# An Introduction to Qualitative Analysis

Topics: Ion, Ammonia, Solubility Pages: 8 (1574 words) Published: May 29, 2014
﻿An Introduction to Qualitative Analysis
Purpose:
Tests the ions of Mg2+, Ca2+, Sr2+, and Ba2+,
and identify them separately. By using these
observations, identify the unknown ion. Then tests
the ions of SO42-, CO32-, Cl-, and I-,identify them separately, and use the observation to identify the unknown.

Procedure
Part I - Qualitative Analysis of Group 2 Elements

Mix 0.02M K2CrO4 with each Mg(NO3)2, Ca(NO3)2, Sr(NO3)2 and  Ba(NO3)2 together. Secondly, mix 0.1M (NH4)2C2O4 instead of 0.02M K2CrO4  together with the same reactants used before. Thirdly, mix 0.1M Na2SO4 with those reactants. Then, mix 0.1M NaOH with the same reactants used before again. Some precipitates should forms ,record the observations in Table 1. At last, identify those two unknown solution.

Part II- Qualitative Analysis of Selected Anions

First mix 1M HNO3 with each Na2CO3, Na2SO4, NaCl and NaI together.  Repeat these steps by placing 0.1M Ba(NO3)2 instead of 1M HNO3. Then  mix 1M HNO3 for the reactants that formed precipitates. Repeat the first  step by placing 0.1M AgNO3 instead of 1M HNO3. Then add 6M NH3 to those mixtures that contains precipitates in, and 1M HNO3 the mixtures contains precipitates . Using these observation, identify an unknown union. Recording all the observations in  Table 2.

Data and Observations:
Part I -Qualitative Analysis of Group 2 Elements
Table 1

REAGENTS
0.1M SOLUTIONS OF GROUP 2 CATIONS (AS NITRATES)

Mg2+
Ca2+

Sr2+

Ba2+

Unknown D
0.02M K2CrO4
no
no
Light ppt
Light ppt(yellow)
No
0.1M (NH4)2C2O4
no
Heavy ppt(white)
Heavy ppt(white)
Light ppt(white)
Heavy ppt(white)
0.1M Na2SO4
no
no
Light ppt
Light ppt(white)
no
0.1M NaOH
Light ppt
Light ppt
no
Light ppt(white)
Light ppt(white)
Part II- Qualitative Analysis of Selected Anions
Table 2
REAGENTS
0.1M SOLUTIONS OF GROUP 2 CATIONS (AS Na SALTS)

CO32-
SO42-
Cl-
I-
Unknown Z
1M HNO3
Bubble
No
No
No
No
0.1M Ba(NO3)2
heavy ppt
immediately
heavy ppt
immediately
No
No
heavy ppt

immediately
ppt disappears
immediately
ppt disappears
immediately
No
No
ppt disappears
immediately
0.1M AgNO3
heavy ppt (light yellow)immediately
No
heavy ppt (light yellow)immediately
heavy ppt (light yellow)immediately
no
ppt disappears

immediately
No
ppt partially disappears

immediately

ppt partially disappears
(yellow)
immediately
No
6M NH3 added to precipitates from AgNO3
light ppt
(yellow)
immediately
light ppt
(yellow)
immediately
light ppt
(yellow)
immediately

light ppt
(yellow)
immediately

light ppt (yellow)
immediately

Questions:
Part 1:
1. Write net ionic equations for each combination in which a  precipitate occurred.

Sr2+(aq)+ CrO42-(aq) ＝ SrCrO4(s)

Ba2+(aq)+CrO42-(aq) ＝ BaCrO4(s)

Ca2+(aq)+ C2O42-(aq) ＝ CaC2O4(s)

Sr2+(aq)+ C2O42-(aq) ＝ SrC2O4(s)

Ba2+(aq)+C2O42- (aq) ＝ BaC2O4(s)

Sr2+(aq)+SO42-(aq) ＝ SrSO4(s)

Ba2+(aq)+ SO42-(aq) ＝ BaSO4(s)

Mg2+(aq)+ 2OH-(aq) ＝Mg(OH)2(s)

Ca2+(aq)+ 2OH-(aq) ＝ Ca(OH)2(s)

Ba2+(aq)+SO42-(aq) ＝ BaSO4(s)

2. State the identity of your unknown (along with its sample  number). Give the reasoning you used to arrive at this conclusion.

From our observation, Unknown D should be Ca2+ because it has a same  property as Ca2+ does. By the observation in table 1, we know that Ca2+  forms ppt with C2O42- and OH-. The unknown anions forms ppt with C2O42-  and OH- as well, therefore we conclude that the unknown cation should  be Ca2+.

Part 2:

1. Write net ionic equations for each combination in which a  precipitate formed or another reaction occurred.

Ba2+(aq)+ CO32-(aq)＝BaCO3(s)

Ba2+(aq)+ SO42-(aq) ＝BaSO4(s)

2Ag+(aq)+ CO32-(aq) ＝ Ag2CO3(s)

Ag+(aq)+ Cl-(aq) ＝ AgCl(s)

Ag+(aq)+ I-(aq) ＝AgI(s)

2. Write net ionic equations for each situation in...