If you want to make 0.5 l of a 0.01 m solution of bromine (br2) in water, how much bromine would you need? a. 0.8 grams. b. 0.8 moles. c. 1.6 grams. d. 1.6 moles.

The answer is A. 0.8 grams.

The atomic mass of bromine is: A(Br) = 80
The molecule Br₂ consists of 2 Br atoms. Thus, the molecular mass of bromine is: Mr(Br₂) = 2*A(Br) = 2*80 = 160
This means there are 160 grams/l of Br₂ in 1 M.

Let's write a proportion. If 160 grams/l of Br₂ are present in 1 M, how much of Br₂ will be in 0.01 M:
160 g/l : 1 M = x : 0.01 M
After crossing the products:
x = 80 * 0.01 = 1.6 g/l

Let's write another proportion. If there are 1.6 g of Br₂ in 1 liter, how many of Br₂ will be present in 0.5 liter:
1.6 g : 1 l = x : 0.5
After crossing the products:
x = 1.6 * 0.5 = 0.8 g