How Do I Solve This Chemistry Question: How Many Moles Are Contained In 25 G NaOH?Can You Please Explain Step By Step How I Would Solve This?


2 Answers

Oddman Profile
Oddman answered
You solve this by realizing
moles = (grams)/(grams/mole)

The grams/mole value of a substance is its molecular weight. That is found by adding the atomic weights of the constituent atoms. The atomic weights are ...
Na: 22.9898
O: 15.9994
H: 1.0079.
There is one atom of each in NaOH, so the molecular weight is the sum of these numbers: 39.9971.

moles = (25 g)/(39.9971 g/mol) = .625 moles.

Naja Ellis Profile
Naja Ellis answered
Hello I am writing only to illuminate the inaccuracies as I see them, I do not want to step on toes. First I congratulate you the simple fact of coming to the correct answer, but how you have with the the relationships in a simple factor label method problem is this. The relationship is incorrect and the value used in place of their calculated value 39.99gm/mole is 25 gms?.

Using your equation as listed: Moles = (grams)/(grams/mole)
the answers written would yeild the answer moles = (25G)/(25G/mole NaOH)=625 G2/mole, NO Way

Even with the correct MW = 39.99/ 1mole NaOH
mole = (25G)(40G/mole) = 999.75 G2/mole

The PROPER EQUTION can always be obtained by first writing down what you have and where you want to go.

Moles =  25 gms NaOH x (1mole NaOH/39.99 gms) = 0.73 moles of NaOH.
This way the units of grams will cancell out and you are left with the desired units of moles.
thanked the writer.
Oddman commented
You seem to be getting confused between multiplying by (g/mol) and dividing by (g/mol). You are correct that (g)*(g/mol) is a meaningless g^2/mol. Also, you seem to be confusing units with the quantity that has those units. I can have 150 miles and 50 miles/hour, and I can divide the former by the latter to get 3 hours. When I write the equation describing what happens to the units (miles/(miles/hour) = hours), it doesn't mean that I have to put 150 wherever miles are shown.
Naja Ellis
Naja Ellis commented
The question asked for a step by step answer so he/she could follow and apply to other questions similar. The original author was not clear at all, so I tried to clarify...that all.

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