Chemistry Calculations with moles?

I was given these 4 problems on moles and mole calculations but I honestly do not get it in the least bit. Can any one help explain it and possibly work through them? Thanks sooo much!





1) How many moles are present in 34 grams of Cu(OH)2?





2) How many moles are present in 2.45 x 1023 molecules of CH4?





3) How many grams are there in 3.4 x 1024 molecules of NH3?





4) How much does 4.2 moles of Ca(NO3)2 weigh?

Chemistry Calculations with moles?
For mass (grams) to moles problems, use the molecular weights found in the periodic table. If molecules/atoms are involved, use the Avogadro's number (6.02 x 10^23 particles/mole).





Just use dimensional analysis from there.





1) 34 g / (97.5 g/mol) = 0.35 moles





2) 2.45 x 10^23 molecules / Avogadro's number = 0.407 moles





3) 3.4 x 10^24 molecules / Avogadro's number * 17 g/mol = 96 g





4) 4.2 moles * 164 g/mol = 6.9 x 10^2 g

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