Qualitative Analysis Lab Report

The qualitative determination of the of presence of cations in solution

Purpose
The purpose of this activity is to determine the identity of four household substances, and to understand how to create and use a qualitative analysis scheme. This activity utilizes qualitative observation.

Data Table

Unknown
Solubility
Iodine
Phenolphthalein
Identity
Unknown A insoluble brown
Na
CaCO3
Unknown B insoluble blue
Na
cornstarch
Unknown C soluble Na pink NaCO3
Unknown D soluble Na
Colorless
Scrouse

Identity Of Unknowns
A: CaCO3:
B: Cornstarch
C: Na2CO3
D: Sucrose

Why does a a qualitative analyses scene work?
Quantitative annalise schemes identify chemicals based on their physical and chemical properties. A qualitative analysis, separates …show more content…

What cation(s) are present in the unknown sample? Explain your reasoning for both the presence and absence of each ion.

Unknown 2: Silver ; Unknown 2 Forms precipitate with HCl, then confirms by turning black with NaOH. It remains clear when tested with NaOH after silver removal indicating that iron is not present. No reaction takes place during the reaction with SCN and HCl further indicating that iron is not present. Potassium ferrocyanide does not form a blue precipitate indicating that zinc is not present. Therefore unknown two only contains silver.

Unknown 6: Iron and Zinc; Unknown 6 does not form a precipitate with HCl indicating that silver is not present. No reaction occurs when NaCl is added to the centrifuge tube. When NaCl is added to the supernatant unknown 6 forms a red precipitate indicating the presence of iron then further confirms by turning red after SCN and HCl are added. Unknown 6 forms a Blue-Black precipitate when potassium ferrocyanide is added indicating the presence of zinc. In conclusnunknown 6 contains iron and zinc.

2. Write a net ionic equation for each of the following steps in your qualitative analysis scheme.

a. Separation of silver …show more content…

Why is it necessary to use excess sodium hydroxide solution when separating iron (III) and zinc ions?
Extra NaOH must be used when precipitating iron (iii) ions because three NaOH molecules are needed to react with each ion of iron as shown in the reaction below.
Fe3+ (aq) + 3NaOH (aq) ---> Fe(OH)3 (s) (red) + 3Na+ (aq)

4. Precipitation reactions are often used in quantitative analysis to determine the precise amount of metal cation in solution. The most common method for the analysis of barium ions, for example, involves precipitation with sodium sulfate to form barium sulfate, which is insoluble in water.

a. Write a formula equation and a net ionic equation for the precipitation reaction of barium chloride with sodium sulfate.
Here is the formula equation
BaCl2(aq) + Na2SO4(aq) ---> BaSO4(s) + 2NaCl(aq)
And here is the Net ionic equation
Ba + SO4(aq) ---> BaSO4(s)

b. How much sodium sulfate must be added to an aqueous solution containing 0.50 g of dissolved barium ions to ensure that all of the barium precipitates as barium sulfate?
.05 g of sodium sulfate must be added since barium ions react in a 1 to 1 ratio with sulfate