A sample consists of one or two of the following salts: Na,CO, KNO, CaCl. It is

Question

A sample consists of one or two of the following salts: Na,CO, KNO, CaCl. It is known that the sample completely dissolves in water and when dilute HCl is added to the solution effervescence is observed. You may need to use additional resources (like your tect book) to answer these questions. 4. a· b. c. Look at the solubility rules; are all of the salts soluble? Write out the equations of the dissolution of each salt. If any of the ions produced from the dissolution of each salt were mixed together would an insoluble precipitate form? If yes, list the salt that would form and why it would not be soluble and list the two original salts that must not both be present. Which of the salts, Na,Co, KNO, or Cacl, would form effervescence when HCl is added? Write out the balanced net-ionic equation. d. e. What salt, Na,co, KNO, or CaCl, must be absent and why? f. What salt, Na,CO,, KNO, or CaCl, must be present and why? g What salt, Na,CO,, KNO, or CaCl, is unknown if it is present or absent based on the information given?

Explanation / Answer

a)

Solubility rules:

- Most alkali metal (group I metals) are always soluble

- Cations/Anions such as NH4+, HCO3-; ClO3-, NO3- are always soluble

- Most halides are soluble, F-,Cl-,Br-,I-, exceptions = Ag+, Hg2+2, Pb+2 compounds

- Most sulfates are soluble (SO4-2); exceptions = Ag+, Ca+2, Sr+2, Ba+2, Hg2+2, Pb+2 compounds

- In general (except all alkali metals) these ions will NOT be soluble: PO4-3, CrO4-2, S-2, CO3-2

b)

dissolution:

Na2CO3= 2Na+ + CO3-2

KNO3 = K+ + NO3-

CaCl2 = Ca2+ + 2Cl-

c)

if we mix:

Ca+2 and CO3-2 ions, we will form CacO3(s)

original salts, CaCl2 + Na2CO3

d)

only Na2CO3, since it will form

CO3-2 + 2H+ --> H2O + CO2(g)

e)

CaCl2, since there is no precipitate, and Na2CO3 is present

f)

Na2CO3 must likely, due to gas /efervencese

g)

KNO3, since it will not react with anything

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