MEASUREMENT OF ph: INTRODUCTION TO BUFFER AND BASICS OF ph METER

Transcription

1 Theory module: 04(MCQ) METER 1. To prepare 1000 ml of 0.1M phosphate buffer of ph 7.5 (pka of NaH2PO4= 7.2). how many ml of each buffer components will be required? Molecular weight of Na2HPO4 and NaH2PO4 is , and g respectively. A M sodium acetate, M acetic acid B M sodium acetate, 0.04 M acetic acid C M sodium acetate, 0.062M acetic acid D. 06 M sodium acetate, M acetic acid 2. To prepare 1000 ml of 0.1M phosphate buffer of ph 7.5 (pka of NaH2PO4= 7.2). how many ml of each buffer components will be required? Molecular weight of Na2HPO4 and NaH2PO4 is , and g respectively. A. 600 ml Na2HPO4, 400 ml NaH2PO4 B. 666 ml Na2HPO4, 334 ml NaH2PO4 C. 400 Na2HPO4,600 ml NaH2PO4 D. 660 ml Na2HPO4, 440 ml NaH2PO4 3. In terms of molar concentrations, water at 250C contains A. Only hydrogen ions B. Only hydroxide ions C. Equal number of hydrogen and hydroxide ions D. Numbers of hydrogen ions are more 4. Acids are defined as compounds that dissociate in water to release A. Chloride ions B. Calcium ions C. Hydrogen ions D. Hydroxide ions 5. Acids the hydrogen ion concentration and the hydroxide ion concentration. A. Increase, decrease B. Decrease,increase C. Both increases D. Both decreases CHRIST COLLEGE, RAJKOT, GUJARAT. Page 1

2 6. Which of the following is incorrect regarding a neutral solution A. Hydrogen ion concentration exactly equals the hydroxide ion concentration B. At 25 C, a neutral solution has ph 7 C. At any temperature the ph of the neutral solution is same D. None of these 7. ph meter is a which measures the voltage between two electrode placed in a solution A. Ammeter B. Galvanometer C. Potentiometer D. None of these 8. The calomel electrode has the following characteristic A. It is an external reference electrode B. Its electrical potential is always constant C. Its electrical potential depends on the ph of the test solution D. Both 1 and 2 9. The glass electrode contains A. Mercury B. Silver C. Potassium D. Sodium 10. Buffer capacity is A. Magnitude of buffer action B. Measured by the amount of strong base or strong acid required to alter the ph by one unit C. Measured by the amount of weak base or weak acid required to alter the ph by one unit D. Both 1 and 2 CHRIST COLLEGE, RAJKOT, GUJARAT. Page 2

3 Theory module: 04 (Assignment) Meter Answer specifically 1. Define ph 2. What is the working principle of ph meter? 3. ph meter is standardized with , and what is buffer? 5. How buffer solutions can be prepared? 6. How many moles of sodium acetate and acetic acid are required to prepare 1 liter of a buffer, ph 5.0, which is 0. 1 M in total available acetate (dissociated and undissociated). Acetic acid has a pk of 4.74.? 7. To 100 ml of 0.2 M formic acia, pka 3.77, is added 10 mmole of solid NAOH. What will be the final ph? 8. The dissociation constant for lactic acid is 1.38 x 10-4 How much lactic acid must be added to 2 g of NAOH to make 500 ml of buffer at ph 4.00? M ammonium hydroxide, K, 1.8 x 10-,5, is added to an equal volume of 0.03 M HCI. What is the resulting ph? 10. What are the factors effecting selection of buffers? CHRIST COLLEGE, RAJKOT, GUJARAT. Page 3

4 Theory module: 04 (References) Meter Principles and techniques of biochemistry and molecular biology. Sixth edition. Edited Keith Wilson & John Walker. Cambridge University press Analytical biochemistry and separation techniques. A laboratory manul for B.Sc and M.Sc students. Palanivelu, Introductory practical biochemistry. Edited by S.K Sawhney & Randhir Singh. Narosa Publishing house Pvt Ltd. CHRIST COLLEGE, RAJKOT, GUJARAT. Page 4

5 Theory module: 04 (Edutainment) Meter CHRIST COLLEGE, RAJKOT, GUJARAT. Page 5

6 Across 49. The Hasselbalch equation is of central importance in the preparation of buffer solutions. 40. Spectrophotometer uses the deuterium or a lamp for uv light. 59. The ph is a way to express the acidity of a solution without using cumbersome numbers. 31. Weak produce only very small amounts of OH- when dissolved in water. 69. The range over which there is only a small ph change upon the addition of acid or base is called the buffer. 21. The actual or potential ability to perform, yield or withstand or The largest weight the balance is capable of weighing. 1. The calomel electrode contains. 9. An important class of weak acids and bases are called, ions that a0 are simultaneously positively and a negatively charged. 77. The glass electrode contains Down 33. A acid is one that dissociates completely into its ions. 22. As mentioned earlier, buffer resist change in ph on addition of small amount of alkali or acid. This resistance is known as buffer 52. The two used are a calomel and a glass 4. buffer solution consists of an aqueous mixture of a weak acid and its base 67. As ph increases by 1 unit,[h +],decreases by factor ( two, ten, six) 63. It is a potentiometer which measures the voltage between two electrode placed in a solution. CHRIST COLLEGE, RAJKOT, GUJARAT. Page 6