Name: ______Per: _____ Performance:

Biochemistry Lab 2: Qualitative Analysis Testing for Cations Anions

Background

Take a look at the lab report shown below.

What cations and anions do you see listed in this lab report? Cations and anions play very important roles in health and medicine. Ions such as sodium, potassium, calcium, chloride, phosphate, and bicarbonate are needed to maintain proper hydration and blood pH, and they are needed for the proper function of nerve and muscle tissue. Abnormal levels of these ions in the body can have severe consequences leading to cardiac and neuronal problems, and if not treated can even cause death.

When a doctor orders a chemistry panel (also known by a variety of other names such as Chem12, Chem 7, SMA 20, SMAC, CMP, etc.) for a patient a sample of the patient’s blood is sent to a lab where a series of tests are carried out to measure the presence and quantity of certain chemicals, some of which are ions. Ever wondered what the lab technician does to find out what chemicals are in these blood samples?

Lab technicians perform a series of chemical reactions that give distinct results, such as color changes, the formation of gases or insoluble precipitates, for each of the ions being tested. The results of a given chemical reaction are specific to the presence or absence of one particular ion, and the expected results have been tabulated using solutions containing the specific ion of interest (known as a standard). When the lab technician performs a given test on the blood sample s/he records his or her observations of the results. By comparing these observations to the expected outcomes, the lab technician can determine the presence or absence of a given ion in the blood sample.

This type of analysis, where only the presence or absence of a particular substance (in this case ions) is determined, is called qualitative analysis. A thorough clinical analysis however will move beyond simply measuring the presence/absence of certain substances. It will include quantification which is called quantitative analysis. Most of the blood work done these days involves quantification and then comparing it to a certain standard. Values are then determined in range or out of range giving the clinitian an idea what’s going on in a sick patient.

Pre-laboratory Questions

(1). Write the chemical symbol or formula for the following:

Sodium ion:

Potassium ion:

Calcium ion:

Chloride ion:

Phosphate ion:

Bicarbonate ion:

Sodium chloride:

Sodium bicarbonate:

Potassium phosphate:

Calcium bicarbonate:

Potassium bicarbonate:

Calcium phosphate:

Calcium Chloride:

Strontium nitrate:

Copper (II) Nitrate:

(2). There are different testing goals in chemistry, there is qualitative as well as quantitative analysis. What is the difference between them?

(3). You detect the presence of calcium ions in a sample using the flame test. What additional test could you do to confirm this finding?

(4). You are given a solution that is supposed to contain calcium phosphate. What tests can you perform to confirm the presence of this calcium phosphate? Provide a brief procedure including any observations you are likely to make.

(5) For which substances is the patient’s log on page 1 in or out of range?

Procedure

The goal of this laboratory is to introduce you to the process of qualitative analysis by determining the ionic composition of an unknown solution (imagine it is the serum from a patients blood sample). You will first carry out a series of experiments on solutions containing a particular cation or anion (standard solutions) and record your observations. Then you will repeat these experiments and record your observations on a solution containing unknown ions (the unknown solution). You will then compare your observations for the unknown with those obtained for the standard solutions and make a qualitative determination as to the ionic composition of the unknown solution.

A. Tests for Cations

A 1. Flame test for sodium, potassium, calcium, strontium, copper

·  Obtain the standard NaCl, KCl, CaCl2 ,Cu (NO3)2 ,Sr (NO3)2 solutions (these are your known solutions). Place the wire loop of the flame test wire into the vial with the NaCl solution and then into the flame. Record the color produced by the Na+ ion. Repeat the test with the KCl solution. The color (pink-lavender) of K+ does not last long, so look for it immediately. Record the color of the K+ ion. Repeat the flame test with Ca2+. Record the color of the Ca2+ flame.

A 2. Oxalate test for calcium

·  Place 5-6 drops of the standard CaCl2 solution in a plastic well (this is your known solution). Add 1-2 drops of ammonium oxalate solution, (NH4)2C2O4. Look for a cloudy, white solid (precipitate). If the CaCl2 solution remains clear, transfer the solution by pipette to a ceramic plate well and heat gently on the hot plate. Set the hot plate to its lowest setting. Look for a precipitate. The net equation for the reaction is:

Ca2+ (aq) + C2O42- (aq) → CaC2O4 (s)

white precipitate indicates the presence of Ca2+

A 3 Test for ammonium ion, NH4+

·  Place 5-6 drops of the standard NH4Cl solution in one well of a ceramic plate (this is your known solution). Add 2 drops of sodium hydroxide (NaOH). You may notice the odor of ammonia. Place a strip of moistened red litmus paper across the top of the well and set the plate on a hot plate to warm. Set the hot plate to its lowest setting. The NH3 (g) given off will turn the red litmus paper blue. Record the results.

NH4+ (aq) + OH- (aq) → NH3 (g) + H2O

B. Tests for Anions

B 1. Silver nitrate test for chloride

·  Place 5-6 drops of the known NaCl solution in a plastic well. Add 1 drop of AgNO3 and 1-2 drops of nitric acid (HNO3). Caution: AgNO3 stains the skin. Any white solid that remains is AgCl (s) which should not dissolve upon the addition of HNO3. Record the results.

Ag+ (aq) + Cl- (aq) → AgCl (s)

white precipitate remains after HNO3 is added

B 2. Ammonium molybdate test for phosphate

·  Place 5-6 drops of the Na3PO4 solution in a well of the ceramic plate. Add 1-2 drops of HNO3. After the solutions are warmed on a hot plate (adjust the hot plate setting to 2 or 3), add 2 drops of ammonium molybdate solution, (NH4)2MoO4. The formation of a yellow precipitate indicates the presence of PO43-. Record the results.

B 3. Carbon dioxide test for carbonate/bicarbonate

·  Place 5-6 drops of the standard Na2CO3 solution in a plastic well. While carefully observing the solution, add 1-2 drops of HCl. Watch for the evolution of bubbles of CO2 gas as you add the hydrochloric acid (HCl). The gas bubbles are formed quickly, and may be overlooked. If gas bubbles were not observed, add another 2-3 drops of HCl as you watch the solution. Record your results.

Na2CO3 (aq) + 2 HCl (aq) → CO2 (g) + H2O + 2 NaCl (aq)

gas bubbles

C. Testing a solution for unknown cations and anions

C 1. Write down the unknown sample number.

C 2. Repeat each of the tests (A1, A2, A3, B1, B2, and B3) for the unknown solution and write down

your observations. Repeat each test A1, A2, A3, B1, B2, and B3 as you did in parts A and B

but now you will be using the unknown solution.

·  For example when performing the flame test place 8-10 drops of unknown solution into an empty well of a plastic well plate. Place the wire loop into the solution and then into the flame. Record your observations. Dip the wire loop in an HCl solution to remove any remaining residue when you are finished.

C 3. Compare these observations to those that you obtained in sections A and B. Determine the

cation(s) and anion(s) present in your sample.

Report Sheet

A. Tests for cations

Procedure / Cation tested / Observation
A 1. Flame test / Sodium
Potassium
Calcium
Strontium
Copper (II)
A 2. Oxalate test / Calcium
A3. Ammonium Test / Ammonium

B. Tests for anions

Procedure / Cation tested / Observation
B 1. Silver nitrate test / Chloride
B 2. Ammonium molybdate test / Phosphate
B 3. Carbon dioxide test / Carbonate

C. Testing a solution for unknown cat/Anions Test 2 Samples

Procedure / Cation tested / Observation Sample #_____ / Observation Sample # _____
Flame test / Sodium
Potassium
Calcium
Strontium
Copper (II)
Oxalate test / Calcium
Silver nitrate test / Chloride
Ammonium molybdate test / Phosphate
Carbon dioxide test / Carbonate
Ammonium test / Ammonium

C3: Based on your observations above, complete the following chart:

Sample # ___ had the following: / Cations: / Anions:
Sample # ___ had the following: / Cations: / Anions: