Examples and Problems only, no solutions

Ten Examples | Problems #1 - 10 | Problems #11 - 20 | Return to Mole Table of Contents |

Determine empirical formula when given mass data

Determine empirical formula when given percent composition data

Determine identity of an element from a binary formula and a percent composition

Determine molecular formula using the Ideal Gas Law

Determine the formula of a hydrate Hydrate lab calculations

**Example #1:** 100.0 g of XF_{3} contains 49.2 g of fluorine. What element is X?

**Example #2:** A 1.443 g sample of an unknown metal is reacted with excess oxygen to yield 1.683 grams of an oxide known to have the formula M_{2}O_{3}. Calculate the atomic weight of the element M and identify the metal.

**Example #3:** When the element A is burned in an excess of oxygen, the oxide A_{2}O_{3}(s) is formed. 0.5386 g of element A is treated with oxygen and 0.711 g of A_{2}O_{3} are formed. Identify element A.

**Example #4:** A 2.89 g sample of osmium oxide, Os_{x}O_{y}, contains 2.16 g of osmium. What are the values of x and y?

**Example #5:** 7.8 g of an element X reacts with oxygen to form 9.4 g of an oxide X_{2}O. What is the relative atomic mass of X? What is the element X?

**Example #6:** A 64.8 g sample of the compound X_{2}O_{5} contains 48.0 g of oxygen atoms. What is the atomic weight of element X? What element is element X?

**Example #7:** The chloride of an unknown metal is believed to have the formula MCl_{3}. A 1.603 g sample of the compound is found to contain 0.03606 mol of Cl. Determine the atomic weight of element M and identify it by name.

**Example #8:** The 64.8 g sample of the compound X_{2}O_{5} contains 48.0 grams of oxygen atoms. What is the molar mass of element X? What is the identity of element X?

**Example #9:** A 47.3 g sample of the compound X_{3}(PO_{4})_{2} contains 8.78 g of phosphorus. Identity X

**Example #10:** A 30.6-g sample of the compound M_{2}O_{3} contains 14.4 g of oxygen atoms. What is the molar mass of element M? Identify the element M most probably is.

**Problem #1:** An unknown metal M reacts with oxygen to give the metal oxide MO_{2}. Identify the metal based on the following information.

mass of metal: 0.356 g

mass of metal oxide: 0.452 g

**Problem #2:** 16.5 g of element X reacts completely with 9.6 g of oxygen to produce a pure sample of XO_{2}. Find the atomic weight and identity of X.

**Problem #3:** An element reacts with bromine to give the bromide, MBr_{5}. If 2.009 g of the element gives 10.648 g of MBr_{5}, what is the element?

**Problem #4:** A student places 5.00 g of an unknown metal (X) ribbon in a crucible. The crucible is heated until the unknown metal reacted with oxygen to form a white product with the formula X_{2}O_{3} . The mass of product is determined to be 7.19 g.

(a) What is the molar mass of the unknown metal (X)?

(b) What element is the unknown metal?

**Problem #5:** A 30.6-g sample of the compound M_{2}O_{3} contains 9.79 g of oxygen atoms. What is the molar mass of element M? Identify the element M most probably is.

**Problem #6:** From a specific heat measurement, the approximate atomic weight of a metal (M) is found to be 135 Daltons. A 0.2341 g sample of M is heated to constant weight in air to convert it to the oxide The weight of the residue is 0 2745 g Find the true atomic weight of the metal (and therefore its identity), and determine the formula of the metal oxide.

**Problem #7:** Identify M in the compound M_{2}(C_{2}O_{4})_{3} if the mass of the M atoms is 1371 g in a sample containing 5.92 x 10^{24} molecules of M_{2}(C_{2}O_{4})_{3}

**Problem #8:** If 3.72 g of element X exactly reacts with 4.80 g of oxygen to form a compound whose molecular formula is shown, from other experiments to be X_{4}O_{10}, what is the relative atomic mass of X? What element is X?

**Problem #9:** Determine the atomic weight of element A, given that 8.00 g of A_{2}O_{3} contains 2.40 g of oxygen.

**Problem #10:** A 2.00 g sample of a metal X (that is known to form X^{2+} ions) was added to 0.100 L of 0.500 M H_{2}SO_{4}. After all the metal had reacted, the remaining acid required 0.0637 L of 0.500 M NaOH solution for neutralization. Calculate the atomic weight of the metal and identify the element.

**Problem #11:** 11.2 g of a metal carbonate, containing an unknown metal, M, was heated to give the metal oxide and 4.40 g CO_{2}. What is the identity of the metal M?

**Problem #12:** A certain metal oxide has the formula MO where M denotes the metal. A 39.46 g sample of the compound is strongly heated in an atmosphere of hydrogen to remove oxygen as water molecules. At the end, 31.70 g of the metal is left over. Given that O has an atomic mass of 16.00 amu, calculate the atomic mass of M and identify the element.

**Problem #13:** A 30.6 g sample of the compound X_{2}O_{3} contains 14.4 g of oxygen atoms. What is the atomic mass of element X?

**Problem #14:** Given a solution of XCl_{2} has a molar concentration of 0.0250 mol dm¯^{3} and a mass concentration of 2.375 g dm¯^{3}, find the relative atomic mass of X and identify its most probable identity.

**Problem #15:** In an experiment, hydrogen gas was passed over the metal oxide, MO_{x}. It was found that the mass of the oxide was reduced from 1.59 g to 1.27 g. (a) Calculate the percentage composition of metal M and oxygen in the metal oxide. (b) Then, find the value of x if the molar mass of the oxide is 79.5 g/mol and identify element M.

**Problem #16** A chloride of a metal M contains 65.5% chlorine. The mass of 0.100 L vapour of metal chloride at STP is 0.72 g. What is the empirical formula of the metal chloride? Identify what element M most probably is.

**Problem #17:** 31.87 g of a solid compound, known to have the formula X_{3}N_{2}, is produced when 25.85 g of element X is reacted with excess nitrogen. What is the molar mass of the element and what is the name of the element?

**Problem #18:** 1.250 g of a metal, M, is reacted with excess sulfuric acid, yielding 1.860 g of a compound whose molecular formula is MSO_{4}. Determine the identity of the element M.

**Problem #19:** A metal oxide of formula M_{x}O is heated until it completely decomposes into the pure metal and oxygen gas. it was found that 11.71 g of oxygen was produced when 69.00 g of the oxide decomposed. What is the identity of M?

**Problem #20** A metal X forms two different chlorides. 12.7 g of chloride A contain 7.10 g and 16.3 g of chloride B contains 10.7 g of chlorine. Determine the formula of the compound.

Ten Examples | Problems #1 - 10 | Problems #11 - 20 | Return to Mole Table of Contents |

Determine empirical formula when given mass data

Determine empirical formula when given percent composition data

Determine identity of an element from a binary formula and a percent composition