Pure Substances
Mixtures
Density
Physical Properties and Changes
Chemical Changes
100
two kinds of pure substances
element and compound
100
two kinds of mixtures
homogeneous and heterogeneous
100
which is less dense - iron or feathers?
feathers
100
example of a physical property
color, size, shape, density, temperature, weight, mass, etc.
100
Name a clue that suggests that a chemical change/reaction has occurred.
unexpected change in color; unexpected change in temperature; production of a gas
200
example of a pure substance
any element (found on the periodic table) or compound (ex. H2O, CO2, C6H12O6,NaHCO3, etc.
200
example of a heterogeneous mixture
(any mixture in which you can see different ingredients)
200
what do you need to know to determine an object's density?
the mass (grams) and volume (cm cubed) of the object
200
how is a physical change different from a chemical change?
after a physical change, the substance is still the same substance - it is just hotter, colder, broken into smaller pieces, mixed with something else, etc. After a chemical change, a new substance has been formed.
200
How can you prove that a chemical change/reaction has taken place?
You must show that a new substance has been formed.
300
example of a compound
many examples, such as compound H2O (water), CO2 (carbon dioxide), C6H12O6 (glucose),NaHCO3(baking soda), etc.
300
another name for a homogeneous mixture
solution
300
describe the particles in gold (density 19.3 g/cm cubed) as compared to the particles in aluminum (density 2.7 g/cm cubed)
gold particles are closer together (packed more tightly)
300
Which describes a physical property and why? 1. a block of wood has a density of 0.75 g/cm cubed 2. a block of wood can burn
Only #1 - you don't need to change the wood into anything else to find its density. You just need to measure its mass and volume. For #2, you would need to change the wood into something else (ashes) to show that it can burn.
300
You mix red Kool-Aid with blue Kool-Aid, and the result is purple Kool-Aid. Do you think there was a chemical change? Why or why not?
No chemical change. Red and blue normally make purple - you have just made a mixture, not a new substance.
400
difference between an element and a compound
element has only one kind of atom; compound has more than one kind.
400
You put chocolate ice cream, milk, and chocolate sauce in the blender. Then, you turn the blender on to make a milkshake. What kind of mixture do you have AFTER you used the blender?
homogeneous - the blender "homogenizes" everything, so the milkshake looks the same everywhere.
400
will an object whose volume is 150 cm cubed and mass is 50 grams float?
yes - density is mass divided by volume. 50 divided by 150 is 0.333 g/cm cubed, which is less than 1, so the object will float.
400
When a muffin gets bigger in the oven, is it a physical change or a chemical change?
Could be physical (size) or chemical (production of carbon dioxide from baking soda)
400
When iron gets rusty, for every 4 iron atom reactants, 6 oxygen atom reactants are needed. Describe the atoms in the product of the reaction (rust).
For every 4 irons, there are 6 oxygens.
500
how are pure substances different from mixtures?
all of the particles in a pure substance are the same; more than one kind of particle (ingredient) in a mixture
500
how is a mixture of hydrogen and oxygen different from a compound made of hydrogen and oxygen?
the hydrogen and oxygen are not attached to each other in the mixture and the ratio is not constant/fixed; the hydrogen and oxygen atoms are attached (bonded) to each other in the compound in a constant ratio (H2O, H2O2)
500
You have a block of pure aluminum (density = 2.7 g/cm cubed) which sinks in water. You also have a boat made of pure aluminum. Why doesn't your boat sink?
Although the boat has a lot of mass, the space inside causes the boat to take up a lot space, so its mass/volume is less than 1 g/cm cubed.
500
It is easy to pull the pepperoni out of the mixture known as a pepperoni pizza. Since it is not easy to pull the flour out of the mixture known as chocolate chip cookie dough, is the mixture the result of a physical change or a chemical change? Why or why not?
Physical change - no gas released, no unexpected change in termperature, no unexpected change in color - the flour was just mixed with the sugar, butter, and chips.
500
What happens to the atoms in the substances that go into a chemical reaction?
The atoms are rearranged.
M
e
n
u