Chemistry Qtr 3 Review Guide Stoichiometry of Chemical Reactions Gases Solutions Acid and Bases

Released Question 1 A mass of 6.0 grams of Carbon disulfide reacts with an excess of Chlorine gas, as shown in the unbalanced equation below: CS2 + Cl2 - CCl4 + S2Cl2 Approximately, what mass of carbon tetrachloride is produced? A 3 g C 76 g B 12 g D 152 g Answer is 12 g

Problem is solved! Equation is balanced 1st! The unknown and given is written underneath equation. Substances not involved in the problem are crossed out! The formula or molecular weights are calculated for both unknown and given. Problem is solved!

When solving stoichiometry problems involving chemical reactions… 1. Check if the equation is balanced or unbalanced. If not, balance it! 2. Write the given and unknown underneath the balanced equation and cross out all reactants and products NOT involved in the problem. 3. Derive the mole-to-mole relationship between the given and unknown by using the coefficients in the balanced equation. 4. Solve!

Released Question 2 The set up shown below was used to describe the atmospheric pressure at sea level: How might this same set up look like when taken to lower altitudes? A Height “h” will be shorter. B Height “h” will be longer. C Height “h” will be remain the same. D Height “h” will equal to 0.

Pressure… Defined as Force per Unit Area. The SI unit for pressure is the Pa (Pascal) which is equivalent to 1 Newton of force acting on one square meter. Since gas particles are constantly in motion, they bump into each other and against the walls of the container this creates pressure. Other units: 1 atm = 760 mmHg = 101, 325 Pa

Released Test Question 3 At room temperature, which of the following gases would have the fastest rate of diffusion? A Nitrogen B Xenon C Helium D Oxygen

Diffusion of gases… Occur spontaneously as gas particles are in constant motion. Can be described by stating its rate or how ‘fast’ the particles move randomly. NET movement is from areas of high pressure to areas of low pressure. Molecular weight affects diffusion rate. Heavier molecules diffuse slower.

Released Test Question 3 Study the graph below: Which law is being illustrated? A Charles’ Law B Gay-Lussac’s Law C Boyle’s Law D Avogadro’s Law Charles’ Law

About gases… Charles’ Law: describes the relationship between the volume of a gas and how it relates to temperature Boyles’ Law: describes the relationship between the volume of a gas and how it relates to pressure.

Released Test Question 4 Gas Temperature Pressure 1 0oC 1 atm 2 273oK 600 mmHg 3 0oK 1 atm 4 100oC 600 mmHg Which of the four gases above is at STP? A) 1 C) 3 B) 2 D) 4

About gases… Any 1-mole sample of a gas, will occupy a volume of 22.4 L, at STP. What is STP? Standard Temperature and Pressure (conditions defined by a temperature of 0oC and 1 atm of pressure). An ‘ideal gas’ is a gas that behaves as describes by all the gas laws. The ideal gas constant is 0.0821 L-atm/oK-mol

Released Question 5 The boiling point of methanol is 64.7 °C. The boiling point of methanol on the Kelvin scale is approximately — A. -100 K B. 148.4 K C. 337.8 K D. 446 K Answer is C.

Released Question No. 6 Gas A Gas B Gas C Gas D 32.0 g 4.0 g 70.9 g 83.8 g All four gases described above occupy a volume of 22.4 L at STP. Gas A is most likely... A N2 B He C O2 D Kr C. Oxygen gas

Released Question No. 7 A student was assigned to take water samples from a lake near his home. He measured the pH of one of the water samples to be 7.5. Which of the following best describes this sample of water? A highly acidic B highly basic C slightly acidic D slightly basic

Which is the BL acid and which is the BL base? Acids and Bases Definitions- 1) Bronsted-Lowry Acid: any substance that can donate a hydrogen ion (proton). 2) Bronsted-Lowry Base: any substance that can accept a hydrogen ion (proton). Which is the BL acid and which is the BL base?

Released Question No. 8 Consider this chemical equation: In this reaction, why is the ammonia considered a base? A NH3 increases the hydronium ion concentration. B NH3 decreases the hydroxide ion concentration. C NH3 accepts a proton. D NH3 donates a proton.

Solutions… Components of Solution- a. Solvent: present in greatest quantity b. Solute: all other substances dissolved in the solvent. Equilibrium: Soluteundissolved Solutedissolved Ions dissolved in polar solvents are ‘hydrated’; they more around the solution surrounded by water molecules.

Molarity of Solution refers to the number of moles of solute present per liter of solution.

Released Question No. 10 What is the molarity of a solution of HNO3 if 2 liters of the solution contains 80 g of HNO3? A 0.5 M B 0.63 M C 1 M D 4 M

Step 1. We need moles for the Molarity Formula- so start by converting gHNO3 to moles. Step 2. Use the Molarity Formula to calculate molarity. Plug “grams” HNO3.