Chem Exam 1

The molecular formula of aspirin is C9H8O4. How many aspirin molecules are present in one 500-milligram tablet?

1.67x10^21 molecules

The reaction of 60.0g of aluminum oxide with 30.0g of carbon produced 22.5g of aluminum. What is the percent yeild for this reaction? Al2O3 + 3C -> 2Al + 3CO

70.9%

A block of iron has a mass of 483g. What is the mass of a block of graphite that has the same volume as the block of iron? The following densities at 25 degrees C are provided: magnesium - 1.7g/cm^3 graphite - 1.8g/cm^3 iron - 7.9g/cm^3

110g

Calculate the mass of FeS formed when 9.42g of Fe reacts with 8.50g of S. Fe(s) + S(s) -> FeS(s)

14.8g

What percentage of the mass of a carbon-12 atom is contributed by its electrons? Given the mass of an electron is (1/1836) amu.

0.027%

A special flask used in the determination of densities, called a pycnometer, has a mass of 16.3179g when empty, and it has a mass of 48.0250g when filled with water at 20 degrees C. When this same pycnometer is filled with ethyl alcohol at 20 degrees C, it is found to have a mass of 41.3934g. Find the density of ethyl alcohol at 20 degrees C. (Given: at 20 degrees C, the density of water is 0.9982g/mL)

0.7894g/mL

The diameter of Earth is 12.7Mm. Express this diameter in centimeters.

1.27x10^9cm

The density of lead is 11.4g/cm3 at 25 degrees C. Calculate the volume occupied by 25.0g of lead.

2.19 cm3

How many sulfur atoms are there in 21.0g of Al2S3?

2.53x10^23 atoms

How many square kilometers are equivalent to 28.5cm^2?

2.85x10^-9km^2

Give the correct number of significant figures to the problem below. 2.4x10^-4 + 3.1x10^-2 =

3.1x10^-2

The total number of electrons present in a sulfate ion (SO4^-2) is

50

Give the number of protons (p), neutrons (n), and electrons (e) in one atom of ^238U

92 p, 146 n, 92 e

The table below describes four atoms. Atom A I Atom B I Atom C I Atom D # of protons I 79 80 80 79 # of neutrons I 118 120 118 120 # of electrons I 79 80 80 79 Which atoms represent the same element?

Atoms A and D the same element, Atoms B and C represent the same element (look at protons and electrons NOT neutrons)

The percent composition by mass of a compound is 76% C, 12.8% H, and 11.2% O. The molar mass of this compound is 284.5g/mol. What is the empirical formula of the compound?

C9H18O

List the chloride ion, chlorate ion, and perchlorate ion, in that order.

Cl-, ClO3-, and ClO4-

Ammonia reacts with diatomic oxygen to form nitric oxide and water vapor: 4NH3 + 5O2 -> 4NO + 6H2O When 20.0g NH3 and 50.0g O2 are allowed to react, which is the limiting reagent?

NH3

Complete the following chart, in order from left to right. Isotope I Mass # I Protons I Neutrons I Electrons 4 2 0

^4He^2+, 2

Complete the following chart, in order from left to right. Isotope I Mass # I Protons I Neutrons I Electrons 40 57 40

^97Zr, 97