Module 1
A block of metal has a mass of 25.3 g and a volume of 4.2 cm³. What is its density, expressed with the correct number of significant figures?
6.0 g/cm^3
A compound is found to always contain 40% sulfur and 60% oxygen by mass, no matter the quantity or source. If you decompose a 10-gram sample of this compound, you obtain 4 grams of sulfur and 6 grams of oxygen.
Which fundamental law of chemistry is illustrated here? Briefly explain your reasoning.
Law of Definite Proportions
An organic compound has the molecular formula C6H12O6
How many moles are in 90 grams of this compound? What is the molecular mass?
0.5 mol
A laboratory technician has 250 mL of a 1.2 M potassium nitrate (KNO₃) solution. She wants to prepare 500 mL of a 0.60 M KNO₃ solution for an experiment. How much of the 1.2 M solution should be used, and how much water should be added to attain the desired concentration?
Use 250 mL of 1.2 M solution and add 250 mL of water to make 500 mL of 0.60 M solution.
You have 0.2 mol of NO2NO2 gas in a 1.5 L balloon and add 0.1 mol more. What is the new volume of the balloon?
2.25 L
A laboratory technician measures the length of a metal rod five times and obtains the following results in centimeters: 12.01, 12.03, 12.00, 12.02, and 12.01. The actual length of the rod is 12.40 cm.
Discuss whether the measurements are accurate, precise, both, or neither.
The technician's measurements are precise but not accurate.
An ion is represented as
Calculate the number of protons, neutrons, and electrons in this ion.
Also find the element this ion can represent
11 protons
12 neutrons
10 electrons
Na
Given the reaction:
Al(s) + Cl₂(g) → AlCl₃(s)
How many grams of aluminum chloride (AlCl₃) can be produced from 10.8 g of aluminum metal?
64.17 g
A solution has a hydrogen ion concentration of 1.8×10−5 M. What is the pH of this solution? Is this solution acidic, basic, or neutral?
4.74
Since pH < 7, the solution is acidic.
A sample of gas occupies 24 L at 9.0 atm and 275 K. If the volume changes to 20 L and the temperature to 300 K, what is the new pressure?
11.78 atm.
A scientist records the volume of a liquid as 2.75 cubic inches (in³). Convert this volume into liters (L), given that 1 inch = 2.54 cm.
0.0451 L
What is the name of Mn(NO₃)₂
Manganese(II) nitrite
For the reaction:
N₂ (g) + H₂ (g) → NH₃ (g),
If you start with 7.0 g of N₂ and 6.0 g of H₂,
Which reactant is limiting?
What is the maximum mass of ammonia (NH₃) formed?
Limiting reactant: N₂
8.51 g
When 35.0 mL of 0.200 M HCl is mixed with 40.0 mL of 0.150 M NaOH, does the resulting solution contain excess acid or excess base, or is it neutral?
0.00100 mol HCl excess
Solution is acidic with remaining HCl.
What volume of hydrogen gas at 299 K and 1.07 atm is produced when 55.8 g of zinc reacts with excess HCl?
19.6 L
A car travels at a speed of 90 kilometers per hour (km/h). Convert this speed into meters per second (m/s) and miles per hour (mph), knowing that 1 mile = 1.609 kilometers.
56 mph
What is the name of H₃PO₄
Phosphoric acid
A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. If the molar mass is 180 g/mol, determine its empirical and molecular formulas.
Empirical formula: CH₂O
Molecular formula: C₆H₁₂O₆
Aqueous solutions of silver nitrate (AgNO₃) and sodium chloride (NaCl) are mixed. Write the balanced molecular and net ionic equations for the reaction, and identify the precipitate formed.
Molecular Equation:
AgNO₃(aq)+NaCl(aq)→AgCl(s)+NaNO₃(aq)
Net Ionic Equation:
Ag⁺(aq)+Cl⁻(aq)→AgCl(s)
Precipitate: Silver chloride (AgCl)
A gas with unknown molar mass has a density of 1.853 g/L at 745.5 mmHg and 23.8°C. Calculate the molar mass of this gas using the ideal gas law principles.
46.03 g/mol.
A gas thermometer is calibrated in degrees Celsius. During an experiment, the temperature of the gas is recorded as 68°F. The volume of the gas at this temperature is measured to be 1.25 liters. If the gas volume varies directly with absolute temperature (in Kelvin) according to Charles’s Law, calculate the volume the gas would occupy at 293 K after heating.
1.25 L
An element has two naturally occurring isotopes: Isotope A with a mass of 63.93 amu and Isotope B with a mass of 65.93 amu. The average atomic mass of the element is given as 64.22 amu.
Calculate the percent natural abundance of each isotope.
A: 85.5 %
B: 14.5 %
12.915 g of a biochemical substance containing only carbon, hydrogen, and oxygen was burned in an atmosphere of excess oxygen. Subsequent analysis of the gaseous result yielded 18.942 g of carbon dioxide and 7.749 g of water. Determine the empirical formula of the substance.
CH₂O
In the reaction between zinc metal and copper(II) sulfate solution:
Zn(s)+CuSO₄(aq)→ZnSO₄(aq)+Cu(s)
Identify which element is oxidized and which is reduced. Write the corresponding half-reactions and state the oxidizing and reducing agents.
Oxidation (loss of electrons):
Zn(s)→Zn2+(aq)+2e−
Reduction (gain of electrons):
Cu²⁺(aq)+2e⁻→Cu(s)
Zinc is oxidized (reducing agent), and copper ion is reduced (oxidizing agent).
A 2.00 L container holds a gas mixture of helium, nitrogen, and neon at 255 K and a total pressure of 815 mmHg. Helium and nitrogen exert partial pressures of 201 mmHg and 351 mmHg, respectively. Calculate the mass of neon gas present.
0.67 g