Presentation on theme: "Hı: my name ıs Brıan Wrıght Lets take a moment so you can get to know me a lıttle. I LOVE TEACHING CHEMISTRY However ıt was not my fırst career..."— Presentation transcript:
Hı: my name ıs Brıan Wrıght Lets take a moment so you can get to know me a lıttle. I LOVE TEACHING CHEMISTRY However ıt was not my fırst career...
Acids HCl, Hydrochloric acid H 2 SO 4,Sulfuric acid HNO 3, nitric acid All are soluble in water. When placed in water they disassociate to become H + Cl - 2H + SO 4 2- H + NO 3 -
H +, Hydronium, Proton When acid dissolve in water they release a positive charged hydrogen ion. A bare proton H+ cannot exist in solution because of its strong tendency to attach itself to atoms or molecules with electrons. However, the term 'proton' is used loosely to refer to positively charged or cationic hydrogen, denoted H+. To avoid the convenient fiction of the naked "solvated proton" in solution, acidic aqueous solutions are sometimes considered to contain the hydronium ion (H3O+), which is organized into clusters to form H9O4+. Other oxonium ions are found when water is in solution with other solvents.
HCl (aq) +H 2 O (l) H 3 O + (aq) + Cl - (aq) These are the most common models for hydronium.
Keep it Simple Students (KiSS) You can certainly think of the hydrogen ion from acids as hydronium. However for many aspects of chemistry it is far easier to think of it only as a proton. Thus HCl (aq) H + Cl - When the hydrogen and the chlorine in this example disassociate the chlorine keep the electron and leave only the hydrogen proton behind.
Brønsted-Lowery definition of acid Definitions Acid proton donor [H + ] [OH - ] Base proton acceptor [H + ] [OH - ] There are more complicated definitions however this will work well for this now.
Acids simplified So in the most simple form when you add acid to water you end up with a lot of this H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + In a aqueous solution.
Bases simplified When you add base to water you get a lot of this OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH - OH -
Indicators One way to determine if a solution is either an acid or base is to use an indicator. Acid base indicators can also be used to provide a rough estimate regarding the concentration of the acid or basic solution.
Indicators are weak acids or weak bases. The generalized formula for a Acid base indicator is Hin when protanated and In - when it is depotonated. HIn H + In - Just like a normal acid HCl H + + Cl -
Various acid base indicators
We will use phenolphthalein
Limitations to Indicators Indicators can not be effectively used to measure instantaneous pH. If there is a dynamic chemical reaction, like a titration, indicators are not useful for providing pH data as a function of time.
pH meters A pH meter can measure the concentration of H + quickly and accurately. This makes them Ideal for measuring H + concentration while conducting a titration.
HOW DOES IT WORK A pH probe is a sensitive galvanic cell. It has two half cells each using silver and silver chloride. Ag + + 1e − ↔ Ag 0 (s) Ag + + 1e − ↔ Ag 0 (s) Ag + + Cl − ↔ AgCl(s) or an overall reaction can be written: Ag 0 (s) + Cl − ↔ AgCl(s) + e -
1.a sensing part of electrode, a bulb made from a specific glass 2.sometimes the electrode contains a small amount of AgCl precipitate inside the glass electrode 3.internal solution, 0.1M HCl for pH electrodes 4.internal electrode, usually silver chloride electrode 5.body of electrode, made from non-conductor 6.reference electrode, usually the same type as 4 7.junction with studied solution, usually made from ceramics or capillary with asbestos or quartz fiber.
Calibrate pH probe Buffer 4 Rinse Buffer 7 Rinse If probe needs to be adjusted please follow instructions.
Laboratory setup How to stir (be very careful the probe is very fragile) White paper underneath (if lab counter is dark) (if lab counter is dark) May be easiest to set up two stands One for the buret One for the buret One for the probe. One for the probe.
How to Pipette Use you index finger Twist Let gravity work Touch once to the glass Your class may prefer to use two burets instead of pipetting the acid.
This is not last years Lab Last year when you did a titration it was only necessary to find the end point. In the this lab you will be monitoring the pH level. Then the pH level goes up.15 you then stop the flow of base and record the buret volume. It is critical to this lab that you are skilled at reading a buret.
How Read a Buret This is the most important skill to the successful completion of this lab. Reading you buret accurately will provide you with precise and accurate data.
Significant Figures and the Buret The buret has 1.0 mL graduations These are further divided into 0.1 mL graduations It is then possible to estimate to the 0.01 mL The uncertainty is +/ mL
Reading a Buret Remember you will be reading to the bottom of the meniscus. This sound pretty easy however there are 3 visible layers to the meniscus. Always read to the bottom layer. Keep in mind that the thickness of the line on the buret is typically about 0.02mL
One other thing to remember. One any precision analog device the thickness of the graduations must be considered when taking measurements Keep in mind that the thickness of the line on the buret is typically about 0.02mL
Lets Try a Few readings. Remember you will be reading to the bottom of the meniscus. This sound pretty easy however there are 3 visible layers to the meniscus. Always read to the bottom layer. Keep in mind that the thickness of the line on the buret is typically about 0.02mL
The reading is 1.28 mL
The reading is 6.89 mL
The reading is mL
The reading is 46.36mL
Lets Make it Easier Place something behind the buret. You can use your finger or even better a card that is ½ black and ½ white
The reading is 1.95 mL
The reading is A little hard to read because the graduations are over to the side mL
Lab Group Assignments Each task must be complete by the same person for the whole trial. Do enough trials that each person get a chance to do each task. Data collection, Qualitative and quantitative. Pipette acid or deliver acid with a buret Stir and run the buret Read the buret Read the pH data. Clean up.