Autoprotolysis constant, water

STRATEGY When Ba(OH)2 dissolves in water, it provides OH ions most hydroxides of Groups 1 and 2 can be treated as fully dissociated in solution. Decide from the chemical formula how many OH ions are provided by each formula unit and calculate the concentrations of these ions in the solution. To find the concentration of H,Oj ions, use the water autoprotolysis constant Kw = [H,0 1 [OH ]. 

Water, autoprotolysis constant, AUTOPROTOLYSIS WATER, BOUND-... 

In dilute aqueous solutions (the only ones we consider in this chapter), the solvent, water, is very nearly pure, and so its activity may be taken to be 1. The resulting expression is called the autoprotolysis constant of water and is written Kw ... 

The values of pH and pOH are related. To find that relation, we start with the expression for the autoprotolysis constant of water Kw = [H3Oh [Of I ]. Then we take logarithms of both sides ... 

Now consider a very dilute solution of a strong base, such as NaOH. Apart from water, the species present in solution are Na+, OH, and H30+. As we did for HCl, we can write down three equations relating the concentrations of these ions by using charge balance, material balance and the autoprotolysis constant. Because the cations present are hydronium ions and sodium ions, the charge-balance relation is... 

The calculation of pH for very dilute solutions of a weak acid HA is similar to that for strong acids in Section 10.18. It is based on the fact that, apart from water, there are four species in solution—namely, HA, A, H,0 +, and OH. Because there are four unknowns, we need four equations to find their concentrations. Two relations that we can use are the autoprotolysis constant of water and the acidity constant of the acid HA ... 

The pK for the autoprotolysis (more precisely, the autodeuterolysis, because a deuteron is being transferred) of heavy water (D20) is 15.136 at 20.°C and 13.8330 at 30.°C. Assuming AH° for this reaction to be independent of temperature, calculate A.Sr°for the autoprotolysis reaction. Suggest an interpretation of the sign. Suggest a reason why the autoprotolysis constant of heavy water differs from that of ordinary water. 

The water term in the denominator of Equation (6.3) is always large when compared with the other two concentrations on the top, so we say it remains constant. This assumption explains why it is rare to see the autoprotolysis constant written as Equation (6.3). Rather, we usually rewrite it as... 

Water dissociates to form ions according to Equation (6.2). The ionic product of the concentrations is the autoprotolysis constant Kw, according to Equation (6.4). Taking logarithms of Equation (6.4) yields ... 

A medicine or skin lotion is often described as pH neutral as though it was obviously a good thing. A solution is defined as neutral if it contains neither an excess of solvated protons nor an excess of hydroxide ions. Equation (6.4) tells us the autoprotolysis constant Kw of super-pure water (water containing no additional solute) is 10-14 (moldm-3)2. Furthermore, we saw in Worked Example 6.1 how the concentration of the solvated protons was 10-7 mol dm-3 at 298 K. 

Blood plasma is that part of the blood remaining after removal of the haemoglobin cells that impart a characteristic blood-red colour. According to Table 6.4, most people s plasma has a pH in the range 7.3-7.5. So, what is the concentration of solvated protons in such plasma We met the autoprotolysis constant Kw in Equation (6.4). Although we discussed it in terms of super-pure water, curiously the relationship still applies to any aqueous system. The product of the concentrations of solvated protons and hydroxide ions is always 10 14 at 298 K. 

Kw autoprotolysis constant of water AC/ change in internal energy, e.g. during... 

The recent introduction of non-aqueous media extends the applicability of CE. Different selectivity, enhanced efficiency, reduced analysis time, lower Joule heating, and better solubility or stability of some compounds in organic solvent than in water are the main reasons for the success of non-aqueous capillary electrophoresis (NACE). Several solvent properties must be considered in selecting the appropriate separation medium (see Chapter 2) dielectric constant, viscosity, dissociation constant, polarity, autoprotolysis constant, electrical conductivity, volatility, and solvation ability. Commonly used solvents in NACE separations include acetonitrile (ACN) short-chain alcohols such as methanol (MeOH), ethanol (EtOH), isopropanol (i-PrOH) amides [formamide (FA), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA)] and dimethylsulfoxide (DMSO). Since NACE—UV may present a lack of sensitivity due to the strong UV absorbance of some solvents at low wavelengths (e.g., formamides), the on-line coupling of NACE... 

The product of the molar concentrations (or, more accurately, the activities) of the species produced as a result of autoprotolysis. The autoprotolysis constant for water is K, equal to [H30+][0H ], or 1.0 x IQ i at 25°C. It is a temperature-dependent constant, increasing with... 

Symbol for the product of the H+ concentration (or, H3O+ concentration) and the OH concentration of an aqueous solution the autoprotolysis constant. See Water, Temperature Effects of pK, of... 

The positive ion is a hydrated hydrogen ion and the negative ion is a water molecule minus one hydrogen ion. The water molecules act equally as acids and bases this type of behaviour is termed amphiprotic. The extent of the autoionization is very slight. The autoprotolysis constant,... 

The autoprotolysis constant (autoionization constant) of water, Kw = q(l l jO )q(OI1 ) ss [H30+][0H, is often called the ion product constant of water. The value of -logKw varies with temperature as in Table 3.2. In water, there exists the following relation between K l of an acid and Kb of its conjugate base ... 

The autoprotolysis constant for H20 has the special symbol Kw, where w stands for water Autoprotolysis... 

H20(1) H3CT(aq) + OH-(aq). autoprotolysis constant The equilibrium constant for an autoprotolysis reaction. Example For water, Km with Kw = [H30+][0H-]. 

As pointed out by Mayr,28 Ritchie,15 and Hine33,34 KR also measures the relative affinities of R+ and H30+ for the hydroxide ion. It can be regarded as providing a general affinity scale applicable to electrophiles other than carbocations.33,35 It can also be factored into independent affinities of R+ and H30+ as shown in Equations (2) and (3). Such equilibrium constants have been denoted If by Hine.33 AR corresponds to the ratio of constants for reactions (2) and (3) and, in so far as Kc for H30+ is the inverse of Kw the autoprotolysis constant for water, KR = KCKW... 

The product of these two concentrations is known as the ionization constant of water, Kyf (or as the ionic product of water, or maybe sometimes as the autoprotolysis constant, Kap)... 

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