Calculate the mass of sodium hydroxide formed by a reaction formed by the reaction of 70g sodium metal & H20?

Answer 1

firstly type down the equation and balance it:

2Na + 2H2O = 2NaOH + H2

with this sorted out youre ready to proceed.

the next step requires you to find the mol sodium used. from the formula, mol = mass/molar mass.
since the mass of sodium metal used is 70g and the molar mass of sodium is 23g/mol, hence the mol of sodium metal used = 70/23 mol.

the ratio of the mol of sodium metal used to the mol of NaOH formed is 2:2 from the formula above.
hence the number of moles of NaOH formed is also 70/23 mol.

to find the mass of NaOH formed, you just have to tweak the formula a little.
mass = mol x molar mass

the mol of NaOH = 70/23 and its molar mass = 40
hence the mass = (70/23 x 40)g = 122g (3sf)

noticed that i only used one formula (the mol = mass/molar mass formula)? questions like these are easy to solve, all you have to do is to ensure that you have written down the equation and that you know how to use and manipulate the formula to get what you want. the rest is all practice.

good luck and i hope this helped.
cheers.

Answer 2

This is very simple. You should learn how to do this, so I will explain the steps involved:

1) Write an equation for this reaction. (Note: I must assume there is an excess of water available to answer this question):

Na + H20 gives NaOH + H2 (where 'gives' means an arrow)

2) Now balance the equation correctly:

2Na + 2H2O gives 2NaOH + H2

3) Next, convert 70 grams of Na into moles:

70 g Na divided by 23 g/mol of Na = 3 moles of Na

(there is only one significant figure in the number "70" so you should round of your answer to just one significant figure ("3").
Note: If someone tells you the answer is slightly different than mine, then it is because they are not using significant figures correctly, or just plain ignoring them, which many people do.

4) Now look at your balanced equation. If 2 mol Na produces 2 mole of NaOH, that is the correct ratio of Na reactant to Na product, in other words, a 2:2 ratio, which is the same as a 1:1 ratio.

5) So.............................................

3 moles of Na will produce 3 moles of NaOH

(assuming you have an excess of H2O)

6) And lastly, convert 3 moles of NaOH into grams:

3 mol NaOH X 40 g/mol of NaOH = 120 grams.

and that's the answer! (USING significant figures; any other answer than this is ignoring the significance of the 70 gram measurement, which of course, makes their answer wrong).

The key thing to remember is that you must always convert to moles, (and of course, start out with a properly balanced equation).

This is called "stoichiometry", and is simple, once you get the hang of it. But you must practice!

Answer 3

2Na + 2H2O -> 2 NaOH + H2

Mass of NaOH formed = 40 * 70 / 23 = 121.73

P.S : Yippeeee! I got another 2 points for the wrong answer :p

Answer 4

Douglas Z really hit the spot! Too bad I can't rate people yet. However, if the actual value of the AR of Na is used (23.1 instead of 23), the mass of NaOH produced will differ slightly, ie it will be 121.5g. Hope this helps too.

Answer 5

2Na(s)+2H2O(l)=2NaOH(aq)+H2(g)
70g/23g/mol=xmol
x multiply by (23+16+1)