Precipitation Test of Cations and Anions

Qualitative Analysis

Purpose:

In this lab, we would tests the ions of Mg2+, Ca2+, Sr2+, and Ba2+,

and enable each to be identified separately. And by using these

observations, we could also identify an unknown. We also would tests

the ions of SO42-, CO32-, Cl-, and I-, that also enable each to be

identified separately, and to be use to identify the unknown.

Safety:

Chemicals include toxic. Remember to wash hands after the experiment.

Procedure Summary;

Part I - Qualitative Analysis of Group 2 Elements

We first mix 0.02M K2CrO4 with each Mg(NO3)2, Ca(NO3)2, Sr(NO3)2 and

Ba(NO3)2 together. Secondly, we mix 0.1M (NH4)2C2O4 instead of 0.02M K2CrO4

together with the same reactants used before. Thirdly, we mix 0.1M Na2SO4

as the added reagent. Then, we mix 0.1M NaOH as the added reagent

before. Precipitates should forms for some, and be recorded in Table 1

with observations. At last, we obtain an unknown solution to identify

the cation by mixing it with the 4 reagents we used before.

Part II- Qualitative Analysis of Selected Anions

We 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

mix1M HNO3 for the onces that formed precipitates. Repeat the first

step by placing 0.1M AgNO3 instead of 1M HNO3. Divded the contents of

the ones that contains ppt in half, then add 6M NH3 to one set of them

and for the other set add 1M HNO3. Using these observation, we obtain

and identify an unknown union. All observations should be recorded in

Table 2.

Pre-lab Questions:

1. What is the difference between qualitative and quantitative

analysis.

Qualitative analysis is a set of procedures used to identify a

particular ion or a sample. Quantitative analysis is used to identify

the amount of ion presence in a solution.

2. What type of reaction will use to identify the cation in part I?

Double replacement and precipitate-forming reaction will be used to