Question

#1: You heat two substances, A and B. Both substances change color. When cooled, substance A returns to its original color, but substance B does not. What most likely happened?

A. A physical change occurred in both substances.

B. A physical change occurred in substance A, and a chemical change occurred in substance B.

C. A chemical change occurred in substance A, and a physical change occurred in substance B.

D. A chemical change occurred in both substances.
***my answer : A physical in both
is that right??

Answer 1

#2: How many grams are in a 5 pound sample? Express your answer in scientific notation with two significant figures. (1 pound = 453.592 grams)

A. 2.26 x 10^2g

B. 2.268 x 10^3g

C. 1.1 x 10^4g

D. 2.3 x 10^3g
**Idk this one.. please help!!

Answer 2

do u understand these?? is #1 correct?? is it A?? and idk #2.. :(

Answer 3

I don't think #1 is (A). If substance A returned to its original color, then that was probably just a physical change for A, but substance B stayed the new color after cooling. That makes me think that its color change was more than just physical.

Answer 4

#2 is just a unit conversion.
You can set it up like this
\[\large 5 Lbs. = 5 Lb \times \frac{453.392g}{Lb}\]

Answer 5

wait so for #1, if it isn't A,then what is it?

Answer 6

and idk how to simplify #2 further :(

Answer 7

You don't know how to multiply 5 by 453.392?

Answer 8

\[5\times453,392\]

Answer 9

1C

Answer 10

=2,266,960
????

Answer 11

wait so #1 is C???

Answer 12

wich is A

Answer 13

\[\large 5 \space \cancel{pounds} \times \frac{453.392 \space grams}{1 \space \cancel{pound}} = 5 \times 453.392 \space grams.\]

Answer 14

It is not (A) for #2, @Jonask

Answer 15

wait so what??? what was the answer to #1?? I'm confused now :(

Answer 16

no i was just asking

Answer 17

A)it is

Answer 18

I gave you the answer to #1 @iheartfood

Answer 19

C was the answer to #1???

:)

Answer 20

Why do you think C?
Reread what I wrote about that.

Answer 21

oh so it's B?

B. A physical change occurred in substance A, and a chemical change occurred in substance B.
is that the answer to #1??

Answer 22

@CliffSedge ???

Answer 23

That's my best guess because A returned to its original color, but B didn't.

Answer 24

okay yhanks!! what about #2 then???

Answer 25

Did you multiply the numbers?

Answer 26

yeah i got this: 2,266,960

Answer 27

That looks a little large. Make sure you put the decimal point in the right place.

Answer 28

oh 2,266.960
???

Answer 29

@CliffSedge ???

Answer 30

Right. Now for scientific notation, you want it in the form #.##... ×10^n
where n is the number of digits after the first.

Answer 31

B. 2.268 x 10^3g

is this my answer???

Answer 32

Also note that for numbers that represent measurements and include units, you need to consider significant figures. The weight you were given was 5 pounds. That is only one significant figure, but lets' be generous and assume it's 5.0 pounds for two significant figures.

Answer 33

A. 2.26 x 10^2g
or is it this??

Answer 34

It has to be ×10^3 because the 2 is in the thousands' place.
Also see that 2,266.960 would round off to 2,267 and not 2,268.

Answer 35

so what is my answer then?? A,B,C, or D??

Answer 36

As I was saying about the significant figures ("sig. figs"), since you are limited to the precision of your least precise value, you can't have more than two sig. figs. in your answer.

Answer 37

(This is why I don't like multiple choice questions, it all comes down to guess-and-check or process-of-elimination, and it doesn't teach you how to think through it using the concepts)

Answer 38

yeah :( so heres what i think now based off of what u said.. is the answer D. 2.3 x 10^3g cuz u can't have more than 2 sig figs right?? is that correct???

Answer 39

@CliffSedge is that correct???

Answer 40

@Jonask !! does answer D look right to you>???? :D

Answer 41

yeah d

Answer 42

mmk thanks :)