Chemical Relations What is the difference between a mixture and a compound?

Chemical Relations E lements combine

separating with hands straining filtering evaporating

Chromatography- the science of separating colors.

Brass- an alloy of copper and zinc.

Read online article on science site on mixtures. Add additional information to your class notes. Complete the worksheet Chemical Relations 1-12 for homework. Eat fruit cocktail!!

Winter Outdoor Observation due February 4, 2014!

Why do some things float and some things sink?

The pressure pushing up on an immersed object is greater than the pressure pushing down on it. This difference results in the buoyant force. Weight is a force in the downward direction. The buoyant force is in the upward direction. An object will float if the upward force is equal to the downward force.

The amount of buoyant force determines whether an object will sink or float in a fluid. If the buoyant force is less than the objects weight, the object will sink. If the buoyant force equals or is greater the objects weight, the object floats.

Sometimes the buoyant force on an object is greater than the weight. This force is what seems to pull a helium-filled balloon upward in the air. When the balloon is released, the unbalanced buoyant force causes the balloon to accelerate upward.

Acc ording to Archimedes’ principle, the buoyant force on an object in a fluid is equal to the weight of the fluid displaced by the object. If you place a block of pinewood in water, it will push water out of the way as it begins to sink-but only until the weight of the water it displaces equals the block’s weight. The block floats at this level. Archimedes, a Greek mathematician who lived in the third century B.C., made a discovery about buoyancy.

Archimedes' Principle and Buoyancy Force Mixtures: Homogeneous & Hetergeneous THINK, THINK, THINK

Separating Mixtures Mixtures are separated by taking advantage of differences in the properties of the substances that make up the mixture. There are many ways to separate mixtures, as we have discussed in class. Discuss with your partner some ways to separate a mixture. Observe the plastic beads on the lab table and suggest some ways to separate the beads into groups. Today we are going to separate a mixture by using density. Everything has its own characteristic density, just as the colored plastic pieces have. Follow the procedure below to easily separate the different pieces from each other.

Procedure: Put a sample of the mixture (about a tablespoon) into a 250 mL beaker. Add water until the beaker is about half full. Stir the mixture so that any plastic piece that ends to float will not be held down by other pieces. (Sometimes small objects may float even though their density indicates they shouldn’t. Air bubbles and the water’s surface tension may keep objects afloat that should sink. Force the plastic pieces under the water to make sure only the pieces with a density less than water is floating.) Only one kind of plastic piece should be floating. Use the spoon to remove them and place them in one of the small cups provided. Change the density of the water by pouring out about half the water into the water supply, and refill the 250 mL beaker about half way with the salt solution. Stir carefully and observe. Remove the colored particles that are floating and put them into a small cup. Add a measure of salt to the beaker and stir well. Remove the floating particles and put them into a small cup. Strain the material in the cup and collect the last set of objects from the cup. Put all your plastic pieces into the strainer that is provided, and rinse carefully with pure water. Drain well. Put the plastic pieces back in their original container, clean off table and sit down.

D E N S I T YD E N S I T Y Particles are denser than the fluid, they all sink. Red articles are less dense than the fluid, they float, while the other particles all sink. Blue particles are suspended in the fluid. They are equal in density to the fluid. Blue, red and green particles are less dense than the fluid. The black particle is more dense than the fluid.

READ, HIGHLIGHT, LEARN Archimedes' Principle and Buoyancy Force Packet Also read Lab Procedure for tomorrow. THINK, THINK, THINK

The density of the fluid is less than the density of the beads. All the beads are on the bottom of the beaker, because they are more dense than the fluid. The buoyancy force is greater pushing down than pushing up so all the bead sink.

The red beads are less dense than the fluid, while the blue and green beads are more dense. Anything less dense than the fluid will float. The buoyancy force pushing down on the red beads is less than the force pushing up so the beads float. The force pushing down on the blue and green beads is greater than the upward force, so these beads sink

The blue beads are suspended in the fluid. The density of the blue beads is equal to the density of the fluid. The green beads are more dense than the fluid and are on the bottom of the beaker.

MOLDED MATTER A DENSITY INVESTIGATION