Which of the following is true for a buffered solution? The solution resists any change in its [OH-]. The solution will not change its pH very much even if a concentrated acid is added. The solution resists any change in

51,043 results
  1. ALGEBRA CHECK ANSWERS

    Solve each equation by graphing the related function. If the equation has no real-number solution, write no solution. NOTE: when I write + it has a minus on the bottom too x^2+7=0 a. x= +7 b. x = +3.5 c. x= 0 d. no solution *** 3x^2=0 a. +3 b. +1/3 c. 0

  2. Math

    1. What is the solution of n^-49=0 A. -7 B. 7 C. += 7*** Sorry I couldn't find this symbol D. no solution 2. What is the solution of x^2+64=0? A. -5 B. 8 C. += 8 D. no solution*** 3.What is the side length of a square with an area of 144x^2? A. 12 B.

  3. AP Chemistry

    DrBob222 thank you for your previous response. I am reposting the entire question. Two different 1.2 L buffered solutions were prepared using HOBr and LiOBr. Both buffered solutions had a pH of 5.2 at 25C. After 0.17 mols of HI were added to each of the

  4. Chemistry-Dr.Bob222

    Calculate the molar solubility of calcium hydroxide in a solution buffered at each pH. a. pH=4 b. pH= 7 c. pH=9

  5. CHEMISTRY

    HOW CAN U TELL IF HNO3 +KNO3 IS A BUFFER SOLUTION A buffer solution must contain a weak acid and its conjugate base OR a weak base and its conjugate acid. HNO3 is a strong base and KNO3 is the salt of a strong base (KOH) and a strong acid (HNO3);

  6. AP Chemistry

    A buffered solution was created by mixing solutions of NH4Cl and NH3 at 25 C. Which species, NH4+ or NH3, has the highest concentration in this buffered solution?. Justify your answer.

  7. Chem

    Which of the following is NOT true for a solution buffered at a selected pH? 1. The buffered solution could be made to be either acidic or basic. 2. The solution pH will increase a lesser amount than a non-buffered solution, when base is added. 3. The

  8. Chemistry

    A 100 milliliter sample of 0.100-molar NH4Cl solution was added to 80 milliliters of a 0.200-molar solution of NH3. The value of Kb for ammonia is 1.79 x 10^-5. (a) What is the value of pKb for ammonia? (b) What is the pH of the solution described in the

  9. chemistry

    Which of the following is true for a buffered solution? The solution resists any change in its [OH-]. The solution will not change its pH very much even if a concentrated acid is added. The solution resists any change in its [H+]. All of the the statements

  10. chemistry

    A 5.00 L solution has [HC7H5O2] = 0.100 M and [Ca(C7H5O2)2] = 0.200 M . What is the pH of the solution after 10.0 mL OF 5.00 M NaOH is added? Assume the volume of the solution does not change .Ka for HC7H5O2 = 6.3x10^-5.

  11. College chemistry

    A buffered solution is made by adding 50.0 g NH4Cl to 1.00 L of a 0.70 M solution of NH3. Calculate the pH of the final solution. (Assume no volume change.)

  12. chemistry 1046

    Calculate the solubility (in grams per 1.00 102 mL of solution) of magnesium hydroxide in a solution buffered at pH = 9 the ksp of Mg(oh)2 = 2.06e-13

  13. chem 1046

    Calculate the solubility (in grams per 1.00 102 mL of solution) of magnesium hydroxide in a solution buffered at pH = 9. Enter your answer to 2 significant figures.) Ksp = 2.06e-13

  14. Chemistry

    Captain Kirk, of the Starship Enterprise, has been told by his superiors that only a chemist can be trusted with the combination to the safe containing the dilithium crystals that power the ship. The combination is the pH of Solution A described below,

  15. Chemistry

    A buffer solution of volume 100.0 mL is 0.150 M Na2HPO4(aq) and 0.100 M KH2PO4(aq). Refer to table 1. (a) What are the pH and the pH change resulting from the addition of 80.0 mL of 0.0500 M NaOH(aq) to the buffer solution? pH pH change (include negative

  16. chemistry

    What is solubility of CaF2 in a solution buffered at pH 5

  17. Chemistry

    The pH of a solution is 1. Which of the following statements are also true for the solution? (Select all that apply.) It will change the color of red litmus to blue. The concentration of hydronium ion is equal to the concentration of hydroxide ion. The

  18. Chemistry

    What should the molar concentrations of benzoic acid and sodium benzoate be in a solution that is buffered at a pH of 4.84 and has a freezing point of -2.0 ∘C? (Assume complete dissociation of sodium benzoate and a density of 1.01 g/mL for the solution.)

  19. Chemistry

    A solution buffered at a pH of 5.00 is needed in an experiment. Can we use acetic acid and sodium acetate to make it? If so, how many moles of NaC2H3O2 must be added to a 1.0L of a solution that contains 1.0 mol HC2H3O2 to prepare the buffer. The Ka of

  20. Chemistry

    1)A buffer solution that is 0.10 M sodium acetate and 0.20 M acetic acid is prepared. Calculate the initial pH of this solution. The Ka for CH3COOH is 1.8 x 10-5 M. As usual, report pH to 2 decimal places. *A buffered solution resists a change in pH.*

  21. Chemistry

    Solution x has a pH of 4.35. Solution y has 10- times high [OH-] compared to solution x. Solution z has a pH 4.0 units higher than that of solution x. calculate the ration of [H3O+] between solutions x&y and between x&z. What is the pH of solutions y and

  22. chemistry

    Select only the True statements about buffer systems. Select all that are True. 1. Starting with NH3(aq) and adding a small amount of HCl(aq) will make a buffered solution. 2. The blood buffer, among other things, is supported by carbonic acid and its

  23. Buffer Solutions

    A buffered solution is made by adding 75.0g sodium acetate to 500.0 mL of a .64 M solution of acetic acid. What is the pH of the final solution? (Ka for acetic acid, CH3COOH, is 1.8 x 10^-5)

  24. chemistry

    Calculate the solubility (in grams per 100 mL of solution) of magnesium hydroxide in a solution buffered at pH = 12. I can get the answer in grams per mole, but i am having difficulty changing it to g/100ml.

  25. Chemistry

    What is the molar solubility of Fe(OH)3(s) in a solution that is buffered at pH 2.75? The Ksp of Fe(OH)3 is 6.3 × 10-38.

  26. Chemistry

    Wht is the solubility of Ni(OH)2 in a solution buffêred at pH = 11.3? The Ksp of Ni(OH)2 at 25 oC is 6.0 × 10-16.

  27. science: chemistry

    How many moles of NaOH must be added to 1.0 L of 2.6 M HC3H5O3 to produce a solution buffered at each pH? 1)pH= 4.28 2)pH=pKa

  28. science: chemistry

    A buffered solution is made by adding 47.4 g C2H5NH3Cl to 1.00 L of a 0.68 M solution of C2H5NH2. Calculate the pH of the final solution. (Assume no volume change. Assume that all solutions are at 25°C.)

  29. Math. Check my answers

    1. What is the solution to 89+k=-42? a. K = 131 b. K = 47 c. K = -47 d. K = -131** 2. What is the additive inverse of -7? a. -7 b. 7** c. -|-7| d. -(-(-7)) 3. What is the solution to y-7=-7? a. y=14 b. y=7 c. y=0** d. y=-7 4. What is the value of

  30. Chemistry

    A solution has [OH-] = 3.5 × 10-6. Based on that, what must be true about this solution? A. It is an acidic solution. B. It is a strong base. C. It is a strong acid. D. It is a basic solution.

  31. Chemistry

    If some NH4Cl is added to an aqeous solution of NH3: A. pH of solution will decrease B. PH will not change C. pH will increase D. NH4Cl cannot be added to NH3 E. The solution will not have pH I think the answer is B, because if NH4Cl is added to the

  32. math

    19. Which set of numbers are ordered from least to greatest? a. 5, -5, |-2|, 3, -|2| b. -5, -|2|, |-2|, 3, 5 c. 5, 3, |-2|, -|2|, -5 d. -|2|, |-2|, 3, -5, 5 18. What is the solution to 9/-7 = 6? a. q = -42 b. q = -13 c. q = 13 d. q = 42 17. What is the

  33. Chemistry

    1)A buffer solution that is 0.10 M sodium acetate and 0.20 M acetic acid is prepared. Calculate the initial pH of this solution. The Ka for CH3COOH is 1.8 x 10-5 M. As usual, report pH to 2 decimal places. *A buffered solution resists a change in pH.*

  34. chemistry

    What does a buffer do? A. It resists a change in pH when H+ or OH- is added to a solution. B. It prevents an acid-base reaction from happening. C. It prevents an acid or base from being neutralized. D. It prevents a salt from forming in solution.

  35. chemistry help

    calculate the PH of a buffered solution of HF and F (Pka of HF is 3.2)

  36. Chemistry

    1-A sample of potassium hydrogen oxalate, KHC2O4, weighing 0.717 g, was dissolved in water and titrated with 18.47 mL of an NaOH solution. Calculate the molarity of the NaOH solution. 2-A 35 mL drinking water sample, whose pH is buffered to 10, is titrated

  37. chemistry

    Investigating changes in colligative properties involves the measurement of a solution’s concentration in molality instead of molarity because of which of the following? the mass of the solvent does not change, but its volume does change, as temperature

  38. Chemistry

    A buffered solution is made by adding 48.6 g C2H5NH3Cl to 1.00 L of a 0.77 M solution of C2H5NH2. Calculate the pH of the final solution. (Assume no volume change. Assume that all solutions are at 25°C.)

  39. science

    1. Which of the following is TRUE regarding this situation: Solution A has a pH of 7.38, and Solution B has a pH of 7.42? a.Solution B is more acidic than Solution A b.The pH of Solution A falls within the homeostatic pH range for extracellular body

  40. Jill

    State the relationship of A to B (i.e. , = or can't be determined). 1. Using a 0.05 M Ag+ titrant A.VEP in titration 25-mL of 0.01 M MgCl2 B.VEP in titrating 25-mL of 0.01 M AlCl3 2. A 25.0-mL solution contains 0.015 M NaCl and 0.010 M HCl A.VEP (Mohr)

  41. Chemistry

    Calculate the pH of a buffered solution prepared from 0.25 mol KF and 0.75 HF after the addition of 0.05 mol of NaOH (assume a 1.0 L volume of solution) I get that i need to use two separate ice tables, but i don't really understand how to go about doing

  42. Chemistry

    Calculate, 1,the PH of0.1M CH3COOH buffered solution with 0.2M CH3COONa 2,when 9.5M HClis added to75ml of the buffer solution in(1) 3,compaire the PH of the two questions whre added to pure water?(Ka ofCH3COOH=0.00008)

  43. Chemistry

    A 100 milliliter sample of 0.100-molar NH4Cl solution was added to 80 milliliters of a 0.200-molar solution of NH3. The value of Kb for ammonia is 1.79 x 10^-5. (a) What is the value of pKb for ammonia? (b) What is the pH of the solution described in the

  44. chemistry

    If 1.70 liters of 0.670 M CuSO4 solution is electrolyzed by passing 4.70 amps through the solution for 3.00 hr using inert electrodes. (a) As electrolysis proceeds, how does the acidity of the solution change? (b) How many grams of Cu metal are formed at

  45. biology

    2more questionsss ! dats it ! 1. Which statement is TRUE? a. A cell placed in an isotomic solution will swell. b. A cell placed in a hypotonic solution will swell. c. A cell placed in a hypotonic solution will shrink. d. A cell placed in a hypertonic

  46. Chemistry

    You make 1.00 L of a buffered solution (pH = 5.10) by mixing propanoic acid and potassium propanoate. You have 1.00 M solutions of each component of the buffered solution. What volume of each solution do you mix to make such a buffered solution? propanoic

  47. Chemistry

    1 Calcium solution 2 Barium solution 3 Strontium solution In which solution or solutions does not precipitate form when potassium ferro cyanide solution is added to the above solutions buffered with ammonia and ammonium chloride?

  48. Chemistry

    1) Give an example of a buffer solution? 2) Explain how the buffer solution named in 1) resists changes in pH when an acid or alkali is added to it.

  49. Chemistry AP

    What are the concentrations of benzoic acid and sodium benzoate in a solution that is buffered with a pH of 4.55 and has a freezing point of -2.0 degrees Celsius? (assume complete dissociation and a density of 1.01g/mL for the solution.)

  50. Chemistry

    A 1X Phosphate Buffered Saline solution was prepared by adding 1.44g of Na2HPO4 and 1.44g of H2PO4- to 800mL of water. Additional components were dissolved in the solution: 8g of NaCl, 0.2g of KCl and 0.24g KH2PO4. The resulting buffer solution had a pH of

  51. chemiestry

    One liter of buffered solution should be prepared with a general concentration of 0.320M with a pH of 5.83 : - Pyridine solution (formula: C5H5N) in water at a concentration of 1.00M - HCl solution in water at a concentration of 0.85M - Distilled water In

  52. Pre Calculus

    a biologist has three salt solutions: some 5% solution, some 15% solution, and some 25% solution. She needs to mix some of each to get 50 liters of 20% solution. She wants to use twice as much of the 5% solution as the 15% solution. How much of each

  53. chemistry

    what is the molar solubility of Fe(OH)3 in a buffered solution with pH=8.2 at 25 degrees Celsius given ksp =4.0*10^-38.

  54. Chem 1A

    Help please! How many moles of NaOH must be added to 1.0 L of 3.0 M HC2H3O2 to produce a solution buffered at each pH? 1) pH= 3.78 2) PH= 6.52

  55. Chemistry

    when 5.0g of KOH is added to 100mL, of water, the temperature of the solution increases by 3 degrees celsius. Assume the density of the solution to be 1g/mL and specific heat capacity of the solution to be 4.184 J/g K. a. calculate the amount of heat

  56. Chemistry

    Hello Jiskha, I'm hoping you are able to help me with my homework. Its on General Chemistry. Question One - When the solid NH4NO3 is dissolved in water at 25 C, the temperature of the solution decreases. What is true about the signs of enthalpy (H) and (S)

  57. Math

    If the pH of a solution increases by 4 (from 4 to 8), how much does the hydrogen ion concentration change? Does the change make the solution more acidic or more basic?

  58. chemistry

    A flask containing 200 mL of solution is labeled 0.300 M CuBr2. A sample containing 0.0500 moles of Br− is added to the solution. What is the molarity of the Br− ion solution? Assume no volume change. a) 0.850 M b) 0.667 M c) 1.10 M d) 1.00 M e) 0.400

  59. Chem

    The following questions refer to the following system: A total of 30.0 mL of a .10M solution of a monophonic acid (Ka = 1.0 x 10 ^-5) is titrated with .20M sodium hydroxide solution. 1) Before the titration begins, the pH of the solution is about A) 2 B) 5

  60. Chemistry

    What is the molarity of a solution of Mg(OH)2 if the solution contains 1.35 g in exactly 100 mL of solution??? A 15.0 mL solution of H2SO3 is neutralized by 12.0 mL of a standradized 1.00M NaOH solution. What is the concentration of the H2SO3

  61. chemistry

    50.0 mL of a 0.00200 M Cd^2+ solution is titrated with 0.00400 M EDTA in the presence of 0.0750 M NH3 buffered at pH = 9.00. Determine pCd^2+ when 28.5 mL of EDTA solution have been added. Cd^2+ + Y^4- ? CdY^2- Kf= 3.16 x 10^16 Cd^2+ + NH3 ? CdNH3^2+ ß1 =

  62. Chemistry

    1)A buffer solution that is 0.10 M sodium acetate and 0.20 M acetic acid is prepared. Calculate the initial pH of this solution. The Ka for CH3COOH is 1.8 x 10-5 M. As usual, report pH to 2 decimal places. *A buffered solution resists a change in pH.*

  63. chemistry

    A buffered solution is made by adding 50.0 g NH4Cl to 1.00 L of a 0.84 M solution of NH3. Calculate the pH of the final solution

  64. Chemistry

    Can someone please explain to me whats the difference between a buffered and non-buffered solution?

  65. Science

    5. You have made the following two solutions: X) hydrogen ion concentration = 1 x 10-5M Y) pH = 4 State which statements below are true and which are false: a. Solution X contains 1 x 10-9M hydroxide ions. b. Solution X contains more H+ ions than Solution

  66. chemistry

    I am having trouble with how to approach this problem. I have the solution but can't figure out how to get it. How many moles of NaOH must be added to 1.0 L of 2.0M HC2H3O2 to produce a solution buffered at each pH? a) pH=pKa b)pH=4 c)ph=5

  67. Chemistry

    I am having trouble with how to approach this problem. I have the solution but can't figure out how to get it. How many moles of NaOH must be added to 1.0 L of 2.0M HC2H3O2 to produce a solution buffered at each pH? a) pH=pKa b)pH=4 c)ph=5

  68. Biology

    Decide and then explain why you concluded the following statements are true or false. a) If glucose concentrations in solution A and B separated by a semi permeable membrane are the same, the net movement of water will be zero. b) If glucose concentration

  69. chemistry

    Acetic acid, CH3CO2H, is the active ingredient in vinegar. It's often abbreviated "HOAc". Vinegar is acidic because acetic acid makes H3O+ when it partially ionizes in water: HOAc(aq) + H2O H3O+(aq) + OAc–(aq) Suppose that you have a solution of

  70. Chemsitry

    Hello. I'm not n=sure about these answers so i was wondering if someone could check them out? 27, A: Which is a stronger acid - sulfuric or carbonic acid? (Answer: Sulfuric acid.) 27, B: Imagine you have two glasses. One contains a solution of carbonic

  71. Biochem

    Assuming that the value of the equilibrium constant for the aldolase reaction Keq=6.43*10^-5 at pH=7 a.) What will be the equilibrium concentration of dihydroxyacetone phosphate (DHAP) if 1 mM of fructose-1,6-biphosphate is added to a buffered solution

  72. Business English

    What are two or three solution that might improve the efficiency of my office What does each solution involve and how much work and money is required to introduce that change How exactly does each change solve the problem? which is the best solution at

  73. chemistry

    100.0 mL of a dilute NaCl(aq) solution is heated in an open beaker. After 15 minutes the burner is turned off. Which of the following is true of the resulting solution? a more concentrated than the initial solution b less saturated than the initial

  74. Chemistry

    I am confused about why this is the answer to a practice problem I was given. (answer is c). Could someone explain why/why not for each answer? 2) Solution A is made from 1 L of water and 0.1 moles of Na(CH3COO), and Solution B is made from 1 L of water

  75. Chemistry

    Help needed on a homework problem - solution of HCN and CN- , Ka 6.2x10^-10 . Is this a buffered solution? Shouldn't the pH be greater than 7, and [OH] >[H]? Does adding a strong acid have more effect than adding a strong base? Thanks.

  76. Chemistry

    What should the molar concentrations of benzoic acid and sodium benzoate be in a solution that is buffered at a pH of 4.75 and has a freezing point of -2.0 ∘C? (Assume complete dissociation of sodium benzoate and a density of 1.01 g/mL for the solution.)

  77. Chemistry

    A solution has a pH of 2. How does the pH change if 1 mL of the solution is diluted to 100 mL with pure water? How does the pH of a solution with pH 10 change under the same dilution?

  78. Chemistry

    A solution containing 22.18 mL of a .1212 M H2CO3 solution is mixed with 17.22 mL of a .1234 M Na2CO3 solution. What is the pH of the final mixture? Ka1 = 6.2x10-7 Ka2 = 4.4x10-11. If you diluted the mixture up to 100 mL, would the pH change? If it does

  79. Chemistry

    A 0.60 L portion of a 1.2 M AgNO3 solution is mixed with a 0.3 L potion of a 1.2 M Na2CrO4 solution in an constant pressure calorimeter. Upon mixing, the solid Ag2CrO4 is formed and the heart released is 48.2 kJ. The specific heat of the solution is 4.18

  80. Chemistry

    What is the molar solubility of Fe(OH)3(s) in a solution that is buffered at pH 2.75? The Ksp of Fe(OH)3 is 6.3 × 10-38.

  81. chemistry

    is it better to describe a buffered solution as resisting or preventing all changes in pH? why?

  82. Chemistry

    calcutate 1,the Ph of 0.1MCH3cooH buffered solution with 0.2Mch3cooNa

  83. Math Algebra , high school

    A biologist has three salt solutions: some 5% solution, some 15% solution, and some 25% solution. She needs to mix some of each to get 50 liters of 20% solution. She wants to us twice as much of the 5% solution as the 15% solution. How much of each

  84. Chemistry

    How many moles of NaOH must be added to 1.0 L of 2.2 M HF to produce a solution buffered at each pH? (a) pH = pKa (b) pH = 4.24 (c) pH = 4.60

  85. Math

    What must be true about the solution to this system of equations? x+4y+9z = -96 -2y+9z = -47 z = -7 a) The solution will describe the intersection point(s) of the 3 graphs. b) The value of z must be -7. c) The solutions will have values for x, y, and z. d)

  86. Science

    Consider a basic solution diluted by a factor of 10. Calculate the pH of a 0.10 M solution of OH- and a 0.010 M solution of OH-. How did the pH change? Please help ASAP!!! :(

  87. Chemistry 2 - pH

    You are given an aqueous salt solution and have determined that its pH is 5.19 at 25°C. Predict which of the following three salt solutions it is most likely to be. solution (1): a solution of ammonium nitrate (NH4NO3) solution (2): a solution of

  88. chem

    A solution is prepared by dissolving 0.87mol of MgCl 2 in 0.40kg of water. How many moles of ions are present in solution? What is the change in the boiling point of the aqueous solution?

  89. Chemistry

    In the qualitative analysis scheme, magnesium and nickel precipitate from solution upon the addition of sodium hydroxide. Once separated from the remaining cations by filtration or decanting, the solid mixture is acidified and warmed to dissolve magnesium

  90. College Chemistry/Lab Math

    I think I have this problem figured out correctly, but is there anyone who can tell me if I'm doing something wrong. The question is... "One troy ounce of gold is worth $380. There are 33.8 grams per troy ounce. You have a stock colloidal solution of a

  91. CHEM UNI

    2. In a calorimetry experiment, 50.0 g of a 2.04 mole/kg HCl solution is mixed with 50.0 g of a 2.13 mol/kg NaOH solution. The specific heat of the resulting solution is 3.90 J·˚C−1·g−1. The temperature of the mixture rises from 22.1 ºC to 37.0

  92. chemistry

    A 1.00M solution of a hypothetical weak acid (HB) has a pH of 2.85. A solution is created using 0.10M of a salt NaB ('B' being the anion of the weak acid HB) and 50.0 ml of 2.0M acid HB (assume no change in volume). What would be the pH of the solution and

  93. Chemistry

    If 50.0 mL of a 1.00 M solution of CaCl2 (solution A) is mixed with 85.0 mL of pure water to produce solution B and then 42.5 mL of solution B is mixed with 52.0 mL of solution A to give solution C, what is the concentration of CL^-(aq) in the final

  94. Chemistry

    A teacher prepares a saturated NaCli solution at 55 Degree C. What is the % by mass 9m/m0 of this solution? what is the concentration of this solution expressed in ppm? What is the molality of this solution? If the density of the solution is 1.07 g/ml,

  95. chemistry-confirm please

    Only a chemist can be trusted with the combination to the safe containing a ton of money. The combination is the pH of solution A, followed by the pH of solution C. (for example: is the pH of solution A is 3.47 and the pH of solution C is 8.15 the

  96. Fractions

    A technician has prepared three solutions from a 600 mL stock solution. • In preparing the first solution ½ of the original volume of the stock solution was used. • The second solution required ¼ of the remaining stock solution. • Preparation of

  97. Math - urgent

    2. A technician has prepared three solutions from a 600 mL stock solution. • In preparing the first solution ½ of the original volume of the stock solution was used. • The second solution required ¼ of the remaining stock solution. • Preparation of

  98. Chemistry 114

    Write the balanced ionic equations for the following precipitations and complex forming reactions: a) AgNO3 solution + copper sulphate solution b) copper sulphate solution + lead nitrate solution c)CoCl2 solution + conc. HCl d) Zinc chloride solution +

  99. Chemistry

    Question : State whether the following are true or false. SO2 gas changes the colour of a KMnO4(aq) solution They have taken this as false and given the following equation: SO2+H2O+2KMnO4-->K2SO4+MnSO4+H2SO4 (not balanced) But why they have taken this as

  100. chemistry

    The concentration of NaOH in a solution is 7.00 10-6 M. What is the [H3O+] in the solution? _______________M What is the [OH-] in the solution? __________M What is the pH of the solution? What is the pOH of the solution? HELPP?? i don't understand any of

Pages

  1. 1
  2. 2
  3. 3
  4. 4
  5. 5
  6. 6
  7. 7
  8. 8
  9. 9
  10. 10
  11. 11
  12. 12
  13. 13
  14. 14
  15. 15
  16. 16
  17. 17
  18. 18
  19. 19
  20. 20