# Homework Help: Finding mass of water by subtracting graduated cylinder mass

1. May 29, 2013

### porksoda

1. The problem statement, all variables and given/known data
Ok so I have to do this lab that I just started today, I have a link to the entire assignment so you guys can see everything here: http://www.bclearningnetwork.com/LOR/media/ch11/course_files/Unit_Labs/Unit_1_density_lab.pdf

I asked my teacher how I'm supposed to do it, all she said was to find the mass of water and methanol, I just subtract the mass of the cylinder from the mass of cylinder plus water/methanol. When I did it with the methanol it made a bit more sense, but when I did it with water I had the same mass of water as volume of water, so that's really got me confused.

I have to find slope too, but I'm not 100% sure how to find slope. I'm doing the course online so I have limited information given on how to find things and minimal practice worksheets, I only had one for how to graph so far but it didn't ask me to find the slope.

2. Relevant equations

3. The attempt at a solution

Like I said earlier, when I subtracted the cylinder mass from the cylinder +water mass, I got the same numbers for mass as I did for volume, I feel like that really shouldn't be the case.. thanks for helping, it's my first time here~

2. May 29, 2013

### Staff: Mentor

What is the density of water? How are the density, volume and mass related?

3. May 29, 2013

### porksoda

I don't know the density or the mass, neither are given, I just have different volumes, different masses of water in graduated cylinders, and all the graduated cylinders before water is added has 35.00 g +/- 0.001g (interchangeable with 25 mL). I just need to know if I really do just subtract the mass of the cylinder from the mass of the cylinder+ water because when I do the first question (Mass of water graduated cylinder= 40.00 and subtract 35.00) the answer is 5.0 which is the same as the volume. The entire water table is like that which has got me confused, but in the methanol table the mass is different from the volume.

4. May 29, 2013

### Staff: Mentor

You should know the density of water, as it is one of the most common constants you will encounter. In the past it was part of the mL and liter definition. If it was not given just google it, knowing it will pay off in the future.

You don't have to know values of density, mass and volume, I am asking how they are related to each other. Do you know how is the density defined?

5. May 29, 2013

### epenguin

You haven't done slope in math? (I mention it becasue a lot of students master a concept in math and then don't recognize it any more if they meet the same concept again in any other science.)

Anyway, when you have done the graph, take two convenient, widely separated points on it, then the slope is the vertical distance between them divided by the horizontal difference. Not hard, I hope, to see what this means in physical terms.