Which compound contains the highest percentage of magnesium by mass?

In the diagram above the paired open spheres represent H₂ molecules and the paired solid spheres represent N₂ molecules. When the molecules in the box react to form the maximum possible amount of ammonia (NH₃) molecules, what is the limiting reactant and how many molecules of NH₃ can be formed?

Vanillin, C₈H₈O₃ (M = 152 g/mol), is the molecule responsible for the vanilla flavor in food. How many oxygen atoms are present in a 45.0 mg sample of
vanillin?

The solubility of K₂Cr₂O₇ in water is 125 g/L at 20 °C. A solution is prepared at 20 °C that contains 6.0 grams of K₂Cr₂O₇ in 50. mL of water. This solution is

What is the molarity of sodium ions in a solution prepared by diluting 250. mL of 0.550 M Na₂SO₄ to 1.25 L?

Which of the following is a weak electrolyte in aqueous solution?

Which list gives nonmetals that are found in their elemental forms in nature?

Which one of the following cannot act as an oxidizing agent?

Which substance is the primary component in stalactites and stalagmites in caves?

Five successive determinations of the density of an alloy gave the following results: 10.29 g/mL, 9.95 g/mL, 10.06 g/mL, 9.89 g/mL, 10.18 g/mL
What value should be reported for the density of this alloy?

A student is asked to analyze a water sample from a stream for total solids (TS), dissolved solids (DS), and suspended solids (SS). She carries out the experiments below.

1. A 25-mL portion of the water sample is evaporated to dryness in a pre-weighed evaporating dish to give mass 1.

2. A separate 25-mL portion is filtered into a second preweighed evaporating dish and evaporated to dryness to give mass 2.

How are values for TS, SS and DS (per 25 mL water) determined?

Which method(s) can be used to determine the concentration of HNO3 in an aqueous solution of nitric acid?

I titration with a standard base
II titration with a standard oxidizing agent
III precipitation with Ag+

The kinetic theory of gases assumes all of the following EXCEPT:

A sample of He gas in a flexible container at room temperature exhibits a certain pressure. What will be the new pressure when the absolute temperature and volume of the container are both halved? The pressure of the He will be

The molecules in a sample of pure liquid dichloromethane, CH2Cl2, experience which of the following intermolecular forces?

I dispersion forces
II dipole-dipole forces
III hydrogen bonding

Which property best distinguishes metals from other types of solids?

What type of solid is silicon carbide, SiC?

The normal boiling point and vapor pressure at 25 °C are measured for liquids in two flasks. Flask A contains pure water and flask B contains a 1.0 M aqueous NaCl solution. Which flask contains the liquid with the higher boiling point? Which flask contains the liquid with the higher vapor pressure?

Higher boiling point                                          Higher vapor pressure

Given chemical equations for these reactions
S(s) + O₂(g) → SO₂(g) ΔH˚= –296.8 kJ•mol^–1
H₂(g) + ½ O₂(g) → H₂O(l) ΔH˚= –285.8 kJ•mol^–1
H₂(g) + S(s) → H₂S(g) ΔH˚= –20.6 kJ•mol^–1

What is the value of ΔH for the reaction below?
2 H₂S(g) + 3 O₂(g) → 2 H₂O(l) + 2 SO₂(g)

Consider the following reactions
I    2 NO₂(g) → N₂(g) + 2 O₂(g)
II  2 IBr(g) → I₂(s) + Br₂(l)

For which reaction is ΔS° < 0?

Calculate the energy released by the reaction
4 Fe(s) + 3 O₂(g) → 2 Fe₂O₃(s)
when a 55.8 g sample of iron reacts completely with 1.00 mole of oxygen. The enthalpy of formation (ΔH_f˚) of Fe₂O₃(s) is –826 kJ•mol^–1.

The specific heat capacities of three metals are given below.

If 1.00 g of each metal is heated to 100 °C and added to 10.0 g of H₂O at 25.0 °C, what is the order of the temperatures of the final mixtures from the lowest to the highest?

The enthalpy of formation, ΔH_f˚, equals zero at 25 °C for which of the following in their standard states?

Liquid water is injected into an oven at 400 K. What are
the signs for ΔG, ΔH, and ΔS for the physical
transformation that occurs?

C(s) + CO₂(g) → 2 CO(g) ΔH = 172 kJ•mol^–1
In a suitable reaction vessel, pieces of graphite are mixed
with carbon dioxide gas at 1.00 atm and 1000 K. Which
of the following changes will result in an increase in
reaction rate?

The reaction CH3NC → CH₃CN is first order. Which
reaction characteristic changes as the reaction proceeds?

A(g) + B(g) → C(g)
The data below were obtained for the reaction between A and B. What is the rate law for this reaction?

A first-order reaction is carried out at several different temperatures. The data are plotted as ln k vs 1/T. How is the slope of the graph related to E_a?

Which statement about the behavior of a catalyst is correct?

An endothermic reaction has a positive value for ΔS. Which of the following is true about the equilibrium constant for this reaction?

Phosphoric acid, H₃PO₄, establishes the following
equilibria in aqueous solution.
H₃PO₄(aq) + H₂O(l) H₃O+(aq) + H₂PO₄^– (aq)      K1
H₂PO₄^–(aq) + H₂O(l) H₃O⁺(aq) + HPO₄^2–(aq)     K2
HPO₄^2–(aq) + H₂O(l) H₃O⁺(aq) + PO₄^3–(aq)         K3

What is the relationship among the K values?

Which pair of solutes could be used to prepare an aqueous buffer solution with a pH < 7?

What will be the result when 15.0 mL of 0.040 M lead(II) nitrate is mixed with 15.0 mL of 0.040 M sodium chloride?

PbCl₂(s) Pb²⁺(aq) + 2 Cl^–(aq) [K_sp = 1.7 × 10^–5]

What is the oxidation number of As in the compound K(NH₄)₂AsO₄•6H₂O?

When the equation

__ MnO^4–+ __ SO₃^2–+ __ H⁺ → __ Mn²⁺ + __ SO₄^2–+__ H₂O

is balanced correctly with the smallest whole number coefficients, what is the coefficient for H₂O?

According to the equations and data in the table above, which species is the strongest reducing agent of the following choices?

Use the E° values in the table above to determine which of the following reactions will give the highest potential in a voltaic cell.

The cell potential for the voltaic cell depicted below is 0.109 V under standard conditions, 1M Ni²⁺(aq) and 1 M Pb²⁺(aq).

Which change will increase the voltage?

Aluminum is produced commercially by the electrolysis of Al₂O₃. How many hours would be required to produce 250. g of Al using a 5.00 Ampere current?

A sulfur atom in its ground state has the electron configuration

1s² 2s² 2p⁶ 3s² 3p⁴

How many orbitals are occupied by at least one electron?

For which of the following transitions would a hydrogen atom absorb a photon with longest wavelength?

Which set of quantum numbers is not possible?

What property of the oxygen atom is represented by the equation O(g) + e^– → O^–(g)?

Which of the following isoelectronic species has the largest radius?

Which group best illustrates the transition from nonmetallic to metallic behavior with increasing atomic number?

Which atom is least likely to violate the octet rule in its compounds?

In the Lewis structure for formic acid, HCOOH, how many bonding pairs and lone pairs of electrons are present?

Which ionic compound has the largest lattice energy?

When 1.0 mole of H2O2 decomposes to form H₂O and O₂, 103 kJ of energy is released. Given the bond energies below, what is the bond energy of the O–O single bond in H₂O₂?

Which species has a different number of pi bonds than the others?

Which molecule is correctly matched with its shape as predicted by VSEPR theory?

Which of the following statements regarding structural isomers is correct? They have

What is the IUPAC name for the compound CH₃CH₂CH₂CH₂CHO?

Which compound will react rapidly with Br₂?

The reaction below is best classified as

CH₃OH + HCOOH → HCOOCH₃ + H₂O (acid catalizator is present – H⁺ )

Which element is not found in common amino acids?

Which of the following is not classified as a carbohydrate?