Science Investigation 7

A student dissolved 20 g of salt in a cup of water. She left the cup uncovered in an area where nobody could touch it. When she returned to the cup 10 days later, she found that all the water was gone, and there were crystals in the bottom of the cup. Why did this occur?

This is due to evaporation

What makes a mixture a solution?

A mixture is a solution when it has a solvent and solute

When a mixture is made does it undergo a chemical reaction or a physical reaction? How do you know?

A mixture undergoes a physical change. It does not change into something new. The substances that make it up can still be separated.

A student hangs a wet T-shirt on a clothesline. A few hours later, the T-shirt is dry. What happens to the water particles as the T-shirt dries? (Mark the one best answer.)

D The water particles move faster and become part of the air.

Tell me how the processes of dissolving and melting a substance are the same. Tell me how they are different.

How they are different: Dissolving-to mix one substance uniformly into another substance at the particle level Melting- to change phase from solid to liquid How they are alike: Both are physical changes Both affect matter

Why would the shirt dry faster on a sunny, hot day than on a cloudy, cool day?

More energy is available from sunlight and hotter surrounding air to evaporate the water particles from the shirt on a hot day than on a cloudy, cool day.

In a solution of lemonade that includes water and lemonade mix. Identify the solute and the solvent.

Solute- Lemonade Mix Solvent- Water

In a solution of gases that is 78% nitrogen and 22 % Oxygen, which substance is the solute and which is the solvent?

Solute- Oxygen Solvent- Nitrogen

A student put the same amount of sugar in 1 cup of hot tea and 1 cup of cold tea, and stirred. The sugar in the hot tea dissolves faster than the sugar in the cold tea. Use your understanding of kinetic energy to explain this phenomenon.

The liquid particles of the hot tea have more kinetic energy than the liquid particles of the cold tea. With more kinetic energy, the liquid (solvent) particles move faster and collide more, causing the sugar particles (solute) to break apart faster

Write M next to each statement related to melting; write D next to each statement related to dissolving. Write MD next to each statement that could be related to both melting and dissolving.

_D____ Requires two substances __M___ Requires a change in kinetic energy __M___ Is a phase change _MD____ Does NOT require a chemical reaction