Self-Check 9 CHAPTER 9 Counting Atoms: The Mole

While studying this chapter, tick off each item after your teacher has covered it.

A. What I should know:

That chemists count numbers of particles in moles.

The number of particles in a mole.

The definition of molar mass.

Molar masses for substances consisting of atoms, molecules and ions.

Three different kinds of chemical formulae and examples of each.

The procedure for calculating the empirical formula of a compound from

experimental data.

Avogadro’s law.

Definition of molar volume of a gas and its value at room temperature and pressure.

The idea of concentration and the units for measuring concentration.

B. What I should be able to do:

Calculate number of moles from number of particles and vice versa.

Perform calculations related to molar mass.

Carry out an experiment to determine the empirical formula of a compound.

Calculate empirical formulae of compounds from given data.

Perform calculations related to molar volume of gases.

Calculate the concentrations of solutions given amounts of solute and vice versa.

Use a spreadsheet for calculations.

C. What I should have developed:

An appreciation that mass of particles can be used to count numbers of particles.

An appreciation of the large number of particles in a mole.

A recognition of the importance of the mole concept in the study of quantitative

Chemistry.

Definitions

1. Relative Atomic Mass

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2. Relative Molecular Mass

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3. Relative Formula Mass

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4. Molar Mass

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5. Mole

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6. Avogadro’s Constant

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Calculation of Number of Atoms and Molecules

Chemical Calculations (Level 3)

One mole is a number which is approximately equals to 6 × 1023. The mass of one mole of any substance is called the molar mass.

For atoms of elements, the molar mass is the relative atomic mass of the element expressed in grams. For example, the relative atomic mass of carbon is 12. So the molar mass of carbon atoms is 12 g because 12 g of carbon contains one mole of carbon atoms.

For molecules, the molar mass is the relative molecular mass of the substance expressed in grams. For example, the relative molecular mass of water is 18. So the molar mass of water is 18 g because 18 g of water contain one mole of H2O molecules.

Find the mass of the following.

1 5 mol of CH4 6 2.5 mol of H2O

2 0.5 mol of CaCO3 7 5 mol of SO2

3 4 mol of H2 8 3 mol of CO2

4 2 mol of NaCl 9 0.25 mol of Br2

5 3 mol of CH3COOH 10 1.5 mol of KOH

How many moles of molecules are contained in 100 g of the following?

11 HCl 16 H2SO4 21 LiCl

12 NH4Cl 17 CuSO4 22 C2H6

13 Fe2O3 18 NaOH 23 Al(NO3)3

14 CaCl2 19 NO2 24 NH3

15 N2 20 KMnO4 25 H2S

Calculation of Molar MassCalculate the Molar Mass of the following. You will find data concerning Relative Atomic Masses on the periodic table. When you have finished this set of calculations keep the answers for reference. You will find them useful in some of the other questions in this workbook.

Calculation of the number of moles of material in a given mass In each case calculate the number of moles of the material in the mass stated.

Calculation of the mass in a given number of moles In each case calculate the mass with the number of moles stated.

Calculation of the number of moles of gas in a given volume of that gasIn each case, calculate the volume of the number of moles of gas stated.

Calculation of the mass of a given volume of gasCalculate the mass of the volume of gases stated below.(Assume that all volumes are measured at room temperature and pressure and that1 mol of gas has a volume of 24 000 cm3 under these conditions).

Calculation of the Relative Molecular Mass of a gas from mass and volume data for the gasIn each case you are given the mass of a certain volume of an unknown gas. From each set of data calculate the Relative Molecular Mass of the gas.(Assume that all volumes are measured at room temperature and pressure and that1 mol of gas has a volume of 24 000 cm3 under these conditions).

Calculations based on concentrations in solutionCalculate the number of moles of the underlined species in the volume of solution stated.

What is the concentration in mol/dm3 of the following?

Mass in a given volume of solution

Calculation of a formula from experimental dataIn Section a. calculate the empirical formula of the compound from the data given. This may be as percentage composition or as the masses of materials found in an experiment. For Section b.you are given the data for analysis plus the Relative Molecular Mass of the compound, in these cases you are to find the empirical formula and thence the molecular formula. Section c. is more difficult, the data is presented in a different fashion but the calculation of the empirical formula/molecular formula is essentially the same.

Section A

Section B

Section C