Chem Lab Report

Topics: Chlorine, Sodium chloride, Hydrochloric acid Pages: 6 (1164 words) Published: March 2, 2014

Synthesis Procedure 1
-1.0 Introduction
A Cobalt-Amine-Halide compound is synthesized from cobalt (II) chloride hexahydrate. An orange-tinted solid is produced and is considered to be unknown since the specific ligand amounts are unknown. By determining the percent composition of various elements and compounds in the unknown, its true identity can be predicted. Chloride, ammonia, and cobalt are three examples of percent compositions determined to help narrow the selection of possible unknowns. Titrations using Na2S2O3 and HCl to determine percent cobalt and ammonia, respectively, are used. Silver nitrate is used to precipitate the chloride ions in the unknown, which can be measured to determine the percent composition of chloride in the unknown. The results from these three major analyses helped to draw the conclusion that the unknown is in fact [Co(NH3)6]Cl3. -2.0 Synthesis/Analysis of Cobalt-Amine-Halide Compund (Procedure 1, pgs 16-7))

A cobalt (III) amine halide compound was prepared by making a solution of cobalt (II) chloride hexahydrate and ammonium chloride (NH4Cl) to liberate the Co (II) in the solution. “Activated” charcoal and ammonia are then added to the solution. The Co (II) is then oxidized to Co (III) using hydrogen peroxide (H2O2). This yields an orange crystalline solid of 8.9379 grams, later found to be [Co(NH3)6]Cl3. [Co(H2O)6]+2 + 6 NH3  [Co(NH3)6]+2 + 6 H2O

2 [Co(NH3)6]+2 + 2 H+ + H2O2  2 [Co(NH3)6]+3 + 2 H2O
-3.0 Analysis for Percent Halide In The Synthesized Cobalt-Ammonia-Halide Compound (pgs 23-4) HNO3 is used to acidify the soluble chloride-containing cobalt compound. Silver nitrate is used in excess to precipitate chloride ions (Cl-) as AgCl in an approximately .2400 grams of the unknown compound. This is done in duplicate and purple-tinted precipitates are placed in Gooch crucibles. The precipitates are suction dried using ethyl alcohol then acetone to rinse. After being dried in the oven for thirty minutes, they are weighed to be .3655 grams and .3824 grams. The silver halide precipitates can be used to calculate the percent halide in the precipitate and in the unknown. The average percent halide was found to be 38.00% with 3.08% deviation between trials 1 and 2 (Table 1&2). X Cl = 35.45 g/mole Cl= .0904g Cl- .0904g Cl- * 100 = 36.78% Cl .3655g 143.34 g/mole AgCl .2458g Co sample Mass of Co-sample

Mass of precipitate
% halide in Co-sample
.2458g
.3655g
36.78%
.2412g
.3824g
39.22%

Average 
38.00%

-4.0 Preparation & Standardization Of An HCl Solution (pg 25)
The amount of 12M HCl needed to prepare 500mL of 0.3M HCl was found to be 12.5mL. After the HCl is prepared, it is titrated in triplicate with about .9605 grams of THAM each time. Brom-cresol-green indicator is used to determine when the solution has reached its endpoint or equilibrium. The molarity of HCl came to an average of .3045M with a percent deviation of .0657% (Table 3).

(HOCH2)3CNH2 + HCl  (HOCH2)3CNH3+ + Cl-
1) (12M HCl)(V) = (0.3M)(500mL)

V= 12.5mL
2) 26.00mL * 1L = .02600L HCl
1000mL
.9610g THAM * 1 mol THAM * 1 mole HCl = .0079255 mole HCl 121.14 g/mole THAM 1 mole THAM
.0079255 mole HCl = .3048M HCl
.02600L
Grams of THAM
Final volume – initial volume
Molarity of HCl
.9610g
26.00ml
.3051M
.9602g
26.05ml
.3043M
.9602g
26.05ml
.3043M
Averages .9605g
26.03ml
.3045M

-5.0 Analysis Of Percent NH3 Using Standardized .3M HCl (pgs 26-8) Excess of the strong base NaOH was added to about .37 grams of the unknown cobalt compound. NH3 reacts with boric acid and is liberated. This solution was then titrated with the .3045M HCl using about 26.05mL. An average percent NH3 of 38.25% was found with a percent deviation of 2.240% (Table 4).

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