# Density problems (work check)

• September 13th 2009, 04:22 PM
hemi
Density problems (work check)
Here's a question I was working on:

A crystal of sulfur has a density of 1.94 g/cc.
(a) What is the mass (in grams) of a sulfur crystal with a volume of 2.534 cm3?
(b) What is the density of sulfur in kg/m3?
(c) What is the volume (in mL) of a sulfur crystal that weighs 9800 mg?

Here is the solutions I've arrived at:

(a) Well we know $D = M / V$ thus rearrange as $M = D * V$ to obtain the value of $4.91596g$ which I rounded to $4.92g$ as taking into account significant digits.

Correct or incorrect?

(b) I know $D = 1.94 g/cc$ thus I can write $1.94 g/cc / 1000 = 0.00194 kg/m3$

I'm not so sure about the sig figs on that final answer there, or if it's even the correct conversion at all?

(c) I rearrange as such: $V = M / D$ and plugged in $9800mg / 1.94g per cc = 5051.5mL$

Is this correct?

If you could help me with the mistakes I made and offer advice, etc. that would be appreciated. Thanks a lot for reading. :)
• September 13th 2009, 05:27 PM
VonNemo19
Quote:

Originally Posted by hemi
Here's a question I was working on:

A crystal of sulfur has a density of 1.94 g/cc.
(a) What is the mass (in grams) of a sulfur crystal with a volume of 2.534 cm3?
(b) What is the density of sulfur in kg/m3?
(c) What is the volume (in mL) of a sulfur crystal that weighs 9800 mg?

Here is the solutions I've arrived at:

(a) Well we know $D = M / V$ thus rearrange as $M = D * V$ to obtain the value of $4.91596g$ which I rounded to $4.92g$ as taking into account significant digits.

Correct or incorrect? correct

(b) I know $D = 1.94 g/cc$ thus I can write $1.94 g/cc / 1000 = 0.00194 kg/m3$

I'm not so sure about the sig figs on that final answer there, or if it's even the correct conversion at all? corect. If your worried about sig figs switch to scientific notation.

(c) I rearrange as such: $V = M / D$ and plugged in $9800mg / 1.94g per cc = 5051.5mL$ you're dividing mg's by g's?

Is this correct?

If you could help me with the mistakes I made and offer advice, etc. that would be appreciated. Thanks a lot for reading. :)

..
• September 13th 2009, 06:14 PM
hemi
Thank you very much for the reply again Von. As for (c), I take it I'd need to make both units the same. When I do this however, that is, convert 1.94g per cc to 0.00194 mg per cc I get the same result when plugging it back into my equation.

I have a feeling I'm just doing this wrong. What direction should I look in?
• September 16th 2009, 01:05 PM
hemi
I've reworked the question (c) and this is my work...

$(9800mg)$ $(\frac{1cm^3}{1.94g})$ $(\frac{1g}{1000mg})$

And the final answer is equal to $5mL$, is this technique correct?