exam 2 chem lec 2

conjugate base of HF

F-

At a certain temperature 4.0 mol of NH3(g) is introduced into a 2.0 L container and it partially dissociates according to the following reaction: 2 NH3(g) ⇄ N2(g) + 3 H2(g)At equilibrium, 2.0 mole of NH3 remains. What is the value of Kc for this reaction at this temperature?

Kc= 1.7

If Kc = 0.042 for PCl3(g) + Cl2(g) ⇄ PCl5(g) at 500 K, what is the value of Kp for this reaction at the same temperature?

Kp= 0.0010/1.0x10^-3

write a balanced equation that shows the reaction of ammonia with water

NH3 + H2O ⇌ NH4+ + OH-

bronstead lowry base

accepts H+

is NH4Cl acidic, basic or neutral?

acidic

When the following reactions reach equilibrium, do they contain mostly reactants, mostly products, or approximately equal concentrations of reactants and products? N2(g) + O2(g) ⇄ 2 NO(g); Kc = 1.5 x 10-10 2 SO2(g) + O2(g) ⇄ 2 SO3(g); Kp = 2.5 x 109

mostly reactants, mostly products

is KCL acidic, basic or neutral?

neutral

The molarity of a KOH solution is 0.76 M. Calculate the pH and pOH of this solution.

pH= 0.12 pOH= 13.88

What is the final pH of the solution that forms when 50.0 mL of 0.50 M HCl is reacted with 75.0 mL of 0.10 M NaOH?

pH= 0.85

Determine the pH of the solution that results from the combination of the following: 30.0 mL of 0.50 M HCl 20.5 mL of 0.25 M Ca(OH) 20.5 mL of 0.25 M HNO3 50.0 mL of H2O

pH= 1.08

The concentration of a hydrochloric acid solution is 0.055 M. What are the pH and pOH of this solution?

pH= 1.26 pOH= 12.74

Calculate the pH of an ammonia solution with a concentration of 0.10 M. What is the percent ionization of the base? The Kb for ammonia is 1.8 x 10-5

pH= 11.11 %i= 1.3%

Calculate the pH of a 0.20 M Na2CO3 solution. For H2CO3 Ka1 = 4.5 x 10-7 and Ka2 = 4.7 x 10-11

pH= 11.81

An acetic acid (HC2H3O2) solution has a concentration of 0.55 M. The pKa of acetic acid is 4.74. What is the pH of the acetic acid solution? What is the percent ionization of the acetic acid in this solution?

pH= 2.51 %i= 0.56%

Calculate the pH of the solution prepared by combining 40.0 mL of 0.20 M lactic acid (HC3H5O3) with 30.0 mL of 0.20 M sodium hydroxide.Ka for lactic acid is 1.4 x 10-4

pH= 4.32

A solution is prepared by combining 0.300 mol HC2H3O2 and 0.300 mol NaC2H3O2 with enough water to make 1.00 L of solution. The pH of the solution is 4.74. The Ka for HC2H3O2 is 1.8 x 10^-5. Neglect any volume changes and calculate the pH of this solution after 0.020 mol of HCl is added.

pH= 4.68

A solution with a volume of 1.5 L contains 0.100 M HC3H5O2 (propanoic acid) and 0.100 M NaC3H5O2 (sodium propanoate).Ka for propanoic acid = 1.3 x 10-5 Calculate the pH of the solution. Calculate the pH after adding 20.0 mL of 0.50 M HCl to the original solution. Calculate the pH after adding 20.0 mL of 0.50 M NaOH to the original solution.

pH= 4.89 pH after added HCl= 4.82 pH after added NaOH= 4.96

Calculate the pH of a 0.12 M NaCl solution.

pH= 7.0

What is the pH of a KNO2 solution that was prepared by dissolving 25.0 g of the salt in enough water to make 750. mL of solution? (Ka of HNO2 = 7.1 x 10-4)

pH= 8.36

Calculate the pH of a 0.050 M solution of C5H5N (a weak base called pyridine). The Kb for pyridine is 1.7 x 10-9

pH= 8.96

Calculate the pH of a solution containing 1.0 g of ammonium chloride (NH4Cl) dissolved in 150. mL of 0.10 M NH3. Assume the total volume of the solution is 150. mL.Kb for NH3 is 1.8 x 10-5

pH= 9.15

Calculate the pH of an aqueous 0.36 M NaC2H3O2 solution. (Ka for HC2H3O2 = 1.8 x 10-5)

pH= 9.15

A solution with a total volume of 950.0 mL contains 0.50 M ammonia and 13.5 g of ammonium chloride. Kb for ammonia is 1.8 x 10-5 Calculate the pH of this solution. Calculate the pH of after adding 150.0 mL of 0.50 M sodium hydroxide to the original solution.

pH= 9.54

Lactic acid (HC3H5O3) is the acid present in milk and milk products. The Ka of lactic acid is 1.38 x 10-4 Calculate the pKa of lactic acid. Give the chemical formula of the conjugate base of lactic acid. Calculate the pKb of the conjugate base of lactic acid. Calculate the pH of a 0.50 M solution of lactic acid. Calculate the percent ionization of the lactic acid in the lactic acid solution from part d.

pKa= 3.860 cB= C3H5O3- pKb = 10.140 pH= 2.08 %i= 1.7%

arrhenius acid

produces H+ when dissolved in water

arrhenius base

produces OH- when dissolved in water

Consider the equilibrium reaction: 2 NO(g) + Cl2(g) ⇄ 2 NOCl(g) H = -77.1 kJ In which direction will the reaction shift when NO is added Cl2 is removed The temperature is increased The volume is doubled The pressure is increased A catalyst is added

right left left left right no shift

Dinitrogen tetroxide decomposes to form nitrogen oxide and nitrogen dioxide according to the following equilibrium reaction: N2O4(g) ⇄ NO(g) + NO2(g) ΔH° = 40.5 kJ. In which direction will the reaction shift when N2O4 is added NO2 is added The volume of the container is increased The temperature is decreased

right, left, right, left

The pH of a sample of milk was determined to be 6.77 at room temp. Calculate the [H+] in the milk and calculate the mass percent of H+ in the milk (assuming density is 1.0g/mL.)

[H+]= 1.7x10^-7 M mass %= 1.7x10^-8%

A solution has [OH-]= 3.4x10^-5. Calculate each of the following for the solution: [H+], pOH, pH, (basic, neutral or acidic?)

[H+]= 3.0x10^-10 pH= 9.53 pOH= 4.47 the solution is basic

A solution has pOH of 7.55. Calculate each of the following for the solution: [H+], [OH-], pH (basic, neutral or acidic?)

[H+]= 3.5x10^-7 [OH-]= 2.8x10^-8 pH= 6.45 the solution is acidic

A solution has a pH of 9.20. Calculate each of the following for the solution: [H+], [OH-], pOH, (basic, neutral or acidic?)

[H+]= 6.3x10^-10 [OH-]= 1.6x10^-5 pOH= 4.80 the solution is basic

The reaction between hydrogen gas and chlorine gas to produce hydrogen chloride gas is : H2(g) + Cl2(g) ⇄ 2HCl(g)The reaction has a Kc of 3.125 x 1033 at 500 °C. A 5.00 L flask initially contains 0.25 moles of HCl gas and is allowed to reach equilibrium. Calculate the equilibrium concentration of each species.

[H2]=[Cl2]= 8.9X10^-19M [HCl]= 0.050 M

A mixture of nitrogen gas and hydrogen gas react in a rigid container at a certain temperature as follows: N2(g) + 3H2(g) ⇄ 2NH3(g)The equilibrium concentrations are [H2] = 5.0 M, [N2] = 8.0 M, and [NH3] = 4.0 M. What were the initial concentrations of the nitrogen gas and hydrogen gas?

[N2]= 10.0M [H2]= 11.0M

A solution of ammonia has a pH of 11.70. Kb for ammonia is 1.8 x 10-5 Calculate the molarity of the ammonia in this solution. Calculate the mass percent of ammonia in this solution. Assume the density of the solution is 1.0 g/mL.

[NH3] = 1.4 M mass % = 2.4%

At 2000 °C, the equilibrium constant for the reaction 2 NO(g) ⇄ N2(g) + O2(g) is Kc = 2.4 x 10^3 . If the initial concentration of NO is 0.175 M, what are the equilibrium concentrations of NO, N2, and O2?

[NO]= 0.002M [N2]=[O2]= 0.087M

A solution has [H+]= 3.8x10^-3M. Calculate each of the following for the solution: pOH, [OH-], pH (basic, neutral or acidic?)

[OH-]= 2.6x10^-12 pH= 2.42 pOH= 11.58 the solution is acidic

A biochemist needs to prepare 3.5 L of a buffer with a pH of 7.5 for an enzyme study. The following acids are available: trichloracetic acid (HC2O2C13); Ka = 2.2 x 10-1 1acetic acid (HC2H3O2); Ka = 1.8 x 10-5 formic acid (HCHO2); Ka = 1.8 x 10-4 hypochlorous acid (HClO); Ka = 2.9 x 10-8 hypoiodous acid (HOI); Ka = 2.3 x 10-11 Which acid would be the best choice? Give the chemical formula of the compound that would need to be added to the acid to form a buffer.

hypochlorous acid NaClO, KClO, LiClO

The following equilibria were attained at 823 K: CoO(s) + H2(g) ⇄ Co(s) + H2O(g) Kc = 67 CoO(s) + CO(g) ⇄ Co(s) + CO2(g) Kc = 490 Based on these equilibria, calculate the equilibrium constant for H2(g) + CO2(g) ⇄ CO(g) + H2O(g) at 823 K.

0.14

A solution was prepared by dissolving Ba(OH)2 in water to a final solution volume of 255 mL. If the pH of the solution is 12.50, how many grams of barium hydroxide were dissolved to prepare the solution?

0.70 g barium hydroxide

How many grams of sodium acetate (NaC2H3O2) must be added to 2.5 L of 0.10 M acetic acid (HC2H3O2) to prepare a solution with a pH of 4.50? Assume the total volume of the solution is 2.5 L. Ka for acetic acid is 1.8 x 10-5

12 g NaC2H3O2

A mixture of hydrogen and nitrogen in a reaction vessel is allowed to attain equilibrium at 472°C. The equilibrium mixture of gases was analyzed and found to contain 7.8 atm hydrogen, 2.46 atm nitrogen, and 0.166 atm ammonia (NH3). From this information, calculate the equilibrium constant, Kp, for the following reaction: N2(g)+ 3H2(g) ⇄ 2NH3(g)

2.4x10^-5

The pH of a weak acid (HX) solution is 6.20. Calculate the Ka of the acid if the molarity of the acid is 0.010 M.

4.0x10^-11

How many grams of NaCN must be dissolved in 1.5 liter of solution to have a pH of 11.50? (Ka of HCN = 6.2 x 10-10)

47 g NaCN

A closed system initially containing 1.000 x 10—3 M hydrogen gas and 2.000 x 10—3 M iodine gas at 448°C is allowed to reach equilibrium. Analysis of the equilibrium mixture shows that the concentration of hydrogen iodide gas is 1.87 x 10—3 M. Calculate Kc at 448°C for the reaction taking place. H2(g) + I2(g) ⇄ 2HI(g)

50.3

At high temperatures, nitrogen gas and oxygen gas react with each other to form nitrogen oxide according to the following reaction: O2(g) + N2(g) ⇄ 2 NO(g) Suppose the system is analyzed at a particular temperature and the equilibrium concentrations are found to be [O2] = 0.0078 M, [N2] = 0.041 M, and [NO] = 4.7 x 10-4 M. Calculate the equilibrium constant (Kc) for this reaction.

6.9x10^-4

conjugate base of HCN

CN-

conjugate base pairs in H20 + HONH3+ ⇌ H30+ + HONH2

H2O and H3O+ pair (H2O base) HONH3+ and HONH2 (HONH3+ acid)

conjugate acid of HPO4(2-)

H2PO4(-)

write a balance chemical equation that shows the reaction of HBr with water

HBr +H2O ➡ Br- + H3O+

conjugate acid of C2H3O2-

HC2H3O2

conjugate base of H2CO3

HCO3-

Which of the following combinations can act as a buffer? Explain your answer. HCl and KCl H2SO4 and KHSO4 HNO2 and KNO2

HNO2 and KNO2 since HNO2 is a weak acid

conjugate base pairs in HOCl + C6H5NH2 ⇌ OCl- + C6H5NH3+

HOCl and OCl- pair (HOCl acid) C6H5NH2 and C6H5NH3+ pair (C6H5NH2 base)

is KCN acidic, basic or neutral?

basic

is Na3PO4 acidic, basic or neutral?

basic

is NaNO2 acidic, basic or neutral?

basic

bronsted lowry acid

donates H+

The decomposition of hydrogen chloride gas to hydrogen gas and chlorine gas is an endothermic process and occurs as follows: 2 HCl(g) ⇄ H2(g) + Cl2(g)In which direction will the reaction shift when HCl is added Cl2 is removed The volume of the container is increased The temperature is increased The pressure is increased A catalyst is added

right, right, no shift, right, no shift, no shift

At 2000 K the equilibrium constant (Kc) for the formation of NO(g) is 4.0 x 10^-4. N2(g) + O2(g) ⇄ 2 NO(g) You have a container at 2000 K in which [N2] = 0.50 M, [O2] = 0.25 M, and [NO] = 4.2 x 10-3 M. Predict in which direction the reaction needs to proceed to reach equilibrium. Show work to support your answer.

shifts right