in an Erlenmeyer flask until the reaction is judged to be complete
Burette
Precisely marked glass cylinder with a stop cock at one end, it allows you to control and measure the volume of the reacting solution.
When doing a titration there will be a point when it is complete. Chemically equivalent amounts mole ratio will have been added
Equivalence point
Point at which the exact theoretical amount of titrant has been added to completely react with the sample, look for sudden change in observable property (color, pH, conductivity)
Endpoint
Point during a titration when this sudden change is observed, titration is stopped and the volume of titrant is determined
Standard solution
A solution of a highly certain concentration
Primary standard
A chemical that can be obtained at high purity with a mass that can be measured to High accuracy and precision, this is not possible with some chemicals
Standardizing a solution
Means finding the concentration of the solution after it is prepared by reacting with another solution that has been prepared from a primary standard, stoichiometry is used to find unknown concentration
Acid base reactions
Normally invisible in solution so it is difficult to tell just by looking when reaction is complete, use Indicators (will change color whether they are in an acid or a base) to give you an observable endpoint
Interpreting titration pH curve
When creating pH curve the addition of titrant is not stopped at the endpoint, is continued until large excess has been added will be a very rapid change in pH passing equivalence point
**equivalence point is at the centre of change where curve is nearly VERTICAL
Titration curve of acid and bases
Strong base reacting with acid, the pH abruptly changes from high to low
If titration is done in reverse pH starts low and ends high
Net ionic equations for monoprotic bases
Strong monoprotic base reactions net ionic equation will always be: OH-(aq) + H+ (aq)»_space; HOH (l)
Ions other than hydrogen/hydroxide are spectator ions
Strong monoprotic» strong monoprotic base titration
Must have a pH of 7 at equivalence point
For every other acid-base reaction equivalence point solution will contain ions or molecules that are not spectators, pH will vary depending on which entities are present in what concentration
Reading equivalence point
An equivalence point is read from a pH curve by estimating the inflection point position in the curve where it steepens.
Inflection point
Is the point where the direction of the curvature changes like the centre point of the letter S
If diprotic (reacts twice with hydrogen ions)
2 places where curve steepens, use the second equivalence point= we want pH value when reaction is complete
Choosing acid base indicators
Must plot pH titration curve, endpoint observed must match equivalence point of the reaction. Pick an indicator that will change colour across a pH range that has a central value close to pH of sample
