Density
What is the formula for density? (Use the heart)
density = mass/volume
d = m/v
1) What are the three types of variables considered in an experiment?
2) Define each type.
1) independent, dependent, and controlled.
2)
independent - variable that is manipulated (changed each time to get a different result)
dependent - variable that is studied as a result (sometimes, changed -- not necessarily always)
(we change the independent to see how that affects the dependent
controlled - variable that may get in the way of the experiment, so it is held constant
1) Matter has two qualities: ______ and ______.
2) Name an example of matter.
1) mass, volume
2) anything with those two qualities
If two objects have the same density, we can conclude what?
The two objects are made of the same material. (ex. if one of the objects was known to be aluminum, then the other object must also be aluminum.)
In the following research question, identify the independent, dependent variable and list 2 possible controlled variable.
Will changing the amount of dye added to saltwater affect the density of saltwater?
independent - amount of dye
dependent - density of saltwater
controlled - amount of salt in water, volume of water used, color of dye chosen, etc. (list is NOT exhaustive)
1) Every type of matter can be characterized according to their properties. What are the two types of properties and define them?
2) List two examples for each category.
3) Out of the two types of properties, which is used to distinguish between different substances?
1) Intensive property & Extensive property
Intensive - depend on type of matter
Extensive - depend on amount of matter2)
Intensive - boiling point, melting point, color, hardness, temperature, density, etc.
Extensive - mass, volume, etc.
3) To tell different substances apart, we use intensive properties.
What are the relationships involved with density? (think back to your analysis questions --
ex.
As _____ (increases/decreases), ____ will (increase/decrease) if ____ is held constant.
mass & density relationship - directly proportional
If mass increases, density will increase if volume is held constant.
OR
If mass decreases, density will decreases if volume is held constant.
volume and density relationship - inversely proportional
If volume increases, density will decrease if mass is held constant.
OR
If volume decreases, density will increase if mass is held constant.
At most in an experiment, we can have ___ independent variable(s), ___ dependent variable(s), and ___ controlled variable(s).
One of the blanks is not a number.
1 independent variable
1 dependent variable
as many as possible controlled variables that can be considered.
If you place pure copper on a hotplate for a short period of time, nothing much happens. However, if you place a shiny new penny with a recent date on a hotplate, the color changes. Propose an explanation for why this might happen.
Pennies are known to be made of copper. Since pure copper and penny did not change in the same way after being placed on the hotplate, this means that penny may not be JUST copper or there is something in a penny that allows it to behave differently.
You have two different cubes with one being white and one being black. Both cubes take up the same amount of space, but the black cube is heavier and has a higher mass reading when weighed on a scale. Which of the cubes has a high density and why?
The black cube has a higher density because if the volume is the same, the one with the larger mass has a larger density.
Why do we need controlled variables? (It may help to answer if we consider what happens if a variable is not held constant in an experiment.)
Controlled variables help to ensure the the research questions is answered. If a controlled variable is not held constant, it may be possible to conclude that the dependent variable changed because of changing the controlled variable.
Think back to the "Will changing the volume of alcohol affect the boiling point of the liquid?". If we allowed the liquids to be of different types of alcohol, then it is possible to conclude that the different boiling point of alcohols is due to the type of alcohol (WHICH DOES NOT ANSWER THE QUESTION).
How could you prove that air is matter?
We need to show that air has mass and volume.
If we have an empty balloon, we can blow air into the balloon and we see that the balloon expands. Since the balloon expands, the air must have to take up space (or has volume) since it was the only thing to enter the empty balloon. Alternatively, we could use the volume for a sphere and measure the radius of it to use a formula.
Using that same empty balloon, we could measure the empty balloon alone on a balance and then place the balloon filled with air on the balance. The balloon with air should weigh more than the balloon without air, this means that the air in the balloon should have mass.
[DAILY DOUBLE]
Imagine a recycling plant has a mixture of small pieces of plastics listed in the table. Design a process to separate milk cartons from egg cartons from egg cartons from cling wrap, using saltwater with different densities. (SEE THE BOARD FOR THE DIFFERENT TYPES OF PLASTIC)
*Water has a density of 1 g/mL ( or 1 g/cm^3)
We can create saltwater using different amount of salt. The amount of salt added decides how much the density of the saltwater increases. So if we place the mixture of plastics into water, the milk cartons (polyethylene) will float as it is less dense than water, and the other two material (egg cartons and cling wrap) will sink because they are more dense than water. To separate egg cartons and cling wrap, we need to add enough salt so that the egg cartons will float (so density needs to be larger than 1.05 g/cm^3) and not too much that the cling wrap sinks (density has to be less than 1.38 g/cm^3).
[DAILY DOUBLE]
Using the idea that adding salt can change the density of a liquid (if it dissolves), come up with a research question that involves this concept.
Include the dependent variable, independent variable, and list 2 possible controlled variables. Give a small procedure that you would use to complete this experiment and a data chart to express this data.
[You may NOT use the amount of salt as an independent variable.]
Possible questions include (not limited to):
Will changing the type of liquid that dissolves salt in a salt-water density experiment affect the density of the salt-liquid solution?
Will changing the volume of water affect the density of the liquid in a salt water density experiment?
Suppose you had a beaker with a piece of clay in it and place it in a graduated cylinder filled with water. The volume is of the water before was 100 mL and the volume after the clay was inserted was 130 mL.
Taking out the same piece of clay, the clay's shape was changed and placed back into the same amount of water. The graduated cylinder with the water and the clay is at 130 mL.
1) The total volume does not change. Explain why.
2) Does the total mass change? Explain.
1) We see that the clay in the water no matter the shape of the clay, goes up to the same volume in the graduated cylinder. The amount of water displaced (or moved up) is the same, meaning the clay has the same volume.
We can conclude that total volume did not change because the clay still takes up the same amount of space no matter how the shape is changed.
2) The mass is not changed. Mass depends on the amount of substance, changing the shape of something does not the change the amount of substance.