A scientist claims that a certain chemical will make fabric waterproof. Which option describes a controlled experiment that will produce evidence that will
support or refute her claim?
A. One group of fabric is treated with the chemical, and the other
group is not. Then each group is exposed to water.
B. One group of fabric is treated with a small amount of the
chemical, and the other group is treated with a large amount. Then
each group is exposed to water.
C. Two groups of fabric are treated with the chemical. One group is
cotton and the other is polyester. Then each group is exposed to
water.
D. Two groups of fabric are treated with the chemical. Then one
group is exposed to a small amount of water, and the other group
is exposed to a large amount.

Why do scientists look for patterns in the world? a. patterns can explain observations. b. patterns never change, no matter what. c. patterns are easy for scientists to detect. d. patterns are all the same, through all time.

Astudent is given a sample of a blue copper sulfate hydrate. he weighs the sample in a dry covered porcelain crucible and got a mass of 23.875 g for the crucible, lid, and sample. the mass of the empty crucible and lid was found earlier to be 22.652 g. he then heats the crucible to expel the water of hydration, keeping the crucible at red heat for 10 minutes with the lid slightly ajar. on colling, he finds the mass of crucible, lid, and contents to be 23.403 g. the sample was changed in the process to very light clue anhydrous cuso4. if there are again 100.0 g of hydrate, how many grams of cuso4 are in it? how many moles of cuso4? (hint: molar mass of cuso4 = 159.6 g / mole. what per cent of the hydrate is cuso4? you may convert the mass of cuso4 to moles.)

When a spring is compressed, the energy changes from kinetic to potential. which best describes what is causing this change?