The topic on Water Cycle has been examiners’ all time favourite during examinations. In fact, it is also related to Heat Energy, which tests the students’ understanding on BOTH topics in a single question. Unfortunately, the Water Cycle topic has been a tricky one amongst students as many tend to underperform for both of these topics. As such, we will be going through common misunderstandings for this topic and how to avoid them!

 

 Let’s kick off today’s blog post with a typical Water Cycle question:

The below picture shows Pail A, containing water at 2˚C and was left in a room with room temperature at 28˚C.

 

 

Temperatures of the water and mass of Pail A were measured at 5-minute intervals. Results were recorded in the table below.

 

Time (Minutes)	Temperature of water in Pail A (˚C)	Mass of Pail A with water (g)
0	2	200.0
5	5	200.4
10	9	200.6
15	14	201.0

 

Question: Explain why the mass of Pail A increased despite not adding water? 

Let’s look at the below answer and point out the common errors that caused this student to only achieve 1 out of 2 full marks.

Answer: The surrounding water vapour touched the cooler outer surface of Pail A and lost heat, condensing into water droplets.

 

In this question, students are required to answer 2 parts.

1. Explain how the water droplets were formed
2. Explain the increase in mass of Pail A with water

 

Common Mistake 1

Recall: In containers of hot and cold water, which cooler surface does the warmer water vapour come into contact with: Outer or Inner?

 

Container of HOT water

The warmer water vapour comes into contact with the cooler INNER surface of the container.

Container of COLD water

The warmer water vapour comes into contact with the cooler OUTER surface of the container.

 

Common Mistake 2

Recall: Where is the warmer water vapour losing heat to?

 

Whenever there is a mention of heat gain or loss, students need to identify clearly the 2 objects where the heat transfer is occurring. 

In the abovementioned question, the warmer water vapour is losing heat TO the cooler OUTER surface of Pail A.

 

Common Mistake 3

Remember to always LINK the answer BACK to the question

 

The above answer failed to identify and explain the increase in mass of Pail A with water. 

The increase in mass is due to the formation of water droplets on the outer surface of Pail A, resulting in an increase of the original mass of Pail A with water. The common mistakes listed above may be hard for students to spot and correct, but fret not. At Mega Minds, teaching our students to IDENTIFY and UNDERSTAND various question types is a crucial component of our lessons.

 

With the provided information in the question, students must be able to recall the essential steps in answering it effectively.

The question type will be “Formation of Water Droplets for on surfaces BELOW room temperature”. 

 

Students should recall the following steps whenever answering such questions:

1) State the object present in the surrounding air?

2) Which surface would the object touch?

3) Identify the heat transfer and the process involved?

4) What would form?

 

Question: Explain why the mass of container B with water increased even though no water was added. [2m]

Answer: Container B would lose heat to the water at 4˚C to become cooler.

 

At Mega Minds, students will not only be taught how to avoid tricky yet commonly made mistakes, but also how to apply our simple yet effective answering techniques!