Grammar/ Spelling check, please!?

I have a teacher who is obsessed with spelling. Anyways, after getting a 98 on a lab for missing a comma, I am asking to see if anyone can proof read the following sentences. Thanks! My hypothesis is that a penny will have slightly less mass if it is older. I think so because items tend to wear down as they age.... show more I have a teacher who is obsessed with spelling. Anyways, after getting a 98 on a lab for missing a comma, I am asking to see if anyone can proof read the following sentences. Thanks!

My hypothesis is that a penny will have slightly less mass if it is older. I think so because items tend to wear down as they age. If a penny wears down, it's mass will decrease.

Age does not affect the mass of penny.

I think that the older and new coins may be made of different metals which would affect their mass.

All coins probably will be affected the same way a penny will be. I think that age will have little effect on the mass of a nickel, dime, or quarter.

My histogram shows that there were a few stray pennies amongst the most popular masses, 2.5 g and 3.1 g. It also identified the two main masses.

In 1982 the penny's composition was changed. The penny changed from being made from 95% copper and 5% zinc to about 98% zinc and 2% copper. This switch of materials changed the mass of the penny.
Update: The second line should actually be:

Older pennies tend to have a greater mass then newer ones.
Update 2: I changed the second sentence. Please check this as well. Thanks so much!

All coins probably will be affected the same way a penny will be. I think that age will have little effect on the mass of a nickel, dime, or quarter unless their components have been changed.
Update 3: Thanks so much for all the help! To clear up the confusion about the differences in my hypothesis. My first hypothesis was made prior to an experiment. The second was a new one I was asked to write after the experiment. Thanks again :) I just hope that my answers are correct :)
6 answers 6