The content of chromium trioxide (Cr2O3) affects the fullness, softness, elasticity and shrinkage temperature of the finished leather to a certain extent. When its content is 3% to 5%, the physical and mechanical properties of the finished leather are better. By measuring the chromium trioxide content in leather, we can not only understand the chromium tanning situation and the performance of the leather blank, but also evaluate the chrome tanning agent and chrome tanning process.
Principle
The leather ash is oxidized with perchloric acid (or melted with alkali), and the content of hexavalent chromium is determined using a quantitative method.
The content of chromium oxide in leather is the amount of chromium compounds obtained in leather, calculated as the amount of chromium trioxide (Cr2O3).
Product List
Click the product name to view product details.
| CAS NO. | Product Name | Inquiry |
| 1308-38-9 | Chromium Oxide (Cr2O3) | Inquiry |
| 12182-82-0 | Chromium oxide (Cr2O3),hydrate | Inquiry |
| 57921-51-4 | Aluminum oxide-chromium oxide | Inquiry |
| 12018-01-8 | Chromium dioxide | Inquiry |
| 27787-63-9 | CUPRIC CHROMATE | Inquiry |
| 1308-38-9 | Chromium(III) oxide | Inquiry |
| 116374-21-1 | PHOSPHORIC ACID-17O4 | Inquiry |
| 7681-11-0 | Potassium iodide | Inquiry |
| 9005-28-8 | STARCH SOLUBLE | Inquiry |
| 7772-98-7 | Sodium thiosulfate | Inquiry |
| 5968-11-6 | Sodium carbonate 1-hydrate | Inquiry |
| 584-08-7 | Potassium carbonate | Inquiry |
| 1303-96-4 | Sodium Tetraborate Decahydrate | Inquiry |
| View More | Inquiry |
Reagents, Materials, and Apparatus
Unless otherwise stated, only reagents confirmed to be of analytical grade and distilled or deionized water or water of equivalent purity are used in the analysis.
(1) Perchloric acid method
① Concentrated sulfuric acid
② Perchloric acid (60% ~ 70%)
③ Phosphoric acid (85%)
④ Potassium iodide solution (10%), or 1 g of granular potassium iodide
⑤ Starch solution (1%), freshly prepared or added with a small amount of mercury iodide (can be stored for several months), or soluble powdered starch
⑥ Sodium thiosulfate standard solution (0.1 mol/L)
⑦ 300 mL Erlenmeyer flask, heat-resistant, with ground glass stopper, or Kjeldahl flask
⑧ Glass funnel, glass beads, bisque pieces
⑨ Burette
(2) Melting method
① Melt mixture. A suitable melt mixture is equal parts of anhydrous sodium carbonate, potassium carbonate, and sodium tetraborate, or potassium chlorate alone as the solvent.
② Crucible or evaporating dish
③ Concentrated sulfuric acid (relative density 1.18)
④ Potassium iodide solution (10%), or 1 g of granular potassium iodide
⑤ Starch solution (1%), freshly prepared or added with a small amount of mercury iodide (can be stored for several months), or soluble powdered starch
⑥ Sodium thiosulfate standard solution (0.1 mol/L)
⑦ Glass beaker, 200~250 mL
⑧ 300 mL or 500 mL Erlenmeyer flask with ground glass stopper
⑨ Buret
⑩ Funnel, filter
Experimental Steps
(1) Perchloric acid method
Put 1 to 5 g of leather ash into a 300 mL Erlenmeyer flask, add 5 mL of concentrated sulfuric acid and 10 mL of perchloric acid, and heat on a medium flame with a wire mesh until boiling. Place a funnel over the mouth of the Erlenmeyer flask so that water can evaporate without splashing out. When the reaction mixture begins to turn orange, lower the flame, wait until all colors change, and then slowly heat for 2 minutes. After a short period of cooling in air, quickly cool in cold water and dilute the contents to approximately 200 mL. In order to eliminate the chlorine produced due to these operations, bisque pieces can be added (glass beads are not enough to prevent bumping) and boiled for about 10 minutes.
After cooling again, add 15 mL of phosphoric acid (to mask iron) and 20 mL of potassium iodide solution or an appropriate amount of granular potassium iodide, and leave it in a dark place for 10 minutes. Then use 5 mL of starch solution or starch as an indicator, and titrate with sodium thiosulfate standard solution until it reaches light green.
Note: Transfer the ash from the crucible to a heat-resistant Erlenmeyer flask, wash the crucible thoroughly with sulfuric acid, and then wash with perchloric acid or a mixed acid of the two. Pour the washing liquid into the Erlenmeyer flask. All the washing liquid in the crucible should be poured out. After washing with perchloric acid, it can also be washed with distilled water.
(2) Melting method
Mix 1 to 5 g of leather ash and 2 to 3 times the amount of molten mixture with a platinum wire or thin glass rod. First, slowly heat the crucible on a Bunsen burner, and then heat it with a strong flame for about 30 minutes.
After cooling, place the crucible into a beaker containing 100 to 150 mL of boiling distilled water, and heat the beaker on a water bath until the melt is completely dissolved.
Filter the above solution into an Erlenmeyer flask and wash the filter paper thoroughly with hot distilled water. Carefully neutralize the filtrate with hydrochloric acid and then add excess acid.
Let the mixture cool to room temperature, add 20 mL of potassium iodide solution or 2 g of granular potassium iodide, and leave it in a dark place for 10 min. Then use 5 mL of starch solution or starch as an indicator, and titrate with sodium thiosulfate standard solution until it reaches light green.
