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Chem 1800 Midterm 1 solutions. It has questions and answers
Typology: Exams
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(2 marks) Answer to the correct number of significant figures:
(1 mark) The average distance between nitrogen and oxygen atoms is 115 pm in a compound called nitric oxide. What is this distance in millimeters?
(2 marks) An automobile uses gasoline at a rate of 36.8 mi/gal, which is the same as ________ km/L. Note: 1 km = 0.6214 mi, 1 gal = 3.78 L
(3 marks) A student prepared a stock solution by dissolving 20.0 g of KOH in enough water to make 150. mL of solution. She then took 15.0 mL of the stock solution and diluted it with enough water to make 65.0 mL of a final solution. What is the concentration of KOH for the final solution?
(4 marks) Dibutyl succinate is an insect repellent used against household ants and roaches. Its composition is 62.58% C, 9.63% H, and 27.79% O. What is the empirical formula?
(9 marks) Determine the number of milliliters of 0.00358 M phosphoric acid required to neutralize 25.00 mL of 0.00203 M calcium hydroxide. Be sure to include the balanced molecular equation.
Stoichiometry = mass to mole relationships used in chemical calculations
General scheme is: given n = m/MM mol ratio desired m = n x MM
Reducing agent = a substance that cause a reduction by donating an electron
Titration = an analytical procedure for determining the concentration of an unknown
solution
General scheme is: given n = C x V mol ratio desired C = n/V
Base = a substance that provides hydroxide (OH-) ions when dissolved in water
Precipitation reaction = a reaction in which an insoluble solid precipitate forms from
the mixture of two soluble aqueous solutions
Bonus:
Answer the following about the periodic table:
a) The elements of the periodic table can be categorized into three groups. What are the names of these groups? i) What are the properties of the elements in these groups? b) What are the columns of the periodic table called? i) How are the elements in the same column related? c) What are the rows of the periodic table called?
a) Metals, non-metals, and metalloids (semi-metal) i) Metals are found in the lower left side and middle of the periodic table and share common properties – they are good conductors of heat and electricity, they can be pounded into flat sheets (malleability), they can be drawn into wires (ductility), they are often shiny (called a metallic luster), and they tend to lose electrons when they undergo chemical changes. ii) Nonmetals are found in the upper right side of the periodic table. The dividing line between metals and nonmetals is the zigzag diagonal line running from boron to astatine. Nonmetals have varied properties – some are solids at room temperature, others are liquids or gases – but as a whole, they tend to be poor conductors of heat and electricity and they all tend to gain electrons when they undergo chemical changes. iii) Metalloids exhibit mixed metal and nonmetal properties. In most respects, metalloids behave as nonmetals, both chemically and physically. However, in their most important physical property, electrical conductivity, they sometimes resemble metals. Several metalloids are classified as semiconductors because of their intermediate (and highly temperature dependent) electrical conductivity. b) Columns in the periodic table are called groups or families i) Elements in the same group have similar chemical properties c) Rows in the periodic table are called periods