1

Your Lab Final - 21 points

• 25-30 min on the last day of lecture, Wed Dec 9

• Short answer & multiple choice

• Bring your calculator & common sense

• Review your old labs

• Take note of basic calculations (including stats), chemical equations, techniques used

2

Volumetric Determination of Zinc and CalciumUsing Complexometric Titration

First Week:

1) Preparation and Standardization of EDTA solution (10ppt) – save for week 2

2) Use SciFinder Scholar or Web of Science to find reference (page 3)

Second Week:

1) Analyze Water Sample for Ca2+ You must do this first!!! Geology will use your data!

2) Analyze Cold-Eeze Lozenge for Zn2+

3) Check-in & Course Evaluations

3

PrecipitationGravimetric Ca: calcium oxalate

Acid/BaseVolumetric Acid: KHP + OH ¯

RedoxGasiometric Nitrite:

NO2- + H+ NH2SO3¯ → N2 + HSO4¯ + H2O

Complexation This lab – our final experiment!

Volumetric Ca & Zn: EDTA

4 Classes of ReactionsUsed quantitatively

4

Development of Cold-Eeze Lozenges

One of the people involved in the designed to reduce the duration and severity of the common cold by introducing zinc ions into the body is J. C. Godfrey

We are going to get one of the references in his research that talks about this research to treat the common cold, using Scifinder Scholar or Web of Science.

The Libraries of The Claremont Colleges

You will do this in the computer room (113) after completing standardization.Write down the reference and a one sentence summary of the abstract inyour report.

5

Polydentate or Multidentate Ligands

Like CO32-

Called Chelates (claw)

1 Ligand, but2 bonds

Like :NH3

6

O

OO

ON

N

O

O

O

O

-

--

-

....

Fully deprotonated EDTA can bind to metal ion at 6 sites

1

3

2

5

4

6

7

8

Eriochrome Black- T Indicator

Deprotonated indicator (In-) in the presence of excess metal ions (Mg+2) forms a wine-red complex (MgIn-)

Add EDTA → at the endpoint MgEDTA forms

InH turns greyish – blue

Make mock solution for comparison

Note that there are 2 different indicators-

one for Ca+2 and one for Zn+2

9

Week 1 – Standardize EDTA

Prepare 500 ml of a 0.020 M EDTA solution

Use 250 ml volumetric flask to the mark emptying (2x) into a clean 800 mL beaker, repeat. Dissolves slowly (> 5 min). Heat if necessary but cool before titrating.

Preparation of the CaCO3 in beaker, transfer to volumetric flask

Also, after titrating (3 trials, 5-10ppts), use SciFinder Scholar or Web of Science in 113. If time permits, titrate water sample (step 3, page 4).

10

Week 2 – Evaluations, Water and Lozenge Analysis, Check out

Titrate water samplesWater hardness results go to

Prof.Reinen of Geology (obtain 100mL from lab assistant)

Use 6-7 drops of indicator

Titrate three lozengesMake buffer solution

Remember to take masses of each before crushing with mortar & pestal and determine amount used in each titration

11

How are you going to make the buffer?

• pH = pKa + log [A-]/[HA] where A- = acetate ion in this case

• [HA] = 0.02500L (1.00M)/0.250L = 0.100 M • pKa (HA) = 4.74

• 5.5 = 4.74 + log [A-]/0.100

• [A-] = 0.5754 M

• n(A-) = 0.5754 M (0.2500L) = 0.1439 moles• m(NaA3H2O) = 0.1439 moles (136.08 g/mole) = 19.6 grams for the hydrate• m(NaA) = 0.1439 moles (82 g/mole) = 11.8 grams for the anhydrous salt