Q1. Use the appropriate prefix to write 7.12 x 10-6 s without the use of exponents.

Background

Topic: Metric Prefixes and Scientific Notation

This question tests your understanding of metric prefixes and how to convert numbers written in scientific notation to a form using a prefix instead of an exponent.

Key Terms and Formulas:

• Metric Prefixes: micro (μ), milli (m), nano (n), kilo (k), etc.

• Scientific Notation:

Step-by-Step Guidance

1. Identify the exponent in the scientific notation: .

2. Recall the metric prefix that corresponds to , which is micro (μ).

3. Rewrite the value using the micro prefix: .

4. Check that the units are correct and that no exponents remain.

Try solving on your own before revealing the answer!

Q2. The number 0.000539 is which number in scientific notation?

Background

Topic: Scientific Notation

This question tests your ability to convert a decimal number into scientific notation, which is a standard way to express very small or very large numbers in chemistry.

Key Terms and Formulas:

• Scientific Notation: , where is a number between 1 and 10, and is an integer.

Step-by-Step Guidance

1. Count the number of decimal places the decimal point must move to get a number between 1 and 10.

2. Move the decimal point to the right until you have .

3. Each move to the right increases the negative exponent by 1.

4. Set up the scientific notation: .

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Q3. What is the density of a piece of magnesium metal measuring 5.30 cm x 3.25 cm x 1 cm and with a mass of 30.0 g?

Background

Topic: Density Calculations

This question tests your ability to calculate density, a fundamental property in chemistry, using mass and volume.

Key Terms and Formulas:

• Density ():

• Volume of a rectangular solid:

Step-by-Step Guidance

1. Calculate the volume: .

2. Multiply the values to find the volume in cm3.

3. Use the mass given: .

4. Set up the density formula: .

Try solving on your own before revealing the answer!

Q4. What is the chemical symbol for element X with 54 electrons and a charge of +2?

Background

Topic: Atomic Structure and Chemical Symbols

This question tests your understanding of how to determine the chemical symbol of an element based on its electron count and charge.

Key Terms and Formulas:

• Atomic Number: Number of protons in the nucleus

• Charge: Positive charge means loss of electrons

• Neutral atom: Number of electrons = atomic number

Step-by-Step Guidance

1. Recall that a +2 charge means the atom has lost 2 electrons.

2. Calculate the atomic number: (since the neutral atom would have 56 electrons).

3. Find the element with atomic number 56 on the periodic table.

4. Identify its chemical symbol.

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Q5. The daily recommended limit for sodium is 2,300 mg. How many nanograms of sodium is this limit?

Background

Topic: Unit Conversions (Metric System)

This question tests your ability to convert between different units of mass, specifically from milligrams (mg) to nanograms (ng).

Key Terms and Formulas:

• 1 mg = g

• 1 ng = g

• Conversion factor:

Step-by-Step Guidance

1. Start with the value: .

2. Convert mg to g: .

3. Convert g to ng: .

4. Combine the conversion factors to get the value in nanograms.

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Free Response Example 1: What is the mass to four decimal places for K-41?

Background

Topic: Isotopes and Atomic Mass

This question tests your understanding of isotopic masses and how to use percent abundance to calculate atomic mass.

Key Terms and Formulas:

• Isotope: Atoms of the same element with different numbers of neutrons

• Percent Abundance: The percentage of each isotope in nature

• Atomic Mass Formula:

Step-by-Step Guidance

1. List the percent abundances for K-39 and K-40.

2. Subtract their abundances from 100% to find the abundance of K-41.

3. Set up the atomic mass equation using the given masses and abundances.

4. Rearrange the equation to solve for the mass of K-41.

Try solving on your own before revealing the answer!

Free Response Example 2: What is the maximum safe content of cadmium in a 45.0 pound child? [Give the value to 3 significant figures, in ng of cadmium.]

Background

Topic: Unit Conversions and Significant Figures

This question tests your ability to convert between units (pounds to kilograms, mL to dL, μg to ng) and apply significant figures.

Key Terms and Formulas:

• 1 pound = 453.6 g

• 1 kg = 1,000 g

• 1 dL = 100 mL

• 1 μg = 1,000 ng

Step-by-Step Guidance

1. Convert 45.0 pounds to kilograms.

2. Calculate the total blood volume: .

3. Convert mL to dL.

4. Multiply the blood volume by the maximum safe concentration (μg/dL).

5. Convert μg to ng.

Try solving on your own before revealing the answer!

Free Response Example 3: The fastest serve ever recorded in tennis is 151 miles per hour. The distance the tennis ball has to travel to the net once served is 11.89 meters. A. What is the tennis ball velocity in meters per second (m/s)? B. How many milliseconds (ms) does it take for the tennis ball to reach the net once served?

Background

Topic: Unit Conversions and Speed Calculations

This question tests your ability to convert units of speed and calculate time using distance and velocity.

Key Terms and Formulas:

• Speed:

• Unit conversions: miles to kilometers, hours to seconds

Step-by-Step Guidance

1. Convert 151 miles per hour to meters per second using conversion factors.

2. Set up the calculation for velocity in m/s.

3. For part B, use the formula .

4. Convert the time from seconds to milliseconds.

Try solving on your own before revealing the answer!

Q6. What is the mass of one atom of tungsten (W) in grams?

Background

Topic: Atomic Mass and Avogadro's Number

This question tests your ability to use atomic mass units and Avogadro's number to find the mass of a single atom.

Key Terms and Formulas:

• Atomic mass unit (amu):

• Atomic mass of tungsten (W): found on the periodic table

Step-by-Step Guidance

1. Find the atomic mass of tungsten (W) from the periodic table.

2. Multiply the atomic mass (in amu) by the conversion factor to grams.

3. Set up the calculation: .

Try solving on your own before revealing the answer!

Q7. One atom of an element has a mass of 4.480 x 10-23 g. What is the element? (1g = 6.022 x 1023 amu)

Background

Topic: Atomic Mass and Identification

This question tests your ability to convert mass in grams to atomic mass units and identify the element based on its atomic mass.

Key Terms and Formulas:

• Avogadro's number: atoms per mole

• Atomic mass unit (amu):

Step-by-Step Guidance

1. Convert the mass of the atom from grams to amu using the given conversion factor.

2. Set up the calculation: .

3. Compare the calculated atomic mass to known values on the periodic table.

Try solving on your own before revealing the answer!

Q8. How many cubic cm (cm3) are in a cubic cubit? How many liters? (1 cubit = 18.2 inches)

Background

Topic: Volume Conversions

This question tests your ability to convert between different units of length and volume, including inches, centimeters, and liters.

Key Terms and Formulas:

• 1 inch = 2.54 cm

• Volume of a cube:

• 1 cm3 = 1 mL; 1,000 cm3 = 1 L

Step-by-Step Guidance

1. Convert 18.2 inches to centimeters using the conversion factor.

2. Calculate the volume of a cube with this side length in cm.

3. Convert the volume from cm3 to liters.

Try solving on your own before revealing the answer!

Q9. Give the number of protons, neutrons, and electrons in 23Na. If Na forms an ion: what ion? Number of p, n, e?

Background

Topic: Atomic Structure and Ions

This question tests your understanding of atomic structure, including how to determine the number of protons, neutrons, and electrons in an atom and its ion.

Key Terms and Formulas:

• Atomic number: Number of protons

• Mass number: Number of protons + neutrons

• Electrons: Equal to protons in a neutral atom; adjust for ion charge

Step-by-Step Guidance

1. Find the atomic number of Na (sodium) on the periodic table.

2. Calculate the number of neutrons: .

3. For the ion, determine the charge and adjust the electron count accordingly.

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Q10. Give the number of protons, neutrons, and electrons found in the 88Sr2+ ion.

Background

Topic: Atomic Structure and Ions

This question tests your ability to determine the number of protons, neutrons, and electrons in a specific ion.

Key Terms and Formulas:

• Atomic number of Sr (strontium): Number of protons

• Mass number: Number of protons + neutrons

• Electrons: Adjust for ion charge

Step-by-Step Guidance

1. Find the atomic number of Sr on the periodic table.

2. Calculate the number of neutrons: .

3. For the 2+ ion, subtract 2 electrons from the neutral atom's electron count.

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Q11. An “average person” weighs 135 lbs. If the “average person” contains 0.008% selenium, what is the amount of selenium in the “person”?

Background

Topic: Percent Composition and Mass Calculations

This question tests your ability to calculate the mass of an element in a sample based on percent composition.

Key Terms and Formulas:

• Percent composition:

• 1 pound = 453.6 g

Step-by-Step Guidance

1. Convert 135 lbs to grams using the conversion factor.

2. Multiply the total mass by 0.008% (as a decimal).

3. Set up the calculation for the mass of selenium.

Try solving on your own before revealing the answer!