Volumetric properties of itaconic acid aqueous solutions

J. Chem. Thermodynamics 47 (2012) 42–47

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Volumetric properties of itaconic acid aqueous solutions Alexander Nisenbaum, Alexander Apelblat ⇑, Emanuel Manzurola Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva, Israel

a r t i c l e

i n f o

Article history: Received 1 July 2011 Received in revised form 15 September 2011 Accepted 19 September 2011 Available online 5 October 2011 Keywords: Itaconic acid Densities Apparent molar volumes Cubic expansion coefficients Structure of aqueous solutions

a b s t r a c t Densities of itaconic acid aqueous solutions were measured at 5 K intervals from T = (278.15 to 343.15) K. From the determined densities, the apparent molar volumes, the cubic expansion coefficients and the second derivatives of volume with respect to temperature which are interrelated with the derivatives of isobaric heat capacities with respect to pressure were evaluated. These derivatives were qualitatively correlated with the changes in the structure of water when itaconic acid is dissolved in it. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Itaconic acid (propylenedicarboxylic acid) is a naturally occurring, non-toxic and readily biodegradable compound (it occurs in some fermentations of sugars). Itaconic acid is an important intermediate in many fields of chemical technology (paints, plastic films, deodorants, synthetic resins) but is primarily used as a comonomer in the production of styrene–butadiene–acrylonitrile and acrylate latexes with applications in paper, metal and architectural coating industry. In the literature, there is only a very small number of investigations which are devoted to physical properties of aqueous solutions of itaconic acid. Solubilities of the acid in water from (274 to 338) K were measured by Krˇivánková et al. [1] and from (278 to 345) K by Apelblat and Manzurola [2]. Jones reported electrical conductivities from (273 to 338) K [3] and these conductances were used in the evaluation of dissociation constants of itaconic acid by Apelblat et al. [4]. In this work, continuing our previous density determinations in systems with important organic compounds [5–7], a number of volumetric properties of aqueous solutions of itaconic acid is considered. They include densities, apparent molar volumes, cubic expansion coefficients and the change of heat capacities with pressure P (they are interrelated with the second derivatives of the volume with respect to temperature), all of them as a function of concentration (m < 0.4 mol  kg1) and temperature. Measurements of density were performed at 5 K intervals over the

⇑ Corresponding author. E-mail address: [email protected] (A. Apelblat). 0021-9614/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2011.09.014

(278.15 to 343.15) K temperature range. To the best of our knowledge, such determinations were never reported in the literature. The reported volumetric properties of itaconic acid solutions are related to changes in the structure of water when the acid is dissolved in it. 2. Experimental Itaconic acid, HOOCCH2C(:CH2)COOH, (mass fraction > 0.99) was from Aldrich Chemical Company and was used without further purification. Densities of prepared weight degassed solutions (itaconic acid + double distilled water) were determined using a Metler-Toledo DA 310 M densimeter. Calibration of the densimeter, applied procedures are similar to these described in our previous investigations [5–8]. The uncertainty of our density measurements is about ±0.00002 g  cm3 and discussed in a detail in [8]. 3. Results and discussion Determined densities q(m, T) of aqueous solutions of itaconic acid at given molality m in the T = (278.15 to 343.15) K temperature range are presented in table 1. These densities served to determine the apparent molar volumes V 2;/ ðm; TÞ from

V 2;/ ðm; TÞ ¼

  M2 1000 1 1 ; þ   m qðm; TÞ q ðTÞ qðm; TÞ

ð1Þ

where M2 = 130.1 g  mol1 is the molecular mass of itaconic acid and q⁄(T) are densities of pure water [9].

43

A. Nisenbaum et al. / J. Chem. Thermodynamics 47 (2012) 42–47 TABLE 1 Densities q(m, T) itaconic acid aqueous solutions as a function of concentration m and temperature. m/m0

q(m, T)/(g  cm3)

T/K

278.15

283.15

288.15

293.15

298.15

303.15

308.15

0.03003 0.03959 0.06012 0.06991 0.08013 0.09380 0.09977 0.19999 0.30018 0.39986

1.00129 1.00166 1.00246 1.00287 1.00319 1.00375 1.00404 1.00792 1.01174 1.01553

1.00098 1.00134 1.00212 1.00253 1.00284 1.00339 1.00366 1.00745 1.01117 1.01489

1.00037 1.00073 1.00150 1.00188 1.00220 1.00273 1.00300 1.00670 1.01034 1.01397

0.99944 0.99979 1.00055 1.00092 1.00121 1.00173 1.00201 1.00565 1.00921 1.01276

0.99828 0.99863 0.99938 0.99975 1.00005 1.00055 1.00082 1.00438 1.00788 1.01137

0.99686 0.99721 0.99793 0.99831 0.99861 0.99910 0.99936 1.00287 1.00629 1.00972

0.99519 0.99554 0.99624 0.99661 0.99689 0.99739 0.99764 1.00110 1.00447 1.00783

m/m0

q(m, T)/(g  cm3)

T/K

313.15

318.15

323.15

328.15

333.15

338.15

343.15

0.03003 0.03959 0.06012 0.06991 0.08013 0.09380 0.09977 0.19999 0.30018 0.39986

0.99335 0.99369 0.99436 0.99473 0.99501 0.99552 0.99574 0.99918 1.00247 1.00578

0.99133 0.99167 0.99236 0.99271 0.99299 0.99348 0.99370 0.99709 1.00032 1.00361

0.98914 0.98950 0.99015 0.99049 0.99076 0.99125 0.99147 0.99483 0.99806 1.00124

0.98678 0.98711 0.98780 0.98811 0.98839 0.98888 0.98908 0.99238 0.99556 0.99872

0.98428 0.98462 0.98526 0.98561 0.98587 0.98633 0.98657 0.98973 0.99298 0.99607

0.98162 0.98194 0.98261 0.98292 0.98319 0.98363 0.98387 0.98699 0.99020 0.99318

0.97884 0.97915 0.97982 0.98013 0.98038 0.98084 0.98107 0.98409 0.98730 0.99024

m0 = 1 mol  kg1.

TABLE 2 Apparent molar volumes V2,u(m, T) of itaconic acid as a function of concentration m and temperature. V2,u(m, T)/(cm3  mol1) 278.15

283.15

288.15

293.15

298.15

303.15

308.15

0.03003 0.03959 0.06012 0.06991 0.08013 0.09380 0.09977 0.19999 0.30018 0.39986

85.70 87.01 88.30 88.22 89.50 89.36 88.84 89.59 89.80 89.76

87.37 88.54 89.64 89.38 90.64 90.44 90.06 90.66 90.86 90.75

87.74 88.82 90.01 90.13 91.18 91.11 90.70 91.45 91.67 91.60

89.11 90.13 91.06 91.18 92.48 92.34 91.76 92.31 92.54 92.47

89.17 90.19 91.28 91.39 92.54 92.62 92.12 92.93 93.18 93.12

89.91 90.77 92.20 92.04 93.13 93.24 92.81 93.57 93.91 93.85

92.01 92.39 93.64 93.44 94.61 94.42 94.02 94.48 94.72 94.66

m/m0

V2,u(m, T)/(cm3  mol1)

T/K 0.03003 0.03959 0.06012 0.06991 0.08013 0.09380 0.09977 0.19999 0.30018 0.39986

313.15 92.79 93.26 94.76 94.41 95.48 95.07 94.94 95.10 95.45 95.37

328.15 94.87 95.19 95.83 96.27 97.17 96.78 96.78 96.95 97.21 97.19

333.15 95.36 95.34 96.85 96.57 97.72 97.60 97.15 97.95 97.68 97.77

338.15 96.21 96.55 97.18 97.49 98.41 98.44 97.95 98.64 98.35 98.61

343.15 96.38 96.98 97.53 97.81 98.98 98.73 98.34 99.46 98.96 99.22

318.15 93.58 93.89 94.88 94.82 95.86 95.62 95.47 95.69 96.09 95.94

323.15 94.39 94.01 95.69 95.69 96.76 96.41 96.22 96.28 96.54 96.59

90

85 0.00

m0 = 1 mol  kg1.

q ðTÞ=g  cm3 ¼ 0:999883 þ 5:509202  105 h  7:867989  106 h2 þ 5:026034  108 h3  1:933126  1010 h4 ;

95

3

V2,φ /cm mol

T/K

-1

m/m0

100

ð2Þ

h ¼ T=K  273:15: Values of the apparent molar volumes of itaconic acid as calculated by equation (1) are given in table 2. At constant temperatures, they are plotted in figure 1, and as can be seen, the function V 2;/ ðm; TÞ = f(m) has two distinct concentration regions. In concentrated solutions, when itaconic acid is practically undissociated, a

0.10

0.20

0.30

0.40

-1

m/molkg

FIGURE 1. The apparent molar volume of itaconic acid V2,u as a function of concentration m. T = 278.15 K ; T = 298.15 K ; T = 318.15 K ; T = 338.15 K .

very small change is observed. The apparent molar volumes in this region almost linearly decrease with decreasing of molality m. In dilute solutions, as a result of dissociation into ions, V 2;/ ðm; TÞ decreases more rapidly. At constant concentration of itaconic acid, the function V 2;/ ðm; TÞ = f(T) monotonically increases with temperature T (figure 2). Itaconic acid is dibasic carboxylic acid and dissociates in water in two steps

H2 Itac ! Hþ þ HItac1 ;

K1;

HItac1 ! Hþ þ Itac2 ;

K2

ð3Þ

and in terms of the dissociation constants they can be expressed as

K1 ¼ K2 ¼

½Hþ ½HItac1  mða þ 2bÞa F1 ¼ F1; ½H2 Itac 1ab ½Hþ ½Itac2  ½HItac1 

F2 ¼

mða þ 2bÞb

a

F2;

ð4Þ

44

A. Nisenbaum et al. / J. Chem. Thermodynamics 47 (2012) 42–47 1

V 0 ðH2 ItacÞ=cm3  mol

100

¼ 92:70 þ 0:147ðT=K  298:15Þ

ð7Þ

and V0(HItac1) as a function of temperature are reported

V 0 ðHItac1 Þ=cm3  mol

¼ 8:5 þ 1:43ðT=K  298:15Þ:

ð8Þ

Equation (8) is valid for T 6 313 K and above this temperature the partial molar volumes of itaconic ions at infinite dilution have nearly constant value of about (32 to 33) cm3  mol1. The cubic expansion coefficients of a solution (isobaric thermal expansibilities) are defined by

3

V2,φ /cm mol

-1

95

1

90

aðm; TÞ ¼ 325

350

T/K FIGURE 2. The apparent molar volumes of itaconic acid V2,u as a function of temperature. m = 0.08013 mol  kg1 ; m = 0.03003 mol  kg1 .

where F1 and F2 are the corresponding quotients of activity coefficients (usually represented by the Debye–Hückel or others expressions) and a and b are the fractions of itaconic anions (i.e. m(HItac1) = ma; m(Itac2) = mb; m(H2Itac) = m(1  ab) and m(H+) = m(a + 2b). The dissociation constants K1 and K2 are known [4] and they can be correlated by 3

lnðK 1 =mol  dm Þ ¼ 61:90  3435:0=ðT=KÞ  10:41 lnðT=KÞ; 3

lnðK 2 =mol  dm Þ ¼ 89:23  4110:7=ðT=KÞ  15:61 lnðT=KÞ: ð5Þ

V 2;/ ðmÞ ¼ aV E þ ð1  aÞV U ; pffiffiffiffiffiffiffiffi V E ¼ V 0 ðHItac1 Þ þ AV ma þ bE m;

TABLE 3 Cubic expansion coefficients a(m, T) itaconic acid aqueous solutions as a function of concentration m and temperature. m/m0

a(m, T)  106/K1

T/K

278.15

283.15

288.15

293.15

298.15

303.15

308.15

25.1 26.6 27.5 32.2 32.6 38.8 37.4 60.3 74.5 92.7

92.9 94.2 96.3 99.1 100.0 104.1 104.1 122.5 138.0 154.1

154.6 155.5 158.5 160.1 161.3 163.8 164.8 179.5 195.4 209.7

210.7 211.3 214.8 215.6 216.9 218.3 220.0 231.7 247.2 260.0

261.8 262.1 265.7 266.3 267.5 268.3 270.3 279.9 294.2 305.7

308.3 308.5 311.9 312.5 313.6 314.1 316.2 324.3 336.9 347.5

351.0 351.0 354.0 354.9 355.7 356.3 358.3 365.6 376.1 386.0

0.03003 0.03959 0.06012 0.06991 0.08013 0.09380 0.09977 0.19999 0.30018 0.39986 m/m0

a(m, T)  106/K1

T/K

313.15

318.15

323.15

328.15

333.15

338.15

343.15

0.03003 0.03959 0.06012 0.06991 0.08013 0.09380 0.09977 0.19999 0.30018 0.39986

390.2 390.1 392.7 393.9 394.5 395.2 396.9 404.2 412.3 421.9

426.5 426.6 428.4 430.1 430.5 431.5 432.7 440.7 446.2 455.8

460.5 460.9 461.9 463.8 464.2 465.6 466.0 475.5 478.4 488.4

492.7 493.5 493.7 495.7 496.2 497.9 497.6 509.1 509.6 520.3

523.7 525.1 524.5 526.3 527.1 528.8 527.7 542.0 540.4 552.3

553.9 556.3 554.9 555.9 557.3 559.0 557.0 574.8 571.4 585.0

583.9 587.5 585.5 585.2 587.6 588.8 586.0 608.0 603.5 619.0

m0 = 1 mol  kg1.

600

400 6

Similarly to many other organic acids, the first dissociation constant of itaconic acid K1 has a maximal value (at about 330 K) when the second dissociation constant decreases with increasing of temperature. In the investigated range of concentrations, differences in dissociation constants as expressed in molar or molal concentration units are negligible. Introducing K1(T) and K2(T) values into (40), the set of equilibrium equations was solved for any m to obtain the a and b fractions of itaconic anions. The results of calculations showed that in the investigated range of concentrations, actually itaconic acid can be considered as the monobasic acid because b values are very small as a result of large differences in dissociation constants. For example at 298.15 K, K1 = 1.32  104 mol  dm3, K1 = 1.37  106 mol  dm3 and for the lowest concentration m = 0.03003 mol  kg1 we have a = 0.0666 and b = 0.000057. In order to reproduce the V2,u(m, T) function over entire concentration region, King [10] proposed to treat the apparent molar volumes of weak electrolytes as the sum of additive contributions which are coming from two parts, the first part from the formed ions (i.e. proportional to degrees of dissociation) and the second part from the undissociated molecules of the acid. At constant temperature, considering itaconic acid as 1:1 weak electrolyte we have

They were calculated by expressing the measured densities q(m = constant, T) as polynomials of T. The cubic expansion coefficients are reported in table 3. Typical behaviour of a(m, T) at constant temperature is presented in figure 3 and at constant

-1

300

ð9Þ

α 10 /K

85 275

    1 @V @ ln qðm; TÞ ¼ : V @T P;m @T P;m

ð6Þ

0

200

V U ¼ V ðH2 ItacÞ þ bV m; where V0 of ions are the partial molar volumes at infinite dilution (it is assumed that V0(H+) = 0). AV = 1.868 cm3  kg1/2  mol3/2 is the limiting slope and bE, bV are adjustable parameters. Continuous lines in figure 1 are calculated using the set of (4) to (6) equations. However, large scattering of experimental points in the first concentration region and small degrees of dissociation make uncertain contributions coming from formation of ions. Therefore, at this moment, only estimated values of V0(H2Itac)

0 0.00

0.10

0.20

m/molkg

0.30

0.40

-1

FIGURE 3. Cubic expansion coefficients of itaconic acid solutions, a. 106 as a function of concentration m. T = 278.15 K ; T = 298.15 K ; T = 318.15 K ; T = 338.15 K .

45

A. Nisenbaum et al. / J. Chem. Thermodynamics 47 (2012) 42–47

TABLE 4 Values of T(@ 2V/@T2)P = (@CP/@P)T of itaconic acid aqueous solutions as a function of concentration m and temperature.

600

m/m0

6

α 10 /K

-1

450

300

150

0 275

300

325

350

T/K FIGURE 4. Cubic expansion coefficients of itaconic acid solutions, a. 106 as a function of temperature. m = 0.39986 mol  kg1 ; m = 0.03003 mol  kg1 .

concentration in figure 4. As can be seen, the function a(m, T) increases with increasing m and T. The knowledge of thermal expansion coefficients, a(m, T), and their derivatives with regards to temperature, @ a(m, T)/oT, is important because this permits to interrelate the volumetric and thermal properties of solutions. From the Maxwell relation as applied to the differential of enthalpy

    @V dP dH ¼ C P dT þ V  T @T P

T(@ 2V/@T2)P/(cm3  K1)

T/K

278.15

283.15

288.15

293.15

298.15

303.15

308.15

0.00000 0.03003 0.03959 0.06012 0.06991 0.08013 0.09380 0.09977 0.19999 0.30018 0.39986

4.01 3.96 3.95 4.04 3.92 3.96 3.83 3.92 3.68 3.82 3.73

3.70 3.67 3.66 3.73 3.64 3.67 3.57 3.64 3.43 3.52 3.43

3.42 3.41 3.39 3.44 3.38 3.40 3.33 3.38 3.21 3.24 3.17

3.17 3.16 3.15 3.17 3.15 3.15 3.11 3.14 3.01 2.99 2.94

2.94 2.94 2.93 2.94 2.93 2.93 2.91 2.92 2.84 2.78 2.74

2.74 2.75 2.74 2.73 2.74 2.73 2.73 2.73 2.69 2.59 2.57

2.58 2.58 2.57 2.55 2.57 2.56 2.57 2.56 2.56 2.44 2.43

m/m0

T(@ 2V/@T2)P/(cm3  K1)

T/K

313.15

318.15

323.15

328.15

333.15

338.15

343.15

0.00000 0.03003 0.03959 0.06012 0.06991 0.08013 0.09380 0.09977 0.19999 0.30018 0.39986

2.44 2.43 2.44 2.40 2.43 2.42 2.44 2.41 2.46 2.32 2.34

2.34 2.32 2.33 2.29 2.32 2.31 2.33 2.30 2.39 2.24 2.28

2.27 2.24 2.26 2.21 2.23 2.23 2.26 2.21 2.35 2.20 2.27

2.24 2.18 2.22 2.17 2.17 2.19 2.20 2.15 2.34 2.21 2.30

2.24 2.17 2.22 2.17 2.14 2.18 2.18 2.12 2.37 2.25 2.37

2.30 2.18 2.26 2.21 2.15 2.20 2.19 2.13 2.43 2.35 2.50

2.39 2.24 2.34 2.30 2.19 2.27 2.23 2.17 2.53 2.49 2.69

m0 = 1 mol  kg1.

ð10Þ 4.0

3

ð11Þ

where CP is the isobaric heat capacity of solutions. Equation (11) can be expressed in terms of the cubic expansion coefficients and their derivatives as

T

@ 2 Vðm; TÞ

!

@T 2

"

  # @ aðm; TÞ ¼ TVðm; TÞ a ðm; TÞ þ ; @T P;m

P;m

@ Vðm; TÞ @T

3.0

ð12Þ 2.5 0.00

or directly from the derivatives of density

T

3.5

2

1000 þ mM2 Vðm; TÞ ¼ qðm; TÞ

2

-(dCp/dp)m/cm K

!   @C P @2V ¼ T ; @p T @T 2 P

-1

we have

2 P;m

"  #2 2 @ qðm; TÞ ¼ @T qðm; TÞ :qðm; TÞ P;m 9 ! = @ 2 qðm; TÞ  : 2 ; @T

0.20

0.30

0.40

-1

m/molkg

8 TVðm; TÞ <

!

0.10

FIGURE 5. The change in the isobaric heat capacity with pressure (@CP/@P)T of itaconic acid solutions as a function of concentration m. T = 278.15 K ; T = 283.15 K ; T = 288.15 K ; T = 293.15 K ; T = 298.15 K ; T = 303.15 K .

ð13Þ

P;m

The change in the isobaric heat capacity with pressure (oCP/oP)T or the product of temperature and the second derivative of volume with respect to T, f(T, m) = T(@ 2V/@T2)P, were calculated from polynomials of density and they are presented in table 4. In figure 5 are plotted (oCP/oP)T values at constant temperature and a nearly linear dependence on concentration m is observed. At constant concentration m, (oCP/oP)T values are presented in figure 6. They decrease strongly with temperature having the minimum near 325 K. According to Hepler [11] (for the case of nonelectrolytes see [12]), changes in the structure of water can be related to the change in heat capacities with pressure or to the behaviour of

the second order derivatives of volume with respect to temperature. The ‘‘abnormal’’ high heat capacity of water is usually attributed to a highly ordered hydrogen-bonded structure of water and this structure is affected by pressure and temperature. Hepler postulated that for the structure-breaking solutes, the second order derivative of partial molar volume of solute at infinite dilution V 2 ðTÞ with respect to temperature should be negative, increases with T and the curve is concave downward (f00 (x) < 0). In the case of the structure-making solutes, the second order derivative is positive, also increases with T but the curve is concave upward (f00 (x) > 0). Unfortunately, the proposed Hepler criteria are usually difficult to apply because the apparent molar volumes at very dilute solutions are not enough accurate to give the correct temperature dependence of V 2 ðTÞ. However, in dilute solutions, it is

46

A. Nisenbaum et al. / J. Chem. Thermodynamics 47 (2012) 42–47

possible to assume that the partial molar volume of solvent V 1 ðm; TÞ (in our case water), is nearly equal to that of pure water, V 01 ðTÞ and this permits to replace the Hepler criteria by [13]

-(dCp/dp)m/cm3K-1

4.0

3.5

T

@ 2 V 2 ðm; TÞ

!

@T 2

P;m

3.0

2 ! ! 3 1 4 @ 2 Vðm; TÞ @ 2 V 1 ðTÞ 5;  T T m @T 2 @T 2 P;m P;m ¼

ð14Þ 2.5

where V 1 ðTÞ ¼

55:51V 01 ðTÞ 2

Df ðm; TÞ ¼ mT 2.0 275

300

325

350

T/K FIGURE 6. The change in the isobaric heat capacity with pressure (@CP/@P)T of itaconic acid solutions as a function of temperature. m = 0.39986 mol  kg1 ; m = 0.03003 mol  kg1 .

3

Δ f(m,T)/cm K

-1

0.0

-0.1

-0.2 275

300

325

350

T/K FIGURE 7. Values of Df(m, T) function of itaconic acid solutions as a function of temperature. m = 0.03003 mol  kg1 ; m = 0.03959 mol  kg1 ; m = 0.39981 mol  kg1 ; m = 0.03003 mol  kg1 .

-1

0.4

0.2

3

Δ f(m,T)/cm K

1 1 ½f ðm; TÞ  f ð0; TÞ ¼ Df ðm; TÞ; m m

0.0

@ V 2;/ ðm; TÞ @T 2

! ¼ P;m

  @ðC P  C P;1 Þ : @P T;m

ð15Þ

Since f ð0; TÞ ¼ Tð@ 2 V 01 =@T 2 ÞP values for pure water are available from [8] and f(m, T) = T(@ 2V/@T2)P,m from equation (12), (13), the sign and curvature of the function Df(m, T) can be determined to give an indication about the character of solute when dissolved in water. As can be observed, Df(m, T) (plotted in figures 7 and 8) have two distinct concentration regions, the first region covers dilute solutions when m < 0.1 mol  kg1 and the second region more concentrated solutions. In the first concentration region (curves in figure 7 and the first curve in figure 8), the Df(m, T) curves pass maximum at about 305 K, but they are always negative and the curves have concave downward curvature. Thus, according to the Hepler criteria, in dilute aqueous solutions, itaconic acid (mixture of ions and undissociated molecules) behaves essentially as a structure-breaking solute. Decreasing of Df(m, T) when T increases was explained by Hepler by considering that pressure and temperature have similar effect on the heat capacity when the structure of water is destroyed. That means that at higher temperatures water starts to behave as a ‘‘normal’’ liquid. In more concentrated solutions, m > 0.1 mol  kg1 (figure 8), Df(m, T) always increases with increasing temperature, the curves have concave upward curvature, but they have positive values only at temperatures above 315 K. However, the form of curves clearly indicates that molecules of undissociated itaconic act as the structure-making solute. 4. Conclusions Volumetric properties of itaconic acid aqueous solutions (the apparent molar volumes, the cubic expansion coefficients, the second derivatives of volume with respect to temperature and the isobaric heat capacities with respect to pressure) were determined from densities of solutions which were measured at 5 K intervals from T = (278.15 to 343.15) K. It was found that for m < 0.1 mol  kg1, itaconic acid behaves as a structure-breaking solute. In more concentrated solutions, when itaconic acid is completely undissociated, it acts as a structuremaking solute. References

-0.2

-0.4 275

and

300

325

350

T/K FIGURE 8. Values of Df(m, T) function of itaconic acid solutions as a function of temperature. m = 0.09977 mol  kg1 ; m = 0.19999 mol  kg1 ; m = 0.30018 mol  kg1 ; m = 0.39986 mol  kg1 .

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