Como pensou
We need answer question in Portuguese, as candidate. Need solve. Let's parse.
We have reverse osmosis process? Text: Consider reverse osmosis process as figure. Piston where solution is suffers pressure π in reversible compression. Piston containing pure solvent also movable. Two compartments separated by semipermeable membrane, allows only solvent passage; both same initial volume, base area 1 dm^2; initial height of movable piston relative to base = 10 dm. Aqueous solution contains 0.2 mol of a substance, molar mass 80 g/mol. Substance solubility 4 g/L. All process at constant T=305 K. From info, present calculations and construct graph of osmotic pressure π (atm) as function of displacement of piston (dm), per figure, from initial position, as zero, until value 9 dm.
Need solve likely calculate osmotic pressure as function of piston displacement (volume change) due to reverse osmosis? Need derive graph points? We need include calculations. Let's understand.
Setup: two compartments separated by semipermeable membrane. Left: solution, right: solvent. Both have movable pistons. Pure solvent side pressure P_atm, solution side pressure P_atm + π. Compressing solution side? Actually reverse osmosis: applied pressure greater than osmotic pressure to force solvent from solution to pure solvent (or from solution to solvent? Osmosis normally solvent flows from pure solvent to solution; reverse osmosis applies pressure > osmotic pressure on solution side to force solvent from solution to solvent side). Figure: left is Solução (solution), right is Solvente (solvent). Pistons on top. Left piston pressure P_atm + π, right P_atm. So solution side compressed, solvent side maybe expands? Initially same volume? The solution contains 0.2 mol solute in volume? Initial height 10 dm, area 1 dm² => volume = 10 dm³ = 10 L? Wait 1 dm² area, height 10 dm = 100 cm? 1 dm = 10 cm; area 1 dm² = 100 cm²; height 10 dm = 100 cm; volume = 10 dm³ = 10 L. Yes. But solution contains 0.2 mol, molar mass 80 g/mol => mass = 16 g. Solubility 4 g/L. Wait if mass 16 g and solubility 4 g/L, need volume at least 4 L to dissolve? Actually solubility 4 g/L means saturated solution concentration 4 g/L. But solution contains 0.2 mol =16 g; volume 10 L gives concentration 1.6 g/L, below solubility, so unsaturated? Wait maybe solubility used to determine if precipitation? Hmm.
Maybe "substância" is solute, molar mass 80, solubility 4 g/L, so maximum dissolved = 4 g/L. Initial solution volume 10 L, solute mass 16 g => 1.6 g/L < 4 g/L, so all dissolved. As reverse osmosis removes solvent, solution volume decreases; concentration increases. At some point reaches solubility 4 g/L, then solute may precipitate? But only solvent passes through membrane, solute remains (if dissolved or precipitated?). They ask graph of osmotic pressure π as function of displacement of piston (dm), from initial position to 9 dm. Displacement of piston? Need understand sign. Piston on solution side moves down? It says "deslocamento do êmbolo (em dm), conforme a figura, da posição inicial, como sendo igual a zero, até o valor de 9 dm." So displacement variable maybe x = 0 at initial height 10 dm; until 9 dm. If piston moves downward by x dm? Initially at 10 dm above base; final height = 10 - x? If x=9 dm, height =1 dm. So solution volume decreases by x L (since area 1 dm², displacement x dm = volume x L), from 10 L to 1 L. Yes.
But osmotic pressure depends on concentration of solute particles; as volume changes, concentration increases; if solubility exceeded, some solute precipitates and concentration remains saturated. Need calculate π = c R T? For dilute solutions, van't Hoff: π = (n_solute/V) R T or with i? Since substance non-electrolyte? likely nonelectrolyte. Mass molar 80 g/mol. Solubility 4 g/L. Need account.
Initial: n = 0.2 mol. Volume = 10 L. Molar concentration = 0.02 mol/L. Osmotic pressure = c R T. R = 0.0821 atm L K^-1 mol^-1? Given 8,21 ×10^-2 atm L K^-1 mol^-1 = 0.0821. T=305 K. π = 0.02 * 0.0821 * 305 = 0.02 * 25.0405 = 0.50081 atm ≈ 0.501 atm. At x=0, π ≈ 0.501 atm.
As solvent removed reversibly by applied pressure on solution greater by π, the osmotic pressure against which work is done? The graph π vs displacement: requires calculate π at various volumes after concentration, considering solubility. Solute amount n=0.2 mol remains unless precipitation? Solubility = 4 g/L = 4/80 = 0.05 mol/L saturated concentration. At initial 0.02 M < 0.05 M, unsaturated. When volume V < n/C_sat? Actually total solute n = 0.2 mol; saturated concentration 0.05 mol/L; volume at saturation = 0.2 / 0.05 = 4 L. So when solution volume reaches 4 L, saturated; for V < 4 L, dissolved solute amount = 0.05 mol/L * V = 0.05V mol; precipitated solute = 0.2 - 0.05V mol. But osmotic pressure depends only on dissolved solute particles, so π = C_sat R T = 0.05 * R * T for V ≤ 4 L (constant). Wait but if precipitation occurs, dissolved concentration remains 0.05 M (assuming solid present). So osmotic pressure becomes constant at max value: 0.05*0.0821*305 = 1.252025 atm ≈ 1.252 atm. Is that the plateau? Need graph up to x=9 dm, which corresponds V = 10 - x = 1 L. So from V=10 to 4 L unsaturated, π increases hyperbolically; from V=4 to 1 L saturated, π constant = 1.252 atm. But wait at x=6 dm, V=4 L, π=1.252 atm; at x >6? π same. However maybe "solubilidade 4 g/L" means maximum concentration; yes.
But let's be careful: The question might expect graph π vs displacement, maybe calculate values at x=0, x=6, x=9? Need construct graph. It asks "A partir dessas informações, apresente os cálculos e construa um gráfico da pressão osmótica (π, em atm) em função do deslocamento do êmbolo (em dm), conforme a figura, da posição inicial, como sendo igual a zero, até o valor de 9 dm." So need provide calculations and graph. We can describe graph and maybe table.
Need decide if pressure applied is exactly π, reversible. The pressure on solution side is P_atm + π, where π is osmotic pressure? In reverse osmosis, the applied pressure difference equals osmotic pressure for equilibrium/reversible? Wait if pressure difference equals osmotic pressure, no net solvent flow? But "processo de compressão que ocorre de modo reversível" maybe π is the additional pressure needed to prevent osmosis or to reverse? Actually if solution side pressure is P_atm + π, and π is osmotic pressure of solution, then at all times the chemical potential of solvent equal? The piston displacement changes volume, solvent passes through membrane? Let's model.
There are two compartments: left solution, right pure solvent. Semipermeable membrane. Both pistons movable. The applied pressure on solution side exceeds solvent side by π. This is exactly the osmotic pressure of the solution at any moment, so system is at equilibrium? In reversible compression, as solution volume decreases (by applying external pressure), solvent molecules are forced from solution (left) to solvent (right) through membrane; external pressure does work. The osmotic pressure π depends on concentration. So π is the pressure difference needed to just prevent osmosis? Wait if pressure difference = π, net flow zero? But they say "processo de osmose reversa" so pressure difference > π? But they denote π as pressure action maybe osmotic pressure? The figure labels P_atm + π, P_atm. In reverse osmosis, applied pressure on solution side is greater than osmotic pressure by an amount to drive flow; here label π maybe applied pressure difference. But question asks "gráfico da pressão osmótica (π, em atm) em função do deslocamento do êmbolo" So π is osmotic pressure, not applied pressure. They probably assume reversible compression, i.e., at each displacement, external pressure difference equals osmotic pressure, so π computed by van't Hoff. Need perhaps graph π vs x.
Now, there may be subtle issue: The solvent also moves? Initially both compartments same volume 10 L. As solution volume decreases from 10 L to 1 L? Wait if solution volume decreases by x L (piston moves down by x), where does solvent go? Through membrane into solvent compartment. But solvent compartment piston is movable, initially volume 10 L; it receives solvent, volume increases by x L, so piston rises by x dm (from 10 to 19 dm?). The problem says "O êmbolo que contém o solvente puro também é móvel." The graph x-axis is displacement of "êmbolo" (which one? Figure shows dm scale on left solution side? Actually the figure has scale on left with 0-9? Let's inspect: Figure: two compartments; left solution side with piston at top; right solvent side. There is a ruler from 0 to 9 dm? Wait scale labels: left side has 0,1,2,...,9 downward from top? The piston initial height is 10 dm, but scale maybe extends beyond? In image, left vertical has ticks 0-9, with a vertical arrow pointing down "dm" and labels: top is 0? Let's parse: The figure: left compartment with solution; right solvent. There are lines at top? Maybe a graduated cylinder? It shows numbers 0,1,...,9? The bottom? Let's zoom mentally: Left side has a vertical scale with numbers 0,1,2,3,4,5,6,7,8,9 descending from top to bottom? There is an arrow at bottom pointing down with "dm". The piston initial position maybe at 0? Wait text: "altura inicial do êmbolo móvel em relação à base é igual a 10 dm. ... construa um gráfico ... em função do deslocamento do êmbolo (em dm), conforme a figura, da posição inicial, como sendo igual a zero, até o valor de 9 dm." In figure, scale maybe from 0 to 9? Hmm The ruler labels 0 to 9 dm maybe not absolute height, but displacement from initial? Let's see: Figure has horizontal lines across compartments maybe 0 at top? Actually top of solution compartment has piston; above piston arrow P_atm+π. There is a vertical scale along left side with marks 0 to 9? If initial piston height is 10 dm, scale 0-9 could be below piston? Maybe they draw a ruler where 0 is initial position? Let's examine: left compartment's piston at top; below it numbers 0 to 9? The base is at 10 dm below piston? The numbers maybe mark depth of piston from initial position? The figure may show the piston can move downward from initial (0) to 9 dm. The scale 0 at top initial position, 1,2,...9 downward. Yes. The arrow dm indicates displacement. So x-axis is displacement downward of solution piston (left), from 0 to 9 dm. This decreases solution volume by x L. The pure solvent piston moves upward by x dm? But graph only π vs x for solution.
Need calculate for x from 0 to 9 dm. At x=0 π = 0.5008 atm; for x from 0 to 6? Let's compute concentration.
V_solution = 10 - x L (since area 1 dm², x dm³ = x L). n_total = 0.2 mol. If unsaturated (until saturation): c = n/V = 0.2 / (10 - x) mol/L. Saturation concentration = solubility / M = 4 g/L / 80 g/mol = 0.05 mol/L. Set c = 0.05 => 0.2/(10-x) = 0.05 => 10-x = 4 => x=6 dm. So for 0 ≤ x ≤ 6, π = c R T = [0.2/(10-x)] * 0.0821 * 305. Compute 0.0821*305 =? 0.0821*300 = 24.63; plus 0.0821*5=0.4105; total 25.0405. Then π = 0.2*25.0405/(10-x) = 5.0081/(10-x) atm? Let's compute: 0.2 * 25.0405 = 5.0081. Yes π = 5.0081/(10-x) atm. At x=0: 0.50081 atm. At x=6: 5.0081/4 = 1.252025 atm. Good.
For x > 6, saturation: c = 0.05 mol/L; π = 0.05 * 25.0405 = 1.252025 atm (constant). Up to x=9, V=1 L; dissolved amount = 0.05 mol/L * 1 L = 0.05 mol, precipitated 0.15 mol? Actually total 0.2, dissolved 0.05, solid 0.15 mol? But if solid present, dissolved concentration fixed. Osmotic pressure same. However, at x=9, solution volume = 1 L; solid may precipitate. Need perhaps note solubility allows maximum 4 g/L; at V=1 L maximum dissolved mass = 4 g = 0.05 mol; so 0.15 mol precipitate. But osmotic pressure only dissolved.
But wait: Is it possible that as volume decreases by compression, the solution becomes saturated at x=6, then further compression causes precipitation; but the osmotic pressure might also depend on pressure? Osmotic pressure definition for nonideal? But likely ideal dilute. Also solute molar mass 80 g/mol; mass total = 16 g; solubility 4 g/L => volume needed to dissolve all = 4 L; yes.
Need maybe graph: x-axis 0 to 9 dm; y-axis π atm. Two regions: curve π = 5.0081/(10-x) for 0≤x≤6; at x=6 π=1.252; horizontal line from x=6 to x=9. Need maybe table of points.
Let's compute points maybe at x = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9? Could provide graph by plotting. Since cannot actually draw, describe. But user asks "construa um gráfico"; final answer should include explanation and graph perhaps in text? We need solve. We can include a rough graph with values. Since this is text response, we can give data table and describe shape; maybe "gráfico: Nos primeiros 6 dm, ramo de hipérbole; de 6 a 9 dm, reta horizontal." That's enough? But should present calculations.
Let's verify all constants: R = 8.21×10^-2 atm L K^-1 mol^-1; T=305 K. Product = 25.0405 atm L/mol. Good.
Initial volume: base area 1 dm², height 10 dm => 10 dm³ = 10 L. Wait 1 dm³ = 1 L. Yes.
Moles = 0.2 mol; mass = 0.2*80 =16 g; initial concentration = 16g/10L=1.6 g/L < 4g/L. So unsaturated. Volume at saturation = mass/solubility = 16 g / 4 g/L = 4 L. So x_sat = 10 - 4 = 6 dm. Good.
Osmotic pressure formula: π = (n/V) R T = (m/M)/V R T. Alternatively use mass concentration: π = (C/M) R T? Wait c = C/M. For unsaturated C = m/V =16/(10-x) g/L; c = 16/(80(10-x)) =0.2/(10-x) mol/L. Yes.
At saturation: C=4 g/L; c=4/80=0.05 mol/L; π=0.05*25.0405=1.252 atm.
But wait question says "substância apresenta uma solubilidade de 4 g·L⁻¹". Could solubility be in mol/L? But table gives 4 g/L. Good.
Need consider "todo processo ocorre à temperatura constante de 305 K" and reversible; maybe need also include work? No, only graph.
Let's consider if applied pressure difference π maybe osmotic pressure at each x, but if precipitation occurs, does the solute remain as solid? Yes. However, if solute is solid and membrane allows only solvent, no solute passes; solid may sediment but not affect osmotic pressure? But osmotic pressure of saturated solution is same as long as solid present. If all solid dissolved? It's saturated with excess solid.
Need maybe consider volume change due to mixing? Solvent passing from solution to pure solvent: solution volume = solvent volume + solute volume? For dilute solutions, volume approx solvent volume. But maybe exact? Solute molar mass 80, density unknown; but likely assume volumes additive? In osmotic pressure problems, concentration molar in solution volume; volume is total solution volume. The statement "ambos possuem o mesmo volume inicial" and "base área 1 dm²" maybe simple. We used volume = height*area, ignore solute volume / precipitation volume. Good.
Need maybe "pressão osmótica (π) em função do deslocamento do êmbolo" maybe applied pressure π? The pressure on solution side is P_atm + π, with π being the excess pressure applied. If the process is reversible, the applied pressure difference equals the osmotic pressure of solution. So π is indeed osmotic pressure. Good.
Potential subtlety: In reverse osmosis, to cause solvent to flow from solution to pure solvent, the applied pressure must exceed osmotic pressure; if process reversible, at equilibrium infinitesimal difference, so π is osmotic pressure? Actually during reversible compression, the external pressure on solution side may be P_atm + π, where π is the osmotic pressure plus infinitesimal? In the limit, π equals osmotic pressure. The problem labels π as pressure. So yes.
Need maybe compute pressure at x=0 and x=6; maybe also at x=9? At x=9 π=1.252 atm. But graph from 0 to 9. We can include table:
x/dm: 0, 2, 4, 6, 7, 8, 9
π/atm: 0.501, 0.626, 0.835, 1.252, 1.252, 1.252, 1.252? Let's calculate more precise for table:
At x=0: 5.0081/10 = 0.50081 ≈ 0.501
x=2: 5.0081/8 = 0.6260125
x=4: 5.0081/6 = 0.834683
x=6: 5.0081/4 = 1.252025
x=8? V=2 L saturated c=0.05 => 1.252
x=9: same 1.252. But wait at x=9 V=1 L, still saturated? Yes c=0.05 as long as solid present. At V=1, dissolved 0.05 mol, solid 0.15 mol; yes.
But wait, if volume is 1 L, can 0.05 mol dissolve? Solubility 0.05 mol/L, yes. But total solute 0.2 mol; excess precipitates. So π constant. Good.
Need perhaps "a partir da posição inicial, como sendo igual a zero, até o valor de 9 dm": x-axis x = 0 to 9. The graph should be for solution compartment piston displacement. It might be expected to show π increasing hyperbolically then plateau at 1.25 atm. Need indicate axes.
Let's formulate final answer with calculations.
Let's write in Portuguese:
1. Cálculo da concentração e da pressão osmótica inicial:
- V0 = A h = 1 dm² × 10 dm = 10 dm³ = 10 L.
- n = 0,2 mol; m = 0,2 × 80 = 16 g.
- C0 = 16/10 = 1,6 g/L < 4 g/L (insaturada).
- c0 = 0,2/10 = 0,02 mol/L.
- π0 = c0 R T = 0,02 × 0,0821 × 305 = 0,50081 atm ≈ 0,501 atm.
2. Enquanto não saturar, V = (10 - x) L, x em dm. c = n/V = 0,2/(10 - x) mol/L. Sendo insaturada:
- π(x) = [0,2/(10 - x)] × 0,0821 × 305 = 5,0081/(10 - x) atm, para 0 ≤ x ≤ x_sat.
3. Saturação:
- concentração de saturação: c_sat = 4 g/L / 80 g/mol = 0,05 mol/L.
- volume de saturação: 0,2 mol / 0,05 mol/L = 4 L.
- x_sat = 10 - 4 = 6 dm.
- π_sat = c_sat R T = 0,05 × 0,0821 × 305 = 1,252025 atm ≈ 1,25 atm.
- Para 6 ≤ x ≤ 9 dm, π = 1,25 atm (constante).
Could mention a partir de x=6, excesso de soluto precipita, mantendo a solução saturada; a pressão osmótica depende apenas da concentração dissolvida (0,05 mol/L).
4. Gráfico:
- eixo x: deslocamento x (dm); eixo y: π (atm).
- 0 a 6 dm: ramo de hipérbole y=5,0081/(10-x). Valores: x=0 →0,501; x=2→0,626; x=4→0,835; x=6→1,252.
- 6 a 9 dm: reta horizontal y=1,25 atm (ou 1,252 atm).
Need maybe include "conforme figura" maybe graph starts at x=0? It should be from 0 to 9. We can end with "Resposta final: ..." Probably need concise final line with result. The requested output: "Resposta final: <o resultado de cada item, de forma curta>". Since no explicit items a,b,c, only one question, maybe write "Resposta final: π = 0,501 atm no início; π = 5,0081/(10-x) atm para 0≤x≤6 dm; π = 1,252 atm para 6≤x≤9 dm; gráfico..." But "o resultado de cada item" maybe include graph data. It says "Se a questão tiver uma resposta só, escreva só o resultado." But there is a question with multiple calculations and graph. We'll include final response summarizing.
Need ensure no mistakes with unit: area 1 dm², displacement 1 dm = 1 dm³ = 1 L. R = 0.0821 atm L mol^-1 K^-1. We use L.
Let's double-check if maybe "substância" could be electrolyte? Not specified; molar mass given, maybe non-electrolyte. If it were electrolyte, need van't Hoff factor i. But no i. So assume molecular.
Potential issue: The solubility is 4 g/L; initial solution volume 10 L and 16 g solute => 1.6 g/L. But as reverse osmosis removes solvent, concentration increases. At saturation volume 4 L, concentration 4 g/L. Then further removal causes precipitation of 12 g? Actually initial 16 g, at 4 L saturated solution holds 16 g? Wait 4 L *4 g/L =16 g, so all 16 g dissolved exactly at saturation. At lower volume, say 1 L, saturated solution holds 4 g, so 12 g precipitate. Yes.
Wait 4 L * 4 g/L =16 g, yes. At 4 L exactly saturated, no solid? At V=4 L, c=4 g/L; if initially all 16 g dissolved, concentration 4 g/L; saturation; no excess solid? Actually if exactly saturated, no solid may be present; if further volume decrease, some solid appears. So plateau starts at x=6 exactly at saturation. At x=6, no solid? At saturation boundary. Good.
Let's consider if at x=6 π =1.252, and for x>6 same. Since at exact saturation, solution saturated but no solid; still concentration 0.05 M. Good.
Need maybe "pressão osmótica em atm" maybe use R=0.0821 atm L/mol/K. Product 25.0405 atm L/mol. Good.
Could there be a correction for osmotic pressure due to applied pressure? In thermodynamics, osmotic pressure π = - (RT/V_solvent?) ln a_solvent. For dilute solution, π ≈ cRT, but under high applied pressure (P_atm + π) the solvent chemical potential changes; however constant T and pressure? Actually pressure on solution side is high, but osmotic pressure definition? The reversible work of compression? Let's reason more deeply.
The problem may be from ITA; maybe they expect using concept of osmotic pressure and reverse osmosis; maybe "processo de osmose reversa" with semipermeable membrane; the applied pressure π is the osmotic pressure at each point. They ask graph π vs displacement. Could there be effect of pressure on osmotic pressure? Let's see: In equilibrium, chemical potential of solvent in solution under pressure P+π equals chemical potential of pure solvent under pressure P. For ideal dilute solution, μ_solvent(T,P+π) = μ_solvent^*(T,P+π) + RT ln x_solvent? Wait standard state at same pressure? The osmotic pressure equation for incompressible solvent: π = -(RT/V_m) ln x_solvent? Need use activity. For dilute solution, π = cRT. But if applied pressure P+π is high, the standard chemical potential depends on pressure; however solvent chemical potential in solution at pressure P+π: μ_solvent(T,P+π) = μ_solvent^*(T,P+π) + RT ln x_solvent (or activity). Pure solvent at pressure P: μ_solvent^*(T,P). Difference μ_solvent(T,P+π) - μ_solvent^*(T,P) = [μ_solvent^*(T,P+π)-μ_solvent^*(T,P)] + RT ln x_solvent = ∫_P^{P+π} V_m dP + RT ln x_solvent = π V_m + RT ln x_solvent = 0 => π = -(RT/V_m) ln x_solvent ≈ (RT/V_m) x_solute = cRT. The pressure dependence of V_m small; use molar volume. So same.
But possible precipitation affects osmotic pressure? Yes.
Let's perhaps derive from moles dissolved: n_diss = min(0.2, 0.05V). For V > 4 L, n_diss=0.2; for V≤4 L, n_diss=0.05V. π = n_diss RT / V. For V≤4 L, π = (0.05V)RT/V =0.05RT constant. Good.
Let's compute RT more exactly maybe using R=8.21e-2 atm L/mol/K; 305 K = 25.0405. At x=0, π = (0.2/10)*25.0405 = 0.50081 atm. At x=6, π = (0.2/4)*25.0405 =1.252025. Constant after.
Need maybe "pressão osmótica (π, em atm) em função do deslocamento do êmbolo (em dm), conforme a figura, da posição inicial, como sendo igual a zero, até o valor de 9 dm." The figure maybe has a scale already; graph should be plotted in the figure? Since they say "construa um gráfico" maybe they want draw on the exam? We can provide textual graph. In final, include a sketch description.
Let's examine the image with scale: It has 0 to 9? Maybe the graph should be plotted for displacement from 0 to 9, but initial height 10 dm; maybe x-axis "deslocamento do êmbolo" not "volume". The values we computed match.
Let's think if "deslocamento do êmbolo" could be positive upward? The figure maybe piston moves downward due to compression; displacement from initial position zero to 9 dm. We assumed downward. The scale in figure maybe 0 at top, 1-9 downward; yes. The graph has x from 0 to 9. If x increases, the solution piston moves downward; solvent piston moves upward? But question asks "deslocamento do êmbolo" maybe "do êmbolo" (which one? The solution piston? The scale is on left solution side). We'll state.
Need maybe include "para x > 6 dm, o soluto em excesso precipita; a solução permanece saturada, de modo que a pressão osmótica não mais depende do volume." Good.
Now, final answer should be in Portuguese, item by item. Let's compose with calculations. Keep not too verbose but sufficient.
Potential final structure:
"Como a área é 1 dm², cada dm de deslocamento corresponde a 1 L de variação de volume. Inicialmente V=10 L...".
Let's include units and equations.
Let's decide final line:
"Resposta final: π(x) = 5,0081/(10-x) atm para 0 ≤ x ≤ 6 dm; π(x) = 1,25 atm para 6 ≤ x ≤ 9 dm. No gráfico: hipérbole até x=6 dm, seguida de patamar horizontal em 1,25 atm."
Maybe include initial π: "π(0)=0,501 atm". The final line can contain this. The problem likely expects "gráfico" but final answer should summarize.
Let's also maybe include table:
x/dm | 0 | 2 | 4 | 6 | 9
π/atm | 0,501 | 0,626 | 0,835 | 1,25 | 1,25
But maybe too much? It asks construct graph; table is useful. In final answer, maybe not too overboard. But "Resposta final: <o resultado de cada item, de forma curta>" So final line concise. I can include graph description.
Need ensure the final answer line format exactly: "Resposta final: ..." At end. Good.
Let's write:
"V0 = 1 dm² × 10 dm = 10 L. Soluto: n=0,2 mol, m=16 g, c0=0,02 mol/L; π0=0,02×0,0821×305=0,501 atm."
Then "Para 0≤x≤6: V=10-x L; π=(0,2/(10-x))×0,0821×305=5,0081/(10-x) atm." Note: 0,2 mol constant because not precipitated yet.
Then "Para x=6: V=4 L; C=16g/4L=4 g/L (saturação); c=0,05 mol/L; π=0,05×0,0821×305=1,252 atm." Wait at x=6, all 16 g dissolved exactly at saturation. Good.
Then "Para 6≤x≤9: V≤4 L; precipita soluto; concentração dissolvida permanece 0,05 mol/L; π=1,252 atm."
Then "Gráfico..." good.
Let's consider if at x=6, "saturação" maybe maximum solubility but no precipitate; at x=6 the osmotic pressure on the unsaturated formula also gives 1.252; okay.
Potential issue: At x=6, formula 5.0081/(10-6)=1.252. If all dissolved, no solid; plateau starts. At exactly x=6, both. Fine.
Let's maybe compute "massa de soluto = 0,2 mol × 80 g/mol = 16 g; solubilidade = 4 g/L; volume de saturação = 16 g / 4 g/L =4 L; logo x=6 dm." Good.
Let's now produce final answer in Portuguese. Ensure no "graph" impossible? We can describe axes. Maybe include "Gráfico: eixo vertical π (atm), eixo horizontal x (dm)." and "A curva é uma hipérbole y=5,0081/(10-x) no intervalo [0,6] e uma reta horizontal y=1,25 no intervalo [6,9]." Good.
Let's final.
A área da base é 1\ \text{dm}^2. Assim, cada 1\ \text{dm} de deslocamento do êmbolo corresponde a 1\ \text{dm}^3=1\ \text{L} de variação de volume.
Volume inicial da solução:
V_0=1\ \text{dm}^2\times 10\ \text{dm}=10\ \text{L}
Massa de soluto:
m=0{,}2\ \text{mol}\times 80\ \text{g mol}^{-1}=16\ \text{g}
Concentração inicial:
c_0=\frac{0{,}2\ \text{mol}}{10\ \text{L}}=0{,}02\ \text{mol L}^{-1}
Pressão osmótica inicial:
\pi_0=c_0RT=0{,}02\times 0{,}0821\times 305
\pi_0\approx 0{,}501\ \text{atm}
Enquanto não houver saturação, para deslocamento x (em dm):
V=10-x\ \text{L}
\pi=\frac{nRT}{V}=\frac{0{,}2\times 0{,}0821\times 305}{10-x}
\pi=\frac{5{,}0081}{10-x}\ \text{atm}
A saturação ocorre quando a concentração atinge:
c_{\text{sat}}=\frac{4\ \text{g L}^{-1}}{80\ \text{g mol}^{-1}}=0{,}05\ \text{mol L}^{-1}
Volume em que isso ocorre:
V_{\text{sat}}=\frac{0{,}2\ \text{mol}}{0{,}05\ \text{mol L}^{-1}}=4\ \text{L}
x_{\text{sat}}=10-4=6\ \text{dm}
Nesse ponto:
\pi_{\text{sat}}=0{,}05\times 0{,}0821\times 305
\pi_{\text{sat}}\approx 1{,}25\ \text{atm}
Para 6\le x\le 9\ \text{dm}, há precipitação de soluto e a solução permanece saturada, com concentração dissolvida constante 0{,}05\ \text{mol L}^{-1}. Portanto:
\pi=1{,}25\ \text{atm}
Gráfico:
- No intervalo 0\le x\le 6\ \text{dm}: ramo de hipérbole dado por \pi=\dfrac{5{,}0081}{10-x}.
- No intervalo 6\le x\le 9\ \text{dm}: patamar horizontal em \pi\approx 1{,}25\ \text{atm}.
Alguns pontos para o esboço:
\begin{array}{c|c}
x/\text{dm} & \pi/\text{atm}\\
\hline
0 & 0{,}501\\
2 & 0{,}626\\
4 & 0{,}835\\
6 & 1{,}252\\
7 & 1{,}252\\
8 & 1{,}252\\
9 & 1{,}252
\end{array}
Resposta final: \pi(x)=\dfrac{5{,}0081}{10-x}\ \text{atm} para 0\le x\le 6\ \text{dm}; \pi(x)\approx1{,}25\ \text{atm} para 6\le x\le 9\ \text{dm}. Gráfico: hipérbole até x=6\ \text{dm}, seguida de patamar horizontal em 1{,}25\ \text{atm}.