Shawn910018的部落格

Experiment date: 2013/12/6

1. Principle:

EDTA is a kind of Chemical with 6 ligands, and is used very often. EDTA is also a kind of acid, so sometimes we use H₄Y as EDTA. It is often use with EBT. And we often write down as H₃In and will become H₂In^- in water. When pH is about 7~11, most of it will become HIn^2-,and can catch Ca²⁺, Mg²⁺, Zn²⁺, and Hg²⁺, and become a red chelate. When the pH is more than 11, then HIn^2- will lose one more H and become In^3- (orange).

But EBT isn’t good to use when using EDTA to titration Ca²⁺. So will use back titration method to test the milk.

Buffer Solution, is talking about a liquid that can stay near a pH and won’t change too fast if we add acid or bass.

1. Chemicals and their Properties:

EDTA(CAS 60-00-4): 292.24g/mol d: 0.86 g/cm³ mp: 318 °C bp: 1388 °C

EBT(CAS 1787-61-7): 461.381g/mol looks: dark red

MgC_l2‧6H₂O(CAS without water 7786-30-3/ with water 7791-18-6):

95.211 g/mol;203.31g/mol d: 2.32g/cm³;1.56 g/cm³ mp: 714 °C bp:1412 °C

NH₄Cl(CAS 12125-02-9): 53.49 g/mol 1.527 g/cm³ mp: 338 °C

NH₃(CAS 7664-41-7): 17.0306g/mol d: 0.6942 g/cm³ mp: -77.73 °C bp:-33.34 °C

CaCO₃(CAS 471-34-1): 100.0869g/mol d: 2.71 g/cm³(Calcite) mp: 825 °C(Calcite)

NaOH(CAS 1310-73-2): 39.9971g/mol d: 2.13 g/cm³ mp: 318 °C bp: 1388 °C

HCl(CAS 7647-01-0): 36.46g/mol d: 1.18g /cm³ mp:−27.32 °C(38%) bp:48 °C (38%)

1. Tools:

1. Pasteur pipette (10mL/25mL)

2. Volumetric flask(100mL/250mL)

3. Filter paper

4. Burettes

5. Bottle

6. Funnel

7. Erlenmeyer flask

1. Safety and Waste Disposal:

Safety : Always wear your coat, gloves and eye protection.

1. Procedure:

Part. A (Make 0.01M EDTA)

1. Weight out 0.93g Na₂H₂Y‧2H₂O, and 0.125g MgCl₂‧2H₂O.
2. Put them in a Volumetric flask (250mL) and add pure water until full.

Part. B (Buffer Solution)

1. Weight out 1.4 g NH₄Cl and put it in a little bottle (25mL).
2. Add 10mL NH₃ and add water to the total of 20mL.

Part. C (Check the Concentration of EDTA)

1. Weight out 0.072~0.088 g CaCO₃, add 6 M HCl 1mL and wait until it dissolute.
2. Take 25mL of the liquid and put in a Volumetric flask (100mL) then fill it with water.
3. Add 25mL of liquid from part. C step 2 to an Erlenmeyer flask with 1mL Buffer from part. B. Add two drop if EBT and it should be red.
4. Use EDTA to titrate till it become blue and calculate the Concentration of EDTA.

Part. D (Water)

1. Put 100mL target water in an Erlenmeyer flask then add 4mL Buffer and 2 drops of EBT.
2. Use EDTA to titrate till it become blue.
3. Use ppm of CaCO₃ to record the data.
4. Repeat step 1 to 3.

Part. E (Milk)

1. Put 10mL milk, 20mL pure water and 6M HCl 3mL in an Erlenmeyer flask. Then shake it and put it away for 10minutes.
2. Add 0.5M NaOH 2.5mL and add water to the mark.
3. Filter the liquid.
4. Take 25mL filtered liquid, pH=10 Buffer 2mL and 3 drops EBT. Use 0.01M EDTA to titrate till it become blue. Write down the Volumetric.
5. Use EDTA to titrate till it become blue.
6. Use ppm of Ca to record the data.
7. Repeat step 1 to 6.