Alum is an ionic compound, which means its melting and boiling points are likely to be too high to be measured conveniently. The second and third weeks of this exercise will be devoted to characterizing the alum. The overall balanced chemical reaction for the conversion of aluminum to alum, shown below, can be obtained by adding together the balanced chemical equation for each step ( Help Me). The balanced chemical reaction that occurs in this step is Under the experimental conditions, the alum has a limited solubility in water, and so it precipitates from the solution. The second step of the procedure is to convert the KAl(OH) 4 to alum by addition of sulfuric acid (H 2SO 4) in an acid-base reaction. The balanced chemical equation for this oxidation-reduction reaction is The first step in this synthesis, which you will perform during Week 1, is to react metallic aluminum with a concentrated solution of potassium hydroxide (KOH) to form the potassium salt of the tetrahydroxoaluminate complex ion, –. In this experiment you will prepare and characterize alum (potassium aluminum sulfate dodecahydrate, KAl(SO 4) 2♱2 H 2O). A reaction, even though it gives a valuable product, may be unusable because it has a low yield, takes too much time or generates too much waste. Chemists are always trying to strike a balance between the cost of the reactants, the value of the products, the time a reaction requires and the cost of any unwanted by-products that must be handled as hazardous waste. We do these final characterizations of the reaction because it is important to know how efficiently the reaction converts reactants to products. Once the chemical reaction’s products are fully characterized, and the balanced chemical reaction is known, we can compute a theoretical and a percent yield. Qualitative tests often use chemical reactions that result in a visible change (formation of an insoluble solid, a color change, or evolution of a gas) as a way to quickly show whether a particular chemical species is present or not. Sometimes it is sufficient to show only that certain ions or elements are present in a sample, and in this case a chemist will perform a qualitative test. The former is usually accomplished using elemental analysis, mass spectroscopy, X-ray crystallography or some spectroscopic method. e., how the atoms are connected) are determined. In a quantitative characterization, the chemical formula and the structure (i. Characterization of the products may be either quantitative or qualitative. The isolation and purification of the products are based on physical properties such as the ability to form crystals, boiling point, melting point, solubility, etc. The description of a chemical reaction consists of a series of steps: 1) carrying out the reaction, 2) isolating the product(s), 3) purifying the product(s), 4) and characterizing the product(s) and determining its(their) purity. Needless to say, identification of the reactants in a complex reaction mixture can be very difficult, and so we will only work with chemical reactions where the reactants are known. While it may seem a trivial exercise to identify the reactants, this is not always the case. To fully describe a chemical reaction one needs to know the identities of both the products and the reactants, and the proportions in which the reactants combine and the products form. In this and the next laboratory exercise you will learn some of the basics of how chemists carry out chemical reactions and how they characterize the chemical substances involved in these reactions. Even though we know a great deal about chemical reactions, chemists are still finding new chemical reactions and new ways of assembling atoms into molecules and molecules into more elaborate structures. As we have discussed in class, there are rules, such as the Law of Conservation of Mass, by which chemical reactions occur, and it took chemists a long time to understand these basic rules. One of chemistry’s goals is to be able to transform any set of substances (the reactants) to another set of substances (the products) through a chemical reaction.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |