Vitamin K antagonists (VKA) are a group of substances that reduce blood clotting by reducing the action of vitamin K. They are used as anticoagulant medications in the prevention of thrombosis, and in pest control, as rodenticides. 1  1 Mechanism of action.  2 Coumarins (4-hydroxycoumarins)
Calculate the average atomic mass of oxygen. Solution: ((15.994915*99.757) + (16.999132*0.038) + (17.999160*0.205))/100 = 15.999405 . Using our equation for determining average atomic mass, we see that the average atomic mass for oxygen is 15.999405 amu. If we check the periodic table, we will see that our average atomic mass is the same as the atomic mass indicated on the element oxygen. Ã
A molecule of water consists of a single atom of oxygen and two atoms of hydrogen. Oxygen has an atomic weight of 15.9994. One mole of oxygen, therefore, has a mass of just under 16 grams. Hydrogen has an atomic weight of 1.0079, and so a mole of hydrogen weighs just over 1 gram. This means that 18 grams of water contains one 16-gram mole of oxygen and two 1-gram moles of hydrogen. The number of particles in a mole is a constant known as Avogadro's number, which has a value of 6.022 x 10^23. Two moles of hydrogen, therefore, is double Avogadro's number. Learn more about Atoms & Molecules