In desperate need of a Chemistry brain. Any takers? : )?

Question

This one's been stumping me for awhile. Any help would be greatly appreciated.

Here it goes:

Calculate the number of moles of gas produced from the reaction of 2.00 g of potassium with an excess amount of water.

And here is the reaction equation that goes with it:

2K+2H(2)O==>2KOH+H(2)

Answer 1

2K + 2H(2)O ---> 2KOH + H(2)

2.00 g Potassium / 39 [g / mol] = 0.0512 mol Potassium


If there is excess of water, the same number of moles of water will react, since the ratio of K to H(2)O is 2 : 2

The ratio of K to H(2) gas, however, is 2 : 1.
So there are half the number of moles of H(2) as there are moles of K

(0.0512 / 2) moles H(2) = 0.0256 moles H(2)

Answer 2

First, calculate the number of moles of potassium that is used.

This is done by dividing the mass of the potassium, which is 2.00g, with its molar mass, which is 39.

You will then get - 0.051282051282051282051282051282051moles of potassium.

Next, refer to the equation.

According to the equation, if we used 2 moles of potassium, 1 mole of hydrogen gas would result.

Therefore, to obtain the number of moles of gas produced,
simply divide the number of moles of potassium, by 2,
and you get - 0.025641025641025641025641025641026.

Answer 3

A mole is the mass in grams equal to the molecular weight of a substance. The weight of a mole of potassium is 39.1 grams; since a molecule of K is an atom of K. this is its' mole weight. Therefor there are, 2 gr / 39.1 gr, or .051 moles of potassium consumed.

From the equation of its' reaction with water we see that one mole of H(2) is formed for every 2 moles of K consumed. There are then, .051/2 or .0256 moles of Hydrogen gas formed. ( a molecule of H2 gas has two atoms of hydrogen forming it).

Ans: .0256 moles gas.

Answer 4

2K + 2H2O---->2KOH + H2(g)
moles,n=mass(m)/molar mass(Mm)
n(K)=2.00g/39.1g/mol=0.0512mol
n(K)=2
n(H2)=1
hence,n(H2)=0.0512/2=0.0256mol
H2(g) has 0.0256moles
*the mass in your question has 3 significant figures,so i used 3 in all the calculations.