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Distinguish between qualitative and quantitative analysis
Qualitative analysis deals with the identification of elements, ions, or compounds present in a sample. Quantitative analysis deals with the determination of how much of one or more constituents is present
Outline the steps commonly employed in an analytical procedure. Briefly describe each step
1. Define the problem
2. Select a method
3. Obtain a representative sample
4. Prepare the sample for analysis
5. Perform any necessary chemical separations
6. Perform the measurement
7. Calculate the results and report
Distinguish between analyze, determine, sample, and analyte
An analyte is the constituent that is analyzed for, and its concentration is determined
Distinguish between a specific reaction and a selective reaction
A selective reaction is one that can occur with other substances present but exhibits a degree of preference for the substance of interest. A specific reaction is cone that occurs only with the substance of interest
Suggest a method to accomplish the following analyses: (a) the purity of NaCl in table salt, (b) the acetic acid content of vinegar, (c) the pH of swimming pool water
Describe the basic pieces of apparatus used for volumetric measurements. List whether each is designed to contain or to deliver the specified volume
1. Volumetric flasks (contain an accurate volume)
2. Pipets (deliver an accurate volume)
3. Syringe pipets (used for macro- and micro- measurements)
4. Burets (accurate delivery of solution)
Describe the principle and operation of the analytical balance
Electronic balances with a mechanical single-pan balance which sits on the arm of a movable hanger and this movable system is compensated for by a constant electromagnetic force. This current is proportional to the weight placed on the pan
Why is a microbalance more sensitive than an analytical balance?
They measure weight to a greater degree of accuracy
Explain weighing by difference
The sample is weighed, and then a portion is removed and transferred to a vessel appropriate for dissolving the sample. The weighing bottle and the sample are reweighed and from the difference in weight, the weight of the sample is calculated
Distinguish between the zero point and the rest point of a balance
The zero point is the original no-load reading and the position under load is the rest point
Describe the principles of dry ashing and wet digestion of organic and biological materials. List the advantages of each
An organic compound is decomposed by wet digestion by boiling in oxidizing acid or mixture of acids. Dry ashing is done at a high temperature in a muffle furnace and the organic matter is burned off.
What are the two principle means of dissolving inorganic materials?
Use of acids or fusion with an acidic base/flux is useful when acids do not dissolve in the sample
What set of conditions must be carefully avoided to use perchloric acid safely for digesting organic materials?
Perchloric acid should never be added directly to organic or biological material
What happens when microwave energy heats samples?
Microwaves heat by causing molecules to rotate and ions to migrate
Distinguish between accuracy and precision
Accuracy is the degree of agreement between the measured value and the true value. Precision is the degree of agreement between replicate measurements of the same quantity.
What is determinate error? Indeterminate error?
Determinate errors are nonrandom and occur when something is wrong with the measurement (can be avoided or corrected). Indeterminate errors are random and cannot be avoided
What is good laboratory practice?
Rules that must be followed for labs involved in analyzing substances that require regulation
What are SOPs?
Standard operating procedures (descriptions of activities performed by the laboratory)
What are the characteristics of a quality assurance unit?
Responsible for assuring good laboratory practices are implemented and making routine lab audits
Distinguish a technique, a method, a procedure, and a protocol
A technique is the scientific principle selected for providing compositional information. A procedure consists of the written directions necessary to utilize the method. A method is the adaptation of the technique so it is selective for the given analyte. A protocol is a set of specifically prescribed directions that must be followed, without exception, if the results are to be accepted.
What are the essential features of most method validation processes?
Technique, method, procedure, protocol
What is a z-score?
A measure of its deviation from the standard deviation of the known concentrations
Distinguish between the expression of concentration on weight/weight, weight/volume, and volume/volume bases
Define "equivalent weight", used for electrolytes in clinical chemistry. Why is this used?
Equivalent weight is the formula weight divided by the number of reacting units
List the requirements for a titration. What are the four classes of titration?
The reaction must be stoichiometric, the reaction should be rapid, there should be no side reactions, there should be a marked change in some property of the solution when the reaction is complete, there should be an end point and equivalence point, and it should be quantitative.
What is the equivalence point of a titration? The end point?
The equivalence point is the theoretically end of the titration. The end point is the observed end of the titration
What is a standard solution? How is it prepared?
A solution of known composition; prepared by combining a known solution with an unknown solution and diluting to volume.
What are the requirements of a primary standard?
1. 100% pure
2. Stable to drying temperatures
3. Readily available
4. High formula weight
5. Properties required for a titration
Why should a primary standard have a high formula weight?
A high formula weight means a larger weight must be taken for a given number of moles. This reduces the error in weighing
What is the minimum pH change required for a sharp indicator color change at the end point? Why?
What would be a suitable indicator for the titration of ammonia with hydrochloric acid? Of acetic acid with sodium hydroxide?
Explain why boiling the solution near the end point in the titration of sodium carbonate increases the sharpness of the endpoint.
What is the approximate pK of the weakest acid or base that can be titrated in aqueous solution?
What must be the difference in the strengths of two acids in order to differentiate between them in a titration?
Why is a small amount of magnesium salt added to the EDTA solution used for the titration of calcium with an Eriochrome Black T indicator?
Explain the Volhard titration of chloride. The Fajan titration. Which is used for acid solutions? Why?
What should be the minimum potential difference between two half-reactions so that a sharp end point will be obtained in a titration involving the two half-reactions?
Why cannot standard or formal electrode potentials always be used to predict whether a given titration will work?
Describe the different types of ion-selective electrodes. Include in your discussion the construction of the electrodes, differences in membranes, and their usefulness.
What is the selectivity coefficient? Discuss its significance and how you would determine its values.
Why are iodimetric titrations usually done in neutral solutions and iodometric titrations in acid solutions?
Does the end point in a permanganate titration coincide with the equivalence point? Explain and suggest how any discrepancies might be corrected
Explain the function of the Zimmermann-Reinhardt reagent in the titration of iron(II) with permanganate
Used to determine whether there is a significant difference between two methods based on their standard deviations
Used to determine if two methods are statistically different, one being a test method and the other being an accepted method
Used to determine if an "outlier" is due to a determinate error. If it is not, then it falls within the expected random error and should be retained
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