AP Chemistry Question of the Day --65

Welcome back to my blog. Since most schools are doing the unit on acid and base at this time of the year and here is another question related to this topic.

Question 65: Four acids HA, HB and HC and HD solutions have the same pH, which of the following statements is correct:
A. They all have the same concentration
B. They are all strong acids
C. They are all weak acid
D. not enough information to make any conclusion

The correct answer is D. pH represents the concentration of hydronium ion in solution. The pH if an acidic solution is dependent on both the Ka and the concentration of the acid. A solution of a strong acid can have a higher pH due to lower concentration and a solution of a weak acid cna have a lower pH due to higher concentration.

Hope this helpful.

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AP Chemistry Question of the Day --64

I have not written here for a long time. AP season is coming soon in a couple of months. I will resume my series and hopefully it is helpful to anyone who come across to visit this site. Instead of posting a question and answer it the next day, I am going to post the question and answer at the same time.

Question 64: Which one of the following cidic solutions requires the most 0.1000M NaOH aqueous solution to neutralize completely:
A. 0.1000M HCl 25ml
B. 0.1000M HF 25ml
C. 0.05000M H2SO4 25ml
D. 0.05000M H2CO3 25ml
E. They are all the same

The answer to this question is E. When an acid and a base react, whenever there is a strong acid or base involved, the reaction will go to completion. The amount of base required will be totally determined by the mole number of the protons in the acid. It does not matter the acid is strong or weak, monoprtotic or diprotic. It is the number of moles of H+ that is in the acid that determines how much base will be needed to completely neutralize.

Hope this helps with your understanding on acid and base and thank you for visiting my blog.

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AP Chemistry Question of the Day --61

Welcome back to my blog. here is Question 60 I posted earlier.
60. Glycerol has lower vapour pressure than does ethanol at room temperature. Which of glycerol and ethanol has the lower boiling point?

The correct answer should be ethanol.

Vapour pressure is the pressure of the vapour when at a certain temperature the liquid and the vapour reach equilibrium in a closed container. Vapour pressure is only dependent on the nature of the substance and temperature. For a given substance, its vapour pressure is only dependent on temperature.  As temperature increases, vapour pressure increases. When the vapour pressure reaches the atmosphere pressure, the temperature is defined as boiling point. As a result, the higher the vapour pressure, the lower the boiling point.

Following is question 61 of the series:

 61. In an experiment to determine the percentage of water in a solid hydrate by heating, what is the best indication that all the water has been removed?
(A)  The solid melts.
(B)  The solid changes color.
(C)  Water vapor no longer appears.
(D)  Successive weighings give the same mass.

I will post the answer in my next blog.
Thank you very much for visiting my blog. I am available to discuss any topics in Chemistry at all levels. Please shoot me an email at vancouverchemistrytutor@gmail.com or give a call at 604-808-6827.

AP Chemistry Question of the Day --60

Welcome back to my blog. Here is question 59 I posted last week.

59.  Which of the following best helps to account for the fact that the F^- ion is smaller than the O^2- ion?                                                     

(a) F^- has a larger nuclear mass than O^2-    

(b) F^- has a larger nuclear charge than O^2-   

(c) F^- is more electronegative than O^2-        

(d) F^- is more polarizable than O^2-.

The correct answer is b.  Both fluoride and oxygen ions have 10 electrons. They are isoelectronic to each other. The size of the ions is determined by the number of protons in the nucleus. Since fluoride has 9 and oxygen has 8 protons. The electrons in fluoride ion experience more attraction from the nucleus and makes the ions smaller.

Statement A and C are both correct but they are not the right explanation.

Here is question 60 of the series:

60. Glycerol has lower vapour pressure than does ethanol at room temperature. Which of glycerol and ethanol has the lower boiling point?

Thank you very much for visiting my blog. I am available to discuss any topics in Chemistry at all levels. Please shoot me an email at vancouverchemistrytutor@gmail.com or give a call at 604-808-6827.

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