CHEMISTRY TITRATION REVIEW PH. ION CONCENTRATION (mol/l) IONIZATION OF WATER MARCH 2019 COC INTERVIEW

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1 REVIEW PH CHEMISTRY TITRATION MARCH 2019 COC INTERVIEW 1 2 IONIZATION OF WATER And you know that when both H + IS TRANSFERRED FROM ONE H 2 O MOLECULE TO ANOTHER. concentrations are equal -> ph = 7.00 ONE WATER MOLECULE ACTS AS AN ACID, WHILE ANOTHER ACTS AS A BASE. H O H O H O OH [1.0 x 10 7 M] [1.0 x 10 7 M] 3 4 ION CONCENTRATION (mol/l) ph Hydrogen Ion (H + ) Hydroxyl Ion (OH - ) Acid H O OH K Neutral HOH Alkaline H O OH

2 THE PH SCALE CALCULATING ph A solution with a ph of 7 is neutral, a solution with a ph less than 7 is acidic, and a solution with a ph greater than 7 is basic ph IS THE NEGATIVE LOGARITHM (BASE 10) OF THE [H 3 O + ]. ph log H 3 O Sour Not Slippery Bitter Slippery 5 6 FOR A SOLUTION WITH [H 3 O + ] = 1 X 10 4 M: ph log 1 x 1O 4 ph 4. 0 ph 4. 0 SIGNIFICANT FIGURES IN ph WHEN EXPRESSING LOG VALUES, THE NUMBER OF DECIMAL PLACES IN THE PH IS EQUAL TO THE NUMBER OF SIGNIFICANT FIGURES IN THE COEFFICIENT OF [H 3 O + ]. MEASURING PH COEFFICIENT DECIMAL PLACES 7 8

3 MEASURING PH ph METER Electronic meter used to measure the hydronium ion concentration ph PAPER MEASURING PH Paper with multiple indicators saturated on the paper ACID-BASE INDICATOR MEASURING PH A DYE USED TO DISTINGUISH BETWEEN AN ACIDIC AND BASIC SOLUTION BY MEANS OF THE COLOR CHANGES IT UNDERGOES IN THESE SOLUTIONS. ph CHEMICAL INDICATORS The sample beakers show a red cabbage indicator in beakers varying in acidity from highly acidic (left) to highly basic (right)

4 DISCUSS STRONG VS WEAK ACIDS/BASES TITRATION CURVES FOR STRONG ACID VS. STRONG BASE Ideal due to small addition of titrant with large change in ph Running acid into the base Running base into the acid TITRATION CURVES FOR STRONG ACID VS. WEAK BASE TITRATION CURVES FOR WEAK ACID VS. STRONG BASE Titration is more difficult due to small ph change Running acid into the base Running base into the acid Running acid into the base Running base into the acid 15 16

5 STRONG BRØNSTED LOWRY ACID OR BASE WEAK BRØNSTED LOWRY ACID OR BASE COMPLETELY DISSOCIATES HA B A HB PARTIALLY DISSOCIATES HA B A HB Strong football quarterback - Always gets the ball away - Never gets sacked Weak football quarterback - Sometimes gets the ball away - Sometimes gets sacked WHAT IS REALLY GOING ON WHAT IS REALLY GOING ON THE GOAL OF A TITRATION IS TO ACCURATELY MEASURE THE CONCENTRATION OF A SOLUTION A TITRATION IS COMPLETED WHEN THE MOLES OF TITRANT (known concentration) AND TITRAND (unknown concentration) ARE BALANCED AS DEFINED IN THE CHEMICAL EQUATION OUR CURRENT DISCUSSIONS WILL BE LIMITED TO ACID/BASE TITRATION FOR SIMPLE EQUATIONS, WE CAN USE THE FORMULA OF M A V A = M B V B AS WE CANNOT DIRECTLY SEE THE MOLECULES WE WILL BE MEASURING THE ph OF THE TITRATED SOLUTION 19 20

6 PHENOLPTHALEIN DISCUSS ph AND INDICATORS PHENOLPTHALEIN PHENOLPTHALEIN PHENOL RED PHENOL RED METHYL RED 23 24

7 PHENOLPTHALEIN PHENOLPTHALEIN PHENOL RED PHENOL RED METHYL RED METHYL RED BROMOCRESOL GREEN BROMOCRESOL GREEN BROMOTHYMOL BLUE ph CHEMICAL INDICATORS 27 28

8 WHY TITRATION WE PERFORM TITRATION TO DETERMINE THE CONCENTRATION (STRENGTH) OF CHEMICAL SOLUTIONS AN EXAMPLE OF [H 3 O + ] CONCENTRATION IN THE MEDICAL FIELD Blood ph Bicarbonate Partial pressure of carbon dioxide Condition Less than 7.4 Low Low Metabolic acidosis Greater than 7.4 High High Metabolic alkalosis Less than 7.4 High High Respiratory acidosis Common causes Kidney failure, shock, diabetic ketoacidosis Chronic vomiting, low blood potassium Lung diseases, including pneumonia or COPD Greater than 7.4 Low Low Respiratory alkalosis Breathing too fast, pain, or anxiety 31 32

9 TITRATION EXAMPLE ACID BASE TITRATION TITRATION IS A LABORATORY PROCEDURE OFTEN USED TO DETERMINE THE MOLARITY OF AN ACID. USES A BASE, SUCH AS NAOH, TO NEUTRALIZE A MEASURED VOLUME OF AN ACID. Base (NaOH) Acid solution Not Pink Too Acidic Good [Acid]=[Base] Too Pink Too Basic Yes, it looks like too much, but not yet 35 36

10 BEFORE YOU START SOME TITRATION QUESTIONS TO KEEP IN THE BACK OF YOUR MIND QUESTIONS IS THE CONCENTRATION OF ACID/BASE NEARLY THE SAME WILL THE INDICATOR USED INDICATE THE MAXIMUM SLOPE HOW ACCURATE DO I NEED THE RESULT HOW MANY TITRATIONS SHOULD I PERFORM & WHY Titrations BACKUP SLIDES ADDITIONAL SLIDES Standardization Titration Required when a non-primary titrant is used - Prepare titrant with approximately the desired concentration - Use it to titrate a primary standard - Determine the concentration of the titrant - Reverse of the normal titration process!!! titrant known concentration Standardization titrant unknown concentration analyte unknown concentration analyte known concentration 39 40

11 My thoughts on teaching My first job is to keep the students awake. My second job is to make the students think. My most important job is to help the students reach their goals in life. 41