CHEM2315 Introduction To Analytical Chemistry

CHEM2315 Introduction To Analytical Chemistry

CHEM2315 Introduction To Analytical Chemistry

Question:

You have been appointed as an Analytical Chemist Technician in a Chemistry Laboratory.

You have been given a task to write a report about the techniques to find out inorganic chemical compounds as identification of inorganic chemical compounds is the major part of your workload in your new job.

Task 1:

Describe at least four techniques needed to analyse inorganic chemical compounds. You can consider flame test, test for sulphates, Test for carbonates and Test for Halides for this purpose.

You need to identify chemicals needed for each technique.

Task 2 :

You have been given six solutions. You need to classify according to their pH. You need to use Litmus paper and universal indicator to figure out whether they are acidic or basic in nature.  Once you finished, then you need to use pH meter to find their pH values.

Task 3 :

Carry out Experiments to show how chromatography is used to analyse materials.  You need to write the steps you have taken to demonstrate your technique and understanding. CHEM2315 Introduction To Analytical Chemistry

You have been given two unknown amino acids i.e. Lucine    and Tyrosine and one unknown amino acid. You need to first find the Rf values for Lucine and T Tyrosie and the Rf value of unknown amino acid. You need to find the name of the unknown amino acids with the   help of Rf data.

Task 4:

Carry out experiments to identify chemicals in unknown compounds

You have been given two unknown compounds. You need to identify at least one compound correctly to pass the Assessment criteria 4.1 for this unit. You need to find the Cation (Positive ion) and Anion (negative ion) and thus identify the compound by using the flow chart that has been provided.

Answer:

Task 1: Techniques For Analysis Of Substances

Flame Test

The flame test is used in the establishment of the identity otherwise possible identity of a metal or metalloid that is found in ionic compounds. The test works by giving off a characteristic color when a compound is placed in the flame.

Test procedure

The use of a clean wire loop that is made of either platinum or nickel-chromium wire is the classic test technique for performing a flame test. The wire is dipped into the solution or the powder that is to be tested and then place in the hottest part of a flame. Observations are made on the resulting color which is then used in predicting the presence of a particular ion. The wire is cleaned by dipping it into hydrochloric acid and then rinsing with water.  The loop is tested to be clean by putting it into a flame of a gas burner which bursts into colors if the wire is not properly cleaned (Schäffer, 2017).

The clean loop is dipped into the solution or powder which is to be tested and then placed on the blue region of a Bunsen burner flame. The color observed is then comparing against the list of the color for various ions. Still, the flame test can be done using a wooden splint. The wooden splint is soaked in distilled water overnight and then rinsed with more clean distilled water. The ends of the splint can be moistened with water using cotton swabs (Toldrá, 2012). The wooden splint is then dipped into the substance that is to be tested and then placed in the flame of a Bunsen burner.

The flame test works by visually determining the identity of an unknown ion or salt using the color characteristics. The ions turn the flame of a Bunsen burner (Kenneth, 2012). The substances tested in this technique include sodium chloride, sodium acetate, sodium carbonates, lithium chloride, calcium nitrate, sodium hydrogen carbonate, potassium chloride, calcium sulfate, glucose potassium chloride among other substances.

Table 1: List of colors for various metal ions

Test for Carbonates

Carbonate ions, CO3-, are found in metal carbonates.  A two-step experiment can be used in the establishment of the presence of carbonate ions in a compound

Step 1: Reacting the carbonate with dilute acids

This reaction produces carbon dioxide and water as part of the products. An example could be the reaction between magnesium carbonate and sulphuric acid as shown in the equation below

MgCO3+ H2SO4 – MgSO4+CO2+H2O


Step 2:
 Collecting the gas produced and bubbling through lime water

Lime water is the commercial name for calcium hydroxide. When carbon dioxide is bubbled through lime water, a white precipitate is formed as shown in the equation below (Rouessac, 2013)

Ca (OH) 2 + CO2 – CaCO3+ H2O

The presence of a white precipitate is a confirmation of the presence of carbonate ions in the compound being tested.

Fig.1: Test showing presence of carbonates

Test for Halide ions

Halide ions are ions formed when elements in Group 7 of the periodic table gain ions. Among the elements in group 7 include chlorine, fluorine, bromine, and iodine. Nitrate solution is used in test the presence of any of these ions in a solution (Williamson, 2016). To achieve this, the procedure below is used:

  • Add 2-3 drops of dilute nitric acid into the solution to be tested
  • Add 2-3 drops of silver nitrate

Observe any changes with regard to the color of the precipitate

Chloride ions form a white precipitate, bromide ions cream precipitate while iodine ions form a yellow precipitate in the test. These precipitates are silver chloride, silver bromide, and silver iodide respectively.

CHEM2315 Introduction To Analytical Chemistry


Test for Sulphates

Barium chloride is used to test for the presence of sulphate ions, SO42- in a solution. To achieve this a few drops of dilute hydrochloric acid are added to the solution to be tested followed by a few drops of a solution of barium chloride (Hansen, 2011). A white precipitate will be formed which is an indication of the presence of sulphate ions in the solution. An example is as illustrated in the equation below for the reaction between barium chloride and sodium sulphate solution

Na2SO4+ BaCl2 – BaSO4 + 2NaCl

Figure 2: Test showing the presence of sulphates

Task 2

Substances are classified as either acid, basic or neutral depending on their levels of alkalinity. While acids have a sharp taste, bases have a soapy feeling (Rouessac, 2013). An example of an acid is lemon juice which has a sour taste. Toothpaste and detergents are examples of bases. Neutral substances are in between bases and acids. These substances neither burn the body nor have a soapy feeling. An acidic solution is achieved when an acid is dissolved in water. Similarly, a basic solution is achieved when a base is dissolved in water. Indicators are a substance that changes their colors when they are added to a basic or acidic solution.

For the purposes of this task, we have six solutions namely hydrochloric acid, magnesium hydroxide, sodium nitrate, sulphuric acid, water and calcium oxide solution (Schäffer, 2017). The solutions will be tested for acidity, alkalinity or neutrality using litmus paper and universal indicators

Litmus Indicator

A litmus paper indicator changes red when a solution is red and blue when the solution tested is alkaline. When dipped in neutral solutions, the indicator turns purple. To test for the alkalinity and acidity of the solutions, each of the solutions will be put in a test tube. Both red and blue litmus paper will be dipped into each of the solutions (Dargan, 2013). The color changes of the substances will follow the trend as shown in the table below

Red Litmus Blue Litmus
Acidic solution Stays red Turns blue
Neutral solution Stays red Stay blue
Alkaline solution Turns blue Stays blue

While making observations, the term “stays red/blue” as opposed to “no change” or “nothing” is used since it is an illustration of what is actually being seen.