Practice for Test

A. Find moles, grams, and number of particles:

1. 9.35g of Al₂O₃ contains how many molecules?
2. 0.253 moles of BN has a mass of…
3. Calculate the number of moles of 8.46 x 10²⁴ atoms of F.
4. Calculate the number of moles of 4.35g of Cs₂CO₃.
5. 0.692moles of CsH contains how many molecules?
6. How many moles are in 14.49 g of CoSO₄.
7. What is the mass of 7.20 x 10²³ atoms of Ne?
8. 50.82 g of Cr₂O₃ has how many moles?
9. 2.84 moles of N₂H₄ has how many molecules?
10. 5.29 x 10²⁴ molecules of HCl has a mass of…

B. % Composition when given mass

1. In a 30.0 g sample of Pb(NO₃)_2, Pb has a mass of 2.535 g, N a mass of 8.694 g, and O a mass of 18.768 g. What is the % composition?
2. In a 25.0 g sample of Hg₂Cl₂, Hg has a mass of 3.755 g and Cl has a mass of 21.245 g. What is the % composition.
3. In a 20.0 g sample of Ni(NO₃)₂, Ni has a mass of 3.066 g, Ni has a mass of 6.426 g, and O has a mass of 10.508 g. What is the % composition?

C. % Composition when given empirical formula?

1. What is the % composition of KMnO₄?
2. What is the % composition of Sc₂O₃?
3. What is the % composition of H₂SeO₄?
4. What is the % composition of Cl₃HSi?
5. What is the % composition of NaBrO?

D. Finding empirical formula from % composition

1.  Na_Al_O_

• Na: 28.05%
• Al: 32. 92%
• O: 39.03%

2. Na_Mn_O_

• Na: 16.20%
• Mn: 38.71%
• O: 45.09%

3. S_O_Cl_

• S: 32.76%
• O: 23.71%
• Cl: 52.53%

4. Zr_O_

• Zr: 74.03%
• O: 25.97%

5. Pb_Cl_

• Pb: 75.51%
• Cl: 25.49%

6. H_Cl_O_

• H: 1.92%
• Cl: 67.58%
• O: 30.50%

7. B_H_

• B: 21.86%
• H: 78.14%

E. Stoichiometry 

1. Using the following equation, answer the questions:
    PCl₃ + 3H₂O ➝ H₃PO₃ + 2HCl

    A. How many moles of HCl are produced if 3.4 moles of H₂O are used?

    B. How many grams of PCl₃ are needed to produce 12.0 moles of HCl?

    C. How many grams of H₃PO₃ are produced if 13.40 g of H₂O are used?

2. Using the following equation, answer the questions:
    2CaH₂ + 5O₂ ➝ 4CO₂ + 2H₂O

    A. How many moles of O₂ are used to make 23.0 grams of H₂O?

    B. How many moles of CaH₂ must be used to make 12.0 moles of CO₂?

    C. How many grams of H₂O are made when 25.0 grams of CaH₂ are used?

ANSWERS:

A. Find moles, grams, and number of particles:

1. 5.52 x 10²² molecules of Al₂O₃
2. 6.28 g of BN
3. 14.05 mol F
4. 0.013 mol CsCO₃
5. 4.17 x 10²³ molecules CsH
6. 0.093 mol CoSO₄
7. 24.13 g Ne
8. 0.334 mol Cr₂O₃
9. 1.71 x 10²⁴ molecules N₂H₄
10. 320.28 g HCl

B. % Composition when given mass

1. Pb: 8.46%; N: 28.98%; O: 62.56% 
2. Hg: 15.02%; 84.98%
3. N: 15.33%; 32.13%; O: 52.54%

C. % Composition when given empirical formula?

1. K: 24.74%; Mn: 34.76%; O: 40.50%
2. Sc: 65.20%; O: 34.80%
3. H: 1.39%; Se: 54.47%; O: 44.14%
4. Cl: 78.52%; H: 0.74%; Si: 20.73%
5. Na: 19.34%; Br: 67.21%; O: 13.46%

D. Finding empirical formula from % composition

1. NaAlO₂
2. NaMnO₄
3. SO₂Cl₂
4. ZrO₂
5. PbCl₂
6. HClO
7. B₂H₆

E. Soichiometry

1A. 2.27 mol HCl

1B. 823.92 g PCl₃

1C. 20.34 g H₃PO₃

2A. 3.19 mol O₂

2B. 6.0 mol CaH₂

2C. 10.70 g H₂O