In an electrolysis experiment such as the one you are going to perform, 47.4 ml of hydrogen gas were collected. the temperature was 23 degrees celsius and the barometric pressure was 643 mm hg. the vapor pressure of water at 23 degrees celsius is 21 mm hg. the number of moles of hydrogen gas formed in the experiment was

0.0016 moles

Explanation:

According to the ideal gas equation:

P = Pressure of the gas =  barometric pressure - vapor pressure of water =  (643-21) mm Hg = 622 mm Hg = 0.82 atm    (1 atm = 760 mmHg)

V= Volume of the gas = 47.4 ml = 0.0474 L     (1L=1000 ml)

T= Temperature of the gas = 23°C = 296 K (0°C = 273 K)

R= Gas constant = 0.0821 atmL/K mol

n= moles of gas = ?

Thus the number of moles of hydrogen gas formed in the experiment was 0.0016.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.