11 months ago

Final NB 2016-2017 Turley

1. 2.82 2. 8.30 3. 0.00

1. 2.82 2. 8.30 3. 0.00 4. 3.485 5. 12.000 6. 4.00 Sörenson also just mentions the reverse direction. That is, suppose you know the pH and you want to get to the hydrogen ion concentration ([H + ])? Here is the equation for that: [H + ] = 10¯pH That's right, ten to the minus pH gets you back to the [H + ] (called the hydrogen ion concentration). This is actually pretty easy to do with the calculator. Here's the sample problem: calculate the [H + ] from a pH of 2.45. This problem can be done very easily using your calculator. However, be warned about putting numbers into the calculator. So you enter 2nd, 10 x , (-), 2.45, enter. The answer, to the proper number of significant digits is: .00355. The pH of an acidic pond is 5. What is the hydrogen ion concentration (moles per liter)? The answer is: pH = -log (hydrogen ion concentration) The answer was .00001. Thus, 5 = -log (.00001). We'll take the formula that you started with (pH = -log([H+])) and work to the answer (solve for [H+]). pH = - log ([H+]) Given. pH = log ([H+] (-1) ) Since logarithms are like exponents, when you multiply a log by something, you can just move it to the inside of log as an exponent. 10 pH = 10 log ([H+] (-1)) Take each side to tenth power. 10 pH = [H+] (-1) Since "log" is just another notation for "log base 10", when you raise a log to the tenth power, the log cancels out. [H+] = 10 (-pH) Take the reciprocal of both sides. That is the general form. To answer the specific question, 5 = - log ([H+]) 5 = log ([H+] (-1) ) 10 5 = [H+] (-1) 10 (-5) = [H+] [H+] = .00001 mol/L 158

On your calculator you would input 10, ^, (-), 5 and you would get 0.00001. This is also the way to find the amount of OH + that are present in a base. To find the pH: -log(concentration) To find the concentration: 10 -pH Define these terms: pH scale pH is a numeric scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. It is roughly the negative of the logarithm to base 10 of the concentration, measured in units of moles per liter, of hydrogen ions. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion. Hydronium ion Hydronium ion is a water molecule with an extra hydrogen ion attached to it. (H2O + H+ → H3O+). It usually used to determine the acidity of a chemical compound. When a compound is put into water solution, the more the hydronium ion is produced, the higher the acidity is. Arrhenius acid/base The Arrhenius acid-base concept classifies a substance as an acid if it produces hydrogen ions H(+) or hydronium ions in water. A substance is classified as a base if it produces hydroxide ions OH(-) in water. Lewis acid/base Lewis acid is a chemical species that reacts with a Lewis base to form a Lewis adduct. A Lewis base, then, is any species that donates a pair of electrons to a Lewis acid to form a Lewis adduct. For example, OH − and NH 3 are Lewis bases, because they can donate a lone pair of electrons. Bronsted-Lowry acid/base A Bronsted-Lowry acid is a substance that donates a proton in the form of a hydrogen ion. The Bronsted- Lowry base, in turn, accepts this proton, and the resulting products are a conjugate acid and a conjugate base. The conjugate acid is the result of the base accepting the proton, so the charge increases by +1. Strong acid/base Sulfuric acid, as its name suggests, is not a base…. Sulfuric acid is a strong acid as it dissociates readily to give H+ ions. The dissociation of sulfuric acid in water in complete and all H+ ions are dissociated when dissolved in water. Weak acid/base The ionization of weak acids and bases is a chemical equilibrium phenomenon. The equilibrium principles are essential for the understanding of equilibria of weak acids and weak bases. The conjugate acid-base pairs have been discussed in Acids and Bases. Neutralization reaction In chemistry, neutralization or neutralisation (see spelling differences), is a chemical reaction in which an acid and a base react quantitatively with each other. In a reaction in water, neutralization results in there being no excess of hydrogen or hydroxide ions present in solution. Titration Titration, also known as titrimetry, is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of an identified analyte. Since volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the titrant or titrator is prepared as a standard solution. 159

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