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19 Nov 2019
Measuring pH: Always calibrate a pH Meter pH is a measure of acidity or basicity. An acid has a pH less than 7, a neutral compound (like water) has a pH near 7, and a base has a pH from 7-14. A pH meter uses an electrode to measure the pH of a solution. The electrode is stored in distilled water in order to keep it at a neutral pH. In this lab we will calibrate our pH meters. Your instructor will guide you how to do this with Logger-Pro. Standardizing a Sodium Hydroxide (NaOH) Solution Solutions of sodium hydroxide are virtually impossible to prepare to a precise molar concentration because the substance is hygroscopic. In fact, solid NaOH absorbs so much moisture from the air that a measured sample of the compound is never 100% NaOH. On the other hand, the acid salt potassium hydrogen phthalate (KHP), KHC_8H_4O_4, can be measured out in precise mass amounts. It reacts with NaOH in a simple 1: 1 stoichiometric ratio, meaning that 1 mole of KHP will neutralize 1 mole of NaOH. This makes KHP an ideal substance to be used to standardize a solution of NaOH. To do this we titrate a NaOH solution with a known concentration of KHP solution and plot a titration curve. We then calculate the moles of KHP at equivalence point, which will be the moles required to neutralize a known volume of the NaOH solution. Since we know the moles in a known volume, we can easily calculate the molarity of the NaOH solution. 1. Calculate the mass of sodium hydroxide needed to prepare 100 mL of a 0.10M solution. 2. Calculate the mass of KHP needed to react completely with 25 mL of a 0.10 M NaOH solution. Consider the reaction equation to be as shown below. HP^- (aq) + OH^- (aq) rightarrow H_2O(l) + P^2- (aq) 3. Calculate the mass of KHP needed to prepare 100 mL of 0.10 M solution.
Measuring pH: Always calibrate a pH Meter pH is a measure of acidity or basicity. An acid has a pH less than 7, a neutral compound (like water) has a pH near 7, and a base has a pH from 7-14. A pH meter uses an electrode to measure the pH of a solution. The electrode is stored in distilled water in order to keep it at a neutral pH. In this lab we will calibrate our pH meters. Your instructor will guide you how to do this with Logger-Pro. Standardizing a Sodium Hydroxide (NaOH) Solution Solutions of sodium hydroxide are virtually impossible to prepare to a precise molar concentration because the substance is hygroscopic. In fact, solid NaOH absorbs so much moisture from the air that a measured sample of the compound is never 100% NaOH. On the other hand, the acid salt potassium hydrogen phthalate (KHP), KHC_8H_4O_4, can be measured out in precise mass amounts. It reacts with NaOH in a simple 1: 1 stoichiometric ratio, meaning that 1 mole of KHP will neutralize 1 mole of NaOH. This makes KHP an ideal substance to be used to standardize a solution of NaOH. To do this we titrate a NaOH solution with a known concentration of KHP solution and plot a titration curve. We then calculate the moles of KHP at equivalence point, which will be the moles required to neutralize a known volume of the NaOH solution. Since we know the moles in a known volume, we can easily calculate the molarity of the NaOH solution. 1. Calculate the mass of sodium hydroxide needed to prepare 100 mL of a 0.10M solution. 2. Calculate the mass of KHP needed to react completely with 25 mL of a 0.10 M NaOH solution. Consider the reaction equation to be as shown below. HP^- (aq) + OH^- (aq) rightarrow H_2O(l) + P^2- (aq) 3. Calculate the mass of KHP needed to prepare 100 mL of 0.10 M solution.
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23 Jan 2019