SBMPTN 2021 Chemistry Problem Solution Highest Freezing Point Explained

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Hey guys! 👋 Are you prepping for the SBMPTN and feeling a bit overwhelmed by chemistry questions? Don't worry, we've all been there! In this article, we're going to break down a tricky SBMPTN 2021 chemistry problem step-by-step. We'll focus on understanding freezing point depression and how to tackle similar questions in the future. So, grab your calculators and let's dive in!

Understanding Freezing Point Depression

Before we jump into the problem, let's quickly recap the concept of freezing point depression. This is a colligative property, which basically means it depends on the number of solute particles in a solution, not the type of particles. Think of it like inviting friends to a party – the more friends you invite (regardless of who they are), the more crowded the party gets! In chemistry terms, the more solute particles you dissolve in a solvent (like water), the lower the freezing point of the solution will be compared to the pure solvent.

Freezing point depression is a fascinating phenomenon governed by colligative properties. To truly grasp its essence, we need to delve a bit deeper into the underlying principles. When a solute is dissolved in a solvent, it disrupts the solvent's crystal lattice structure, making it more difficult for the solvent to solidify. This disruption arises because the solute particles interfere with the attractive forces between solvent molecules, hindering their ability to arrange themselves into the highly ordered structure characteristic of a solid. Consequently, a lower temperature is required to overcome this disruption and induce freezing.

The magnitude of freezing point depression is directly proportional to the concentration of solute particles in the solution. This relationship is quantified by the van't Hoff factor (i), which represents the number of particles a solute dissociates into when dissolved in a solvent. For instance, sodium chloride (NaCl) dissociates into two ions (Na+ and Cl-) in water, so its van't Hoff factor is 2. Similarly, magnesium nitrate (Mg(NO3)2) dissociates into three ions (Mg2+ and 2NO3-), giving it a van't Hoff factor of 3. Substances that do not dissociate, such as glucose, have a van't Hoff factor of 1. This factor plays a crucial role in determining the extent of freezing point depression, as solutions with higher van't Hoff factors exhibit greater freezing point depressions at the same molality.

To illustrate this concept, consider two solutions with equal molalities, one containing NaCl and the other containing glucose. Since NaCl dissociates into two ions, it effectively doubles the number of particles in the solution compared to glucose, which does not dissociate. As a result, the NaCl solution will exhibit a freezing point depression approximately twice as large as that of the glucose solution. This underscores the significance of the van't Hoff factor in determining the colligative properties of solutions.

In addition to the van't Hoff factor, the molality of the solution is another key factor influencing freezing point depression. Molality is defined as the number of moles of solute per kilogram of solvent and is a measure of concentration that is independent of temperature changes. The greater the molality of a solution, the greater the freezing point depression will be. This is because a higher molality indicates a higher concentration of solute particles, leading to a greater disruption of the solvent's crystal lattice structure.

Moreover, the nature of the solvent itself influences the magnitude of freezing point depression. Different solvents have different cryoscopic constants (Kf), which reflect their susceptibility to freezing point depression. A solvent with a high cryoscopic constant will exhibit a greater freezing point depression for a given concentration of solute than a solvent with a low cryoscopic constant. This is because the cryoscopic constant is directly proportional to the solvent's molar mass and inversely proportional to its enthalpy of fusion, which are intrinsic properties of the solvent.

Understanding freezing point depression has numerous practical applications in various fields. For example, it is used in the production of antifreeze for vehicles, where solutes such as ethylene glycol are added to water to lower its freezing point and prevent it from freezing in cold weather. Similarly, it is employed in the preservation of food, where high concentrations of solutes such as salt or sugar are used to lower the water activity and inhibit microbial growth. In scientific research, freezing point depression measurements are used to determine the molar masses of unknown compounds and to study the properties of solutions.

In summary, freezing point depression is a colligative property that depends on the number of solute particles in a solution. The van't Hoff factor, molality, and the nature of the solvent all play crucial roles in determining the magnitude of freezing point depression. By understanding these principles, we can predict and manipulate the freezing points of solutions for various practical applications.

Breaking Down the SBMPTN Question

Okay, let's look at the question: “Larutan yang memiliki titik beku paling tinggi adalah… A. NaCl 0,2 m. B. Mg(NO3)2 0,2 m. C. Glukosa 0,2 m. D. Al2(SO4)3 0,2 m E. K3PO4 0,2 m.”

Translation: Which solution has the highest freezing point? A. NaCl 0.2 m B. Mg(NO3)2 0.2 m C. Glucose 0.2 m D. Al2(SO4)3 0.2 m E. K3PO4 0.2 m.

Key takeaway: Notice that all the solutions have the same molality (0.2 m). This is a huge clue! Since molality is constant, the factor that will determine the freezing point is the van't Hoff factor (i). Remember, the higher the number of particles in solution, the lower the freezing point. So, we're looking for the solution with the fewest particles.

To effectively break down this SBMPTN question, it's essential to employ a systematic approach that combines fundamental chemical principles with careful analysis of the given options. The question revolves around identifying the solution with the highest freezing point among a set of options, all having the same molality. This immediately suggests that the key factor differentiating the solutions lies in their van't Hoff factors (i), which reflect the number of particles each solute dissociates into when dissolved in water.

The first step in tackling this question is to understand the relationship between freezing point depression and the van't Hoff factor. As we discussed earlier, freezing point depression is a colligative property, meaning it depends on the concentration of solute particles in the solution. The van't Hoff factor quantifies this concentration by indicating the number of particles a solute dissociates into. For instance, an ionic compound like sodium chloride (NaCl) dissociates into two ions (Na+ and Cl-) in water, resulting in a van't Hoff factor of 2. In contrast, a non-electrolyte like glucose does not dissociate and has a van't Hoff factor of 1.

Given that all the solutions in the question have the same molality (0.2 m), the solution with the highest freezing point will be the one with the lowest freezing point depression. This is because the freezing point of a solution is depressed relative to that of the pure solvent, so a smaller depression corresponds to a higher freezing point. Since freezing point depression is directly proportional to the van't Hoff factor, the solution with the lowest van't Hoff factor will exhibit the smallest freezing point depression and thus have the highest freezing point.

With this understanding, the next step is to determine the van't Hoff factor for each of the given solutions. This involves identifying whether the solute is an electrolyte (dissociates into ions) or a non-electrolyte (does not dissociate), and if it's an electrolyte, determining the number of ions it dissociates into. Let's consider each option in turn:

  • A. NaCl 0.2 m: Sodium chloride (NaCl) is an ionic compound that dissociates into two ions (Na+ and Cl-) in water. Therefore, its van't Hoff factor is 2.
  • B. Mg(NO3)2 0.2 m: Magnesium nitrate (Mg(NO3)2) is also an ionic compound, dissociating into three ions (Mg2+ and 2NO3-) in water. Its van't Hoff factor is 3.
  • C. Glukosa 0.2 m: Glucose is a non-electrolyte, meaning it does not dissociate into ions when dissolved in water. Its van't Hoff factor is 1.
  • D. Al2(SO4)3 0.2 m: Aluminum sulfate (Al2(SO4)3) is an ionic compound that dissociates into five ions (2Al3+ and 3SO42-) in water. Its van't Hoff factor is 5.
  • E. K3PO4 0.2 m: Potassium phosphate (K3PO4) is an ionic compound that dissociates into four ions (3K+ and PO43-) in water. Its van't Hoff factor is 4.

Now that we have the van't Hoff factors for each solution, we can compare them to determine which solution has the lowest value. The solution with the lowest van't Hoff factor will have the highest freezing point. From the above analysis, it's clear that glucose (C) has the lowest van't Hoff factor of 1.

Therefore, the solution with the highest freezing point is C. Glukosa 0.2 m. This systematic approach of understanding the underlying principles, identifying key factors, and analyzing each option allows us to confidently arrive at the correct answer.

Finding the Van't Hoff Factor

Here's the breakdown for each solution:

  • A. NaCl: Dissociates into 2 ions (Na+ and Cl-), so i = 2.
  • B. Mg(NO3)2: Dissociates into 3 ions (Mg2+ and 2NO3-), so i = 3.
  • C. Glucose: Doesn't dissociate (it's a sugar), so i = 1.
  • D. Al2(SO4)3: Dissociates into 5 ions (2 Al3+ and 3 SO42-), so i = 5.
  • E. K3PO4: Dissociates into 4 ions (3 K+ and PO43-), so i = 4.

Remember, the lowest 'i' means the highest freezing point.

Identifying the van't Hoff factor (i) for each solution is a crucial step in determining the solution with the highest freezing point. The van't Hoff factor represents the number of particles a solute dissociates into when dissolved in a solvent, and it plays a significant role in colligative properties like freezing point depression. To accurately identify the van't Hoff factor, we need to consider the chemical formula of each solute and understand how it ionizes or dissociates in water.

Let's start with A. NaCl (Sodium Chloride). NaCl is an ionic compound composed of sodium (Na+) and chloride (Cl-) ions. When NaCl dissolves in water, it dissociates into its constituent ions, Na+ and Cl-, effectively producing two particles in solution for every one molecule of NaCl. Therefore, the van't Hoff factor for NaCl is 2.

Moving on to B. Mg(NO3)2 (Magnesium Nitrate), this compound is also an ionic compound. It consists of a magnesium ion (Mg2+) and two nitrate ions (NO3-). When Mg(NO3)2 dissolves in water, it dissociates into one Mg2+ ion and two NO3- ions, resulting in a total of three particles in solution. Consequently, the van't Hoff factor for Mg(NO3)2 is 3.

Next, we have C. Glucose. Glucose is a molecular compound, specifically a sugar. Unlike ionic compounds, molecular compounds do not dissociate into ions when dissolved in water. Instead, they dissolve as intact molecules. Therefore, for glucose, the number of particles in solution is the same as the number of glucose molecules dissolved, and its van't Hoff factor is 1.

Now, let's consider D. Al2(SO4)3 (Aluminum Sulfate). This ionic compound is composed of two aluminum ions (Al3+) and three sulfate ions (SO42-). When Al2(SO4)3 dissolves in water, it dissociates into two Al3+ ions and three SO42- ions, resulting in a total of five particles in solution. Thus, the van't Hoff factor for Al2(SO4)3 is 5.

Lastly, we have E. K3PO4 (Potassium Phosphate). This ionic compound consists of three potassium ions (K+) and one phosphate ion (PO43-). When K3PO4 dissolves in water, it dissociates into three K+ ions and one PO43- ion, giving a total of four particles in solution. Therefore, the van't Hoff factor for K3PO4 is 4.

In summary, to determine the van't Hoff factor for a given solute, we need to consider whether it is an ionic compound or a molecular compound. Ionic compounds dissociate into ions in water, and the van't Hoff factor is equal to the number of ions produced per formula unit. Molecular compounds, on the other hand, do not dissociate, and their van't Hoff factor is 1. By carefully analyzing the chemical formula and the dissociation behavior of each solute, we can accurately determine its van't Hoff factor.

Once we have determined the van't Hoff factors for all the solutions, we can use this information to compare their freezing points. The solution with the lowest van't Hoff factor will have the highest freezing point because it will have the smallest freezing point depression. This is a direct consequence of the colligative nature of freezing point depression, which depends solely on the concentration of solute particles in the solution.

In the context of this SBMPTN question, identifying the van't Hoff factors allows us to quickly narrow down the options and pinpoint the solution with the highest freezing point. This approach not only saves time during the exam but also demonstrates a solid understanding of colligative properties and solution chemistry.

The Answer!

The solution with the highest freezing point is C. Glucose 0.2 m because it has the lowest van't Hoff factor (i = 1).

Guys, remember this key concept: For solutions with the same molality, the solution with the smallest number of ions will have the highest freezing point. This is a common trick in these types of questions, so keep an eye out for it!

Let's Try Another One!

Here's a similar question to test your understanding:

“Larutan yang mengandung 0,01 mol AlCl3 dalam 100 g air memiliki titik didih yang…“

We will break this down in another article! Stay tuned, and keep practicing! You got this! 💪