Aclass is given a demonstration of solution chemistry and solubility equilibria. passage: a 6.57-g sample of niso4•6h2o (molar mass 262.84) is dissolved in enough water to make 50.00 ml of a green solution, and 7.15 g of na2co3•10h2o (molar mass 286.14) is dissolved in enough water to make 50.00 ml of a colorless solution. the two solutions are mixed, and a green precipitate forms. the resulting slurry is divided into two equal portions. to one portion is added an excess of 6 m hcl, which results in the disappearance of the precipitate and a rapid evolution of a gas. to the second portion is added a few milliliters of 6 m nh3. the precipitate dissolves, and a blue solution forms. question: according to the information in the passage, the gas that evolves is: a) sulfur dioxide. b) sulfur trioxide. c) carbon dioxide. d) carbon monoxide.

The gas that evolves must be carbon dioxide.

Explanation:

There is two reactions taking place: first, nickel sulfate reacts with sodium carbonate yielding sodium sulfate and nickel carbonate, which is a green solid. Then nickel carbonate reacts with hydrochloride, yielding nickel chloride, carbon dioxide and water.

1) NiSO4 (aq) + Na2SO4 (aq) = NiCO3 (s) + Na2SO4

2) NiCO3 (s) + 2 HCl (aq) = NiCl2 + CO2 + H2O

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.

explanation: it gains negative electrons, therefore becoming negatively charged. as charge cannot be created, nor destroyed, only transferred, this leaves the wool positive. now that they have opposite charges, the two items attract.