28 September Science 8 Conservation of Mass–Chemical Reactions–Gases

Today we will begin several reactions. Information will appear in this post and in class. Be sure you keep complete records in your notes.

In 3 of the experiments, you will introduce reactants into a closed bottle and find the total mass. We shall call this the starting mass. Over the next few days, we will watch for any changes and note them. Then we will take the mass again. This will be called the final mass. It is very important that nothing escapes from the bottle and that nothing gets added to the bottle. We want the bottle and the reactants inside to be a “closed system.” For this reason, we shall label each bottle as indicated in the picture. Be sure to record the date and time of setting up each bottle:

label

 

 

 

 

 

 

 

 

Experiment Steel Wool in Moist Air

  • A. Label the bottle appropriately in the manner pictured.
  • B. Take a wad of steel wool and stretch it longways. Shape it so that it is about 12 cm long and 2 cm wide. Make sure the steel wool is moist.
  • C. Put the moistened steel wool into the bottle. Close the lid. Dry the outside completely. Find and record the starting mass.
  • D. What do you think will happen to the steel wool? Why? What do you think will happen to the air? Why? What do you think will happen to the mass? Why?
  • steelwoolair

 

 

 

 

 

 

 

Experiment Steel Wool immersed in vinegar

  • A. Label the bottle appropriately in the manner pictured.
  • B. Take a similar amount of steel wool as in the previous experiment and ball it up.
  • C. Put the ball of steel wool into the bottle. Put in enough vinegar to cover the ball. Close the lid tightly. Dry off the outside completely. Find and record the starting mass. Note the date and time.
  • D. What do you think will happen to the steel wool? Why? What do you think will happen to the air? Why? What do you think will happen to the vinegar? Why? What do you think will happen to the mass? Why?

vinsteelwool

 

 

 

 

 

 

Experiment with Mung bean, soil, water, air

  • A. Label the bottle appropriately in the manner pictured.
  • B. Fill the bottom of the bottle with soil to a depth of 2 cm. Moisten–DO NOT SOAK. Sprinkle 50 or so mung beans on the surface of the soil. Cover with a thin layer of soil
  • C. Close the lid tightly. Dry off the outside completely. Find and record the starting mass. Note the date and time.
  • D. What do you think will happen to the mung beans? Why? What do you think will happen to the air? Why? What do you think will happen to the soil? Why? What do you think will happen to the water? Why? What do you think will happen to the mass? Why?

mung

 

 

 

 

 

 

Experiment with steel wool and moist air in an inverted graduated cylinder.

  • A. Take a small wad of steel wool and stuff it in the bottom of a graduated cylinder.
  • B. Turn the cylinder with the steel wool upside down and put the mouth into a water-filled basin. Make sure the mouth of the cylinder is under the surface of the water. Pull out some of the air with a syringe and plastic tube until the water level sits at 100 ml.
  • C. Take a 2nd cylinder without steel wool and set up in exactly the same way. Label the basin.
  • D. What do you think will happen to the steel wool? Why? What do you think will happen to the air in the cylinder with the steel wool? Why? What do you think will happen to the air in the cylinder without steel wool? Why?

steelcyl

 

 

 

 

 

Experiment Copper and Silver Nitrate (if time)

  • A. Get a microscope slide and a microscope.
  • B. Take a small piece of copper and put it on the slide. Get the piece of copper in focus.
  • C. Add a drop of Silver Nitrate solution.
  • D. Observe. Describe in words. Make a sketch carefully. Take a picture.

*You might find this web article interesting–it shows an example of the copper and silver nitrate reaction and also talks about how chemists think and how students learn (and mis-learn) chemistry: http://www.rsc.org/eic/2015/05/video-molecular-simulation-vischem

TWO IMPORTANT IDEAS:

IN A CHEMICAL REACTION, THE ATOMS THAT MAKE UP THE STARTING MATERIALS ARE REARRANGED INTO NEW MATERIALS WITH NEW PROPERTIES.

IN A CHEMICAL REACTION, THE NUMBER AND KINDS OF STARTING ATOM REMAIN THE SAME FROM THE BEGINNING OF THE REACTION TO THE END. THIS CAN BE INFERRED THROUGH THE RESULTS OF BEFORE AND AFTER MASS MEASUREMENTS. Mass measurement must be conducted on a closed system where nothing escapes and nothing new is added.

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