Question

You have been given a sample rock (1.001 kilograms) that has Silver Carbonate throughout. The rock also has some inert material mixed in that will not affect your analysis. You decide that you want to retrieve the Silver (Ag) from the rock, so that is what we will do.

1) To make the Silver soluble, you need to dissolve it. To do this, you choose to use Nitric Acid.

a. Write the balanced equation for the reaction of Silver Carbonate with Nitric Acid. (Yes, you need to determine the formula for both chemicals and the reaction products.)

b.Write the Net Ionic Equation for the reaction.

c.What would the Equilibrium Constant look like? (Use the N.I.E.)

d.Why must we use Nitric Acid to dissolve the Silver Carbonate and not Hydrochloric, Hydrobromic, or Hydroiodic acid

2) You have a solution of Nitric Acid of unknown concentration, so you decide to titrate it with your 0.1250 M solution of NaOH (Acid-Base Titration is when we add a precise amount of a known base solution to an unknown acid solution. When the solution is neutralized, we know how much acid we have.) You end up adding 18.50 mL of the NaOH solution to 20.00mL of a 1/10th dilution of the Nitric Acid solution to neutralize it.

a. What is the balanced equation for the neutralization? (This is an acid-base reaction.)

b. What is the Net Ionic Equation for the reaction?

c. How many moles of acid are in your 20.00mL sample? What is the concentration of the concentrated acid?(Hint: How many moles of base were added? There was a dilution)

3) Now that you have your Nitric Avid concentration, you pulverize 1.00 gram of your rock sample and mix the two. You do this in a special container that captures all the gas(that's a hint) released. When the reaction is done, you produced 36.65 mL of gas at a partial pressure of 0.9687 atm. The gas was at 25.0-degree Celcius at the end

a. Use PV=nRT to determine the moles of gas you obtained.

b. If the sample was 100.0%(w/w) Silver Carbonate, what volume of gas should you have produced (assumed the same partial pressure)?

c.What is the percent Silver Carbonate in your rock sample?

4) Now that you know the percent Silver Carbonate in your main sample, how much of the concentrated Nitric Acid solution do you need to dissolve all the Silver Carbonate in your 1.0 kg of rock? (You will need your balanced equation, your acid concentration, and the percent mass.)

5) What is the molarity of silver ion in the final solution?

6) What kind of reaction would we need to do to get the Silver ion to become Silver metal?

7) River water can contain up to 1.00 ppb of Silver ion. How much water would you need to collect 1.00 gram of Silver? How much Sodium Carbonate would you need to add to that water to precipitate the Silver ion? Since silver metal is running about $0.55 per gram, would this be very economical option?

Answer 1

1a. The chemical formula for silver carbonate and nitric acid are Ag₂CO₃ and HNO₃ respectively. The balanced chemical equation for the reaction between Ag₂CO₃ and HNO₃ is given as

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

1b. The aqueous species are soluble in water and ionize. Decompose the aqueous species into ions and write the complete ionic equation as

Ag₂CO₃ (s) + 2 H⁺ (aq) + 2 NO₃^- (aq) ----------> 2 Ag⁺ (aq) + 2 NO₃^- (aq) + CO₂ (g) + H₂O (l)

Cancel the common ions from both sides and write the net ionic equation as

Ag₂CO₃ (s) + 2 H⁺ (aq) ---------> 2 Ag⁺ (aq) + CO₂ (g) + H₂O (l)

1c. The equilibrium constant for the reaction is written as

K = [Ag⁺]²P_CO2/[H⁺]²

where [..] denote molar concentrations and P_CO2 is the partial pressure of CO₂.