How many moles of sodium react with 25g of chlorine to produce sodium cholorine?

Answer 1

It's easy to divide the problem into information we know, and what we're looking for,

In this case

1. What we're looking for:
2. how many moles of Na are reacting
3. Information we have:
4. 25 g of chlorine

The first thing you want to do is write out the actual chemical equation and make sure it's balanced:

Na + Cl₂ -> NaCl

1. On the reactants there's 2 moles Cl, while on the products side, there's 1 mole Cl, therefore we give it the coefficient 2 to make it even.
2. This makes our new equation: Na + Cl₂ -> 2NaCl
3. Now our moles Cl are balanced, but now there's 1 mole of Na on the reactants side, and 2 moles of Na on the products side, so we give the Na on the reactants side the coefficient 2 to even it out
4. This makes our new equation: 2Na + Cl₂ -> 2NaCl
5. Our equation is now balanced :)

Next, we want to take 25g Cl, being that it's the only given information, and convert this into moles, since we

want moles as our final unit.

1. The molecular weight of Cl is 35.45g/1 mole Cl.
2. Because we start off with 25g Cl, we multiply this by (1 mol Cl/ 35.45g Cl) to cancel out the grams Cl, which leaves the mol Cl in the numerator, leaving us with the units we want.
3. 25 * (1/35.45) = 0.70521861777 mol Cl (in most classes we only round our final answer)
4. Our equation uses Cl₂ not Cl, so we multiply 0.70521861777 mol Cl by 2 to give us 1.41043723554 mol Cl₂

Next, we can find how many moles of Na actually react with 25 g of Chlorine (or 1.41043723554 mol Cl₂ )

1. Using the chemical equation, we have a ratio of 2 mol Na/1mol Cl₂
2. We start with 1.41043723554 mol Cl₂, which we multiply by (2 mol Na/1mol Cl₂), canceling out the units of mol Cl₂, and leaving the mol Na in the numerator as the final unit.
3. 1.41043723554 mol Cl₂ * (2 mol Na/1mol Cl₂) = 2.82087447109 mol Na

Which is not our final answer, we still need to round. In my experience, most teachers have you round to the smallest given significant figure. The only number provided to us was 25 g which has 2 significant figures, therefore we round our answer to 2 significant figures.

2.82087447109 mol Na rounds to 2.8 mol Na, which is our final answer.

Remember to check with your teacher/notes about the rounding rules used in your class, use them accordingly, and always ensure to keep track of your units.