what is the product of combustion of a hydrocarbon in excess oxygen
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HESI A2

Chemistry Hesi A2

1. What are the products of combustion of a hydrocarbon in excess oxygen?

Correct answer: A

Rationale: The correct answer is A: Carbon dioxide and water. During the combustion of a hydrocarbon in excess oxygen, the hydrocarbon reacts to produce carbon dioxide and water vapor as the final products. This reaction is known as complete combustion, where the hydrocarbon combines with oxygen to form carbon dioxide and water. Choices B, C, and D are incorrect because naphthalene is a specific hydrocarbon compound, chlorine and bromine are not typically formed during the combustion of hydrocarbons in excess oxygen, and carbonium ions are not the products of this reaction.

2. If two workers can finish building a play set in 18 hours, how long will it take 4 workers to build 3 play sets?

Correct answer: A

Rationale: If 2 workers can complete building one play set in 18 hours, it means one worker would take 36 hours to complete the same task. When the number of workers is doubled to 4, the time is halved, so 4 workers would take 18 hours to build one play set. To build 3 play sets, the total time needed would be 3 times the time for one play set, which equals 54 hours. Therefore, 4 workers can build 3 play sets in 27 hours, making choice A the correct answer. Choices B, C, and D are incorrect because they do not account for the correct relationship between the number of workers and the time required to complete the task.

3. Which of the following substances is a base?

Correct answer: C

Rationale: The correct answer is 'Ammonia' (Choice C) as it is a common example of a base. Bases are substances that release hydroxide ions (OH-) in aqueous solutions, helping to increase the pH level. Ammonia is a weak base that can accept a proton (H+) to form ammonium hydroxide. In contrast, water (Choice A), sodium chloride (Choice B), and salt (Choice D) are not bases; water is neutral, while sodium chloride and salt are neutral compounds composed of a cation and an anion.

4. Select the word or phrase that makes the following sentence grammatically correct: 'Why did we ____ try so hard?'

Correct answer: D

Rationale: 'Have to' is the correct choice as it fits the sentence structure. The sentence is in the past tense ('did we') and requires the infinitive form 'have to' to express the idea of necessity or obligation in the past. 'Has to' (Choice A) is incorrect as it is present tense, 'haven't' (Choice B) is a negative form and does not make sense in this context, and 'had to' (Choice C) would imply a past obligation that has already been fulfilled, which is not the intended meaning here.

5. The price of an item increased from $9.00 to $10.00. What percentage did the price increase by?

Correct answer: B

Rationale: To calculate the percentage increase, subtract the original price from the new price, then divide the result by the original price and multiply by 100. In this case, the increase is $10.00 - $9.00 = $1.00. $1.00 divided by $9.00 is approximately 0.1111, which equals 11.11%, making choice B the correct answer. Choice A, 5%, is too low as the increase is more than 5%. Choice C, 20%, and choice D, 25%, are too high, exaggerating the actual increase of $1.00.

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