Question

What are some of the key characteristics of unknown sample of an aqueous solution containing an ionic compound? Specific questions: 1. Given that the cation is from Group 1A, what is the identity of the group 1A metal ion in your solution? 2. Given that the ionic compound contains either chloride or hydroxide, how can you determine which? (Two pieces of evidence are required and one must be related to solubility rules) 3. What is the concentration of your solution? (Your unknown sample is known to be about 1 M, but you need to determine the concentration to 3 significant figures using titration. You should plan ahead so that you know approximately what volume of your sample you will need in order to use approximately 25 mL of 0.100 M sulfuric acid for the titration). I'm confused as to how I would go about figuring out these things when even actual information.

Answer 1

Ans:

Ionic compounds are more appropriately identified with their chemical properties. In the qualitative analysis procedure, the chemical properties of an unknown substance are determined by systematically reacting the unknown with a number of different reagents.And solublity test,flame test,reaction with HNO3,NaOH,NH3 solution,AgNO3 etc. A scheme of analysis is there to test ionic compounds as they show specific reactions and can be identified easily.

1.ans:-

a. All the Group IA cations have soluble hydroxides and carbonates. They do not precipitate from the qualitative analysis scheme.

b. All the Group IA cations are distinguished by flame color: lithium gives a red flame, sodium gives bright yellow (even in trace amounts), potassium gives violet.

[Flame Tests :

1. Clean the end of a nichrome wire (attached to a glass rod) by dipping it into concentrated HCl and heating it to a red glow in the hottest part of a flame (tip of the inner blue cone). Repeat the HCl treatment until the wire imparts no colour when burned in the flame.

2. Dip the end of the loop into one of the solutions and then hold in at the end of the flame (not in the hottest part of the flame). Note the colour of the flame. Repeat the procedure looking through cobalt glass and note whether there is a colour change. ]

2.ans: -

test 1. Acidify the test solution with 3 M HNO₃. Then add several drops of 0.1 M AgNO₃. If a white precipitate forms, centrifuge and remove the supernatant. To the precipitate add 6 M NH₃ with stirring. If the precipitate dissolves, add 6 M HNO₃ to the solution. A white precipitate will form if the original test solution contained Cl^-.

test 2. Chlorides are confirmed by the chromyl chloride test. When the salt is heated with K₂Cr₂O₇ and concentrated H₂SO₄, red vapours of chromyl chloride (CrO₂Cl₂) are produced. Passing this gas through a solution of NaOH produces a yellow solution of Na₂CrO₄. The acidified solution of Na₂CrO₄ gives a yellow precipitate with the addition of (CH₃COO)₂Pb.

Test 3 : - Test for hydroxide ion, OH^-1

(i) It turns litmus blue, variety of colours universal lndicators dark green – violet for weak – strong.

A pH meter gives a value of more than 7, the higher the pH number the stronger the alkali, the higher the OH^– concentration

(ii) Add a little of an ammonium salt.

If strongly alkaline ammonia gas should be released.

3.ans: -

concentration of your solution is 1 M and titrating with

25 mL of 0.100 M sulfuric acid, So

M1V1 = M2V2

25ml x 0.100M = 1M x V2

V2 = 2.5 ml

volume of your sample must be 2.5ml