Chem lecture exam 1

All of the following are properties of sodium. Which one is a physical property of sodium?

Ask if the substance's identity changes to be observed. Physical properties (e.g., density, state) do not change identity; chemical properties (e.g., reactivity) require a reaction to observe.

What would be the mass in pounds of a 1.0 ft × 1.0 ft × 1.0 ft cube of iridium (density 22.5 g/cm³)?

1. Calculate the volume of the cube ($length \times width \times height$). 2. Rearrange the density formula ($d = m/v$) to $m = d \times v$. Ensure volume units match the density unit denominator. 3. Convert units (e.g., ft to cm, g to lbs) using conversion factors.

Give the correct number of significant figures and units to the problem: (5.62 cm – 0.45 cm) / 342 s

1. Follow PEMDAS. 2. For addition/subtraction, align decimals and round based on the least precise decimal place. 3. For multiplication/division, count total significant figures and round to the fewest number present.

Express 7,500 nm as picometers.

Use dimensional analysis. Set up a conversion factor with the starting unit in the denominator and the target unit in the numerator so that the original unit cancels out.

A piece of metal with a mass of 611 g is placed into a graduated cylinder that contains 25.1 mL of water, raising the water level to 56.7 mL. What is the density of the metal?

1. Calculate the object's volume by finding the difference in water levels ($V_b - V_a$). 2. Divide the mass of the object by this calculated volume ($d = m/v$).

What type of compound is NH4NO3?

Classify based on composition: Ionic compounds contain a metal/polyatomic cation and a non-metal/polyatomic anion. Molecular compounds consist only of non-metals.

Name the compound Co2(SO4)3.

1. Identify the charges of the cation and anion. 2. If the cation is a transition metal, use the anion's total charge to determine the metal's specific oxidation state. 3. Write the metal name with the oxidation state in Roman numerals in parentheses.

Name the compound Cl2O5.

Use Greek prefixes to indicate the number of atoms for each element. The second element must end in the suffix "-ide." Do not use "mono-" for the first element.

How many electrons, protons, and neutrons are in a neutral atom of the following isotope of palladium (Pd)?

1. Protons = Atomic Number. 2. Electrons = Protons (for a neutral atom). 3. Neutrons = Mass Number - Protons.

Chlorine has isotopes Cl-35 (34.969 amu) and Cl-37 (36.966 amu), with a known average atomic mass of 35.453 amu. Find the % abundance of each.

Multiply each isotope's mass by its fractional abundance ($x$ and $1-x$), set equal to the average mass, and solve for $x$.

Sodium dichromate is a powerful industrial oxidizing agent. Determine its molecular mass.

Sum the atomic masses of all atoms present in the chemical formula (multiply each atomic mass by the number of atoms of that element).

What is the sum of the coefficient when the following equation is properly balanced: K4Fe(CN)6 + H+ + SO4^-2 + H2O → K+ + Fe+2 + NH4+ + CO?

Count the number of atoms of each element on both sides of the equation. Add coefficients to the compounds until the number of atoms for every element matches on both sides.

Calculate the number of moles in 14.7 g of the antacid magnesium hydroxide, Mg(OH)2.

Convert reactant mass to moles using the compound's molar mass (divide mass by molar mass).

Hydroxylammonium nitrate contains 29.17 mass % N, 4.20 mass % H, and 66.63 mass % O. What is its empirical formula?

1. Assume a 100g sample (so percentages become grams). 2. Convert each element's mass to moles. 3. Divide each mole value by the smallest mole value to find the simplest whole-number ratio.

How many grams of lead(II) chloride is produced if 13.87 g lead(II) nitrate combines with excess hydrochloric acid?

1. Convert reactant mass to moles using molar mass. 2. Use the mole ratio from the balanced equation to find product moles. 3. Convert product moles to product mass using the product's molar mass.

If 3.41 g of nitrogen react with 2.79 g of hydrogen to produce ammonia, what is the limiting reactant and what mass of ammonia is produced?

1. Calculate the amount of product each reactant can produce independently. 2. The reactant that produces the smaller amount of product is the limiting reagent; that smaller amount is the theoretical yield.

How many Cl atoms are in 0.0728 g of PCl3?

1. Convert the given mass to moles using the compound's molar mass. 2. Multiply the moles by Avogadro’s number ($6.022 \times 10^{23}$) and the number of atoms of the element per molecule.

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

1. Convert the given mass to moles using the compound's molar mass. 2. Multiply the moles by Avogadro’s number ($6.022 \times 10^{23}$).

Based on the solubility rules, which one of these compounds is soluble in water?

Apply established solubility rules (e.g., nitrates are generally soluble, certain silver/halide combinations are insoluble) to predict if a compound will form a precipitate.

Which of these compounds is a strong electrolyte?

Identify if the substance dissociates completely in water (e.g., strong acids, strong bases, or soluble ionic salts).

Which of these chemical equations describes a double displacement reaction?

Look for the ion arrangement: two aqueous ionic compounds swap cations/anions to form a precipitate, gas, or water.

What is reduced in the following reaction: Cu(NO3)2 + Zn → Zn(NO3)2 + Cu?

1. Assign oxidation states to all elements. 2. The element that decreases in oxidation state is reduced (gains electrons).

The oxidation number of Cr in NaCrO4 is?

Set the sum of all oxidation states equal to the overall charge of the ion (or 0 for a neutral compound). Assign oxygen a value of -2 and solve for the unknown element.

In the following chemical reaction the oxidizing agent is 5H2O2 + 2MnO4- + 6H+ → 2Mn2+ + 8H2O + 5O2

1. Assign oxidation states. 2. Identify the element that is reduced (the one that decreases in oxidation state). 3. The entire compound containing that element is the oxidizing agent.

A 3.682-g sample of KClO3 is dissolved in 375 mL of solution. What is the chlorate ion concentration?

1. Convert solute mass to moles using molar mass. 2. Convert solution volume to Liters. 3. Divide moles of solute by Liters of solution ($M = n/V$).

Which of these is not a state function?

Determine if the property depends only on the current state (e.g., temperature, pressure, volume) rather than the path taken (e.g., heat, work).

Which of the following is the enthalpy of formation chemical equation of carbon dioxide?

Write the reaction to form 1 mole of the compound from its constituent elements in their standard states.

A system expands from 1.00 L to 2.00 L against a constant external pressure of 1.00 atm. What is the work (w) done?

Use $w = -P\Delta V$ (Pressure $\times$ change in volume). Ensure volume is in Liters and use the conversion factor $1~L\cdot atm = 101.3~J$ to get the final answer in Joules.

Aluminum metal has a specific heat of 0.900 J/g·°C. Calculate the heat to raise 10.5 moles of Al from 30.5 °C to 225°C.

Use the formula $q = m \cdot c \cdot \Delta T$ (mass $\times$ specific heat $\times$ change in temperature). Ensure all units (mass, temperature) are consistent.

A Snickers® candy bar contains 280 Calories, of which the fat content accounts for 120 Calories. What is the energy of the fat content, in kJ?

1. Convert Calories to calories ($\times 1000$). 2. Convert calories to Joules ($\times 4.184$). 3. Convert Joules to kJ ($\div 1000$).

Convert 1205 mmHg to atm.

Divide the given pressure value by the conversion factor (760 mmHg = 1 atm) to obtain the pressure in the desired unit.

How many grams of carbon dioxide are contained in 750 mL of this gas at STP?

1. Use the molar volume of a gas at STP ($22.4~L/mol$) to calculate the number of moles. 2. Multiply the moles by the substance's molar mass to get grams.

6.0 L of gas in a piston at 1.0 atm are compressed until the volume is 3.5 L. What is the new pressure?

Use the appropriate gas law (e.g., $P_1V_1 = P_2V_2$) to solve for the missing variable. Ensure temperatures are in Kelvin.

A gas canister can tolerate 210 atm. If a 2.0 L canister holds 3.5 moles at 1350°C, will it explode?

Rearrange the Ideal Gas Law ($PV = nRT$) to solve for the pressure ($P = nRT/V$). Ensure P is in atm, V in Liters, and Temperature is in Kelvin ($T_C + 273$). Compare result to the limit.

Calculate the root-mean-square speed of methane, CH4 (g), at 98°C.

Use the formula $u = \sqrt{3RT/M}$. Use the gas constant $R = 8.314~J/mol\cdot K$ and ensure the Molar Mass ($M$) is in $kg/mol$ to result in $m/s$.