Question

Aqueous solutions of Na2CO3 and Ca(NO3)2, 0.10 M each, are combined. A white precipitate is observed in the container after mixing. The precipitate is filtered and carefully rinsed with distilled water to remove other ions. A sample of the precipitate is added to 100 mL of 0.1 M NaCl. A second sample of the precipitate is then added to 100 mL of 0.1 M HCl. What would be observed in each case

Answer 1

The question is incomplete. Here is the complete question.

Aqueous solutions of $Na_{2}CO_{3}$ and $Ca(NO_{3})_{2}$, 0.10 M each, are combined. A white precipitate is observed in the container after mixing. he precipitate is filtered andcarefully rinsed with distilled water to remove other ions. A sample of the precipitate is added to 100 mL of 0.1 M NaCl. A second sample of the precipitate is then added to 100 mL of 0.1 M HCl. What would be observed in each case?

                 Observation upon                                         Observation upon

               addition of precipitate                                  addition of precipitate

                      to NaCl(aq)                                                       to HCl(aq)

(A)     additional precipitates forms                        no visible reaction occurs

(B)     no visible reaction occurs                            gas is produced and some                                                                                        precipitate dissolves

(C)     no visible reaction occurs                             no visible reaction occurs

(D)     additional precipitates forms                       gas is produced and some

                                                                                    precipitate dissolves

Answer: (B) No visible reaction occurs; Gas is produced and some precipitate dissolves

Explanation: When aqueous solutions of $Na_{2}CO_{3}$ and $Ca(NO_{3})_{2}$ are combined, it reacts according to the following balanced equation:

$Na_{2}CO_{3}+Ca(NO_{3})_{2}$ → $CaCO_{3}_{(s)}+2NaNO_{3}_{(aq)}$

forming calcium carbonate ($CaCO_{3}$), which, as it is insoluble in water, precipitates as a solid of the color white. This process is Precipitation and this reaction is a Precipitation Reaction.

When calcium carbonate reacts with NaCl it produces:

$CaCO_{3}+2NaCl$ → $CaCl_{2}+Na_{2}CO_{3}$

Now, calcium chloride is an inorganic compound very soluble in water, so, in this reaction, there are no precipitate and no visible reaction occurs.

When $CaCO_{3}$ reacts with hydrochloridric acid, the balanced reaction is

$CaCO_{3}+2HCl$ → $CaCl_{2}+H_{2}CO_{3}$

which, also produces calcium chloride and carbonic acid.

Both are soluble in water but, when carbonic acid is in an "aqueous state", carbonic acid, it dissociates, forming carbon dioxide and water. Therefore, gas is produced and some precipitate dissolves.

In conclusion, sentence B is the correct alternative.