Question 1

If the reaction quotient is greater than the reaction equilibrium, that means:

Accepted Answer

If the reaction quotient is greater than the reaction equilibrium, then that means products need to become reactants for the equilibrium to be reached. Likewise, if Q is less than K, the reaction needs to proceed forward to equilibrium.

Question 2

Which of the following is not a state function?

Accepted Answer

Moles, a unit of concentration, is not a state function. A state function only depends on the 'state' of a system, and not the way the system went into that state. Thus, all concentration units are not state functions.

Question 3

Which of these statements regarding chemical thermodynamics is not correct?

Accepted Answer

Thermodynamically favorable processes do not always occur quickly. If the delta G is even slightly negative, it is favorable, but most likely the reaction will occur very slowly without a catalyst. Only at very large delta G levels will the process occur very quickly.

Question 4

Sean wants to determine the amount of energy released by the combustion of butane. Which instrument should he use?

Accepted Answer

A calorimeter is used to measure released energy. Specifically, a bomb calorimeter can be used to measure the amount of energy released by a reaction process.

Question 5

When ionic compounds, such as NaCl or KOH, enter water, they will:

Accepted Answer

When ionic compounds enter water, or any other polar solvent, they will dissociate. This is due to the nature of the ionic bond, which has a dipole moment, and the polarity of the solvent.

Question 6

Which of the following pairs of solutions will be miscible, in that they will mix easily with one another?

Accepted Answer

Ethanol and water are both polar substances, and will mix easily. The other pairs are all a combination of a polar and non-polar substance that will not mix. Acetic acid, as with all acids, are polar (otherwise they would not be acids) and will not mix with benzene.

Question 7

Which of the following is not a colligative property?

Accepted Answer

Generated heat of mixing is not a colligative property. Colligative properties are properties of solutions that are generated due to dissolved solutes. For example, adding salt to water will create an elevation of the boiling point of water.

Question 8

Which of the following compounds would, if dissolved in water, create the greatest difference in boiling point?

Accepted Answer

MgCl₂ will dissociate into 3 ions in water. Thus, a 1 molar solution of MgCl₂ is 3molality. The other compounds only dissociate into 2 ions in water. Keep in mind that hydrogen cyanide (HCN) dissolves into just H+ and CN-.

Question 9

Jamie has a flask containing 1 liter of water at 50°C. If she adds 1 mole of C6H14O? to the water, what will happen to the vapor pressure of the water?

Accepted Answer

The change in vapor pressure is relative to the molar ratio of the compounds dissolved. 1 liter of water contains 55 moles of water. Only 1 mole of solute has been added. Thus, the added solute will reduce the vapor pressure of the water, but not by much.

Question 10

Given that the boiling point constant(Kb) of water is 0.512, what will be the boiling point of 2 liters of water that has 200 grams of CaCl2 added?

Accepted Answer

The molar mass of CaCl2 is approximately 110 grams. Thus, 200 grams is 1.81 moles, and adding this to 2 liters of water results in a molarity of 0.9M. However, calcium chloride dissociates into three ions, so the molality is 2.7. ?T = Kb * N (where N is molality). Thus, ?T = 1.4 °C, so the new boiling point of water will be 101.4 °C.

Question 11

Alexander is hiking up Mt. Everest, and recently reached the base camp at 12,000 feet. While there, he decides to make some tea, and puts a thermometer in the boiling water. To his surprise, the thermometer tells him the water is boiling at 96 °C. Why is this happening?

Accepted Answer

At higher elevations, the atmospheric pressure is lower. At 12,000 feet, the atmospheric pressure is only 0.70 atm, compared to 1 atm at sea level. The reduction in pressure leads to a reduction in boiling temperature.

Question 12

Ming needs to add some salt solution to his algae culture to emulate seawater conditions. The only salt solution he has is 20% (w/v) of salt. He wants to make 5 liters of 1 molar salt solution. How much 20% salt solution should he add?

Accepted Answer

Salt has a molar weight of about 58.5 grams per mol. In a 20% w/v solution, we have 200 grams of salt. Thus, 1 liter of 20% salt will have 3.41 moles of salt. In order to make 5 liters of 1 molar salt solution, we need 5 moles of salt. 5/3.41 = 1.46 liters needed to provide 5 moles of salt.

Question 13

What is the primary difference between a molecular solution and an ionic solution?

Accepted Answer

In a molecular solution, the dissolved solute does not dissociate. In an ionic solution, the dissolved solute will dissociate into ions. Because of this, ionic solutions can conduct electricity, but molecular solutions cannot.

Question 14

Which of the following compounds is completely insoluble in water?

Accepted Answer

Silver chloride is completely insoluble in water. It should be recognized that the only soluble silver compound is silver nitrate, and a common precipitation reaction is the mixing of silver nitrate with magnesium chloride, resulting in the precipitation of the insoluble silver chloride.

Question 15

Which of the following nitrate compounds is insoluble in water?

Accepted Answer

This is sort of a trick question, because all nitrate compounds are soluble in water. Usually, lead compounds are not soluble in water, with the exception of lead nitrate.

Question 16

Amanda is trying to determine the solubility of nickel chloride (NiCl2) in water. She finds that her 1 liter saturated solution has 0.55 M of chloride ions. What is the solubility of nickel chloride?

Accepted Answer

If a saturated solution has 0.55 M of chloride ions, then that means 0.275 moles of nickel chloride have dissolved. 1 mole of nickel chloride weighs 129 grams. Thus, the solubility is 129 x 0.275 g/L, or 35.4g/L.

Question 17

If an oxidation reaction has occurred:

Accepted Answer

If an oxidation reaction occurs, a reduction reaction must also occur. Oxidation reactions involve the loss of electrons, but they must go somewhere. The accompanying gain of electrons is a reduction reaction.

Question 18

For the following reaction, what is the oxidation half reaction? O? + H?O + SO? ? SO?2- + O? + 2H+

Accepted Answer

The oxidation half reaction must result in the production of electrons in a balanced reaction. Answer C on the other hand, is the reduction half reaction, in which the addition of electrons results in a reduced sulfate product.

Question 19

In the following reaction, which species is becoming oxidized? CO?(g) + H?(g) CO(g) + H?O(g)

Accepted Answer

Hydrogen is becoming oxidized in this reaction. In its initial state, hydrogen's oxidation number is 0. After the reaction and formation of water, its oxidation number is now +1, meaning it lost an electron in the process, which is oxidation.

Question 20

A battery is a standard example of an electrochemical cell. Which part of a battery is being reduced when a battery is used?

Accepted Answer

In a standard battery, a chemical reaction results in the production of electrons (current) that powers whatever device the battery is hooked up to. The negative end of a battery produces electrons and the positive end receives them. The positive end is thus gaining electrons and is being reduced.

Quiz 35: Praxis II Elementary Education Content Knowledge