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Published byJosephine Stevens Modified over 5 years ago

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Acids and bases, when combined in equal quantities, neutralize each other forming salt and water. HCl + NaOHHOH + NaCl 1+1-1+1-1+1-1+1- H 2 SO 4 + Al(OH) 3 HOH + Al(SO 4 ) 1+2-3+1-1+1-3+2- 2 3 23 6 This neutralization can be used to determine the concentrations or molar masses of unknowns. If the right indicator is placed in an acid or a base it will turn colour at the instant of neutralization.

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Standardizing a Base - (Determining its concentration) When a solution of NaOH or KOH is prepared from its solid reagent it will react with water in the air as it is being massed. This means the mass of base measured is less than the recorded quantity. If a massed quantity of stable acid (one which doesn’t react with the atmosphere) is placed in a flask and dissolved in distilled water the concentration of the basic solution can be determined by measuring the volume of base needed to neutralize it.

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Magnetic stirrer Erlenmeyer flask buret

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0.10 - 0.30 g of potassium hydrogen phthalate distilled water few drops phenolphthalein Titrant - NaOH solution 22.52 mL 18.31 mL 4.21 mL m = 0.21 g M = 204.22 g/mol When the solution turns pink the number # of mol of acid = # of mol of base equivalence pt.

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HX + NaOHHOH + NaX 1+1-1+1-1+1-1+1- Given - m HX = 0.21g M HX = 204.22 g/mol V NaOH = 4.21 mL C NaOH = ? C b = 0.21 g/(204.22 g/mol )(0.00421 L) C b = 0.24 mol/L When the solution turns pink n HX = n NaOH m a /M a = CbVbCbVb Cb Cb = ma ma / M a / VbVb

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2.00 1.00 0.00 mL 0.80 0.70 0.78 0.76 0.74 0.72 Estimate - 0.77

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2.00 1.00 0.00 mL Measurements with burets must have 2 decimal places. Don’t record 1.1 instead record 1.10 The extra zero tells us the measuring instrument measures to the nearest tenth of a mL. The last digit of any measurement is an estimated value.

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Measuring the Concentration of a Vinegar Solution A measured volume of vinegar is placed in an Erlenmeyer Flask using a pipette. The standardized base from the 1st part of the experiment is placed in the buret

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Magnetic stirrer Erlenmeyer flask buret

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Measured vinegar solution HC 2 H 3 O 2 few drops phenolphthalein Titrant - NaOH solution 22.52 mL 18.31 mL 4.21 mL When the solution turns pink the number # of mol of acid = # of mol of base equivalence pt.

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Determining the Molar Mass of an Unknown Acid Mass out from 0.10 - 0.30 g of the unknown acid in an Erlenmeyer flask. Dissolve it in some distilled water then add a few drops of phenolphthalein. Place the standardized base in the burette. Measure the volume of base needed to reach the equivalence point. (End point is signaled by the solution turning and remaining pink)

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Magnetic stirrer Erlenmeyer flask buret

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0.10 - 0.30 g of unknown acid distilled water few drops phenolphthalein Titrant - NaOH solution of known concentration m = 0.21 g M = ? When the solution turns pink the number # of mol of acid = # of mol of base equivalence pt.

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