. c

.........1. Set-up (83 mg NAT + ZS)

....2. NAT + ZS

3. Start (mix NAT/ ZS, 1 ml H20)

S..............e4. Products of the reaction

c . Volumetric reaction of baking soda, citric acid and water

Generation of gases in 60 ml syringes are described by Bruce Mattson. Lately Jorge Ibanez demonstrated a chemical reaction in two 1 ml syringes connected by a 2 cm piece of a tube, Kaiser Natron is a sodium hydrogencarbonate available in German food shops (for kitchen, house and journey). Zitronensäure (citric acid) is needed in households to cook jam or to descale percolators. German baking powder as well as effervescent tablets contain sodium hydrogencarbonate and an acid. The experiment is a quantitative model of "dissolving" a effervescent tablet in water.

Material
Tray, container for waste, 1 single-use syringes B|BRAUN Injekt Luer Solo 10 ml, 1 single-use syringes B|BRAUN Injekt Luer Solo 20 ml, digital pocket scale (Diamond Series A04 or High-Precision Pocket Scale PS-20). 2 cm of infusion tube (D,d 4, 2 mm) 1 drinking straw spatula, 1 broad ampoule (5 ml) with stopper, 1 Kaiser Natron tablet, Citric acid, (Photo 1). 1 dropper bottle with lime water.
Procedure
1. Photo 1: Weigh 0.08 g of a Kaiser Natron tablet.
2. Photo 2: Unpack a 20-ml syringe, remove the plunger from the barrel, add the sample (NAT) and 2 spatula tips of citric acid (ZS) close to the bottom. Remove the plunger.
3. Photo 3: Connect the syinge barrel with a 10-ml syringe. Insert the barrel and press it firmly onto the white solids.
4. Photo 4: Mix the water with the solids. Collect all the products inside the 20-ml syringe.
5. Transfer 10 ml of the gaseous product to the 10-ml syringe and from there to the ampoule.
6. Add 10 drops of lime water, close the ampoule and shake vigorously.
Observations
a) Gas formation (about 20 ml). b) Colourless transparent liquid are formed (Photo 4).
c) Lime water turns white and milky.

Explanation
a) b) NaHCO3(s) + H-Ac(s) + water --> NaAc(aq) + CO2(g) + H2O(l) 1 mmol (84 mg) of Ca release 1 mmol (24 ml) H2 at room temperature.
c) Ca(OH)2(aq) + CO2(g) --> CaCO3(s)
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first publication: 10.10.2008 l..l...last modification: 06.11.2008 l..l..l. back