EXPERIMENT 4

EXPERIMENT 4:

Quantitative determination of calcium in powdered milk

I. INTRODUCTION:

1. PURPOSE

Measuring the calcium concentration contains in powdered milk samples to determine

how much of the calcium in milk or knowing the amount of calcium that contain in milk

Understanding the practical steps of doing the experiment

2. GENERAL PRINCIPLE

Oxalate ammonium will precipitate all calcium ion in any solution when the experimenter set up all following conditions severely:

pH of solution environment is greater than 4 The hot, saturated (COONH4)2 solution is filled only one time into the sample containing

calcium ion. Freeze the solution immediately after the solution has heated up for 1 minute

This method can be used for calcium quantification in milk, blood sample, urine, food, etc. and the reactions are performed as following:

Ca2+ + (COONH4)2→ 2NH4+ + Ca(COO)2 (1)

Ca(COO)2 + H2SO4 → CaSO4 + (COOH)2 (2)

5(COOH)2 + 2KMnO4 + 3H2SO4 → K2SO4 + 2MnSO4 + 10CO2

3. MATERIAL:

Equipment CategorizeRacemic crucibles Muffle furnaceDesiccatorBuretteErlenmeyer flasks 250 mLBeakers 100 mLFilter paper 11 mLpH meters

Chemicals Locations

EXPERIMENT 4

Powdered milk Assigned areaSaturated (COONH4)2 Assigned area Concentrated HCl Assigned areaMethyl red Assigned area0.1M NH4OH Assigned area Acetic acid Assigned areaSaturated Calcium chloride Assigned area1N H2SO4 Assigned area0.02N KMnO4 Assigned area

4. METHOD:

Preparation of sample

Step 1: Pretreat milk sample of 0.5g by burning them with absolute ethanol or dehydrate them with concentrated sulfuric acid.

Step 2: After the milk sample is almost completely burned, it turns into black color.

Step 3: Put the pretreated milk samples contained in racemic crucibles into the muffle furnace to heat with temperature of 500oC for 15 minutes, counted from the time that temperature of the muffle furnace reach 500oC.

Step 4: Let the milk ash sample cool down and put them into desiccator over night before performing experiment.

Calcium quantification

Step 1: Take three milk ash samples contained in three separated racemic crucibles out of the desiccator and add 5mL of distilled water, and then 5 drops of concentrated chlohydric acid.

Step 2: Mix well and transfer these solutions separately into 3 different beakers of 250mL to adjust pH.

Step 3: Add 10-15 drops of methyl red and carry out the neutralization by 0.1 ammonium solution.

Step 4: Adjust the pH of the solution to from 5 to 5.2 by acetic acid of weak concentration. At that point, the solution color is orange-pink. Due to the instrumental error, each pH meter will give a different value of pH. Therefore, observe the color of solution is also very important. Do not over-rely on any type of machine.

Step 5: While heating theses beakers by water bath, stirring these solutions and fill 2-3mL of saturated (COONH4)2 solution.

Step 6: Continue to provide heat to these beakers and then mix these solution well for 30 seconds.

EXPERIMENT 4

Step 7: Put these beakers in cool basin of water immediately.

Step 8: Keep the beaker in the basin of water for about 30 minutes.

Step 9: Use filter paper to collect all the precipitate.

Step 10: Use distilled water to wash the filter paper to know whether (COO)22- ions are all

eliminated or not. To check it, we use saturated calcium chloride solution.

Step 11: Collect precipitate retained by filter paper and put them into Erlenmeyer flask

Step 12: Add 20mL of 1N sulfuric acid solution into each Erlenmeyer flask and heat them in water bath with temperature of 70oC for 1 minute.

Step 13: Titrate the solution with 0.02 N potassium permanganate solution to determine the concentration of (COO)2

2- ion in the solution.

Step 14: Use the rule of three to calculate the amount of calcium ion in the solution and in the sample.

II. RESULTS AND DATA ANALYSIS:

1. Result table :

The amount of KMnO4 (mL) is used to titrate the unknown calcium in each flask:

Flask number KMnO4

Flask 1 12.7

Flask 2 13.8

Flask 3 11.9

EXPERIMENT 4

2. Data analysis :

Base on the reaction (3): Mn7++ 5e → Mn2+

The relation between the concentration (M) and the concentration (N) is:

M= Nne

=0.025

=4 × 10−3

It is also the moles of 0.02N KMnO4 that contains in 1 liter of solution.

The moles of 0.02 N KMnO4 that contains in V liter of solution is:

n = V×4×10-3(mol)

Base on the reactions (1), (2), (3), we have:

nCa 2+¿=5

2× nKMnO4=

52

× V ×4 ×10−3=0.01 V (mol)¿

The gram of Calcium that contains in (m) g of milk powder:

mCa2+ = 0.01V×40 = 0.4V (g)

The gram of Calcium that contains in 100g of milk powder:

mCa2+¿=0.4V × 100

0.5=80 V (g)¿

Where:

V: the volume (L) of 0.02 N KMnO4 that is used to determine the quantitative measurement

m: the weight of the powdered milk (m=0.5g)

ne: is quantity of electron(s) that is/are used to transfer from reductive substance to

oxidative substance in the reaction.

Apply the below equation, the the grams of Calsium in 100g of milk powdered are

Flask 1 Flask 2 Flask 3

Calsium(g)/ 100g

milk

1.016 1.104 0.952

Average (g) 1.024

EXPERIMENT 4

III. DISCUSSION:

The result show the average amount of calcium in 100g powderd milk is 1.024g. The number we

got is quitte close in compare with the one that the company powdered on milk packaging (1.1/100g).

The result of this experiment can be affected by:

The equipment are contaminated

The chemicals added are excessive or deficiency.

In the theory, after heat the beaker, we have to put these beakers in cool water container

immediately. However, when doing the experiment, the beaker may not put in cool water quick

enough.

The ammonium solution was added too much or not enough in the sample.

IV. CONCLUSION

In the experiment, it proves that the Oxalate Ammonium is played an important role in

quantitative Calcium in milk powder, which means the calcium ions content in milk was precipitate

and filtered to determine the mass.