NaCl (aq) + HOH (l) + (aq) + Cl (l) Eg. HCl (aq) + NH 3(aq) In both cases the acid and base react and neutralize each other.

Transcription

1 Acid Base Reactions An acid base reaction is called a neutralization reaction. Eg. HCl (aq) + NaOH (aq) NaCl (aq) + HOH (l) In grade 10 you learned that acid base reactions produce salt and water, however, you should be aware that not all acid base reactions produce salt and water. NH 4 + (aq) + Cl (l) Eg. HCl (aq) + NH 3(aq) In both cases the acid and base react and neutralize each other. Did you know these were neutralization reactions? 1. Bee stings are acidic and can be treated with baking powder (basic) 2. Your stomach is acidic (ph ~ 3) and acid reflux can be treated with antacid tablets like Alka Seltzer (NaHCO 3 ) 3. Soil is often acidic and can be treated with limestone (Calcium carbonate, CaCO 3 ) 4. Water treatment plants use various bases like magnesium hydroxide (Mg(OH) 2 ) or calcium oxide (CaO) to control damage from the environment

2 Equivalence Point The point of a chemical reaction at which an added titrant is stoichiometrically equal to the number of moles of analyte present in the sample (the smallest amount of titrant that is sufficient to fully neutralize the analyte) Eg. for the following neutralization reactions 1) HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) You need 1 mole of sodium hydroxide to neutralize 1 mol of hydrochloric acid 2) H 3 PO 4(aq) + 3KOH K 3 PO 4(aq) + 3H 2 O (l) You need 3 moles of potassium hydroxide to neutralize 1 mol of phosphoric acid

3 Knowing when the equivalence point occurs during the reaction allows for the determination of the concentration of acids or bases using a technique called titration. Titration A lab technique used to quantitatively determine the concentration of an acidic or basic solution. Titration Technique Video (7 min) [ ] = concentration in mol/l Acid Base Indicator A substance that changes colour depending on the [H 3 O + ] (i.e. on how acidic or basic the solution is). ex. phenolphthalein in acidin base ex. bromothymol blue in acidin base Endpoint The point during a titration when the acid base indicator changes colour ex. red cabbage in acidin base

4 Are endpoint and equivalence point ever the same? neutralization acidic basic When selecting an indicator for a neutralization reaction, you will get more accurate results if the endpoint is as close as possible to the equivalence point. For precise results select an indicator that gives a vivid colour change.

5 Titration Set Up

6 Titration Problems * write the balanced reaction *Use the mole highway to find the concentration of the unknown 1) In a titration of ml of H 2 SO 4(aq), ml of mol/l NaOH (aq) was required to reach the endpoint. Find the concentration of the acid. ANSWER mol/l sulfuric acid

7 2) A nitric acid solution requires ml of mol/l KOH to neutralize ml of the acid. Calculate the concentation of the acid. ANSWER mol/l HNO 3 (aq)

8 3) A ml volume of barium hydroxide is completely neutralized by ml of mol/l HCl. Find the concentration of the base. ANSWER mol/l

9 4) 32.4 ml of 0.65 mol/l magensium hydroxide are required to reach equivalence with 55.0 ml of phosphoric acid. What is the concentration of the phosphoric acid?

10 5) Distinguish between the equivalence point and the end point in a titration.why might they be different? How would this affect the result of the titration? More Titration Questions p. 404 #4,5,6,7 Read p Instructions for Titrating Skills to Know Rinsing the Burette Filling the Burette Reading the Burette Rinsing the Pipette Filling the Pipette Transferring the Solution Adding the Indicator