Chem 253 – Introduction to Quantitative Analysis – Fall Semester 2006

Instructor:      Dr. Frank Cheng; ifcheng@uidaho.edu; 208-885-6387

Office:           Renfrew Hall 026A

Office Hours: M & F 2:30 - 4:30

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Links of Interest to this Course.

                                                  office hours

Sec 01    Noel Palmer                   M 11:30-12:30 & T 2:30-3:30

Sec 02    Przemeka Brejna            R 8:30-10:30

Sec 03    Emily Hull                      M 9:25 - 10:25 & W 11:25 - 12:25

If you can’t make it to your TA’s office hours, try to see one of the other Chem 253 TAs during their office hours.

Hand-in Assignments

**These assignments are to be worked on only by you with no help from other students**

Check here for the answer to the assignments below.

1] The molality of a solution is 1.88. If the density of that solution is 1.53 g/mL and the molecular weight of the solute is 93.45 g/mol what is the molarity of that solution?

2] A new method for the analysis of N in a sample is developed. An NIST standard indicates that the sample is 0.123% N and the new method of analysis gives results of 0.118, 0.112, 0.119, and 0.115 %. What is the 95% confidence interval for the new method of analysis?

Now consider, does your result indicate the presence of a determinate error? Explain

3] An instrumental analysis was conducted on a soil sample for Cd²⁺ (AW 112.411 g/mol). A 100-gm sample of soil was extracted with 100-mL of 10% CH₃COOH(aq). An analysis of that 100-mL extract yielded a signal of 4.31 mA. 10-mL of 1.51e-3 M solution of Cd²⁺ was added to the sample solution and the signal measured as 6.77 mA. What is the concentration of Cd²⁺ in ppb the original sample?

4] Limestone and marble consists mostly of CaCO₃. Acid rain is formed by the emission of SO₂ and SO₃ forming sulfurous and sulfuric acids respectively:

            SO₂ + H₂O ⇄ H₂SO₃

            SO₃ + H₂O ⇄ H₂SO₄

The average pH of acid rain is 4.2. What is the solubility of CaCO₃ at this pH? See http://wwwbrr.cr.usgs.gov/projects/SW_corrosion/erosion/indexB.html for more information regarding acid rain.

5] A 0.2500g sample contained only NaBr (MW 102.89) and NaCl (MW 58.44). It was dissolved into water and precipitated with excess AgNO₃. The precipitate (AgBr(s) (MW 187.80) & AgCl(s) (MW 143.35)) was dried. The mass of this precipitate weighed 0.5348 g. What is the mass of NaCl and NaBr in the sample?

6] Calculate pCl for the following titration:

            a) 20.00 mL of 0.0600 M Hg₂(NO₃)₂ is added to 4.00 mL of 0.150 M NaCl

            b) 20.00 mL of 0.0600 M Hg₂(NO₃)₂ is added to 16.00 mL of 0.150 M NaCl

            c) 20.00 mL of 0.0600 M Hg₂(NO₃)₂ is added to 32.00 mL of 0.150 M NaCl

    Hg₂Cl₂  K_sp = 1.3e-18

7] Calculate the pH when the following volumes of 0.100 M KOH are added 50.00 mL of 0.150 M of a weak acid HA whose K_a is 8.0e-5

a)      50.00 mL

b)      75.00 mL

c)      100.00 mL

8] Calculate pCa for a titration in which 50.00 mL of 2.00e-2 M Ca(NO₃)₂ is titrated with 0.100 M EDTA at pH 9.00.

a)      0.00 mL

b)      5.00 mL

c)      10.00 mL

d)      20.00 mL

9] What is pZn when 10.00 mL of 1.00e-3 M of Zn²⁺ is titrated with 0, 2.50, 5.00, then 10.00 ml of 2.0e-3 M EDTA in the presence of 0.100 M NH3 at pH 11?

Due 12-10-06

10] Derive the titration curve for the titration of 50.00 mL of 0.0500 M Fe²⁺ with 0.100 M Ce⁴⁺ using these volumes of titrant:

a)       5.00 mL of 0.100 M Ce⁴⁺

b)      25.00 mL

c)       25.10 mL

Rxn: Fe²⁺ + Ce⁴⁺ = Ce³⁺ + Fe³⁺

Chem 253 Lab

Padlock:      A key or combination padlock with up to 3/8 inch diameter shank

Goggles:      Only departmentally approved safety goggles will be permitted to be worn in the laboratory. These are available for purchase from ChemStores (Basement, Renfrew Hall).    It is Chemistry Department policy that safety goggles MUST be worn at all times in the laboratory when anyone is working at an experiment or handling chemicals.

Data Storage   A few of the Chem 253 labs require that you take home computer data for further analysis. It is highly recommended that you have a USB flash memory device (sometimes referred as a “pen drive”) for this purpose. Generally, these devices cost less than $25 for a 128 MB model at any discount, computer, or office supply store.

Sandals:       In light of the fact that hazardous chemicals are frequently used in this course, neither sandals nor shorts may be worn in the laboratory.

Laboratory Schedule

Section 1: REN 337           T, R 8:30-11:20 AM

Section 2: REN 337           T, R 2:30-5:20 PM

Section 3: REN 337           T, R  6:30-9:20 PM

Click on the hyperlinks for the instructions and bring the printed documents to lab with you. You will need a MS Word to view these documents. If you don't have MS Word try Openoffice (It's free!).