Am in a at least 150 words, justify the need for a control in an experiment. use complete sentences.

You need a control group in an experiment because if you did not have a control group your numbers or outcomes can cause an error because you wont have any numbers that are right to compare to. There will be too many things changed in the trial.

The need for control in a experiment is to make a base line for you to compare other data that you have collected. like in some tests it would be the group that you would start with then you will have another group that had the same amount of whatever and it will help you.

For example, you want to find out if a certain class makes student get bored faster. so you have three groups: A-math (control), B-reading, C-science. you ask multiple different students.

at the end of the day you see how many people voted for everything, and you compare it with the control. if groups B and C had the same amount of votes as A then it wont work.

if B and C had the same amount but less than A it would work.

if B and C had the same but less than A it would mean that not all the classes are boring, but one class makes quite a difference in the results.

is what i said put it in your own words though.

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

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e