Question

Part III: On Acid Sokka and Momo drank some yummy cactus juice but it upset their body a bit due to the acidity. Katara asked Aang to help her but when she needed him most he vanished. She has to settle for your help making a remedy for Sokka and Momo. 1) You take out your lab equipment and you have a series of solutions of acids and bases that can be used to offset the acid. They are labeled with their pH value. Katara needs you to explain to her what a pH value is and why you use pH instead of just hydrogen concentrations. (10 pts) 2) What equation does Katara need to use to determine Hydrogen concentration from pH? (5 pts) 3) If the concentration of protons in the cactus juice is equal to 10-4 M , what is the pH? (5 pts) 4) To cure Sokka and Momo you need to use a solution with a pH of 10. What is the concentration of protons in the remedy? (5pts) Part IV: The Big Four ¥ For each of the four images below identify: which type of macromolecule they represent, their subunits, the bonds that hold each subunit together, and their overall function. (5 pts/image)

Answer 1

1) pH:

Every aqueous solution, whether it is acidic, basic or neutral have H+ and OH- ions. The product of concentration of both ions (H+ and OH- ) is always constant, equal to 1x10-14 at 25°C. Acidity or basicity of the solution is depends on which of the two ions is present in higher concentration than the other. If we know the concentration of one ion then we can calculate concentration of other ion and it is convenient to express acidity or basicity of a solution by concentrations of H+ only. As we know that H+ ion concentration can vary within wide range, usually from about 1mole/liter (as in 1MHCl) to about 10-14 mole/liter (as in 1MNaOH). Therefore, a more convenient scale was introduced for indicating H+ ion concentration which is called the pH scale. A pH of solution is the negative logarithm of the concentrations of H+ ion which it contains.

Thus,

pH = -log[H+ ]

All aqueous solutions having pH less than 7 are acidic and those with pH higher than 7 are basic.

2) Katara can use following equation to determine Hydrogen concentration from pH

[H+ ] = log-pH

3. If the concentration of protons in the cactus juice is equal to 10-4 M ,

then, pH = -log[H+ ]

=-log[10-4]

= 4log10 = 4x1

= 4

pH of cactus juice is 4 i.e., acidic.

4. To cure Sokka and Momo we need to use a solution with a pH of 10. We have to know the concentration of protons in the remedy, for thi spurpose we can use following method

pH = -log[H+ ]

log[H+ ] = log-10

we take antilog of pH i.e., log-10 and aftertaking antilog we get 1x1010

Concentration of proton in remedy is 1x1010.