Chemistry Qtr 3 Review GuideStoichiometry of Chemical Reactions

GasesSolutions

Acid and Bases

Released Question 1A 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

Equation is balanced 1st!

The unknown and given is written underneath equation.

The formula or molecular weights are calculated for both unknown and given.

Substances not involved in the problem are crossed out!

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 2The 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 3At room temperature, which of the

following gases would have the fastest rate of diffusion?

A Nitrogen B XenonC HeliumD 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.

Study the graph below:Which law is being illustrated?

A Charles’ LawB Gay-Lussac’s LawC Boyle’s LawD Avogadro’s Law

Released Test Question 3

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 4Gas Temperature Pressure 1 0oC 1 atm 2 273oK 600 mmHg 3 0oK 1 atm

4 100oC 600 mmHgWhich of the four gases above is at STP?A) 1 C) 3B) 2 D) 4

• 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

About gases…

Released Question 5The boiling point of methanol is 64.7 °C. The

boiling point of methanol on the Kelvin scale is approximately —

A.-100 KB. 148.4 K C. 337.8 KD. 446 K

Released Question No. 6Gas A Gas B Gas C Gas D32.0 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

Released Question No. 7A 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 acidicB highly basicC slightly acidicD slightly basic

Acids and BasesDefinitions-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).

Released Question No. 8Consider 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. 10What is the molarity of a solution of

HNO3 if 2 liters of the solution contains 80 g of HNO3?

A 0.5 MB 0.63 MC 1 MD 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.