Calculate pH of : (a) 10^-3 N HNO3 (b) 10^-3 M H2 SO4 (c) 10^-3 NH2 SO4 (d) 0.01 N HCl, (e) 10

Calculate pH of : (a) 10^-3 N HNO3 (b) 10^-3 M H2 SO4 (c)...

Key Concepts

Autoionization of Water in Dilute Solutions

In very dilute acid solutions, the contribution of hydrogen ions from the autoionization of water becomes significant. Water itself produces a concentration of hydrogen ions (10^-7 M at 25°C) which can affect the overall pH calculation when the acid concentration is comparable to or lower than this value. Adjustments in calculations are necessary to account for both the acid and water contributions to the total hydrogen ion concentration.

Normality versus Molarity

Normality (N) is a measure of concentration that accounts for the number of equivalents of reactive species (such as hydrogen ions for acids) per liter of solution. Molarity (M) is the number of moles of a substance per liter of solution. For monoprotic acids (one dissociable proton) these values are the same, whereas for acids that can donate more than one proton, normality may be higher than molarity. This distinction is important when calculating the effective concentration of H+ ions in the solution.

pH Calculation

pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration. It provides a measure of the acidity of a solution. Understanding pH is crucial for evaluating how acidic or basic a solution is, and it is calculated using the formula pH = -log[H+].

Acid Strength and Dissociation

The concept of acid strength relates to how completely an acid dissociates in water. Strong acids, such as HNO3 and HCl, dissociate nearly completely, meaning the concentration of hydrogen ions in the solution closely matches the initial acid concentration (adjusted for the number of ionizable protons). For polyprotic acids like H2SO4, while the first proton typically dissociates completely, the second proton may not, especially at low concentrations, and must be considered separately.

Transcript

00:01 In this question we need to find out the values of ph for the given acids.

00:05 Now the first asset that has been given to us is the first asset that has been given to us is 10 -to -power minus 3 normal nitric acid.

00:15 Now this nitric acid dissociates as h plus and and o3 minus.

00:21 So for ph we need to find out the concentration of h -plus because ph is equal to negative logarithm of h -plus only right if we can find out the the value of concentration of h plus it is going to be very easy for us to find out the ph now since the concentration of this h .m .3 is 10x2b over minus 3 normal we can find it out in terms of molarity by simply using the formula that normality is equal to molarity multiplied by n factor right so molarity is going to be equal to normality divided by n factor here and for nitric acid the n factor is equal to one so molarity is equal to normality and hence we can say that after dissociation the concentration of hno3 is going to be c minus c alpha while for h plus it is going to be c alpha and c alpha for no3 minus.

01:11 Now again since we are saying that hno3 is a very very strong acid so this value of alpha is going to be one and hence the concentration of h plus is going to be equal to c which is 10 to power minus 3 molar.

01:25 Now using the formula of ph we get minus logarithm of 10 to power minus 3 which gives us the value 3.

01:35 So basically the ph of this particular acid is equal to 3.

01:40 Now the second acid given to us is 10 to power minus 3 molar h2s .s .4 or sulfuric acid.

01:48 So it dissociates as 2 moles of h plus and 1 mole of s .o 4 minus 2.

01:53 Now since the concentration of h2 s4 is 10 to power minus 3m and it is given two moles of h plus so basically the concentration of h plus is 2 multiplied by 10 to power minus 3 now again using the formula of ph we get p h equals to negative logarithm of this 2 multiplied by 10 to power minus 3 which gives us 2 .6989 so this is the value of ph for this given acid now for c we have 10 to power minus 3 normal h2 s o 4 again it dissociates the same way 2 h plus plus s o 4 minus 2 now if you want to find out the molarity so we will have to divide this normality by 2 as per this formula right the molarity is going to be equal to normality divided by n factor similarly we have divided the normality by the n factor which is 2 for h2 as a 4 so this is the molarity.

02:53 So now since this is the concentration of this h2 s of 4, it is going to produce twice as that of this concentration of h plus, right? so basically the concentration of h plus here is going to be 10 to power minus 3 and hence using the formula of ph we can get easily the ph which is negative logarithm of 10 to power minus 3.

03:17 So it becomes 3...

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