ВАРИАНТ 5. 1. Какая масса растворённого вещества содержится в 21г. раствора с массовой долей 0,9%
2. Какой объём воды нужно прилить к 24г. соли, чтобы получить раствор с ω=23 %?
3. Какую массу соли нужно добавить к 85 мл. воды, чтобы получить раствор с ω = 17 %
4. Смешали 1,2г соли и 2,4мл воды. Какова массовая доля соли в полученном растворе?
5. К 36г 19% раствора соли прилили 21мл воды. Определите массовую долю соли.
6. К 85г 13%-ного раствора сахара прибавили 14г сахара. Каково процентное содержание сахара во вновь полученном растворе?
7. Сколько миллилитров воды надо прилить к 54 г 18%-ного раствора соли, чтобы получить 5%-ный раствор?

whats the meaning of /

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