Astudent was given a solid containing a mixture of nitrate salts. the sample completely dissolved in water, and upon addition of dilute hcl, no precipitate formed. the ph was lowered to about 1 and h2s was bubbled through the solution. no precipitate formed. the ph was adjusted to 8 and h2s was again bubbled in. this time, a precipitate formed. which compounds might have been present in the unknown?

Explanation:

The will be a precipitation of the nitrates throughout the reactions.

The nitrates form after the pH was increased. One of the properties to this reaction is the slow solubility of the nitrate salts. The nitrates are strongly binding salts. Hence the slow formation of the salts.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2

a is the correct answer