1. Write out a balance reaction for the combustion of benzene (C 6 H 6(l) ). 2.

Question

1. Write out a balance reaction for the combustion of benzene (C6H6(l)).

2. Balance the following: AgNO3 + Mg Mg(NO3)2 + Ag

3. What is the molar mass of ZnSO4? Of CH3OH?

4. What is the percent composition by mass of each element in NH4Cl?

5. How many moles of O atoms are in a mole of H2O? How many H atoms are in a mole of H2O? (Careful, notice the difference between the questions).

6. How many molecules of CH4 are in 0.75 mol CH4? How many atoms of H are present in the sample?

7. Calculate the molar mass of Mg(NO3)2.

8. What is the mass of 0.52 mol NH3?

9. How many moles of H2O are there in 58.8 g? How many molecules of H2O is that?

Explanation / Answer

. Write out a balance reaction for the combustion of benzene (C6H6(l)).

Ans: C6H6 (l) + 15/2 O2 --> 6CO2 + 3H2O

2. Balance the following:

2AgNO3 + Mg Mg(NO3)2 + 2Ag

3. What is the molar mass of ZnSO4? Of CH3OH?

Molar mass of ZnSO4: atomic mass of Zn + Atomic mass of S + 4 Atomic mass of O

= 65.38 + 32 + 4X16 = 161.38

Molar mass of CH3OH = Atomic mass of C + atomic mass of O + 4 X atomic mass of H

= 12 + 16 + 4X1 = 32

4. What is the percent composition by mass of each element in NH4Cl?

Element   atomic mass    number of atoms    Mass %

Nitrogen       14                      1                                26%

Hydrogen     1                        4                                  7.5%

Chlorine     35.3                  1                                    66.5%

5. How many moles of O atoms are in a mole of H2O? How many H atoms are in a mole of H2O? (Careful, notice the difference between the questions).

a) the number of moles of O in H2O = 1 mole

b) number of mole of H in H2O = 2 moles so number of atoms = 2X 6.023 X 10^23 atoms

6. How many molecules of CH4 are in 0.75 mol CH4? How many atoms of H are present in the sample?

7. Calculate the molar mass of Mg(NO3)2.

Molar mass = atomic mass of Mg + 2Xatomic mass of N + 6 X atomic mass of O

Molar mass = 24 + 28 + 96 = 148

8. What is the mass of 0.52 mol NH3?

Mass of each mole of NH3= 14+3 = 17 grams

so mass of 0.52 moles = 0.52 X 17 grams = 7.28 grams
9. How many moles of H2O are there in 58.8 g? How many molecules of H2O is that?

in 18 grams number of moles = 1 moles

so 1 gram will have = 1/18 moles

So 58.8 grams will have = 58.8 / 18 moles = 3.27 moles

So number of molecules = 3.27 X 6.023 X 10^23 molecules = 19.69 X 10^23 molecules

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