Antacids Titration Lab

Teacher Preparation 1.Gather all materials and place them in trays at each lab station. Have extra flasks, beakers & graduated cylinders ready for day 2. 2.Prepare enough 1M HCl & 1M NaOH before & during the lab to supply each group of 4 students with: 1M NaOH 70ml, 1M HCl 80 – 100 ml 3.Day 1 – Have each group practice the procedure of titrating 1 type of antacid to become familiar with the procedure. Coach them to start by titrating with a steady drip until pink flashes are observed in the beaker. Then slow down to 1 drip per 2 seconds to find the least amount required to turn the antacid a persistent pink. 4.Day 2 – Titrate each antacid two times. Each flask of neutralized antacid will have 20+ ml enough for 2 titrations. Have them fill the buret up to the zero with 50ml 1M NaOH. This will be enough for all 6 titrations. 5.Stopcocks occasionally get clogged. Ni-Chrome wire can be used to dislodge any clogs. I’ll include some in the kit. 6.Stir bars end up down drains so the magnetic wand needs to be handy.

Essential Question Which antacid is most effective? Which antacid will neutralize the most stomach acid?

Data Table ItemStarting Volume (ml) Ending Volume (ml) Observations

Materials: Buret, funnel, stand, clamp, magnetic stirrer & magnet, 250ml Erlenmeyer flask, 100ml beaker, rubber stopper, 50ml graduated cylinder, 10ml graduated cylinder, plastic pipet, mortar & pestle, brush, 1M NaOH, 1M HCl, phenolpthalein, antacids: Rolaids, Maalox, Tums, or alternatives

Antacid Neutralization 1.Clean all containers with distilled water. 2.Obtain an antacid tablet. Record the brand. 3.Grind the tablet into a powder with mortar & pestle. 4.Transfer the powder to the 250ml Erlenmeyer flask. Use a brush to transfer residual powder. 5.Measure precisely 40.0ml of 1M HCl in the 50ml graduated cylinder. 6.Transfer the HCl to the Erlenmeyer flask. 7.Swirl the flask to dissolve & react the antacid tablet completely.

Titrate Excess Acid (1 of 2) 1.Make sure the stopcock valve lever is perpendicular so it doesn’t leak. 2.Fill the buret with 1.0M NaOH above 10.0ml. Record the starting volume. 3.Measure precisely 10.0ml of antacid solution with the 10ml graduated cylinder. 4.Place magnet & the 10ml of antacid solution into the 100ml beaker. 5.Add 3 drops of phenolpthalein indicator.

Titrate Excess Acid (2 of 2) 6.Place the beaker on the magnetic stirrer & turn on the stirrer to maintain a steady spin. 7.Turn the stopcock valve lever towards parallel to produce a steady drip. 8.When pink begins to flash in the solution slow the drip down. 9.Use as few drips as possible to turn the solution a steady pink. 10.Record the final volume of 1M NaOH in the buret.

Analysis For Each Sample A (1 of 2) 1.Find the difference between the starting & ending value of 1M NaOH used in the buret. Example: 11.2ml – 4.6ml = 6.6ml 1M NaOH 2.The amount of 1M NaOH used equals the amount of excess 1M HCl un-neutralized by the antacid. Example: 6.6ml 1M NaOH = XS 6.6ml 1M HCl 3.Subtract the un-neutralized 1M HCl from the 10.0ml to determine the amount of 1M HCl that was neutralized by the antacid for every 10ml. Example: 10ml 1M HCl – XS 6.6ml 1M HCl = 3.4ml out of 10ml 1M HCl neutralized by the antacid.

Analysis A SampleVolume of Base Used in Buret Amount of uneutralized acid Amount of acid neutralized

Analysis for Each Sample B (2 of 2) Determine the amount of stomach acid the antacid would neutralize. Since you only titrated 10ml of the 40ml 1M HCl reacted with the antacid, the antacid actually neutralized 4x as much acid. –Example: 3.4ml/10ml x 40ml = 13.6ml 1M HCl The titration uses 1M HCl, however, stomach acid has a concentration of 0.1M HCl. Multiply the amount of 1M HCl by 10 to determine the amount of 0.1M HCl stomach acid the antacid would neutralize. –Example: 13.6ml 1M HCl x 10 = 136ml 0.1M HCl stomach acid

Analysis B SampleTotal Amount of Acid neutralized by tablet Equivalent amount of stomach acid