chemistry 5.4, 6.1-4

1. Select the answer that shows the words in the correct order to complete the passage.

Molarity is defined as the _________ per _________.  A solution with lower amounts of solute is called a _________ solution, while a solution with higher amounts is called a ____________ solution.

• 1. moles of solute; liters of solution; diluted; concentrated

• liters of water; moles of solute; concentrated; diluted

• grams of solute; liters of solution; diluted; concentrated

• liters of solution; moles of solute; concentrated; diluted

What is the molarity of a solution that contains 78.5 g of copper(II) chloride in 1.50 L of solution?

• 52.3M

• 0.390M

• 1.14M

• 0.585M

1. A student is asked to prepare 400.0 mL of a 0.25M HCl solution. The students find a bottle labeled “2.0M HCl”.  How many mL of the 2.0M solution are needed to prepare the 0.25M solution?

• 25 mL

• 3.0 x 10¹ mL

• 5.0 x 10¹ mL

• 2.0 x 10² mL

5. When performing reactions, chemists often begin with solutions of a compound rather than its solid form. One of the reasons this is done is so chemists do not need to wait for the solid to dissolve. 

A chemist is given a 3.00M solution of KBr and needs to measure out 0.733 moles of this solution. How many mL of the 3.00M KBr solution would the chemist need?

• 244 mL

• 4.09 mL

• 2.20 mL

• 1. 212 mL

Vinegar is sold as a 5.00% (v/v) solution of acetic acid. How many mL of water is in a 455 mL bottle of vinegar?

• 23 mL

• 1. 91 mL

• 432 mL

• 455 mL

Hydrogen peroxide decomposes to form water and oxygen. Manganese dioxide is used in the reaction to increase the rate of the reaction and remains unchanged by the end of the reaction. What are the reactant(s), catalyst, and product(s), respectively for the decomposition reaction of hydrogen peroxide?

• hydrogen peroxide and oxygen; manganese dioxide; water

• hydrogen peroxide; manganese dioxide; water and oxygen

• water and oxygen; hydrogen peroxide; manganese dioxide

• water and oxygen; manganese dioxide; hydrogen peroxide

A large amount of heat energy was supplied during a combustion reaction. While writing the chemical equation, which of the following symbols should be used to represent the heat supplied during the reaction?

• a plus sign

• the letter “h” in parentheses

• a triangle placed above the yield sign

• two half arrowheads pointing in opposite directions

1. The skeleton chemical equation for the reaction between zinc metal and hydrochloric acid is shown.

     

Zn + HCl → ZnCl₂ + H₂

     

What should be done to balance the equation?

• change the subscript in H2 to 1

• put a coefficient 2 in front of Zn

• 1. put a coefficient 2 in front of HCl

• change the subscript in ZnCl2 to 1

1. The chemical equation for a reaction between nitrogen and oxygen is shown.

     

N₂ + O₂ → 2NO

     

The energy diagram for the reaction is shown in the image.

Based on the diagram, which statement best describes the energy change during the reaction?

• Energy is absorbed during the reaction because less energy is required to break the bonds than to form new bonds.

• Energy is released during the reaction because more energy is required to break the bonds than to form new bonds.

• Energy is released during the reaction because the bond energy of the reactants is lower than the bond energy of the products.

• Energy is absorbed during the reaction because the bond energy of the reactants is higher than the bond energy of the products.

1. Therapeutic cold packs are particularly beneficial in relieving pain due to athletic and sports injuries. The cold packs developed initially contained toxic chemicals. To make these packs more suitable for use of the general public, a researcher developed a cold pack composed of non-toxic chemicals such as urea, sodium acetate, potassium chloride, ammonium chloride, and quar gum. When a reaction is triggered between these chemical substances, temperature as low as −7℃ are achieved and are reportedly retained for a minimum of 30 minutes. What best explains the type of reaction that takes place in a cold pack?

• An endothermic reaction which lowers the temperature of the reaction surroundings.

• An endothermic reaction which lowers the temperature of the reaction system.

• An exothermic reaction which lowers the temperature of the reaction surroundings.

• An exothermic reaction which lowers the temperature of the reaction system.