Dumbledore decides to gives a surprise demonstration. He starts with a hydrate of Na2CO3 which has a mass of 4.31 g before heating. After he heats it he finds the mass of the anhydrous compound is found to be 3.22 g. He asks everyone in class to determine the integer x in the hydrate: Na2CO3·xH2O; you should do this also. Round your answer to the nearest integer.

Answer : The integer 'x' in the hydrate is, 2

Explanation : Given,

Mass of hydrate = 4.31 g

Mass of anhydrous = 3.22 g

First we have to calculate the mass of water.

Mass of water = Mass of hydrate - Mass of anhydrous

Mass of water = 4.31 g - 3.22 g

Mass of water = 1.09 g

Now we have to calculate the moles of and

Molar mass of = 18 g/mol

and,

Molar mass of = 106 g/mol

Now we have to calculate the ratio of and

The formula of compound is,

The value of 'x' is, 2

So, the formula of compound is,

Thus, the integer 'x' in the hydrate is, 2

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

d.) circle motion requires a force to give it a centripetal acceleration.