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# Regents Chemistry Exam Practice Multiple Choice Questions and Answers: Solutions Topic

January 2023

15 Which term is used to express the concentration of an aqueous solution?

(1) parts per million

(2) heat of fusion

(3) pressure at 0°C

(4) volume at 0°C

Solution: One term used to express the concentration is parts per million. Others include molarity. You can find this in Table T on the Reference Table.

42 Based on Table G, what is the mass of KCl that must be dissolved in 200. grams of H2O at 10.°C to make a saturated solution?

(1) 15g

(2) 30. g

(3) 60.g

(4) 120. g

Solution: Note that table G shows solubility in 100 g of water and we are asked in 200 grams. Find 10.°C at the bottom and scroll up to the KCl line. It is about 30 grams. We must multiply by 2 since this is for 200 grams of water and the table is for 100grams. 30g*2 = 60g choice 3.

August 2022

16. Which unit can be used to express the concentration of a PbCl2(aq) solution?

(1) kelvins

(2) kilojoules per gram

(3) pascals

(4) parts per million

Solution: Concentration can be expressed in a variety of different units. If we look at Table T on the reference table, we see two formulas for concentration: parts per million and molarity (mol/L).

17. Compared to the freezing point and boiling point of water at 1.0 atm, a 0.5 M aqueous solution of NaCl at 1.0 atm has

(1) a lower freezing point and a lower boiling point

(2) a lower freezing point and a higher boiling point

(3) a higher freezing point and a lower boiling point

(4) a higher freezing point and a higher boiling point

Solution: When a compound gets dissolved in water (or any other pure solvent), it increases the boiling point of water (or that pure solvent) and decreases its freezing point. We have NaCl being dissolved in water. Therefore, we should expect the boiling point of solution to increase and freezing point to decrease as compared to water.

39. Based on Table G, which sample, when added to 100. grams of water and thoroughly stirred, produces a heterogeneous mixture at 20.°C?

(1) 20. g of KCl

(2) 20. g of KI

(3) 80. g of KCl

(4) 80. g of KI

Explanation: A heterogeneous mixture is not uniform. If all of KCl or KI would be dissolves in water, the mixture would be uniform and homogeneous. If it is heterogeneous, that means not all of the solute got dissolved. Looking at table G, if we are below the line (either KCl or KI for this question) that means the solution is unsaturated (more solute can be dissolved). If we are on the line that means solution is saturated, maximum amount of solute has been dissolved and above the line means supersaturated (more than maximum has been dissolved and will easily precipitate out).

First we identify all of the points on the graph. We locate the 20 degree temperature on the x axis. Then we locate the correct points of the grams of solute added (20 g and 80 g) as I have shown on the graph. 20 g of KCl fall under the KCl line making the solution unsaturated. 20 g of KI fall under the KI line making the solution unsaturated. 80 g of KI fall under the KI line making the solution unsaturated. 80 grams of KCl fall above the KCl line making the solution supersaturated, which will result in the solute precipitating (coming out of the solution). The will make the mixture heterogeneous.

40 How many milliliters of 1 M HCl(aq) must be diluted with water to make exactly 500 mL of 0.1 M HCl(aq)?

(1) 10 mL

(2) 50 mL

(3) 100 mL

(4) 5000 mL

Explanation: The formula for dilution is M1V1= M2V2 where M stands for molarity and V for volume. Now, all we have to do is plug our values in.

1M (X) = 0.1M (500ml)

X = 50 ml

June 2022

13 Based on Table F, which 10.-gram sample, when thoroughly mixed with 1 liter of water at room temperature, forms a heterogeneous mixture?

(1) ammonium chloride, NH4Cl

(2) potassium iodide, KI

(3) silver bromide, AgBr

(4) sodium nitrate, NaNO3

Solution: Table F on the Reference Table is a solubility table. A compound that is soluble will dissolve in water forming homogeneous mixture. A compound that is insoluble will not be able to dissolve in water and a heterogeneous mixture will be formed. Therefore, we are looking for something that is insoluble. If we look at AgBr, we see that Br- is soluble UNLESS it is combined with Ag^+, Pb^2+, or Hg2^2+

14 Compared to a 1.0 M NaCl(aq) solution at 1.0 atm, a 2.0 M NaCl(aq) solution at 1.0 atm has

(1) a lower boiling point and a lower freezing point

(2) a lower boiling point and a higher freezing point

(3) a higher boiling point and a lower freezing point

(4) a higher boiling point and a higher freezing point

Solution: When a solute is dissolved in pure solvent, like NaCl in water, it causes the boiling point to increase and the freezing point to decrease. Since 2.0 M NaCl(aq) solution has more NaCl dissolved than 1.0 M NaCl(aq) solution , it should have a higher boiling point and a lower freezing point.

41 Based on Table G, which solute sample in 100.g of water at 40.°C can produce a solution equilibrium in a closed system?

(1) 10. g KClO3

(2) 25 g NaCl

(3) 45 g KCl

(4) 55 g KNO3

Solution: Table G on the Reference Table is a solubility curve table. If we end up on the curve, this represents the maximum amount of solute dissolved in 100 g of water and equilibrium for the solution. First, we need to find 40.°C on the x-axis. Next, we need to find the curve for all the solutes in the answer choices. 10. g KClO3 is below the KClO3 curve. 25 g NaCl of NaCl at 40.°C is below the NaCl curve line. 45 g KCl at 40.°C is above the KCl curve. 55 g KNO3 at 40.°C is below the KNO3 curve.

August 2019

39 What is the molarity of 2.0 liters of an aqueous solution that contains 0.50 mole of potassium iodide, KI?

(1) 1.0 M

(2) 2.0M (3) 0.25 M

(4) 0.50M

Solution: Table T on the Reference Table provides the formula for molarity

molarity = moles of solute/liters of solution

Now, all we have to do is plug our numbers. Molarity = 0.5mol/ 2.0L = 0.25M

January 2019

15 A beaker contains a dilute sodium chloride solution at 1 atmosphere. What happens to the number of solute particles in the solution and the boiling point of the solution, as more sodium chloride is dissolved?

(1) The number of solute particles increases, and the boiling point increases.

(2) The number of solute particles increases, and the boiling point decreases.

(3) The number of solute particles decreases, and the boiling point increases.

(4) The number of solute particles decreases, and the boiling point decreases.

Solution: When more solute is dissolved in pure solvent, like sodium chloride in water, it causes the boiling point to increase and the freezing point to decrease.

37 A solution contains 25 grams of KNO3 dissolved in 200. grams of H2O. Which numerical setup can be used to calculate the percent by mass of KNO3 in this solution?

Solution: Table T on the reference table gives the formula for percent by mass calculation.

(Mass of part/ Mass of whole)*100

To calculate mass of whole we need to add 25 g with 200g and get 225 g

We get (25g/225g)*100

38 What is the molarity of 0.50 liter of an aqueous solution that contains 0.20 mole of NaOH (gram-formula mass = 40. g/mol)? (1) 0.10 M

(2) 0.20 M (3) 2.5 M

(4) 0.40 M

Solution:Table T on the Reference Table provides the formula for molarity

molarity = moles of solute/liters of solution

M = 0.20 mol/0.50L =0.40M

August 2018

40 A solution is prepared using 0.125 g of glucose, C6H12O6, in enough water to make 250. g of total solution. The concentration of this solution, expressed in parts per million, is

(1) 5.00 × 10^1 ppm

(2) 5.00 × 10^2 ppm

(3) 5.00 × 10^3 ppm

(4) 5.00 × 10^4 ppm

Solution: Table T on the Reference table gives a formula for calculating concentration expressed in parts per million. Parts per million = (mass of solute/ mass of solution)*1000000

Parts per million = (0.125 g/ 250. g )*1000000 = 500

January 2018

38 Based on Table F, which equation represents a saturated solution having the lowest concentration of Cl- ions

Solution: Table F on the Reference Table is a solubility table. A compound that is soluble, will dissolve in water. If an ionic compound dissolves in water, it will break into ions such as Cl-. We are looking for the lowest concentration of Cl- ions, which means we are looking for a compound that would not dissolve in water and would not dissociate into Cl- ions. NaCl, NH4Cl and KCl are all soluble in water. AgCl is insoluble in water.

39 What is the molarity of a solution that contains 0.500 mole of KNO3 dissolved in 0.500-liter of solution?

(1)1.00 M

(2) 2.00 M (3) 0.500 M

(4) 4.00 M

Solution: Table T on the Reference Table provides the formula for molarity

molarity = moles of solute/liters of solution

M= 0.500 mole /0.500 L = 1.00 M

June 2018

42 What is the concentration of an aqueous solution that contains 1.5 moles of NaCl in 500. milliliters of this solution? (1) 0.30 M

(2) 0.75 M (3) 3.0 M

(4) 7.5 M

Solution: Table T on the Reference Table provides the formula for molarity

molarity = moles of solute/liters of solution

Notice, that we are given milliliters and not liters. We need to first convert milliliters into liters.

500ml/1000 = 0.500 L

M = 1.5 moles/0.500 L

M=3.0 M

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