Understand qualitative analysis

Students usually identify the existence of anions such as carbonate, iodide and sul-fate(VI) by adding a barium/silver(I)/lead(II) solution to the unknown, followed by a dilute acid or vice-versa in qualitative analysis practical work sessions and examinations. Mat r students had difficulty understanding the roles of the bar-ium/silver(I)/lead(II) solution and the dilute acid in the tests for anions. For example, 20% believed that the addition of aqueous barium nitrate(V) followed by dilute nitric(V) acid was to test for sulfate(VI) only. Another 25% believed that to test for a carbonate, acid had to be added directly to the unknown sample, while 20% believed that the addition of barium nitrate(V) invalidated the test for carbonates. When the students were asked the purpose of adding dilute nitric(V) acid following die addition of silver nitrate(V) solution (in one question) and lead(II) nitrate(V in another question) to the unknown solutions, 22% and 35%, respectively, indicated... 

The section on tests for eations is used to illustrate the QATP. Students need to have tacit knowledge of the phenomena involved in qualitative analysis, reagents and apparatus, and to eonstruet explanations of the phenomena at the sub-microscopic level and to write equations to deseribe them. To help students understand precipitate formation, they are instraeted to compare the behaviom of two solutions, sodium chloride and iron(lll) ehloride when aqueous sodium hydroxide is added to the solutions (Fig. 6.1). The students will observe that there is no visible reaction with the sodium chloride solution, but a brown precipitate will be formed in the... 

Tan, K. C. D., Goh, N. K., Chia, L. S., Treagust, D. F. (2002). Development and application of a two-tier multiple choice diagnostic instrument to assess high school students understanding of inorganic chemistry qualitative analysis. Journal of Research in Science Teaching, 39(4), 283-301. 

Seven chemical reactions were identified from the chemistry syllabus. These chemical reactions were selected because they were frequently encountered during the 2-year chemistiy course and based on their importance in understanding concepts associated with three topics, namely, acids, bases and salts, metal reactivity series and inorganic chemistry qualitative analysis. The seven types of chemical reactions were combustion of reactive metals in air, chemical reactions between dilute acids and reactive metals, neutralisation reactions between strong acids and strong alkalis, neutralisation reactions between dilute acids and metal oxides, chemical reactions between dilute acids and metal carbonates, ionic precipitation reactions and metal ion displacement reactions. Although two of the chemical reactions involved oxidation and reduction, it was decided not to include the concept of redox in this study as students had only recently been introduced to ion-electron... 

As well as separating similar ions out of solution, chemists can also use their understanding of solubility and precipitation reactions to identify unknown ions in solution. Qualitative analysis is the hranch of analytical chemistry that involves identifying elements, compounds, and ions in samples of unknown or uncertain composition. The other hranch of analytical chemistry is quantitative analysis. In quantitative analysis, analytical chemists determine how much of a compound, element, or ion is in a sample. 

Qualitative methodology uses small samples of subjects and the method of (usually) personal interviews, based on structured or more usually semi-structured questionnaires. The interviews are tape- or video-recorded and then transcribed and analyzed for patterns and categories in students thinking. Data treatment can also be done by commercial packages for qualitative analysis. This methodology provides the possibility for in-depth monitoring and study of students ideas and understandings about scientific concepts. One could think of written questionnaires as instant pictures, and of interviews as motion pictures. 

Chapter 9, Investigation and Characterisation of Organic Compounds, contains much of the chemical information and preparative methods from the chapter previously entitled Qualitative Analysis. The emphasis of this chapter is now on achieving an understanding of chemical behaviour in association with spectroscopic features, and correlating this information to provide a definitive structural elucidation. In this way we hope that the material fulfils the requirements of a range of courses which deal in this topic. The tables of physical constants (Ch. 10) remain unchanged, and the appendices have been up-dated.. ... 

This approach was very popular in former times when it was impossible to apply HF, DFT, or correlated ab initio methods to systems of more than a few atoms, so that phosphines were almost always modeled as PH3 (see Figures 10.5 and 10.7). In many cases, where the aim of the calculations was to understand qualitative aspects of reaction mechanisms, this type of truncation is perfectly acceptable and indeed offers some benefits beyond the lower computational expense. For example, it facilitates analysis, especially when the truncated system has symmetry absent in the full molecule. Also, it serves to remind the computational chemist that he or she is always studying a model, rather than the real system solvent is not present, and the level of theory used does not give exact results. It is sometimes possible to forget this when modeling the full system. 

With an increase in integration scale it is becoming increasingly necessary to develop tools for the realistic simulation and optimization of the circuitry. An enabling factor is to improve the understanding of device and circuit operation and the awareness of the link between the two. This can be achieved via in-depth transistor modeling, circuit simulation and clever qualitative analysis, as will be discussed after we have introduced our technology. 

The advent of personal computers greatly facilitated the application of spectroscopic methods for both quantitative and qualitative analysis. It is no longer necessary to be a spectroscopic expert to use the methods for chemical analyses. Presently, the methodologies are easy and fast and take advantage of all or most of the spectral data. In order to understand the basis for most of the current processing methods, we will address two important techniques principal component analysis (PCA) and partial least squares (PLS). When used for quantitative analysis, PCA is referred to as principal component regression (PCR). We will discuss the two general techniques of PCR and PLS separately, but we also will show the relationship between the two. 

Qualitative analysis challenges a chemist s creative imagination and chemical understanding. Discover this for yourself in Investigation 9-B. 

A molecular model is proposed for qualitative analysis of the stress-strain behavior for filled PDMS in a wide temperature range. The model emphasizes the importance of the following molecular characteristics for understanding stress-strain behavior of filled PDMS ... 

The classical qualitative analysis scheme is based on solubility rules Acetates, nitrates, and chlorides (except for Ag , Hgi, and Pb ) are always soluble. There are specific solubility patterns for sulfides, carbonates, and phosphates. Find a qual scheme and explain it in terms of your understanding of solution processes. 

Both qualitative and quantitative information can be derived from multivariate analysis. A qualitative classification model provides overviews of how the properties relate to each other and how changes can be made to molecules in a qualitative sense. The main goal for qualitative analysis is to assist understanding and put all the pieces of the puzzle together. A quantitative model focuses on accurate prediction of various desirable properties for designing new molecules and combinatorial libraries with good potency and druglike properties. 

Although many people do not know about or. perhaps, understand the details of qualitative analysis, products for home analysis are becoming increasingly available. In some cases, tests for certain chemicals or elements, such as lead, may be performed directly by the consumer in other cases, the consumer may collect samples to be shipped to a laboratory for professional testing. Of course, the quality of such kits varies, but the everyday applications of qualitative analysis are illustrated by the increasing availability of these kits. 

These types of benchmarking issues can be used to identify other issues that may require further analysis due to the potential for severe consequences or higher perceived likelihood for an accident. The issues identified through a qualitative analysis can be directly used as inputs in a semi-quantitative analysis with a focus on developing a better understanding of these issues and their influence on the level of risk, and need for additional risk mitigation measures. 

Once the specific issues and scope of the analysis are defined, a semi-quantitative risk assessment may be conducted using either risk indexing or a risk ranking matrix. The risk indexing and risk matrix techniques should be built on the information from the earlier analyses. Each level of risk analysis should not be considered a separate effoit, but a continued understanding of the transportation issue. Additionally the information gained from these activities can be used to update the qualitative analysis, especially benchmarking comparisons. 

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