# Conversions between grams, moles and atoms

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Lecture 4-Chemical Substances and Mole concept

## Interconverting mass, moles and number of particles

• Determine the number of moles in 85.00 grams of sodium chlorate, NaClO3
• Determine the number of molecules in 4.6 moles of ethanol, C2H5OH. (1 mole = 6.022 x 1023).

## Exercises

• Determine how many H atoms are in 4.6 moles of ethanol.
• solve the following questions.
• Q1: How many atoms of silver are in 3.50 moles of silver?
• Q2: Determine the number of moles of carbon disulfide in 34.75 grams of CS2.
• Q3: Determine the number of sulfur atoms in 34.75 grams of CS2.
• Q4: How many grams of oxygen are present in 5.75 moles of aluminum oxide, Al2O3?
• Q5: Determine the number of fluorine atoms in 24.24 grams of sulfur hexafluoride SF6.

## Determining the Formula of an Unknown compound Empirical and Molecular Formulas

• Empirical- simplest whole-number ratio of atoms (moles of each element) in a formula (in a compound).
• Molecular - the “true” ratio of atoms in a formula; often a whole-number multiple of the empirical formula
• We can determine empirical formulas from % composition data; a good analysis tool.

## Empirical Formulas

• Steps for success
• Convert given amounts to moles
• Mole ratio (divide all moles by the smallest number of moles)
• The numbers represent subscripts.
• If the numbers are not whole numbers, multiply by some factor to make them whole.
• Note: on multiplying by an integer the relative number of moles will not change because we multiply all the subscripts by same integer.