In an experimental lab problem, a particular mixture contains three out of the f
ID: 900711 • Letter: I
Question
In an experimental lab problem, a particular mixture contains three out of the four compounds listed in the table below.
Compound
Soluble in:
Cold water
Hot water
3M HCl
3M NaOH
Benzoic acid
No
Yes
No
Yes
Mg(OH)2
No
No
Yes
No
Na2SO4
Yes
Yes
Yes
Yes
Zn(OH)2
No
No
Yes
Yes
The mixture is extracted with hot water and then filtered. Compound A is obtained by evaporating the filtrate to dryness. Compound A would not dissolve in 3M HCl.
The solid residue containing the other two compounds dissolves completely in 3M HCl. Then, when excess 3M NaOH is added, Compound B forms a solid again.
After compound B is removed by filtration, the solution is evaporated to yield Compound C as a solid.
What are the identities of Compounds A, B and C?
Benzoic acid
Mg(OH)2
Na2SO4
Zn(OH)2
Compound
Soluble in:
Cold water
Hot water
3M HCl
3M NaOH
Benzoic acid
No
Yes
No
Yes
Mg(OH)2
No
No
Yes
No
Na2SO4
Yes
Yes
Yes
Yes
Zn(OH)2
No
No
Yes
Yes
Explanation / Answer
A is benzoic acid
B is Mg(OH)2
C is Zn(OH)2
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