If I threw a block of sodium into a lake, and the H2 created took up 34 L of space at STP (standard temperature and pressure: 1 atm and 0C), how many grams of Na did I begin with?

70g Na

Explanation:

The sodium reacts with water as follows:

2Na + 2H2O → 2NaOH + H2

Where 2 moles of Na produce 1 mole of H2.

To solve this question we must find the moles of H2. With the balanced equation we can find the moles of Na and its mass as follows:

Moles H2:

PV = nRT; n = PV/RT

Where P is pressure = 1atm,

V is volume = 34L,

R is gas constant = 0.082atmL/molK

T is absolute temperature = 273.15K = 0°C

Replacing:

n = 1atm*34L/0.082atmL/molK*273.15K

n = 1.52 moles H2

Moles Na:

1.52 moles H2 * (2mol Na / 1mol H2) = 3.04 moles Na

Mass Na-Molar mass: 22.99g/mol-

3.04 moles Na * (22.99g / mol) =

the tides are influenced by both the moon and the sun, it's easy to see that when the sun lines up with the moon and the earth, as during a new moon or full moon, the tidal effect is increased. these are known as spring tides, named not for the season, but for the fact that the water "springs" higher than normal. on the other hand, if the sun and the moon are 90 degrees apart in relation to an observer on earth as during the first quarter moon or third quarter moon, then high tides are not as high as they normally would be. this is because despite its greater distance, the sun's mass allows it to exert enough gravitational force on the oceans that it can negate some of the effects of the moon's pull. this phenomenon of lower high tides is called a neap tide. if you need more information on this topic visit moonconnection.com.