Fun Fact: Salt Melts Ice?
Will the question above appear as a PSLE Science Question? This is a common query among students preparing for their PSLE Science Question.
Although the PSLE syllabus on matter and water cycle does not require students to know the effect of impurities on the freezing / melting point of a substance, this concept is commonly introduced in many schools and learning centres. (Here’s the link to the latest MOE Science syllabus)
Understanding the PSLE Science Question is essential for students to excel in their exams.
There’s nothing wrong with this, if not for the fact that it’s either mis-explained or inadequately explained by well-meaning educators.
Let’s use salt (the usual unwitting accomplice in such cases) as an example of an impurity in our discussion.

Why Does Salt Melt Ice? A Simple Explanation for Curious Minds
Many PSLE Science Questions revolve around everyday phenomena, like why salt can melt ice and how it relates to the freezing point of water.
Have you ever wondered why people sprinkle salt on icy roads during winter or why adding salt to ice makes it melt faster? You’ve probably heard that salt can make ice melt, but do you know how it actually works? Let’s break it down in a simple and fun way that’s easy to understand.
The Ice Experiment
Let’s imagine it’s freezing cold, and the temperature is -5°C. At this temperature, any water around would freeze into ice because water turns into ice at 0°C.
Now, let’s do a small thought experiment. Imagine we have two ice blocks:
- Ice Block A: We sprinkle lots of salt on it.
- Ice Block B: We leave it alone, just pure ice.
What do you think will happen?
After some time, here’s what we notice:
- Ice Block A starts melting.
- Ice Block B stays frozen solid.
This might seem magical at first, but there’s a cool (pun intended!) science behind why this happens.
In preparation for the PSLE Science Question, practice explaining how salt interacts with ice.
It is crucial for students to grasp how these concepts might appear in a PSLE Science Question.
Why Does Ice Block A Melt?
Here’s the key: Salt lowers the freezing point of water. Normally, water freezes and becomes ice at 0°C. But when you add salt to ice, it changes the freezing point, lowering it to below -5°C. For the sake of understanding, let’s imagine that the salt brings the freezing point down to -10°C.
So, now the surrounding temperature of -5°C is actually “warmer” than the new freezing point of -10°C. This makes Ice Block A melt because the salt prevents it from staying frozen!
How Does Salt Work on Ice?
You might wonder, “How does the salt interact with the ice?” After all, salt dissolves easily in water, but ice is solid. Can salt really mix with solid ice?
Here’s what happens:
- Ice isn’t completely dry or solid on the outside. There’s always a thin layer of water surrounding ice, even when the temperature is below freezing. Think of it like a thin “water skin” that coats the surface of the ice.
- When you sprinkle salt on the ice, the salt dissolves in this thin layer of water. This forms a salty solution, which has a much lower freezing point than regular water.
- Since this saltwater can’t freeze back into ice, the ice keeps melting slowly, and the melting continues until all the ice turns into water.
This is why salt is so effective at melting ice on roads, sidewalks, or anywhere it’s cold enough for ice to form.
Is There More to the Story?
Yes, there’s actually a bit more to it! When salt dissolves in water, it causes a chemical reaction that can either release heat (called an exothermic reaction) or absorb heat (called an endothermic reaction). This heat transfer can also play a small role in melting the ice. However, you don’t need to worry about this for now, as it’s a more advanced topic. Just knowing that salt lowers the freezing point is enough to understand the basics.
Why Does Salt Matter in Real Life?
So, now you know the science — but why is it important? Let’s explore how this knowledge is applied in the real world.
- Keeping Roads Safe
In countries with cold winters, icy roads can be very dangerous for cars and pedestrians. Workers often sprinkle salt on the roads to melt the ice and make the roads less slippery. This keeps drivers and pedestrians safe during frosty conditions. - Making Ice Cream
Believe it or not, the science of salt and ice is also used when making ice cream! When you use an old-fashioned ice cream maker, salt is added to the ice that surrounds the container. This lowers the freezing point of the ice, making the mixture inside colder and helping the ice cream freeze faster. How cool is that? - Fun Experiments
You can try a fun science experiment at home! Take two identical bowls and place the same amount of ice in each. Sprinkle salt on one bowl but leave the other as it is. Watch what happens over time. You’ll see the ice with salt melting much faster!
Your understanding of how salt affects ice could potentially form the basis of a PSLE Science Question.
What About the PSLE?
Good news! You don’t need to know this level of detail for your PSLE. It will not be a PSLE Science Question. The syllabus doesn’t require you to explain how salt melts ice or the chemistry behind it. However, it’s always fun to learn extra facts and expand your knowledge. You might even impress your friends or your teacher the next time someone brings up this topic!
Recap: The Magic of Salt and Ice
Here’s a quick summary of what we’ve learned about the PSLE Science Question:
When discussing experiments, remember that a PSLE Science Question could include practical applications of concepts like these.
- Water freezes at 0°C.
- Adding salt lowers the freezing point of water, making it harder for ice to stay frozen.
- Salt interacts with the thin layer of water on ice to create a saltwater solution, which doesn’t refreeze easily.
- This is why salt is used to melt ice on roads and even in ice cream making.
Such experiments might lead to a PSLE Science Question that evaluates your understanding of freezing points.
Now that you know how it works, you can understand why people sprinkle salt in cold weather or use it in other cool ways.
Try This Yourself!
Why not test this out at home? Here’s what you need:
- Two identical bowls or plates.
- Ice cubes.
- Salt (regular table salt works).
Place an equal number of ice cubes in each bowl, and sprinkle salt over just one of them. Check on the ice cubes every few minutes and observe the differences. Which one melts faster? This simple experiment will show you the power of salt in action!
Teachers may create a PSLE Science Question based on the principles you’ve learned about salt and ice.
Success in PSLE Science Questions can be achieved through thorough preparation and understanding of key concepts.
In conclusion, understanding the PSLE Science Question about salt melting ice not only prepares you for the exam but makes you more aware of the science around you.
This is why the PSLE Science Question often involves real-world applications.
Being aware of how to answer a PSLE Science Question can significantly improve your understanding and grades.
Let’s Keep Learning!
Learning how the world works can be so exciting, especially when you can try it out for yourself. If you enjoyed this article, share it with your friends or classmates! You can also subscribe to our newsletter for more fun science facts and helpful PSLE tips.
Still, this is not the full story, because the dissolving of salt in water gives rise to chemical reactions that could either release (exothermic) or absorb (endothermic) heat energy, but we’ll save that for another discussion…
Sounds complicated?
Here’s the good news: this explanation is not required according to the PSLE syllabus! Still, it’s good to know what actually happens, in case you’re ever asked by your precocious child.
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