test tubes in stand
Sodium Hydrogen Carbonate solution
Summary of steps
-place material (see key points) in test tube, standing in stand
-holding test tube in metal test tube holder, heat carefully in bunsen flame
-when heating is complete, extinguish flame
Demonstration carried out first heating ammonium chloride (example of solid), then again heating solution of sodium hydrogen carbonate (example of liquid)
Ammonium chloride – chosen because it sublimes – something for students to see
Sodium hydrogen carbonate solution – evolves carbon dioxide gas below 100 degrees C.
Thirdly quick demonstration of how to position test tube in clamp stand if this is used.
2NaHCO3 -> Na2CO3 + H2O + CO2 (g)
NH4Cl (s) -> NH4Cl (g) -> NH4Cl (s)
-put on safety glasses before putting anything into a bunsen flame
-use minimum amount (cost and safety reasons) (reduces chance of spill also)
-this is all the more important if unsure of identity of material being heated
-test tube definitely no more than quarter full.
-bunsen flame blue when material heated, yellow when nothing being heated
-hold test tube with test tube holder (metal), not fingers
-test tube held at angle
-test tube pointed away from any people
-move test tube around gently while heating to spread heat
-hottest part of flame should be on side of test tube quite near bottom of tube
-orange colour around test tube is indication that tube is hot
DIAGRAM SHOWING HEATING OF LIQUID (TEST TUBE HOLDER NOT SHOWN)
When heating a solid the position is the same.