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11 Nov 2019

Solder is an alloy, or mixture, of the metals tin and lead. A 1.50 g sample of solder is dissolved in acid and all of the Sn oxidized to Sn 2+ . The Sn 2+ is reacted with a 0.0525 M solution of sodium dichromate according to the following net ionic equation (included in the picture) and 26.75 mL of the sodium dichromate solution was needed to completely react with the Sn 2+. What is the perect by mass of Sn in the sample of alloy?

Can you please explain the steps you took to solve this problem? I'm given a lot of values here and I'm just not sure where exactly to start or how to utilize these numbers. Please excuse my handwriting in this picture.

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Jamar Ferry
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15 Jan 2019

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Related questions

I'm trying to find the amount of ethanol in an unkown solution by titration but I'm having trouble calculating it. Molarity of thiosulfate: 0.0806 M, amount of dichromate used: 15 mL

here is what my lab manual says:

The titration is based on the oxidation of ethanol with an oxidizing agent, such as potassium dichromate. Depending on the solution pH and the amount of potassium dichromate added, ethanol can be oxidized to ethanal (acetaldehyde, CH3CHO) via reaction 1, or to ethanoic acid (acetic acid, CH3COOH) via reaction 2:

3C2H5OH(aq) + Cr2O72-(aq) + 8H+ ? 3CH3CHO(aq) + 2Cr3+(aq) + 7H2O (1)

3C2H5OH(aq) + 2Cr2O72- (aq) + 16H+ ? 3CH3COOH(aq) + 4Cr3+ (aq) + 11H2O (2)

In order to ensure all ethanol has completely reacted via reaction 2, a known and excess amount of potassium dichromate (let’s call it potassium dichromate total) is added into a sample solution containing ethanol. The amount of unreacted potassium dichromate is then determined by reacting with potassium iodide solution via reaction 3 to form iodine:

Cr2O72- (aq) + 14H+ + 6I-(aq) ? 2Cr3+ (aq) + 7H2O(l) + 3I2 (aq) (3)

From the reaction 3, we know that 1 mole of dichromate ions can produce 3 moles of I2. Therefore, we just need to determine how much moles of I2 is produced in reaction 3, then, we can get the moles of unreacted potassium dichromate. Subtracting the moles of unreacted potassium dichromate from the moles of potassium dichromate total gives the moles of potassium dichromate that have reacted with ethanol. Then, from the stoichiometry of reaction 2, one should be able to know how much ethanol is in the test solution.

How to know the moles of I2 produced in reaction 3? The I2 is titrated with sodium thiosulfate (Na2S2O3) via the following reaction 4:

I2(aq) + 2S2O32-(aq) ? 2I-(aq) + S4O62-(aq) (4)

Experimental data: For the standardization of thiosulfate it took 31.7 mL of thiosulfate to reach the end point, for the unknown solution, it took 23.85 mL of thiosulfate to reach the endpoint. How do I use these numbers to find the amount of ethanol in the unknown solution?

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Thank you

Balance the following Chemical Equations:

____Fe(s) + ____H2O(g) ® ____Fe3O4(s) + ____H2(g)

____C2H6(g) + ____O2(g) ® ____CO2(g) + ____H2O(g)

(C) ___ KClO3 (s) ® ___ KCl (s) + ___ O2 (g)

___ C6H14 (l) + ___ O2 (g) ® ___ CO2 (g) + ___ H2O (g)

___ C3H8O3 (l) + ___ O2 (g) ® ___ CO2 (g) + ___ H2O (l)

___ NaN3 (s) ® ___ Na (s) + ___ N2 (g)

__ C3H5N3O9 ® __ CO2 + ___ N2 + ___ H2O + ___ O2

Write and Balance the equations:

Aqueous calcium hydroxide reacts with aqueous sodium carbonate to produce solid calcium carbonate and aqueous sodium hydroxide.

Solid iron reacts with Oxygen gas to form solid Iron (II) oxide

Copper(II) sulfide is oxidized by molecular oxygen to produce gaseous sulfur trioxide and solid copper(II) oxide. The gaseous product then reacts with liquid water to produce liquid hydrogen sulfate as the only product. Write the two equations which represent these reactions.

Indicate what type, or types, of reaction each of the following represents: (precipitation, acid-base, and oxidation-reduction.)

(A) H2O(g) + C(s) ⟶ CO(g) +H2(g)

(B) 2KClO3(s) ⟶ 2KCl(s) +3O2(g)

(C) Al(OH)3(aq) +3HCl(aq) ⟶ AlCl3(aq) + 3H2O(l)

(D) Pb(NO3)2(aq) + H2SO4(aq) ⟶ PbSO4(s) + 2HNO3(aq)

4. Silver can be separated from gold because silver dissolves in nitric acid while gold does not. Is the dissolution of silver in nitric acid an acid-base reaction or an oxidation-reduction reaction? Explain your answer.

5. Determine the oxidation states of the elements in the compounds listed. None of the oxygen-containing compounds are peroxides or superoxides.

(A) H3PO4

(B) Al(OH)3

(C) SeO2

6. Complete and balance the following acid-base equations:

(A) A solution of HClO4 is added to a solution of LiOH.

(B) Aqueous H2SO4 reacts with NaOH.

7. Write the molecular, total ionic, and net ionic equations for the following reactions:

(A) Ca(OH)2(aq) + HC2H3O2(aq) ⟶

(B) H3PO4(aq) + CaCl2(aq) ⟶

8. Write the balanced equation, then calculate the number of moles and the mass of Mg required to react with 5.00 g of HCl and produce MgCl2 and H2. Ans: 1.67 g Mg

9. H2 is produced by the reaction of 118.5 mL of a 0.8775-M solution of H3PO4 according to the following equation: 2Cr + 2H3PO4 ⟶ 3H2 + 2CrPO4. How many grams of H2 are produced? Ans: .315 g H2

10. Automotive air bags inflate when a sample of sodium azide, NaN3, is very rapidly decomposed.

2NaN3(s) ⟶ 2Na(s) + 3N2(g)

What mass of sodium azide is required to produce 2.6 ft3 (73.6 L) of nitrogen gas with a density of 1.25 g/L?

Ans: 142 g NaN3

11. Urea, CO(NH2)2, is manufactured on a large scale for use in producing urea-formaldehyde plastics and as a fertilizer. What is the maximum mass of urea that can be manufactured from the CO2 produced by combustion of 1.00 x 104 grams of CO2?

CO2(g) + 2NH3(g) ⟶ CO(NH2)2(s) + H2O(l)

Ans: 1360 g urea

12. What volume o f 0.750 M hydrochloric acid solution can be prepared from the HCl produced by the reaction of 25.0 g of NaCl with excess sulfuric acid? NaCl(s) + H2SO4(l) ⟶ HCl(g) + NaHSO4(s)

Ans: .570 L

13. A sample of 0.53 g of carbon dioxide was obtained by heating 1.31 g of calcium carbonate. What is the percent yield for this reaction? CaCO3(s)⟶CaO(s) + CO2(s)

Ans: 92.0 %

14. Citric acid, C6H8O7, a component of jams, jellies, and fruity soft drinks, is prepared industrially via fermentation of sucrose by the mold Aspergillus niger. The equation representing this reaction is

C12H22O11 + H2O +3O2 ⟶2C6H8O 7+ 4H2O

What mass of citric acid is produced from the reaction of 150. grams of sucrose if the yield is 92.30%?

Ans: 155 g

15. The phosphorus pentoxide used to produce phosphoric acid for cola soft drinks is prepared by burning phosphorus in oxygen.

(A) What is the limiting reactant when 0.200 mol of P4 and 0.200 mol of O2 react according to P4+5O2 ⟶ P4O10?

(B) Calculate the percent yield if 10.0 g of P4O10 is isolated from the reaction.

Ans: 88.0 %

16. What is the limiting reactant when 1.50 g of lithium and 1.50 g of nitrogen combine to form lithium nitride, a component of advanced batteries, according to the following unbalanced equation? Li + N2 ⟶ Li3N

Ans: Li

17. What is the concentration of NaCl in a solution if titration of 15.00 mL of the solution with 0.2503 M AgNO3 requires 20.22 mL of the AgNO3 solution to reach the end point?

AgNO3(aq) + NaCl(aq) ⟶ AgCl(s) +NaNO (aq)

Ans: .3374 M

18. In a common medical laboratory determination of the concentration of free chloride ion in blood serum, a serum sample is titrated with a Hg(NO3)2 solution.

2Cl−(aq) + Hg(NO3)2(aq) ⟶ 2NO3−(aq) + HgCl2(s)

What is the Cl− concentration in a 0.25-mL sample of normal serum that requires 1.46 mL of .000825 M Hg(NO3)2(aq) to reach the end point?

Ans: 0.009636 M

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