Why water not weight the same.....?

Question

I tried measure the weight of 10 mL of deionzied water and noticed it didn't weight exactly 10 g on scale but couple grams greater (yes, I did reset the scale before measuring and subtracted the weight of the beaker) So what is the real cause of this?

Answer 1

First, I suspect you mean a couple of mg greater. If it's a couple of g greater then you're doing something wrong. Water is fairly resistant to temperature expansion and contraction, but there is some, so temp can affect weight very slightly. Most likely you did not measure the water into the beaker accurately, your beaker has a faulty measurement line, or your scale is faulty.

Answer 2

I hope you meant "a couple of milligrams greater". Measuring exactly 10.000 mL is difficult. I assume you used a pipette calibrated to deliver (TD) and not to contain (TC). If the pipette wasn't perfectly clean, water can "hang up" and not be delivered. If the temperature of the water was different from the calibration temperature of the pipette. A temperature difference of 5 deg C will result in a weight difference of about 10 mg for a 10.000 mL sample (The densities of water at 25 deg C and 20 deg C are 0.99707 and 0.99823 grams per mL respectively.)

Answer 3

It depends, there are many possible error sources (although a couple of grams shouts for human error). How did you measure this volume? In what kind of tube / flask / beaker / cylinder did you weigh it? In what kind of scale did you weigh it?

This kind of measurement should be done using a picnometer. or at least a volumetric flask, with a four digit analytical scale.

Answer 4

As your saying DE-IONISED water:...just about as pure as you can get...
Put your container of de-ionised water into the fridge with a thermometer in it.
Allow the water to cool to 4°C (the maximum density temperature of pure water), and quickly try your measurement again.
You'll find it's a lot more accurate.

Answer 5

A "couple of grams" in weighing 10 ml is absurd - 20% error. If you really meant a couple of milligrams, then it is going to be really tough to help you if your reporting is so sloppy.

Answer 6

all water is different believe it or not. if you learned that each mL is 10g on the scale in science, it could be PURE water. Each water company prepares and does different things to its water and it's almost never pure.

Answer 7

It would be difficlut for you to get chemically pure water. The stuff which comes out of the tap is way not pure.

Answer 8

So you would be talking about boiled water, right? It is because the oxygen molecules in boiled water evaporate and therfore, the weight of oxygen molecules does not contribute at all to the deionized water. :)

Answer 9

check the temp at which you did the experiment.density varies with temp