What is the mass of 4.09 x 1021 formula units of sodium hydroxide: NaOH (Mw. 40.

Question

What is the mass of 4.09 x 1021 formula units of sodium hydroxide: NaOH (Mw. 40.00 g/mol)?

How many moles is equivalent to 9.32 x 1022 molecules of nitrogen dioxide: NO2 (Mw. 46.01 g/mol)?

How many molecules of hydrofluoric acid (HF) are in 115 g of HF (Mw. 20.01 g/mol)?

What is the mass of 0.105 moles of copper(II) chloride dihydrate: CuCl2·2H2O (Mw. 170.48 g/mol)? Note: The number of moles was supposed to show with three singificant digits. If it only shows two such as 0.19, it dropped a zero at the end and should read 0.190. Please give your answer with three significant digits.

Explanation / Answer

a) 4.09 x 10^21 F.U. divide by Avagadro's Number (6.02x10^23 F.U.) and you will get moles of NaOH, then multiply by the molar mass of NaOH.

no of moles of NaOH = 4.09X10^21/6.02x10^23 = 6.79 X 10-3 moles

b)molar mass of NaOH = 6.80X 10^-3 / 40 = 0.27 grams of NaOH

no of mole = no of molecules of NO2 / avagrado number = 0.15 moles of NO2

c) 1 mole has avagrado number of molecule

no of molecules = no of moles *(6.023X10^23) = (115/ 20.01)*6.023X10^23 = 3.45 X 10^24 molecules

d) mass of the cucl2.H20 = moles X molar mass = 0.105 *170.48 = 17.9004 grams

answer with three significant digits = 17.9 grams

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