3.AP Chem AB FRQ
A sample consisting of 50. mL of 0.400 M solution of the acid, HClO4, is titrated
titrated with a 0.200 M solution of the base, LiOH.
Write the balanced chemical reaction for neutralization reaction:
HClO4 (aq) + LiOH (aq) → LiClO4 (aq) + H2O (l)
Write the NET ionic equation for the neutralization reaction.
OH⁻ (aq) + H⁺ (aq) → H2O (l)
Compute the pH of the titration solution. Show your work
i) before any of the base is added
ii) after 25. mL of base is added
iii) after 50. mL of base is added
A student performs the titration with the same chemicals but with smaller volumes of each chemical . Which of the following titration curves could represent the titration. Explain
A because this entails a strong acid and a strong base.
A student performs a titration of an unknown acid with a strong base and gets the following titration curve:
a) The student consults the list of pKa of acids shown below. If the acid is listed in the table below, which is the most likely identity of the unknown acid? Explain.
7.2 x 10-4
1.8 x 10-5
4.3 x 10-7
2.0 x 10-9
The unknown acid is HBrO because the calculated Ka is in between 50^-4 and 50^-6 and 2.0 x 10^-9 lies in between them.
b) What is the initial molarity of the acid?
10^-3 = 0.001M
a) Describe the components and the composition of an effective buffer solution. Explain how the components of the buffer allow the buffer to maintain its pH.
An effective buffer solution has a weak acid and its conjugate base or a weak base and its conjugate acid. A buffer solution is most effective when the ratio of its component concentrations is close to 1, also when the pH is equal to the pka of the acid.; The components of the buffer allow the buffer to maintain its pH because buffers can absorb excess H+ions or OH– ions.
An employer is interviewing four applicants for a job as a laboratory technician and asks each how to prepare a buffer solution with a pH of 5.0. The following constants may be helpful: hydrazoic acid, pKa = 4.74 Boric acid, pKa = 9.23
Archita A. says she would mix equal molar solutions of hydrazoic (HN3) and sodium azide (NaN3) solutions.
Bradley B. says she would mix equimolar Boric acid (H3BO3) and HCl solutions.
Carlos C. says he would mix equimolar Boric Acid (H3BO3) and sodium dihydrogen borate (NaH2BO3) solutions.
Delia D. says he would mix equimolar hydrazoic Acid (HN3) and NaOH solutions.
b) Which of these applicants has given an appropriate procedure? Explain your answer
Delia because she is using Sodium hydroxide which results in a pH of 5. NaOH is a strong base and in order to have an effective buffer a weak acid must be incorporated which is the HN3.
c) Explain what is wrong with the erroneous procedures.
The rest all incorporate a strong acid and a strong base or a weak acid and a weak base which don’ result in an effective buffer.
d) The applicants have access to the 1 Liter volumes of each of the solutions listed above. They have access to graduated cylinders. In order to make 1.0 Liter of the correct 5.0 buffer solution, what volumes of the two chemicals must be mixed?
4.(a) A 20.0 L container at 303 K holds a mixture of two gases with a total pressure of 5.00
here are 2.00 mol of Gas A in the mixture, how many moles of Gas B are present? (R = 0.0821 L • atm/(K • mol))
(b) The gas in a 250. mL piston experiences a change in pressure from 1.00 atm to 2.80 atm. What is the new volume (in mL) assuming the moles of gas and temperature are held constant?
(c) Small quantities of Oxygen can be produced by the decomposition of mercury(II) oxide as shown below. Typically, the oxygen gas is bubbled through water for collection and becomes saturated with water vapor. Atomic weight of HgO = 216.6 amu, Atomic weight of Oxygen = 32.00 amu)
2 HgO(s) → 2 Hg(ℓ) + O₂(g)
(i) Assuming that 3.05 grams of HgO was used in this reaction, determine the number of moles of oxygen gas formed.(According to the above chemical equation)
(ii) Assuming 310. 0 mL of Oxygen gas was collected at at 29°C, calculate the pressure of the Oxygen gas that was collected. (R = 0.0821 L • atm/(K • mol)
(iii) If the vapor pressure of water at this temperature equals to 0.042 atm, calculate the pressure reading of this experiment.
6.5 (5 points) There is H3PO4 available in stock solution that has an assay of 77% and a density
cific gravity) of 1.24. What is the molarity of this solution?
Using this solution how would 1 L of 2N solution be made.
6 (5 points) H3BO3 is needed to neutralize 20 ML of a 2N solution of NaOH. How much of the acid should I put in 40 ML of the water to exactly neutralize this solution?
7 (6 points) Describe how to make the solutions below :
20% w/v Salt in water.
20% v/v alcohol in water
20% w/w NaCl in water.
8 (three points) I have 0.6 g/dl solution of NaOH. What is M? Whan is N?
9 (six points) There are 3000mL of 3M NaOH. How much of the following do I need to neutralize? (watch your M’s and N’s
a) 3M H3PO4
b) 2M H2SO4
c) 1M HCL
10 (20 points) The following solutions of NaOH are mixed together 20ML of 3N, 40mL of 2N, 60mL of 1N, 80 mL of 4N, and 100mL of 5N.
a) What is the volume and normality of the final solution?
b) How much 4M sulfuric acid would I need to neutralize?
c) How much stock solution of sulfuric acid with an assay of 77% and a specific gravity of 1.14 would I need?
d) How many grams of HCl would I have to put in a 300mL solution of HCl in water to neutralize?
11 (3 points) How much 5N solution can I make with 98 grams of H3PO4 ?
12 (5 points) How much 5N solution of H3AsO4 can I make with 57 mL of stock solution that is 84% assay and 1.14 specific gravity?
13 (5 points) If we have a 4N solution of HCl that has 0.03645g of HCl in the solution, how many microliters of solution do we have?
14 (10 points) If we have 66mL of a solution of concentrated NaOH that has an assay of 88% and a specific gravity of 1.24, how much 3N H3AsO4 can be neutralized?
15 (ten points) If I have 17 mL of a 20% w/v solution of NaOH and I want to neutralize with H2SO4 that is available in a 4% w/v solution, how much of this solution will be required.
16 (ten points)
a) I have an 12mL of Ba(Cl)2 that is 78% assay that contains 8 grams of Ba(Cl)2. What is the specific gravity?
b) How many Moles of Ba(Cl)2 are there?
c) If I have 80 grams of NaOH in a liter of solution that is of an unknown specific gravity, can I calculate molarity and what is it?
d) What is the difference between molarity and normality?
e) I have 77 ml of 77% salt in water. How much 11% can I make?
7.I was wondering if you could help me step up my chem problems, i'm not sure how to begin
estion 1: Draven collected a 1ml sample from a local river. Draven added 99 ml of water to the sample. Draven then took 5 ml of the diluted sample, and determined the 5 ml sample to contained 10 mg of sodium chloride. what is the concentration of sodium chloride in the river?
question 2: how many grams of H2 could be produced when 13 g of H202 decompose?
question 3: how many molecules of carbon dioxide could be produced when 25 ml of a 0.8 M ethanol, c2h60, combusts with 5.18X10^23 molecules of oxygen? the unbalanced equation for the combustion of ethanol is given below:
8.Problem Set 1. Name ________________________
1. For hexachlorobenzene (HCB), log Kow = 5.3, What would be the predicted concentration of HCB
, What would be the predicted concentration of HCB due to bioconcentration in the fat of fish that swim in water containing 0.00006 ppm of the chemical?
2. The fat content of breast milk averages a little over 4.0 g per 100 ml. Calculate the mass of DDE that would have been ingested by a typical breast-fed infant in 1972 consuming 300 ml of breast milk per feeding, if the milk contained about 500 ppb of DDE in its fat content.
3. The PCB concentration in Lake Michigan is declining according to a first-order rate law having a rate constant of 0.078 year-1. If the PCB concentration in the lake averaged 0.057 ppt (parts per trillion) in 1994, what was the concentration in 2004? In what year will the concentration fall to 0.005 ppt.