The molecular weight of NaCl is 58.44 grams/mole. If you had a 1.0 molar solution (1.0 M) you would have to put 58.44 g of salt in 1.0 liter of solution.

How many moles of NaCl would you have in 100 mL of this solution?

If you have 1 mole in 1 litre, how many do you expect to have in 100mL?

It's simple proportion. There'll be, of course, less moles than in a liter. Post back your answer to see if you got it right, k? :)

I know I just can't remember how to convert

I know you have to set it up like

58.44 100mL
_________ x ____________
over something over something


but I can't remember how

This question doesn't involve the mass of NaCl.

Ok, your answer should be 0.1mol in 100mL

Working:
1 L = 1000mL -> 1 mole
1mL -> 1mole / 1000 mL
100mL -> 0.001 x 100 mL -> 0.1 mole

If you were asked concentration in grams per 100mL, then, you'll have to include 58.44g in your calculations.

So would the answer be

5.8 or 5.84?

This question doesn't involve the mass of NaCl.

Ok, your answer should be 0.1mol in 100mL

Working:
1 L = 1000mL -> 1 mole
1mL -> 1mole / 1000 mL
100mL -> 0.001 x 100 mL -> 0.1 mole

If you were asked concentration in grams per 100mL, then, you'll have to include 58.44g in your calculations.

See it? Lol! :p

I understood how you got 0.1

Great then! Understanding is lots better than seeing the answer and just copying! :)