CHM 1045
Dr. Michael Blaber

Name_________________________

SS #__________________________

1. Indicate whether the following are most likely a pure substance, a homogenous mixture or a heterogenous mixture (5 points)

a. A packet of cool aid Heterogenous mixture

b. A packet of cool aid dissolved in water Homogenous mixture

c. A bronze coin Homogenous mixture

d. A gold bullion coin Pure substance

e. A chocolate chip cookie made with blue M&M’s Heterogenous mixture

 

2. Indicate whether the following represent physical or chemical changes (5 points)

a. A sugar cube dissolving in hot water Physical change

b. An Alka-Seltzer tablet dissolving in water Chemical change

c. The heating of water to produce steam Physical change

d. The burning of candle wax to produce soot Chemical change

e. The cooking of eggs to produce an omelet Physical change

 

3. In the following diagram, in which direction would the nucleus of a helium atom be deflected? (the particle is coming directly at you). (5 points)

b

 

4. For the following elements, write down the most likely ionic form (5 points)

a. Be Be²⁺

b. S S^2-

c. P P^3-

d. Li Li⁺

e. O O^2-

 

5. Write the balanced chemical equation for the combustion of pentanol (C₅H₁₂O) (5 points)

2C₅H₁₂O + 15O₂ -> 10CO₂ + 12H₂O

 

 

6. Lithium can react with water to produce the Lithium Hydroxide and Hydrogen gas. Write the balanced chemical equation for this reaction and predict all other elements that you would expect to be able to react with water in a similar type of reaction. (10 points)

2Li + 2H₂O -> 2LiOH + H₂

(Three from Na, K, Rb, Cs, Fr)

 

7. What is the percentage by mass of C, H and O in ethanol (C₂H₆O)? (10 points)

Ethanol molecular mass is (2*12.01)+(6*1.01)+(1*16.0) = 46.08 amu

C: (2*12.01)/46.08 x 100 = 52.1%

H: (6*1.01)/46.08 x 100 = 13.2%

O: 16/46.08 x 100 = 34.7%

 

8. How many grams are there in 1.72 moles of acetone (CH₃)₂CO ? (10 points)

9. A certain combustible compound, containing C, H and O atoms, is 53.3% C, 11.2% H and 35.5% O by mass. The experimentally determined molecular mass is 90.14 amu. What is the empirical and chemical formula for this compound? (10 points)

53.3 g C * (1 mole/12.01 g) = 4.44 moles C

11.2 g H * (1 mole/1.01 g) = 11.1 moles H

35.5 g O * (1 mole/16.0 g) = 2.22 moles O

C = 4.44 / 2.22 = 2.0

H = 11.1 / 2.22 = 5.0

O = 2.22 / 2.22 = 1.0

Empirical formula = C₂H₅O molecular mass = (2*12.01)+(5*1.01)+16 = 45.07 amu

Chemical formula = C₂H₅O * (90.14/45.07) = C₄H₁₀O₂

 

10. Heptanol has the formula C₇H₁₆O and can be combusted in the presence of oxygen. If 15.0 g of heptanol is combusted in the presence of 23.0 g of O₂, how many grams of water will be produced? What is the limiting reagent? (Be sure to show the balanced equation for this reaction). (20 points)

2C₇H₁₆O + 21O₂ -> 14CO₂ + 16H₂O

heptanol molecular mass: (7*12.01)+(16*1.01)+16 = 116.86 amu

15 g * (1 mole/116.86 g) = 0.128 moles

O₂ molecular mass: (2*16.0) = 32 amu

23.0 g * (1 mole/32 g) = 0.719 moles

If oxygen is unlimited:

0.128 moles heptanol * (16 moles H₂O/2 moles heptanol) = 1.03 moles H₂O

If heptanol unlimited:

0.719 moles O2 * (16 moles H₂O/21 moles O₂) = 0.548 moles H₂O

Therefore, O₂ is limiting.

At most we can make 0.548 moles H₂O * (18.02g /1 mole) = 9.87 g

 

11. What is the molarity of a 2.92 liter solution of water containing 27g of of Mg₃(PO₄)₂? (5 points)

Mg3(PO₄)₂ molecular mass = (3*24.3)+2*(31.0+64) = 262.9 amu

27 g * (1 mole/262.9 g) = 0.103 moles

0.103 moles/2.92 liters = 0.035 molar

 

12. You have a stock solution of 3.0 M MgCl₂ and some pure water. How would you use these to produce 0.157 liters of a 0.25 molar solution of MgCl₂? (10 points)