I NEED HELP PLEASE! :)

What's the empirical formula of a compound composed of 22.55% P and 77.45% Cl?

A) PCl2
B) PCl4
C) PCl3
D) PCl5

The most likely empirical formula is choice C:

Explanation:

The empirical formula of a compound gives the molar ratio between atoms of each element in this compound. For example, in the formula , the molar ratio between atoms and atoms is one-to-five.

Assume that the percentages here refer to the composition of this compound by the mass of each element. To find the empirical formula of this compound, start by converting the mass ratio to the molar ratio.

For simplicity, consider a sample of this compound. This

How many moles of atoms and atoms would that be? Look up the relative atomic mass of these two elements on a modern periodic table:

In other words, the mass of one mole of atoms would be , while the mass of one mole of atoms would be . Therefore, in this imaginary sample:

Calculate the ratio between and :

.

Taking the reciprocal might make this ratio more apparent:

.

In other words, there should be approximately three time as many atoms as atoms in this compound. That likely corresponds to the empirical formula .

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.