AP Chemistry Question of the Day --5

Here comes the answer to question 4 I posted yesterday. The correct answer is C. 

To answer this question right, first we need to know that both hydrogen and oxygen gas exist as diatomic molecules. Apart from hydrogen and oxygen, nitrogen, fluorine, chlorine, bromine and iodine also exist as diatomic molecules. Another detail we should notice is that oxygen molecules are bigger than hydrogen molecules in size. This is because oxygen is in the second period and hydrogen is in the first period. If you are good at molecular geometry, you can see that the water molecules are drawn as bent molecules. This is due to the sp3 hybridization of the central oxygen atom. In addition, we need to write the balanced equation correctly as follows.

From this equation,we can see that hydrogen and oxygen and the water produced obey a 2:1:2 ratio.
Only choice C is correct in both ways, so C is the right answer.

Following is Question 5 of the series:

5. A 50.0 mL sample of an acid, HA, of unknown molarity is titrated, and the pH of the resulting solution is measured with a pH meter and graphed as a function of the volume of 0.100 M NaOH added.At point R in the titration, which of the following species has the highest concentration?

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I will post the answer and explanation tomorrow.

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