Answer the following questions that relate to laboratory observations and proced

Question

Answer the following questions that relate to laboratory observations and procedures. An unknown gas is one of three possible gases: nitrogen, hydrogen, or oxygen. For each of the three possibilities, describe the result when the gas is tested using a glowing splint (a wooden stick with one end that has been ignited and extinguished, but still contains hot, glowing, partially burned wood). The following three mixtures have been prepared: CaO plus water, SiO_2 plus water, and CO_2 plus water. For each mixture, predict whether the pH is less than 7, equal to 7, or greater than 7. Justify your answers. Each of three beakers contains a 0.1 M solution of one of the following solutes: potassium chloride, silver nitrate, or sodium sulfide. Three beakers are labeled randomly as solution 1, solution 2, and solution 3. Shown below is a partially completed table of observations made of the results of combining small amounts of different pairs of the solutions. Write the chemical formula of the black precipitate. Describe the expected results of mixing solution 1 with solution 3. Identify each of the solutions 1, 2 and 3.

Explanation / Answer

52. Lab tests

(a) with glowing splint, flammable gases such as Oxygen ignites the flame; Hydrogen would ignite the flame with a squeaky pop sound. No-flammable gas nitrogen would extinguish the lighted splint.

(b) CaO forms Ca(OH)2 which is basic so pH of solution would be greater than 7. SiO2 does not dissolve in water so pH would be equal to 7. CO2 with water forms weak acid H2CO3, so pH is less than 7.

(c) (i) Black precipitate = Ag2S

(ii) solution 1 (AgNO3) would give a white precipitate with solution 3 (KCl) = AgCl

(iii) solution 1 : AgNO3

solution 2 : Na2S

solution 3 : KCl

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