Question

QUESTIONS: Expt. 21 Name: Silver nitrate is added to solution containing an unknown salt. An off-white colored precipitate Torms Nitric acid is added to the mixture the precipitate dissolves and gas is given off Analyze this data and determine the anion present a CH b. Br d POS- e. CO 2 A dark glass bottle of chemicals is found in cleaning out an old basement Part of the label has been eaten away with age. Only the last part of the label is readable. From the legible portion, the word nitrate is found. A small amount of the unknown solid is dissolved in delonized water Sodium chloride is added to the solution. A white precipitate forms which is insoluble in nitric acid. Analyze the data and determine what cation is present in the bottle. Assuming the bottle contains only one substance, what is the formula for the compound in the bottle. (Think creatively on this one.) a. Ca(NO3)2 b. AgNO3 C. CINO d. Ba(NO3)2 e. C2O4(NO3)2 A field geologist many times will carry a small dropper bottle of a strong acid, HCl (very similar to nitric acid), to help with the identification of samples. A rock is found to give off odorless gas bubbles when a few drops of the strong acid are added. From the set of ions in this lab, which anion is most likely in the rock? a. CH b. Br C. d. PO, e. C0,2 4. A solution gives a pale green flame test. Which cation is present? a. Na b. K c. Ca- d. Fe3 e. NHA f. None of the above

Answer 1

1. Ag^+ (silver ion) from AgNO3(silver nitrate) forms precipitates with all the given anions but only CO3^2- will form such precipitate which will give gas (CO2) on adding nitric acid.

No other anion forms such precipitate which given Off gas with HNO3 .

The Reaction is as follows ;

CO3^2-(aq) + 2AgNO3(aq) >>>>>>>>> Ag2CO3(s) + 2NO3^-(aq)

aq = aqueous , s = solid precipitates .

Further on adding HNO3

Ag2CO3(s) + 2HNO3(aq) >>>>>>>> 2AgNO3(aq) + CO2(g) + H2O(l)

Thus CO2 gas is given off on adding HNO3.

Hence option (e) is correct .

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