Basic Chemistry Questions: Understanding the Fundamentals

[RJLiberator]

Hello everyone,

This site is so beautiful. There's an overwhelming amount of information and resources. It is a future scientist's dream to come across this site. I have fully committed to my goals of going further in physics and I am taking it a step up today due to posting here.

My knowledge is low, and I am taking my first General Chemistry class, but I wanted to come here and post some questions I am having over my first assignment of Summer School. It's some rather basic concepts, but I want to make sure I have them down before proceeding:

1) A certain compound, when released from its container, is completely dispersed into the environment. Is this compound more likely to be a solid, liquid, or gas?

My answer: Gas.
It seems logical that gas would disperse fully into the air.

2) Ethylene glycol is very poisonous. This fact is a:
My Answer: Chemical and Extensive property

3) Classify scratching a steel surface as a physical or chemical change.
^^ This one threw me off for a while. I understand when steel tarnishes/rusts it is a chemical change, but my teacher told me this one was a physical change.
My answer: Physical

But I would think that scratching a steel surface adds heat to the environment (motion) and thus, causes a chemical reaction. Am I wrong to think this?

4) Classify heating liquid methane unti it boils as a physical or chemical change.
My answer: Chemical
I'm not too familiar with liquid methane... but I would imagine the addition of the heat forces a chemical change.

5) Do the following calculation reporting your answer with the correct number of significant figures: 67.8x9.8/100.04
*At first, I thought this problem was an error, because due to order of operations I think it should be read as 67.8 * (9.8/100.04). Am I correct in proceeding this way with order of operations? (First division, then multiplication)
*EDIT: Ok, now I feel stupid. It's the same regardless. :|

Okay, that is all for my first assignment. I know it's mainly basic concepts and ideas, but I would like to confirm my thoughts as I take a serious approach. I also want to get more familiar with this site.

Thank you for any guidance.

 

[RJLiberator]

EDIT: This post is now complete.

1-3) I was correct on.
4) I was wrong, it is a physical change.
5) I was correct.

Thank you all for taking a look.

 

[ChiralWaltz]

Ron,

I love how your brain works and how you approach the material. That being said, let's think about your assignment. Everything looks good but 4 and 5 I am not sure about.

#4
I guess I need to be walked through the states of matter. The best way for me to do this is by thinking about water. Let's pretend I have a beaker full of water. The formula for water is H2O.

I jump in my helicopter and fly to the North Pole. What happens to the H2O if I stay there long enough?

Now I need a beach to warm up, what happens to that frozen H2O at the beach?

Swimming is great exercise so I need to relax. Let's take that liquid H2O to the sauna and pour it on the hot rocks in there. What happens to the liquid H2O?

Basics:
Phases of matter: solid->liquid->gas

Advanced:
Bose-Einstien consolidate-> solid->liquid->gas -> plasma

#5
Sig figs

You just need to review your rules. This is a multiplication/division problem. The other type is addition/division. The idea behind sig figs is you do NOT want to report results more accurate than you have measured. Read up on sig figs please. Addition and subtraction versus multiplication and division.

I can't explain sig figs because they are not helping me wrap a present at the moment :/

 

[RJLiberator]

Thank you for your reply. It was particularly insightful in regards to Q4. Since the chemical composition of the substance is not being compromised it is a physical change.

-Ron

 

[ChiralWaltz]

#5

Try playing with your calculator. The order of operations should not matter with that equation. What was your answer for the exercise? Sig figs is the point of the exercise.

 

[RJLiberator]

Yes, Chiral, I goofed thinking the order of operations mattered there, aha.

My answer was 6.6.

 

[ChiralWaltz]

Your sig figs and answer are the same I have.

To solidify those neurons' path, can you explain to me why you used 2 sig figs? Until you teach it, you do not understand it :)

 

[RJLiberator]

Yes. I used two significant figures due to the order of operations with respects to significant figure rules.

First I multiplied, 67.8*9.8 which resulted in a figure that was only certain up to 2 significant figures. To avoid estimation errors, I used the whole initial answer and divided by 100.04 which resulted in a figure that was only certain to two significant figures due to my first equation.

:)

 

[Borek]

Well, 9.8 has only two sig figs, so the final result should not have any more.

Don't pay too much attention to sig figs. I mean - sure, it is OK to use them, sure, it doesn't make sense to report too many digits in your answers. But (regardless of what may be suggested to you) sig figs are not a correct way of dealing with precision, they are a poor mans approximation at best. Sadly, some treat them quite religiously.

 

[ChiralWaltz]

Well, 9.8 has only two sig figs, so the final result should not have any more.

Don't pay too much attention to sig figs. I mean - sure, it is OK to use them, sure, it doesn't make sense to report too many digits in your answers. But (regardless of what may be suggested to you) sig figs are not a correct way of dealing with precision, they are a poor mans approximation at best. Sadly, some treat them quite religiously.

Two sig figs.

Minus 2 points for sig figs. The religious ones usually write that.