An aqueous soulution contains 30% c3h7oh and 70% water by mass. what are the mole fractions of each substance in the solution?

Mole fraction of water = 0.88

Mole fraction of = 0.12

Explanation:

30% means 30 g of is present in 100 g of solution.

70% (water) means 70 g of water is present in 100 g of solution

Calculation of MOLES

Molar mass of   = 18 g/mol

moles of water = 3.89 moles

Molar mass of   = 3(12) + 7(1) + 1(16) +1(1)

                                                                  = 36 +7+16+1

molar mass of = 60 g/mol

moles of  = 0.5 moles

total moles of solution = 0.5 + 3.89 = 4.39 moles

Calculation of MOLE FRACTION

Formula for mole fraction is :

Similarly,

Mole fraction of water = 0.88

Mole fraction of = 0.12

Note :

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years

the answer is b because, investigating whether another species of moth also drinks tears might be interesting, but it would not directly explain why this species of moth does.

to explain why this species of moth drinks tears, the scientist could ask: "what nutrients that moths need are in elephant tears? "

the scientist could experiment with moth repellent or oter ways to keep the moths away, but that would not answer his original question.