HighFour Chemistry Category C: Grades 9 – 10 Round 5 Tuesday, January 10, 2017 The use of calculator is required. Question #1 Question #2 Question #3 Question #4 Question #5 The elements arranged in a horizontal row are referred to as belonging to the same period. What is the chemical name of the element that begins the fifth period of the periodic table? 2.50 cm Calculate the density of a cube that has an edge of 2.50 cm and a mass of 144 grams. Express your answer in terms of g/cm3. 144 grams Nitrogen dioxide (NO2) is composed of nitrogen and oxygen. If the percent composition of O2 by mass is 69.55%, determine the mass of nitrogen (in grams) if the mass of NO2 is 500 grams. Suppose that a student is required to make some calculations, what will be the weighted average mass (amu) of two chlorine atoms with mass 35.0 amu each and four chlorine atoms with mass 37.0 amu? Hint: Solve first for the % abundance of each chorine atom. Ammonium nitrite (NH4NO2) decomposes to nitrogen (N2) and water (H2O). The reaction can be expressed as follows: NH4NO2 ⟶ N2 + H2O However, the chemical equation is unbalanced. How many moles of ammonium nitrite is required to balance to reaction? HighFour Chemistry Category C: Grades 9 – 10 Round 5 Tuesday, January 10, 2017 The use of calculator is required. Question #6 Below is a table showing the number of subatomic particles for neutral atoms of specific isotopes. Identify the missing blanks. Write your answer in the order as indicated in the table, separated by a comma. Question #7 Question #8 Question #9 Question #10 Isotopic Symbol %%&
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#.Mo Atomic Mass No. of No. of No. of Number Number Protons Neutrons Electrons 49 115 49 66 49 (1) 80 34 (2) 34 42 96 42 54 42 The compound KClO3 is an inorganic compound that is white crystalline in appearance in its pure form. This compound is most commonly used as a disinfectant. What is the chemical name of KClO3? Potassium nitrate is an ionic salt of the element potassium, K. It is a natural solid source of nitrogen. One of its major uses is the production of fertilizers. What is the molar mass of KNO3? Calculate the mass of iodine (I2) that will completely react with 35 grams of aluminum (Al) to form aluminum iodide (AlI3). The unbalanced chemical equation for the above reaction is: Al + I2 ⟶ AlI3 Express your answer in terms of grams. If the main shell, n, has a value of 3, what values of ℓ𝓁 are permitted? HighFour Chemistry Category C: Grades 9 – 10 Round 5 Tuesday, January 10, 2017 The use of calculator is required. Question #11 Question #12 Question #13 Question #14 Question #15 Calculate the number of moles of magnesium chloride (MgCl2) present in 50.0 milliliters of 0.200 M MgCl2 solution. Tin(II) fluoride (SnF2) is often added to toothpaste as an ingredient to prevent tooth decay. What is the mass of F in grams if 1 tube (130 grams) of toothpaste is made up of 1.2 grams of SnF2? If the formula for calcium oxide is CaO, what are the formulas for magnesium oxide and strontium oxide? Write your answers accordingly. The atomic mass of element X is 34.42 amu. A 22.77-­‐gram sample of X combines with 81.00 grams of another element Y to form a compound XY. What is the atomic weight of Y? Express your answer in amu. Hint: The equation for this reaction is X + Y ⟶ XY What is the oxidation number of the atom underlined in IF7? HighFour Chemistry Category C: Grades 9 – 10 Round 5 Tuesday, January 10, 2017 The use of calculator is required. Question #16 Question #17 Question #18 Question #19 Question #20 A 50.0-­‐mL of 0.500 M glucose solution is mixed with 150.0-­‐mL pf 2.50 M glucose solution. What is the concentration of the final solution? The chemical formula for glucose is C6H12O6. Hint: The volumes are additive. How much volume of 2.00 M HCl solution is needed to prepare 1.00 L of 0.450 M HCl solution? A sample of unknown gas stored in a container of volume 1.75 L and at a room temperature of 296 degree Kelvin exerts a pressure of 4.45 atm. What is the number of moles of the gas present? Methane gas with a volume of 35.5-­‐L is heated from 25°C to 90°C at a constant pressure. What is the final volume of methane? What is the frequency (in Hertz) of a wave whose speed and wavelength are 700 m/s and 1.20 meters, respectively?