The unknowns in this group may contain 2 to 3 ions. Each ion in the group must be reported as Present, Absent, or Undetermined. Ion Reported Status (P, A, or U) NH," Ba Ca2+ 2+ Mg* Na* K* Balanced, net-ionic equations for final confirmatory tests for all ions reported present. (There is no equation for sodium).
The unknowns in this group may contain 2 to 3 ions. Each ion in the group must be reported as Present, Absent, or Undetermined. Ion Reported Status (P, A, or U) NH," Ba Ca2+ 2+ Mg* Na* K* Balanced, net-ionic equations for final confirmatory tests for all ions reported present. (There is no equation for sodium).
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Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Transcribed Image Text:CHE 122 Lab
Ba-Mg Group Report
The total number of possible points for this report is 14
Name:
Unknown number:
Lab Section:
Lab instructor:
UNKNOWN REPORT
The unknowns in this group may contain 2 to 3 ions.
Each ion in the group must be reported as Present, Absent, or Undetermined.
Ion
Reported Status (P, A, or U)
NH,"
Ва
Ca²+
Mg²*
Na
K*
Balanced, net-ionic equations for final confirmatory tests for all ions reported present.
(There is no equation for sodium).
1.
2.
3.
4.
7
![oct o,
New Note
Ba-Mg Group
Aim: Identification of a group of cations (Ba-Mg group) consisting of barium (Ba?"), calcium (Ca?"),
magnesium (Mg²"), sodium (Na"), potassium (K*), and ammonium (NH,"). With the exception of
ammonium cation, all the cations in this group are either alkali or alkaline-earth metals. All the cations
are biologically important electrolytes. Routine investigations of biological samples like blood involve
the determination of their relative concentrations. Barium salts are routinely employed to diagnose
structural and motility abnormalities of the human digestive tract (Barium meal procedure). The
concentration of K* cations is regularly monitored in water-based muds during drilling of oilfields.
Theory:
All the cations in this group are colorless. Since reagents containing ammonia are used in
detecting the cations in this group, the test for ammonium cation (NH4") should be carried out first.
Since solutions of ammonium salts are slightly acidic, the addition of warm NaOH releases ammonia
(V). The release of NH3 can be checked from both the smell and the change in the color of moist red
litmus to blue.
NH," + H2O + OH' → NH3 + 2H2O
Barium is initially precipitated out as a sulfate when [(NH4)2SO4] is added (VI). The solubility
product (Kp) of barium sulfate (BaSO4), 1.5 × 10°, is smaller than the sulfates of the other cations and
hence it would be precipitated out (in other words, BaSO4 is much less soluble than the sulfates of the
other cations, so it will form a precipitate while the other sulfate compounds remain dissolved in
solution). Barium salts give a characteristic green color in the flame test'.
Ba?"(ag) + SO,(aq) → BaSO4 (s, w)
The solubility product (K) of calcium oxalate (CaC2O4) is 1.3 x 10°, is smaller than the
oxalates of the other cations and hence it is precipitated out (VII). Calcium salts give a characteristic
reddish-yellow color in the flame test'.
Ca* (aq) + C20,² (aq) → CaC204 (s,w)
The addition of ammonium hydroxide (NH,OH) and sodium hydrogen phosphate (Na,HPO4)
leads to the formation of magnesium ammonium phosphate (MgNH4PO4) (VIII).
Mg** (aq) + HPO, (aq) + NH3 (aq) –→ MgNH4PO4 (s, w)
Since phosphates of other metals also precipitate at this point, the addition of an organic dye (p-
nitrobenzene-azo-resorcinol) to the Mg*" ions in the presence of NaOH leads to the formation of a
characteristic blue lake.
Unlike all the ions discussed until now, there are very few sodium and potassium compounds
which are sufficiently insoluble to form distinct precipitates. Hence, flame tests are often used to
identify these ions (IX)'. Potassium ion can also be identified by the formation of a white precipitate
with sodium tetraphenylborate solution.
K* (ag) + NaB(C,H<)4 → K[B(C&H3).] (s.w) + Na*
T
+ :](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F8bdaded0-401d-48e8-a8ea-1a7ee4f60f02%2Fd912c3f0-ba65-40d1-a07b-6a51fa1845fd%2Faaenrud_processed.jpeg&w=3840&q=75)
Transcribed Image Text:oct o,
New Note
Ba-Mg Group
Aim: Identification of a group of cations (Ba-Mg group) consisting of barium (Ba?"), calcium (Ca?"),
magnesium (Mg²"), sodium (Na"), potassium (K*), and ammonium (NH,"). With the exception of
ammonium cation, all the cations in this group are either alkali or alkaline-earth metals. All the cations
are biologically important electrolytes. Routine investigations of biological samples like blood involve
the determination of their relative concentrations. Barium salts are routinely employed to diagnose
structural and motility abnormalities of the human digestive tract (Barium meal procedure). The
concentration of K* cations is regularly monitored in water-based muds during drilling of oilfields.
Theory:
All the cations in this group are colorless. Since reagents containing ammonia are used in
detecting the cations in this group, the test for ammonium cation (NH4") should be carried out first.
Since solutions of ammonium salts are slightly acidic, the addition of warm NaOH releases ammonia
(V). The release of NH3 can be checked from both the smell and the change in the color of moist red
litmus to blue.
NH," + H2O + OH' → NH3 + 2H2O
Barium is initially precipitated out as a sulfate when [(NH4)2SO4] is added (VI). The solubility
product (Kp) of barium sulfate (BaSO4), 1.5 × 10°, is smaller than the sulfates of the other cations and
hence it would be precipitated out (in other words, BaSO4 is much less soluble than the sulfates of the
other cations, so it will form a precipitate while the other sulfate compounds remain dissolved in
solution). Barium salts give a characteristic green color in the flame test'.
Ba?"(ag) + SO,(aq) → BaSO4 (s, w)
The solubility product (K) of calcium oxalate (CaC2O4) is 1.3 x 10°, is smaller than the
oxalates of the other cations and hence it is precipitated out (VII). Calcium salts give a characteristic
reddish-yellow color in the flame test'.
Ca* (aq) + C20,² (aq) → CaC204 (s,w)
The addition of ammonium hydroxide (NH,OH) and sodium hydrogen phosphate (Na,HPO4)
leads to the formation of magnesium ammonium phosphate (MgNH4PO4) (VIII).
Mg** (aq) + HPO, (aq) + NH3 (aq) –→ MgNH4PO4 (s, w)
Since phosphates of other metals also precipitate at this point, the addition of an organic dye (p-
nitrobenzene-azo-resorcinol) to the Mg*" ions in the presence of NaOH leads to the formation of a
characteristic blue lake.
Unlike all the ions discussed until now, there are very few sodium and potassium compounds
which are sufficiently insoluble to form distinct precipitates. Hence, flame tests are often used to
identify these ions (IX)'. Potassium ion can also be identified by the formation of a white precipitate
with sodium tetraphenylborate solution.
K* (ag) + NaB(C,H<)4 → K[B(C&H3).] (s.w) + Na*
T
+ :
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