Answer Key: Combining and Separating

Examples of differences:

• They are different colors
• They are different sizes
• They are different shapes (view under a magnifying glass or microscope)
• Each salt granule is the same color and each iron filing is the same color. There are different colored grains of sand.

Examples of things they will mix with:

• Sand: salt, iron, sugar, flour, etc.
• Salt: sand, iron, water, etc.
• Iron: sand, salt, other metals when melted, etc.

Examples of things they will not mix with:

• Sand: water
• Salt: alcohol
• Iron: water

Here is a hint:

1. Try removing the iron first. Which tool (tweezer, magnet, beaker) might be able to pick up something metal like iron, but will not pick up the sand or salt?
   • Answer: magnet.

2. Next, try to separate the sand. Which tool (tweezers, magnet, filter) could stop the sand, but let the salt through?
   • Answer: filter paper.

3. Now you are left with salt dissolved in water. How can you get the water out? This one will take time and a little bit of sunshine.
   • Answer: leave the saltwater out in the sunshine without a lid. The water will evaporate and leave the salt in the container.

• If you did, can you talk through the steps?
• If you think you didn’t, remember that sometimes you use the scientific method without even knowing it. Take a look at your Scientific Method Nomenclature Cards and see if you used any of the steps.

Magnets are attracted to certain types of metal such as iron, nickel, and cobalt. There are other metals that magnets have varying levels of attraction to as well. There are also metals that magnets are not attracted to like copper and gold.

Remember in the Force of Attraction demonstration from the First Great Lesson we talked about how there are special forces in the Universe that pull things together and push things apart? Magnets are objects that have one of those forces: magnetism. Magnets have a magnetic field around them that pulls certain materials towards them. The force can also pull magnets towards each other, or push them away from each other depending on which way they are facing.

Metals are materials that have special properties. They are often hard, rigid, shiny, and conduct heat (if something hot touches metal, the metal gets hot quickly too).

You can learn more about metals and other elements in the Story of the Elements.

A suspension is a mixture of a solid and a liquid where the solid does not dissolve. When you mix them, the solid will be dispersed and suspended in the liquid. If you stop mixing them, the solid will eventually settle to the bottom of your container.

A solution is a mixture of a solid and a liquid where the solid dissolves into the liquid. When a solution is mixed, the solid is evenly distributed throughout the liquid. A solid will not “settle out” of a solution, but you can separate the solid and liquid through means like evaporation (like when you separate salt from water by evaporating the water).

• Sand and Water: Suspension 
• CaCO3 and Water: Suspension
• Salt and Water: Solution

Filters have pores or holes in them that are small enough for water particles to get through, but not small enough for undissolved solids to get through. There are different grades of filters to stop different sized solids: a coffee filter will stop coffee grounds or sand, but you will likely need special filter paper to stop fine chalk powder.

Ideas to start your research:

• Air filters in your car or home
• Water filters (refrigerator, pitcher, bottle)
• Backcountry camping water filters
• Water filtration plants

You should have seen oil and water mix a little bit. It may have looked like bubbles of oil floating in the water. When you left the mixture for some time, you should have seen a layer of oil start to re-form above a layer of water below.

When you added the soap, you should have seen the oil and water mix much better than they did without the soap.

We know that oil and water don’t like to mix. We also know that oil likes to cling to your skin and to pots and pans. When you try to wash something oily with just water, the oil doesn’t want to come off and go with the water. The water slips right off. 

Soap is special. One end of a soap molecule likes oil, and the other end likes water. When you mix soap, oil, and water, the soap makes bubbles that surround little drops of oil, and make it so it’s able to mix with water. Then, the water can pull the soap bubbles along with the oil off of whatever surface it was on.

An emulsion is a mixture of two liquids that don’t like each other all that much. In order to mix, one liquid forms tiny droplets that are suspended throughout the other liquid. Soap is an emulsifier, which is something that can make two liquids mix when they normally wouldn’t.

You should have seen the mixture bubble up, or fizz.

You should have seen the mixture bubble up, or fizz.

Depending on how much you started with, adding more vinegar can keep the reaction going for a while. Eventually, it will stop, and adding more vinegar will not make it start again. When you add baking soda to vinegar, they combine to make two new things: sodium acetate, and carbon dioxide. Carbon dioxide is the gas that makes the fizz. The sodium acetate is left behind with the water (the vinegar you used was not pure vinegar, it was likely an ~5% solution in water). Once all of the baking soda has been mixed with vinegar and forms these two new components, there is no baking soda left. If you add more vinegar at this point, there will be no reaction, because there is no more baking soda.

• Baking Soda: Solid
• Vinegar: Liquid
• Fizz: Gas

Row A – Baking Soda, Vinegar, Fizz
Row B – Acetic Acid, Carbon Dioxide, Sodium Bicarbonate

Baking soda = sodium bicarbonate

Vinegar = acetic acid

Fizz = carbon dioxide

When you added the vinegar to the milk, you may have seen a little bit of cloudiness or swirls in the milk. When it heated, it should have made this cloudiness much more noticeable, and you should have been able to see white chunks floating in a clear, yellowish liquid.

A precipitate is a solid that comes out of liquid due to a chemical reaction, and cannot be dissolved back in.

Test it out yourself and see!

Test it out yourself and see!

The plastic-like product you ended up with is not really plastic at all. It is more like cheese. Specifically, it is a milk protein called casein. 

When milk and vinegar come in contact with each other, the casein does not want to mix with the acidic vinegar. Instead of mixing, the casein molecules all band together in big clumps.