Practice for Exam I Ch1-3 ChemLibre

Steps to Solve Each Problem

1. Metric Conversion:

• Weight Conversion (145 pounds to kilograms):

  1. Convert pounds to grams: 145 lbs * 453.6 g/lb.

  2. Convert grams to kilograms (divide by 1000).

• Wingspan Conversion (10.0 feet to meters):

  1. Convert feet to inches: 10.0 ft * 12 in/ft.

  2. Convert inches to centimeters: result * 2.54 cm/in.

  3. Convert centimeters to meters (divide by 100).

2. Density Calculation:

• Volume of Human Fat (Density = 0.918 g/cm³, 10.1 pounds):

  1. First, convert 10.1 lbs to grams: 10.1 lbs * 453.6 g/lb.

  2. Use the density formula: volume = mass / density.

3. Significant Figures and Rounding:

• Report measurements to 3 significant figures:

  • Round 180,701.986 to 180,000.

  • Round 156.842 to 156.

• Calculations maintaining significant figures:

  • For 89.3 x 77.0 x 0.08, keep the least number of sig figs (2 in this case).

  • For (42.0217 x 3.00) + 838.80, the answer should be rounded to the least precise decimal place.

4. Dimensional Analysis and Conversion Factors:

• Ibuprofen Suspension (100 mg/5 mL, dose 10 mg/kg for 22.0 lb infant):

  1. Convert lbs to kg (22.0 lb / 2.20462).

  2. Calculate total mg needed: dose (mg/kg) * infant weight (kg).

  3. Convert mg to mL using suspension concentration.

5. Subatomic Particles and Ions:

• To determine ionic charges and subatomic counts:

  1. Look up the atomic number and mass number for the element.

  2. Calculate neutrons: mass number - atomic number.

  3. Assign predictable charges based on group placement in the periodic table.

6. Isotopic Abundance and Atomic Mass:

• Given 85Rb, calculate:

  1. Use the formula: (abundance of 85Rb * mass of 85Rb + abundance of 87Rb * mass of 87Rb) / 100 to find the mass of the other isotope.

7. Molar Mass Conversions and Mass Percent:

• Calculate grams for 0.0893 mols of Ca3(PO4)2:

  1. Find molar mass of Ca3(PO4)2.

  2. Multiply mols by molar mass for grams.

• Determine oxygen atoms in 145g of O2:

  1. Convert grams to moles (145 g / molar mass of O2).

  2. Multiply moles by Avogadro's number to find atoms.

8. Mass Percent and Grams Calculations:

• Find mass percent of copper in copper(I) oxide:

  1. Calculate molar mass of Cu2O.

  2. Divide mass of Cu by molar mass and multiply by 100.

• Calculate grams of hydrogen in 10.8 g of NH4NO3:

  1. Find molar mass of NH4NO3.

  2. Calculate grams of hydrogen based on proportion of hydrogen in the formula.

9. Empirical and Molecular Formulas:

• Empirical formula for nicotine:

  1. Convert percentages to grams (assume 100g total).

  2. Find moles for each element by converting grams to moles.

  3. Determine the mole ratio to find the empirical formula.

  4. Calculate molecular formula using given molar mass.

• Empirical formula of naphthalene from combustion products:

  1. Use the masses of CO2 and H2O to determine moles of carbon and hydrogen.

  2. Find the empirical formula based on proportions.

10. Formulas and Names for Compounds:

• Determine ionic formulas:

  1. Identify oxidation states of elements.

  2. Balance charge to find the correct formula.

• Naming compounds:

  1. Use rules for naming ionic and molecular compounds according to IUPAC guidelines.