Shawn910018的部落格

Experiment date: 2013/11/15

Principle:

Eggshell is made of many inorganic mineral and some protein. And the most inorganic mineral is CaCO₃, with some MgCO₃ and CaPO₄. Because CaCO₃ is hard to dissolute in water so we’ll use HCl to do it.

2 HCl + CaCO₃ ----> Ca²⁺ + CO₂ + H₂O+ 2 Cl^-

Thought this can’t use to titration CaCO₃, we still can use it to do acid-base back titration. And we use NaOH as the base.

HCl + NaOH à H₂O + Na⁺ + Cl^-

Before we use HCl and NaOH, we need to know it’s 濃度. As an easy way, we use potassium biphthalate(KHP)which is used familiar to replace HCl. And we get:

2 HOOCC₆H₄COOK + CaCO₃ à Ca²⁺(^-OOCC₆H₄COO^-) + 2 K⁺ + ^-OOCC₆H₄HCOO^- + CO₂ + H₂O

HOOCC₆H₄COOK + NaOH à ^-OOCC₆H₄HCOO^- + K⁺ + Na⁺+ H₂O

In order to know if KHP is totally reacted, so will add little more KHP which we already know the weight. And heat it to Boiling. Then add NaOH to see if it is OK.

2. Tools:

1. An egg

2. Two Beakers

3. A 25mL

4. Three pasteur pipette

5. Several Spoons

6. Several papers

7. A forceps

8. A Mortar and a pestle

9. Four erlenmeyer flasks with a rubber stopper

10. A crucible tong

11. Two burettes

12. a funnel

13. Heater

14. Balance

Chemicals and their Properties:

Potassium biphthalate(KHP): CAS 877-24-7   204.2212 g/mol d: 1.64 g/cm³ mp: 295 ℃

Sodium citrate dihydrate : Na₃C₆H₅O₇258.07 g/mol d: 1.76 g/cm³ mp:105 °C

Propanone: CAS 67-64-1 58.08 g/mol   d: 0.79 g/cm³   mp:-94.9 °C   bp: 56.53 °C

Phenolphthalein (C₂₀H₁₄O₄): CAS 77-09-8 318.323 g/mol d:1.277g /cm³ mp:262.5 ℃

Safety and Waste Disposal:

Safety:

Need to wear eye protection and gloves

Waste Disposal:

NaOH: Use KHP to make its pH=7 and wash it.

Propanone: Recycle it.

Egg: Wash it

Eggshell: Throw it away.

Procedure:

(A)

1. Wash the Burette, Mortar and pestle.

2. Get the eggshell and turn it into powder.

3.take a 250mL erlenmeyer flasks. And keep using rubber stopper all the time.

(B)

1. Weight out KHP about 0.4g and add 20mL water to dissolute it.

2. Weight out 0.1g eggshell powder into a erlenmeyer flask and add C₂H₅OH and shake it.

3. Weight out 1g KHP and add to the erlenmeyer flask with eggshell.

4. Add five spoon of sodium citrate dihydrate and 15mL water to the erlenmeyer flask in step 2.

5. Heat it and let it Boiling for 5 minets.

6. Add three Phenolphthalein and fill NaOH in the burette.

7. Titration when the liquid is still hot. Add NaOH until it become pink for 15sec.

8. To make sure if KHP is totally reacted, weight out 0.2g KHP and do the step B2 to B7.

9. If the amount of KHP is 1mmole more than NaOH, then we need to do it again.

10. Do all the step two times and get the percent of CaCO₃ in the eggshell.