Navigation
Discovering how to take a mixture apart using tools like sieves or hands.
Imagine you accidentally dropped a box of shiny metal paperclips into a giant bucket of sand. How could you get them all back without picking them up one by one with your fingers?
A mixture is what you get when you put different things together. In your toy box, you might have a mixture of LEGO bricks, marbles, and cards. In chemistry, we often mix solids together. The cool part is that even when they are mixed, the objects don't change into something new! A marble is still a marble, and sand is still sand. Because they stay the same, we can use special tools to separate them, which means taking them apart again. We look for ways the objects are different to help us choose the right tool.
Let's separate a mixture of large glass marbles and fine white flour. 1. Place a sieve (a bowl with small holes) over an empty container. 2. Pour the flour and marble mixture into the sieve. 3. Gently shake the sieve back and forth. 4. The tiny flour particles fall through the holes because they are smaller than the gaps. The large marbles stay inside because they are too big!
Quick Check
If you have a mixture of big rocks and tiny dirt, which tool would help you separate them quickly?
Answer
A sieve (or sifter).
Sometimes, objects are the same size, so a sieve won't work. This is when we look at what the objects are made of. Some metals, like iron and steel, are magnetic. If you have a mixture of plastic beads and iron nails, they might both be small enough to fall through a sieve. But, if you use a magnet, the metal nails will jump up and stick to it, while the plastic beads stay behind. We call this 'magnetic attraction.' It is like a superpower for sorting!
A carpenter dropped a box of steel screws into a pile of sawdust. Both are small and messy. 1. The carpenter holds a strong magnet over the pile. 2. The steel screws are attracted to the magnet and fly out of the dust. 3. The sawdust is not magnetic, so it stays on the floor. 4. The carpenter now has a clean pile of screws and a pile of dust!
Quick Check
Why wouldn't a magnet work to separate plastic buttons from wooden sticks?
Answer
Because neither plastic nor wood is magnetic.
Separating things is easiest when the objects have very different properties. A property is a characteristic like size, shape, color, or magnetism. If you have a mixture of red blocks and blue blocks that are the exact same size, you have to use your hands to sort them by color. This takes a long time! The most difficult mixtures to separate are those where the pieces are the same size, the same weight, and made of the same material. Scientists always look for the one thing that makes an object unique to find the best way to separate it.
Imagine a bowl containing: Large pebbles, small iron filings (metal dust), and fine sand. 1. First, use a sieve with medium holes. The pebbles stay in the sieve, while the sand and iron fall through. 2. Second, take a magnet and pass it over the sand/iron mix. The iron filings will stick to the magnet. 3. Now you have three separate piles: pebbles, iron, and sand!
Which tool is best for separating big sea shells from fine beach sand?
If you use a magnet on a mixture of iron paperclips and copper pennies, only the paperclips stick. Why?
It is harder to separate a mixture if the objects are the same size and material.
Review Tomorrow
Tomorrow, look around your kitchen. Can you find a tool that works like a sieve? (Hint: Look for something used for pasta or flour!)
Practice Activity
Create your own 'Mystery Mix' using rice, dried beans, and metal paperclips. See if you can use a kitchen strainer and a fridge magnet to separate them!