General Chemistry 1032-0001/Fall 2020

Exam 2 Review 9-30-2020

Chapter 5: The Mole and Chemical Formulas

1. What is the empirical formula of a compound with the molecular formula C10H8?

a. C5H3

b. C2H4

c. C5H4

d. CH

2. What is molecular formula for fructose (a sugar found in fruit) from its empirical formula, CH2O, and its molar mass, 180.2 g/mol.

a. C6H12O6

b. C2H8O3

c. CH2Od. C4HO3

3. How many moles of Chlorine are in 3.5 mols of CCl4

a. 1 mol of Cl

b. 14 mols of Cl

c. 3.5 mols of Cl

d. None of the above

4. A compound containing nitrogen and oxygen is decomposed in the laboratory. It produces 24.5 g nitrogen and 70.0g of oxygen . Calculate the empirical formula

a. N1.75O4.38

b. N1O2.5

c. N2O5

d. NO2

e. None of the above

5. A compound is 52.14%C, 13.13%H and 34.73%O by mass. What is the empirical formula of the compound?

a. C2H8O3

b. C2H6Oc. C4HO3

d. C3HO6

6. What is the mass percentage of K in KBr? Now what about the mass of K in 35.5g of KBr?

a. 32.9 % ; 11.7 g of K

b. 39.2% ; 11.7 g of K

c. 39.2% ; 39.10 g of K

d. 32.9% ; 39.10 g of K

What is a Mole?: A mol is the amount of material containing 6.022 x 10 23 particles

Avogadro’s number:______________________

1. Convert 3.5 mol of helium to number of helium atoms

2. Convert 1.1 x 1022 silver atoms to moles of silver

3. Determine the number of CH2Cl2 molecules in 25.0g of CH2Cl2a. 0.294 molecules

6.022 X 1023

b. 1.77 x 1023 moleculesc. 1.28 x 1027 moleculesd. 1.51 x 1025 molecules

7. Determine the number of CH2Cl2 molecules in 25.0g of CH2Cl2

e. 0.294 moleculesf. 1.77 x 1023 moleculesg. 1.28 x 1027 moleculesh. 1.51 x 1025 molecules

Chapter 3: Compounds and Chemical Bonds

8. The image represents a particulate view of a sample of matter? Classify the sample according to its composition

a. The sample is a pure element

b. The sample is a homogenous mixture

c. The sample is a compound

d. The sample is a mixture of an element and a compound

9. Which of the following substances is a pure element?

a. sweat

b. carbon dioxide

c. aluminum

d. vegetable soup

10. What is the formula for sodium hydrogen sulfite?

a. S(HSO3)2

b. S(HSO4)2

c. NaHSO3

d. NaHSO4

11. Name the compound SrI2

a. Strontium iodideb. Strontium diiodidec. Strontium (II) iodided. Strontium (II) diiodide

12. Name the compound NO2

a. Mononitrogen dioxideb. Nitrogen dioxidec. Dinitrogen monoxided. Nitrogen oxide

13. Name the compound HNO2

a. Hydrogen nitrogen dioxideb. Hydrogen nitratec. Nitric acidd. Nitrous acid

14. What is the charge of iron in FeCl3?

a. +1b. +2c. +3d. +4

15. Which substance is an ionic compound?

a. RbI

b. N2O4

c. He

d. CCl4

Chapter 4: How Chemists use Numbers

16. What is the value of 98°F in units of C°.

a. 22

b. 371

c. 37

d. 72

e. None of the above

17. How many significant figures should be reported in the answer to the following calculation?

(95.43)(63.002)(0.0090)a. 3

b. 4

c. 2

d. 1

e. None of the above

18. How many significant figures should be reported in the answer to the following calculation?

(8.01-7.50)/3.002a. 0.1698867

b. 0.17

c. 0.170

d. 0.1700

e. None of the above

19. Express the quantity 33.2 x 10-4m into mm

a. 33.2 mm

b. 3.32 mm

c. 0.332 mm

d. 33.2 x 10-4mm

e. None of the above

20. What is the mass of a 1.75 L sample of a liquid that has a density of 0.921 g/cm3

a. 1.61 x 103 g

b. 1.61 x 10-3 g

c. 1.90 x 103 g

d. 1.90 x 10-3 g

e. None of the above

21. The gas mileage of a certain automobile is 22 km/L. Convert this quantity to miles per gallon.

1 U.S. gallon (gal) = 3.785 liters (L)

1 km = 0.6214 miles (mi)

a. 9.4 mi/gal

b. 1.3 x 102 mi/gal

c. 52 mi/gal

d. 1.90 x 10-3 g

Steps to solving an Empirical Formula:

Ex. Decomposition of Water to 3.0 g H and 24 g O.

1. Determine the amount of mols there are for each element given

2. Write a pseudo-formula for your compound (in this case water):

3. To get whole-number subscripts in our formula, divide all the subscripts by the smallest one, in this case, 1.5.

4. (Additional Step) If decimals remain after dividing; multiply the number by a factor to get rid of the decimal.

Mass Percent Formula

Remember: molecular formula is always a whole number multiple of the empirical formula

Solving Density Problems:

How to use triangle: If you don’t know mass (M) but are given density (D) and volume (V), you would multiply D x V to get M.

In other words, whatever you’re trying to find just cover it up with your thumb on the triangle and solve.

Converting between grams, moles and atoms:

Naming Flow Chart:

Zero Rules

1. All nonzero digits are significant.1.05 0.0110

2. Interior zeros (zeros between two numbers) are significant.I.208 50.1

3. Trailing zeros (zeros to the right of a nonzero number) that fall after a decimal point are significant. 5.10 3.00

4. Trailing zeros that fall before a decimal point are significant. 50.00 1700.24

5. Leading zeros (zeros to the left of the first nonzero number) are NOT significant. They only serve to locate the decimal point.

0.00056. Trailing zeros at the end of a number, but before an implied decimal point, are

ambiguous and should be avoided.

350 350.0 3.5 x 102 (two significant figures) Or 3.50 x 102 (three significant figures)

Multiplication and Division Rule

The result of multiplication or division carries the same number of significant figures as the factor with the fewest significant figures.

Addition and Subtraction

In addition or subtraction calculations, the result carries the same number of decimal places as the quantity carrying the fewest decimal places

Combined Operations

When doing calculations that involve both multiplication or division and addition or subtraction, first do a calculation for the operation shown in parenthesis and round that value to the correct number of significant figures, then use the rounded number to carry out the next operation.

Substances and Mixtures Flowchart

Prefix multiplier

Polyatomic Ions: