4.1: Qualitative Analysis Testing for Cations & Anions Lab Report
- Page ID
- 306762
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Learning Objectives
To perform flame tests of metal cations in order to observe their characteristic colors To test for the presence of cation or anion by carrying out qualitative analysis Identify cation or anion present in an unknown sample
Background
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.
A common blood test that is often ordered by doctors is a chemistry panel (also known by a variety of other names such as Chem12, Chem7, 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.
A series of chemical reactions is carried out that give distinct results, such as color changes, the formation of gases or insoluble precipitates (a solid), for each ion being tested. In this experiment, we will carry-out flame test and qualitative studies to identify different metal ions present in a sample.
Flame Test
Flame tests are used to identify the presence of a relatively small number of metal ions in a compound. Not all metal ions give flame colors. For Group 1 compounds, flame tests are usually by far the easiest way of identifying which metal you have. For other metals, there are usually other easy methods which are more reliable - but the flame test can give a useful hint as to where to look.
Figure \(\PageIndex{1}\): Colored flames from strontium, cesium, sodium and lithium (from left to right). Picture courtesy of the Claire Murray and Annabelle Baker from the Diamond Light Source.
Qualitative Analysis
When a sample of blood is tested, the technician will record their observations of the results, by comparing their observations to the expected outcomes, they 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.
In qualitative analysis, the ions in a mixture are separated by selective precipitation. Selective precipitation involves the addition of a carefully selected reagent to an aqueous mixture of ions, resulting in the precipitation of one or more of the ions, while leaving the rest in solution. Once each ion is isolated, its identity can be confirmed by using a chemical reaction specific to that ion.
Experimental 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 patient’s 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.
Safety
Wear your safety goggles and gloves!
Materials
Spot plate, wood splints, small beaker, test tubes, tube rack, Bunsen burner, stirring rod, hot plate, 0.1 M NaCl, 0.1 M KCl, 0.1 M CaCl2, 0.1 M CuSO4, 0.1 M Sr(NO3)2, 0.1 M (NH4)2C2O4, 0.1 M NH4Cl
Part A. Tests for Cations
1. Flame test for sodium, potassium, calcium, strontium, copper
Obtain the standard NaCl, KCl, CaCl2, CuSO4, Sr(NO3)2 solutions (these are your known solutions). Place the wood splint into the spot plate well 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 2+ 2+ K+ ion. Repeat the flame test with Ca . Record the color of the Ca flame. Repeat test for the remaining cations and record your observations.
2. Oxalate test for calcium
Place 5-6 drops of the standard CaCl2 solution in a test tube (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, place the test tube in a warm water bath and heat gently for 5 minutes. Look for a precipitate. The net equation for the reaction is:
\[\ce{Ca^2+(aq) + C2O4^2-(aq) -> CaC2O4(s)} \]
white precipitate indicates the presence of Ca2+.
3. Test for ammonium ion, NH4+
Place 5-6 drops of the standard NH4Cl solution in test tube (this is your known solution). Add 2 drops of sodium hydroxide (NaOH). You may notice the odor of ammonia. Place the test tube in a hot water bath and gently heat for 5 minutes. Place a strip of red litmus paper across the top of the test tube. The red litmus paper will turn blue as a result of the release of NH3 (g) from the reaction. Record your observations.
\[\ce{NH4^+(aq) + OH^-(aq) -> NH3(g) + H2O(l)}\]
Part B. Tests for Anions
1. Silver nitrate test for chloride
Place 5-6 drops of the known NaCl solution in a test tube. 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 your observations.
\[\ce{Ag^+(aq) + Cl^-(aq) → AgCl (s)}\]
white precipitate remains after HNO3 is added.
2. Ammonium molybdate test for phosphate
Place 5-6 drops of the Na3PO4 solution in a test tube. Add 1-2 drops of HNO3. Warm the test tube in a hot water bath for 5-10 minutes, after the solutions are warmed add 2 drops of ammonium molybdate solution, (NH4)2MoO4. The resulting yellow precipitate indicates the presence of PO43-. Record your observations.
3. Carbon dioxide test for carbonate/bicarbonate
Place 5-6 drops of the standard Na2CO3 solution in a test tube. 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 observations.
\[\ce{Na2CO3 (aq) + 2 HCl (aq) -> CO2 (g) + H2O + 2 NaCl (aq)}\]
gas bubbles are formed
Part C. Testing a solution for unknown cation and anion
- Write down the unknown sample number.
- Repeat each of the tests (A1, A2, A3, B1, B2, and B3) for the unknown solution and write down your observations For example, when performing the flame test place 8-10 drops of unknown solution into an empty well of a ceramic well plate. Place the wood splint into the solution and then into the flame. Record your observations.
- Compare these observations to those that you obtained in sections A and B. Determine the cation and anion present in your sample.