CHM120H5 Lecture Notes - Crc Handbook Of Chemistry And Physics, Chromate And Dichromate, Boca Raton, Florida

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The purpose of the experiment was to identify the ions present in a given unknown solution by performing some standard tests for qualitative detection of some common cations in aqueous solution. Refer to the lab manual1: no deviations were taken from the lab manual. The experimental observations were recorded on the data sheet attached at the end of the report. The observations for the control and the unknown solution were compared and appropriate conclusions were drawn. Table-1 experimental results of the control and the unknown solution. Conclusions on unknown: 2. 5 ml of unknown # 2 and 0. 2 ml of. Add 1 drop of 6m hcl to decant the solution: precipitate from , add 2. 5 ml h2o heat add 3 drops 1m k2cro4, decanted solution from + 0. 5ml of. Decant the clear solution: precipitate from , add 0. 5ml h2o and 0. 5ml of 6m hno3. Cu+2 ions are present: cool solution from , add drops 6m.

Related Questions

What is the main purpose of this experiment?

What are some of the major assumptions of this experiment?

What are some major safety precautions for this experiment?

Qualitative Analysis of Group I Cations

Figure 1. Snack Mix

Are There any Cheese Flavored Snacks in the Mix?

You may have seen bowls of mixed snacks such as the one in Figure 1 at parties or in offices. Which one is your favorite? Some people prefer the salty pretzels, and some like the honey nuts, whereas others prefer the cheese flavored chips.

How do you tell if the bowl contains your favorite flavor snack? You will probably start by looking at the mix and see if you can spot it. If you do, then your search is done. You may however spot a similar snack but still be unsure about the flavor. You could then try to smell it to see if it smells familiar or go straight for the ultimate test: the taste test! Suppose you do not find the snack you are looking for, but you see another one that appeals to you. You will probably follow a similar pattern to identify the flavor of the snack. Similarly, qualitative analysis is used to check for the presence of ions in a mix or to identify unknown ions.

Qualitative Analysis of Ions

Qualitative analysis is used to separate and detect cations (positively charged ions) and anions (negatively charged ions) in a sample substance. The tests that are performed are not concerned with the amount of a substance in the sample as opposed to quantitative analysis, but only with a qualitative answer to the question of whether the substance is present in the sample or not.

The positively charged cations are divided into analytical groups. The groups are defined as sets of substances that can be precipitated with the addition of a single reagent. These groups are not to be confused with periodic system groups. Each cation group can be analyzed with a set of reactions to identify the presence or absence of each member of the group.

Group I Cation Separation and Identification

Qualitative analysis is made easier by the development of a standard scheme that can be followed step by step until all of the cations have either been detected or ruled out. For each group of cations, a flowchart of the scheme is prepared, and one can simply follow the steps and the decision branches in order. The flowchart for the group I cations is shown in Figure 2 below.

Figure 2. Flowchart for Separating and Identifying Group I Cations

Group I cations are silver (Ag+), lead (II) (Pb+2) and mercury (I) (Hg2+2). They can be precipitated from a solution as chlorides in a reaction with HCl. Among these three insoluble chlorides, lead chloride dissolves in hot water. Subsequently, to test whether the lead cation is present, potassium chromate (K2CrO4) is used. Lead cations react with chromate ions to form lead chromate (PbCrO4) as a yellow precipitate. Detection of the mercury (I) cation requires the addition of ammonia solution. This causes mercury (I) chloride to precipitate as the ammonium complex HgNH2Cl, and solubilizes silver chloride as an ammonium complex, [Ag(NH3)2]Cl. Last, the addition of nitric acid (HNO3) confirms the presence of silver ion as it precipitates as AgCl.

About This Lab

In this lab, you will test the identification reactions on individual samples of all three group I cations. You will then use your observations to detect the presence of the Group I cations in two unknown samples.

Lab Report Assistant

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experimentâs questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate studentsâ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Exercise 1: Qualitative Anion Tests

Data Table 1. Anion Confirmation Tests.

Chemical	Anion	Addition of AgNO₃	Addition of HCl
NaBr	Bromide	It became white and cloudy	Still was white and cloudy
Na₂CO₃	Carbonate	Clear inside white and cloudy around the outside	Still white and cloudy but bubbles start to form
NaCl	Chloride	Turn white cloudy on bottom clear on top	Still white cloudy on bottom clear on top
NaI	Iodide	In the middle very dark and cloudy fades out lighter white around the middle	Became a little separate
Na₂SO₄	Sulfate	Clear	Became white and cloudy
Na₂S	Sulfide	Turn a brown color in the middle but separated from the clear	The brown becomes more separate from the clear
Unknown #103	CO3^2-	White and cloudy Small particles	Bubbles form white and cloudy
Unknown #104	S^2-	Turn brown color I the middle around clear	Some of the brown disappeared and become separate

Flow chart:

Solution containing: Br-, CO3^2-, Cl-, I-, SO4^2-, and S^2-

{AgBr(cloudy), Ag2CO3(cloudy), AglCloudy),Agl(very dark), Ag2S-(brown)} {So4^2-}

{AgBr(cloudy), AgCl(cloudy), Agl(very cloudy), Ag2S(brown)} {CO3^2-(decomposes to give CO2 gas)}

Data Table 2. Cation Flame Tests.

Chemical	Cation	Flame Observations
KI	Potassium	LIGHT PINK
CaCl₂	Calcium	RED
LiOH	Lithium	FUSHA PINK
NaCl	Sodium	ORANGE
Cu(NO₃)₂	Copper	TEAL
Unknown #105		TEAL
Unknown #106		LIGHT PINK
Unknown #107		RED

Data Table 3. Complete Chemical Identification.

Chemical	Cation	Anion Test Observations	Anion	Complete Chemical Name and Formula
Unknown #105
Unknown #106
Unknown #107

Just need help answering the ***** question under conclusions. here is my worksheet with information

Record your absorbance measurements for the copper (II) sulfate solution in the table below.

Wavelength (nm)	Absorbance
400	0.00 nm
420	0.00 nm
440	0.00 nm
460	0.00 nm
480	0.00 nm
500	0.00 nm
520	0.00 nm
540	0.00 nm
560	0.02 nm
580	0.05 nm
600	0.09 nm
620	0.14 nm
640	0.22 nm
660	0.35 nm
680	0.50 nm
700	0.63 nm

Record your absorbance measurements for the cobalt (II) chloride solution in the table below.

Wavelength (nm)	Absorbance
400	0.00 nm
420	0.1 nm
440	0.07 nm
460	0.07 nm
480	0.16 nm
500	0.23 nm
520	0.22 nm
540	0.13 nm
560	0.07 nm
580	0.04 nm
600	0.00 nm
620	0.00 nm
640	0.00 nm
660	0.00 nm
680	0.00 nm
700	0.00 nm

Data Analysis

Create and save a graph of absorbance (y-axis) versus the wavelength (x-axis) for both copper (II) sulfate and cobalt (II) chloride. Click the graphing icon below to create your graph.

Experiment 2: Measure Absorbance versus Concentration for Cu⁺² Ions

Lab Results

What wavelength did you use to measure the absorbance of the copper (II) sulfate solutions?

700 nm

Data Analysis

Create and save a graph of absorbance (y-axis) versus the concentration of the copper (II) sulfate solutions (x-axis). Click the graphing icon below to create your graph. Click the box underneath the graph to show the trendline. It will automatically calculate your slope and intercept.

The y-intercept of the plot of absorbance versus concentration is approximately 0. Why is this?

It should be a straight line obtained by having a slope of = 1 and y-intercept = 0.

Experiment 3: Determine the Cu⁺² Concentration in Unknown Solutions of Copper (II) Sulfate

Lab Results

How many mL of the unknown solutions did you use for your absorbance measurements?

10 mL

Data Analysis

Determine the copper (II) sulfate concentrations in your two unknown samples from the calibration plot.

wavelength used: 700 nm

absorbance unknown: a. 0.08 b. 0.12

Conclusions

*******Were the unknown solutions more or less concentrated than the copper (II) sulfate solution used in experiment 1?

Given the data in the table below, what is the concentration of the unknown solution? Both solutions contain the same substance.

standard solution concentration	1.25 M
standard solution absorbance	0.75
unknown solution absorbance	0.38

0.63 M is the concentration of the unknown solution.

CHM120H5 Lecture Notes - Crc Handbook Of Chemistry And Physics, Chromate And Dichromate, Boca Raton, Florida

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