Chem 120 Fritsch

Ch 1 -3 Practice Problems - KEY The following problems are intended to provide you with additional practice in preparing for the exam. Questions come from the textbook, previous quizzes, previous exams, and other sources. A solutions manual is supplied in a separate document. 1. The Earth has an average density of 5.52 g/cm3. Report this density in kg/m3 and lb/ft3.

2. Fill in the table with the correct name or molecular formula.

Formula Name

SO3 Sulfur trioxide

Li3PO4 Lithium phosphate

Cu(NO3)2 Copper (II) nitrate

N2Cl4 Dinitrogen tetrachloride

H2SO4 Sulfuric acid

Chem 120 Fritsch

3. Determine the oxidation state for the requested element in each of the following.

KNO2 oxidation state of N = +3

Na2S oxidation state of S = -2

Cr3(PO4)3(SO4)(Cl) oxidation state of Cr = +4

Ca(OH)2 oxidation state of Ca = +2

4. The Pepperdine pool is 50 m long, 25 m wide, with an average depth of 6.78 ft. What mass of water (in kilograms) does the pool contain?

5. Place an X in the appropriate column corresponding the isotopes and element symbols given.

Symbol # of protons < # of neutrons

# of protons < # of electrons

# of protons > # of electrons

# of neutrons = # of electrons

57Mn4+ X X

37Cl- X X

14N X 34S2- X X X

6. Which of the following pairs of elements will form anions with the same charge in ionic solids?

Na and Cs Mg and S F and Cl Rb and Sr Br and O Answer: F and Cl 7. In Faraday’s experiment with the cathode ray tube, the path of the electrons inside the tube was the result of which properties?

I. mass of the electron

II. volume of the electron

III. charge on the electron

IV. force of the magnetic field

Answer: I, III, and IV

Chem 120 Fritsch

8. The water in the Pacific Ocean contains a number of dissolved cations (magnesium, sodium, calcium, and potassium) and anions (chloride and sulfate). Each kilogram of Pacific Ocean water contains 1,153 mg of magnesium, 412 mg of calcium, and 19,432 mg of chloride. What is the percent mass of magnesium in the water? What is the mass percent of chloride in the water? If you had, 0.578 kg of ocean water, how many calcium ions would it contain?

9. In the General Chemistry lab, you and your lab partners are measuring the masses of pennies to see how they differ. Unfortunately, you measured the masses to different levels of precision with the following measurements: 2.1625 g, 2.043 g, 2.03 g. What is the sum of the masses of the pennies with the appropriate number of significant figures? Answer: 6.24 g

10a. Which of these Cu(s), O2(g), H2O(l), N2(g), and He(g) has the highest density (g/mL)? Answer:_____ Cu(s)_____ 10b. Which of the following pairs of molecular formulas have the same empirical formula? N2O4 and NO2 H2O and H2O2 H3PO4 and H3PO3 C2H6O and C6H12O6 Answer: N2O4 and NO2

Chem 120 Fritsch

11. Combustion analysis was completed on a 0.534 g sample of 1,2-Bis-(4-pyridylthio)propane (molecular formula = C13H14N2S2) in the presence of excess oxygen. Determine the mass (in grams) of the carbon dioxide and nitrogen dioxide that were collected.

12. Hemoglobin is 8.0% heme (C34H32FeN4O4) by mass. A crime scene technician collects a blood sample that contains 0.62 g of hemoglobin. How many Fe atoms are contained in the sample?

Chem 120 Fritsch

13. Mass spectrometry is a highly accurate technique used to determine the mass of ions and molecules. A sample of silicon was placed into the mass spectrometer, and three isotopes were observed. Unfortunately, your lab partner only recorded the observed masses and isotope abundances given in the table at the right. Determine the mass of the third isotope to the same number of significant figures as those data and give the appropriate symbol for this isotope.

Silicon

isotope

Atomic

mass (u)

% natural

abundance

28Si 27.9769 92.23

30Si 29.9738 3.10

Chem 120 Fritsch

14. Ferrocene is a famous compound from inorganic chemistry because it was the first to contain a Fe-C bond. A 0.9437 g sample of ferrocene (containing only C, H, and Fe) was submitted to combustion analysis which yielded 2.233 g CO2 and 0.457 g H2O. Determine the empirical formula of ferrocene.

15. Alum (KAl(SO4)2•12H2O) is a useful food preservative and is prepared from aluminum and other chemicals. How many moles of potassium are in 649 g of alum? What is the percent mass of sulfur in alum? What mass of alum (in grams) can be prepared from 13.2 kg of aluminum?

Chem 120 Fritsch

16. What is the number of chloride ions in 1.235 L of a 6.4 % by mass solution of magnesium chloride in water? (density = 1.037 g/mL)

17. Ernest Rutherford proposed his model of the nucleus based on his experiments with a thin

gold foil and a radioactive particle emitter. Which of the following (ions, atoms, isotopes) would have given the same results as observed by Rutherford’s original experiments.

6Li+ Cl- 16O2 H+ 27Al3+ 18. If the elemental analysis for a compound indicates that it was 50 % carbon by mass and 50 % hydrogen by mass, which of the following statements is true? A. There are more hydrogen atoms than carbon atoms in the empirical formula. B. There are more carbon atoms than hydrogen atoms in the empirical formula. C. There are the same number of hydrogen and carbon atoms in the empirical formula. D. The empirical formula cannot be determined from this information. Answer:_____A_____

Chem 120 Fritsch

19. Propane (C3H8) is sold in metal containers for use as fuel for barbeques or camp stoves. You purchased a camp stove bottle and it had an initial mass of 1.568 kg. After much use, you measured the mass of the empty container and found it to be 0.983 kg. How many moles of propane were in the bottle? How many carbon atoms were in the bottle? How many grams of hydrogen were in the bottle?

20. Calculate the following quantities: a) the mass in grams of 0.53 moles of manganese (II) sulfate b) the number of moles of iron(III) perchlorate in a 63.8 g sample c) the number of nitrogen atoms in a 21.6 g sample of ammonium nitrite.

Chem 120 Fritsch

21. In geology class, you study a 68.74 g rock that is 7.86% by mass fayalite (Fe2SiO4), 13.56% by mass forsterite (Mg2SiO4), and the balance is made up of silicon dioxide. What is the mass percentage of silicon in the rock? How many moles of iron are in the rock?

Chem 120 Fritsch

22. How many oxygen atoms are in each molecule of aluminum sulfate? How many hydrogen atoms are in each molecule of ammonium phosphate? How many oxygen atoms are in each molecule of copper(I) carbonate pentahydrate?

23. Fill in the missing name for the compound or chemical formula.

name Chemical formula

tin(IV) chloride SnCl4

iron(III) bromide FeBr3

ammonium perchlorate NH4ClO4

Cobalt(II) oxide CoO

Potassium nitrate KNO3

Barium sulfate BaSO4

Lithium sulfite Li2SO3

Magnesium phosphate Mg3(PO4)2

Ammonium sulfate (NH4)2SO4

Sodium carbonate Na2CO3

24. Calcium and iodine can combine to form an ionic compound. How many iodide ions would be required to combine with 3.6 x 1022 calcium ions?

Chem 120 Fritsch

25. Calculate the atomic mass of Magnesium from the mass of its isotopes and the percent natural abundance for each isotope.

Isotope Isotope mass (amu) % natural abundance 24Mg 23.9850 78.99 25Mg 24.9858 10.00 26Mg 25.9826 11.01

26. Consider a rigid, ball with a mass of 0.1034 g and a volume of 468.0 L. Air has a density of 1.176 g/L and if the density of the ball is less than the density of air, the ball will float. a. All of the contents of the ball are removed by a vacuum. Will the ball float? b. The ball is filled with carbon dioxide with a density of 1.761 g/L. Will the ball float? c. The ball is filled with helium with a density of 0.113 g/L. Will the ball float?

Chem 120 Fritsch

27. Of the following pairs which have the same number of protons, neutrons, electrons. 3H and 3He 14C and 15N 19F and 18F

28. Brass is an alloy of copper and zinc and the color of brass can be adjusted by varying the percent mass of each element in the alloy. A particular alloy contains 24.65% zinc by mass with the remainder made up by copper. To make 239.5 g of this alloy, how much copper would be required? For another sample of the alloy, 72.2 g of copper was combined with what mass of zinc in grams?

Chem 120 Fritsch

29. An average dorm room at Pepperdine measures 14 ft wide, 18 ft long, and 8 ft high. The heating and air conditioning system is able to replace all the air in the room at a rate of 1432 L/min. How long would it take to replace all the air in the room?

30. In the General Chemistry lab, you collect the weight of an empty test tube and find it to be 37.952g. You fill the test tube to the top with mercury (density = 13.53 g/mL) and collect the mass on a balance and find it to be 217.903g. You empty the test tube and fill it to the top with water. What is the mass would the balance read now?