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.I am trying to figure out the optimal radius that will give the lowest surface area of a cylinder. I
have done the calculus which reveals that the surface area is at a minimum when height is double the radius. I am now trying to find an equation for the relationship between the amount of wasted surface area as a percentage of the minimum surface area and the ratio between height and radius.
If I were to plot it on a graph, the y axis would be the percentage of excess materials needed as a percentage of the minimum possible surface area, and the x axis would be height divided by radius. Since the surface area is minimized when height=2(radius), I know that when x=2, y=0.
The website https://www.datagenetics.com/blog/august12014/index.html explains what I am trying to do quite well and shows the graph below. I am trying to find the equation for this graph, but am unsure how to go about it.
6.A block of mass m1 lies on the horizontal plane, and another block of mass m2 is on it. A
thrown through the system of pulleys shown in the figure. A load of mass M = m1 + m2 is suspended from the movable pulley. At what ratio between the masses m1 and m2 will the blocks not slide over each other if the coefficient of friction between the blocks is µ, and there is no friction between the lower block and the plane? The mass of the thread and pulleys, as well as the friction in the pulleys, should be neglected; the thread is considered unstretchable.