1.) A compound has the following percentage composition, by weight: 22.0% Cu, 12

Question

1.)A compound has the following percentage composition, by weight: 22.0% Cu, 12.9% Fe, 16.6% C, 19.4% N, and 29.1% H2O. Write a plausible (empirical) formula for this compound.

2.)What is the sum of the coefficients when the following equation is balanced?

___ H2SO3 + ___ Al(OH)3   --> ___ Al2(SO3)3 + ___ H2O

3.)What is the sum of the coefficients when the following is balanced:

___ Na + ___ HCl --> ___ NaCl + ___ H2

4.)How many grams of N2 are required to react with 2.30 moles of Mg in the process

         3 Mg + N2 --> Mg3N2 ? (Mg = 24.3 g/mol, N = 14.0 g/mol)

5.)What volume of 6.0 M sulfuric acid is required for the preparation of 500.0 mL of 0.30 M solution?

6.)What is the molarity of methanol, CH3OH (d = 0.792 g/mL) if 150.0 mL is dissolved in enough water to make 4.0 L of solution?

7.)What is the percent yield if 122 grams of SiO2 are made from 246 g of Cr2O3 by the following equation?

         3 Si(s) + 2 Cr2O3(s) --> 3 SiO2(s) + 4 Cr(l)

Explanation / Answer

Masss of Cu= 22 g, Fe= 12.9 g , C = 16.6 g

N = 19.4, H2O = 29.1 g

We find moles of each of the above

Mol cu = 22.0 g / molar mass of Cu = 22.0 g/ 63.546 g per mol = 0.35 mol

Mol Fe = 12.9 g / 55.845 g per mol = 0.23

Mol C = 16.6 g / 12.011 g per mol =1.38 mol C

Mol N = 19.4 g / 14.007 g per mol = 1.38 mol N

Mol H2O = 29.1 g / 18.0148 g per mol = 1.62 mol H2O

Empirical formula : The simplest ratio of moles.

To get empirical formula we divide each of these above by smallest number of moles to find number of each in the formula

# mol Fe = 0.23/ 1.38 = 0.17

#mol Cu = 0.35 / 1.38 = 0.25

# mol C = 1

# mol N = 1

# mol of H2O = 1.17

Now we have to find whole number by multiplying by smallest number

Mol cu = 0.25 * 4 = 1

Mol Fe = 0.167 * 4 = 0.67 rounded to 1

Mol C = 1 * 4 = 4

Mol N = 1 * 4 = 4

Mol H2O = 1.17 * 4 = 4.70

Formula is Cu1Fe1(CN)4 .5 H2O or

CuF(CN)4 .5 H2O

2.)What is the sum of the coefficients when the following equation is balanced?

___ H2SO3 + ___ Al(OH)3   --> ___ Al2(SO3)3 + ___ H2O

Before answering this we balance given equation

3H2SO3 +2 Al(OH)3   --> ___ Al2(SO3)3 +6 H2O

Sum of the coefficient is then 3 + 2 + 1 + 6 = 12

3) 3.)What is the sum of the coefficients when the following is balanced:

2 Na+ + 2 HCl --> 2 NaCl + H2

Sum is 2 +2 +2 + 1 = 7

4.)How many grams of N2 are required to react with 2.30 moles of Mg in the process

         3 Mg + N2 --> Mg3N2 ? (Mg = 24.3 g/mol, N = 14.0 g/mol)

We use reaction stoichiometry

Calculation of mole of N2 required

= mol Mg * 1 mol N2 / 3 mol Mg

= 2.30 mol Mg * 1 mol N2 / 3 mol Mg

= 0.77 mol N2

Now we find mass of N2 from its mol and molar mass

Mass of N2 = moles * molar mass = 0.77 mol * 28.014 g per mol

= 21.5 g

Mass of N2 required in this reaction = 21.5 g

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