In our lab we use a more sophisticated one which included a lid on the cup with an inserted thermometer and a stirrer. Thermochemistry is the study of the heat released or absorbed as a result of chemical reactions. The measurement of the total energy of a thermodynamic reaction is called enthalpy (q). This is the basis for Hess’s law which states that if two reactions are combined to yield a third reaction, the sum of the first two is equal to the third. The energy change is the same whether the process occurs in one step or many.
Archer G11 Partner: Cathy 22 March 2012 Separation and Qualitative Determination of Cations and Anions Purpose: The purpose of this lab is to identify the cations and anions components in the unknown solution. This can be done by using the method called selective precipitation of ions. This uses the solubility rule to dissolve and precipitate the desired ions. The significance of this lab is that forensic scientist can use these skills to identify the components of the substance found in the corpse. Hypothesis: The hypothesis is that the component ions of the solution can be identified.
The first of the two experiments was based in calorimetry. Calorimetry is the science behind measuring the heat change during a chemical reaction or change of state. A major component of calorimetry is the element of specific heat. Every metal has its own unique specific heat. This experiment implemented the use of calorimeters, or devices to measure the equilibrium temperature of water and the metal.
Show ALL your work. The water has absorbed the heat of the metal. So, qwater = qunknown metal Using the formula qunknown metal = m × c × ΔT, calculate the specific heat of the metal. Use the data from your experiment for the unknown metal in your calculation. Show ALL your work.
Since we used our chromatography method, we will be able to figure out which metals our substance contains. It is important to know this especially if we are ingesting and coming in contact with them. Chromatography is a separation technique that works based on the compound interactions as those compounds tend to move within a supporting medium. The compounds interact in two phases; mobile and stationary phase. The techniques help analyzing.
Experiment and Observation: Please note that this procedure was adapted from the “Anions, Cations, and Ionic Reactions” LabPaq Lab manual (Hands-On Labs Version 42-0304-82-00-01, 2015) Please reference this manual for further information on the lab experiments. The first experiment was to perform a qualitative anion test. This was done by observation of chemical reactions and recording the results in Data Table 1. Using the information from the reactions we were able to identify unknown substances and recorded the results in Data Table 1. Data Table 1: Anion Confirmation Tests Chemical | Anion | Addition of AgNO3 | Addition of HCl | NaBr | Bromide | Cloudy white thin solution | Clear with sedimentation | Na2CO3 | Carbonate | Clear with white sedimentation | Bubbles, sedimentation combined to one formation | NaCl | Chloride | Milky white, white sedimentation | No visible change | Nal | Iodide | Pale green cloudy, sedimentation | Sedimentation dispersed to smaller pieces, solution clears in color | Na2SO4 | Sulfate | No visible changes noted | Milky white | Na2S | Sulfide | Clear with amber sedimentation | No visible Change noted | Unknown #103 | CarbonateNa2CO3 | Cloudy white thin solution | Bubbles, Sedimentation combined to one
Double Replacement Reactions & Table F When two substances undergo a chemical reaction, new substances are formed. A double replacement reaction is one type of reaction that can form soluble or insoluble products. The purpose of the lab was to figure out how the solubility of a substance (aqueous or precipitate) can be determined when a double replacement reaction happens. Precipitates are insoluble compounds. A precipitate is a solid product that comes out of solution in a chemical reaction.
The Fajan method is named after American physical chemist Kazimierz Fajans and a dichloroflourescein indicator is used to indicate the equivalence point. The equivalence point in noted when the solution changes to a pink colour. The Mohr method is named after German chemist after Karl Friedrich Mohr and uses potassium chromate (K2CrO4). The colour of the solution at the equivalence point changes to a brownish red colour2. The following reaction has taken place to completion by the equivalence point: 2Ag+ (aq) + CrO42- (aq) → Ag2CrO4 (s)2 The second technique used in the experiment is the gravimetric technique.
In this lab we used Mg as our metallic portion of the organometallic compound. Organometallic compounds are special in that they cause Carbon to become a nucleophile. More specifically in this lab we used R-Mg-Br an alkyl magnesium halide to project the nucleophillic properties onto the Carbon atom, known as a Grignard reagent because of it founder chemist Victor Grignard. The purpose of Grignard reactions is to create a C-C bond, more specifically a tertiary or a secondary alcohol. The Grignard reagents are usually created with the solvents anhydrous diethyl ether or THF and are very air sensitive.
Then, after that we were to determine the density of the same copper cylinder by using the volume found by the water displacement method. Finally, we were attempting to identify three different unknown liquids by density determinations. Knowing the density of a certain material can be very vital to a scientist because density is used in many different ways in a chemistry lab. Undoubtedly the most important use of density is the ability to determine an unknown substances identity. Since every material has a unique density a scientist can simply calculate the mass and volume of an object, find the unknown object’s density and he will, without a doubt, have correctly identified the substance.