# The Mole Concept Exam 2 and Problem Solutions

**The Mole Concept Exam 2 and Problem Solutions**

**1.** Find relation between number of molecules of given matters;

**I.** C_{2}H_{2} that includes 2mol H atom

**II.** CH_{4} that includes N atoms (N is Avogadro number)

**III.** C_{3}H_{4} that includes 1,5 N C atoms

**Solution:**

**I.**

1mol C_{2}H_{4} includes 4mol H atom

?mol C_{2}H_{4}includes 2mol H atom

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?=0,5mol C_{2}H_{4}

**II.**

1mol CH_{4} includes 5N atom

?mol CH_{4} includes N atom

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=0,2mol CH_{4}

**III.**

1mol C_{3}H_{4} includes 3N C atom

?mol C_{3}H_{4} includes 1,5N C atom

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?=0,5mol C_{3}H_{4}

Thus relation between them: I=III>II

**2.** Find relation between number of atoms of given matters.

**I.** 6 PH_{3} molecules

**II.** CO_{2} that includes 24N atom

**III.** 8mol O_{3}

**Solution:**

**I.**

1 PH_{3} molecule contains 4 atoms

6 PH_{3} molecules contain ? atom

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?=24 atoms

**II.**

CO_{2} includes 24 N atoms.

**III.**

1mol O_{3} contains 3N atoms

8mol O_{3} contain ?N atoms

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=24N atoms

**3.** Which one of the following statements is false for 0,5mol C_{2}H_{6}? (C=12, H=1 and take Avogadro Number=6x10^{23})

**I.** It is 15 g

**II.** It includes 3x10^{23} C_{2}H_{6} molecules

**III.** It includes 1mol C atom

**IV.** It includes 4 atoms.

**V.** It includes 3 g H.

**Solution:**

**I.** molar mass of C_{2}H_{6}=2.(12) + 6.(1)=30g/mol

1mol C_{2}H_{6} is 30g/mol

0,5mol C_{2}H_{6} is ?mol

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=15 g/mol I is true

**II.**

1molC_{2}H_{6} includes 6x10^{23} C_{2}H_{6} molecules

0,5mol C_{2}H_{6} includes ?C_{2}H_{6} molecules

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?=3x10^{23} C_{2}H_{6} molecules II is true

**III.**

1mol C_{2}H_{6} includes 2mol C atoms

0,5mol C_{2}H_{6} include ?mol C atoms

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=1mol C atom, III is true

**IV.**

1mol C_{2}H_{6} includes 8N atoms

0,5mol C_{2}H_{6} includes ?N atoms

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=4N atoms, IV is false.

**V.**

1mol C_{2}H_{6} includes 6g H

0,5mol C_{2}H_{6} includes ?g H

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=3 g H V is true

**4.** If, 8,4 g X element includes 9,03x10^{22} atoms and 0,1mol X_{2}Y_{3} compound is 16g find atomic mass of Y element. (Avogadro number is 6,02x10^{23})

**Solution:**

Mole of X element is ;

nx=(9,03x10^{22})/(6,02x10^{23})=0,15mol

Atomic mass of X;

A_{X}=8,4/0,15=56g/mol

Molar mass of X_{2}Y_{3}compound;

M_{X2Y3}=16/0,1=160g/mol

We find atomic mass of Y by;

2.X + 3Y =160

2.(56) + 3(Y)=160

Y=16g/mol is atomic mass of Y.

**5.** Which ones of the following statements are true for 0,2mol C_{3}H_{4} and 0,5mol C_{2}H_{6} gas mixture? (C=12, H=1 and N=Avogadro Number)

**I.** Mass of mixture is 23 g.

**II.** It includes 1,6mol C atom.

**III.** It includes 0,7N molecule.

**Solution:**

**I.** Molar mass of C_{3}H_{4} =3.(12) + 4.(1)=40g/mol

1mol C_{3}H_{4} is 40g

0,2mol C_{3}H_{4} ?g

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?=8g C_{3}H_{4}

Molar mass of C_{2}H_{6}=2.(12) + 6.(1)=30g/mol

1mol C_{2}H_{6} is 30 g

0,5 mol C_{2}H_{6} is ? g

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=15 g C_{2}H_{6}

Total mass of mixture is=8 + 15=23 g **I is true**

**II.**

1mol C_{3}H_{4} contains 3mol C atoms

0,2mol C_{3}H_{4} contains ?mol C atoms

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=0,6mol C atoms

1mol C_{2}H_{6} contains 2mol C atoms

0,5mol C_{2}H_{6} contains ?mol Catoms

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

?=1mol C atom

Total umber of C atoms in mixture is=0,6 + 1=1,6mol C atoms. II is true.

**III.**

0,2mol C_{3}H_{4} + 0,5mol C_{2}H_{6} = 0,7mol molecule

There are 0,7N molecule in 0,7 mol mixture, III is true.