First Unit of General Chemistry some questions.

[1dave]

Hi all! I'm not just looking for answers, as I'm trying to get a head start on a pretty intense course-load coming my way. I will be taking a 3 week intro Chem course starting May 7th, and this is not my specialty, but I'd like to do well in the course and try to have fun . I have gone through the first unit and it hasn't been too difficult until I got to the end of it with some that made my brain hurt a bit , and I'm hoping that I could get a little help on understanding these, so here we go.

 

This one will likely be super easy for you guys lol:

 

1.) A house has an area of 195m² what is its area in:

 

a) km²

-I will address this one first. So what I did was take the 195 meters and make it into 0.195km or 0.195 x 10^-3 km, then moved it to 1.95 x 10^? km². The answer is 1.95 x 10^-4 km². I am just confused how the answer would be to the power of -4.

 

-for this one I will leave the rest out, because I think if I understand this first one, then I'll understand the rest of them.

 

2.) Do each calculation without using your calculator and give the answers to the correct number of significant figures.

 

a) 1.76 x 10^-3 / 8.0 x 10²

 

- At first I was thinking it would want an estimation, so I tried just following the Order of Magnitude estimations. But the answer was exact. Would it be asking me to do it with long division, or am I missing something here? Honestly I've read and done every example up to this point, and nothing in the book addressed calculations without a calculator, except for the Order of Magnitude stuff. Maybe this is excepted of people to know how to do.

 

3.) A steel cylinder has a length of 2.16 in, a radius of 0.22 in, and a mass of 41g. What is the density of the steel in g/cm³?

 

-Okay so I got the right answer for this one, but my only question is how many significant figures should I use leading up to this result? I had to calculate the volume first. Should I use a certain amount when calculating the volume, or should I do the largest number of sig figs before I reach the final result?

 

 

 

4.) The diameter of a ping pong ball in 4.0 cm. Find the length in kilometers of a row of 6.02 x 10²³ ping pong balls.

 

-This is the final question and I'll just address the ping pong ball one for now, as it should help me for the other one. The ping pong ball one also has its answer in the book and the other does not. I tried to answer this by calculating the volume of the ping pong ball, and then calculate the length of one ping pong ball. I had the length of one equal to 2.6666cm, but when I calculated this multiplied by the amount of ping pong balls I got 1.6 x 10¹⁹ km, when the answer is 2.4 x 10¹⁹ km.

 

To get the volume I used this formula: V= (4/3)(pi)(r³) I got 33.510cm³.

 

With this I calculated the length with this formula: L= V/(pi)(r²) and I got 2.6666 cm

 

I then calculated the length of all the ping pong balls to be 1.61 x 10²⁴ cm, which I would have equal 1.6 x 10¹⁹ km.

 

 

 

Helping me with any of these would be greatly appreciated. Thank you in advance.