Chem Lab II Finale
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A solution is standardized to determined the concentration of another solution of unknown concentration
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Why is a solution standardized?
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A substance that has a known high degree of purity, a relatively large molar mass, is nonhygroscopic, and reacts in a predictable way.
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What is a primary standard?
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When a substance is hygroscopic it means that it absorbs water vapor readily. Solid NaOH is hygroscopic, so it therefore can not be a primary standard
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What does it mean for a substance to be hygroscopic? Give an example
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A titrant is the liquid that is dispensed from a buret and the analyte is the liquid in the flask. In experiment 8, the titrant was NaOH and the analyte was KHP
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What is a titrant? What is an analyte? In experiment 8 which substance was the titrant and which was the analyte ?
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The equivalence point is when the moles of the base added are exactly equal to the moles of acid present in the flask. The endpoint is the point when the the indicator being used changes colors. The endpoint is a visual indicator of when the moles of the base are equal to the moles of the acid and that is why we detected the endpoint instead of the equivalence point. The human eye can not see the equivalence point.
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What is an equivalence point and what is an endpoint? Why did we detect the endpoint and not the equivalence point in experiment 8?
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An acid-base reaction. The generic formula is: a base + an acid ---> water + a salt
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What is a neutralization reaction?
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HA ( e.g. HCl). The mole ratio of strong acid to base is 1:1
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What does monoprotic mean?
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H2A (e.g. H2SO4). The mole ratio strong acid to base is 1:2.
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What does diprotic mean?
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CH3COOH
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What is another name for acetic acid?
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We wait to allow for drainage and all of the solute to dissolve.
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When using a volumetric flask, why do we wait before filling to the graduation mark on the flask?
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Molar absorption
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In the Beer's Law equation, A = ?bc, what quantity is represented by "?"?
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- Concentration of absorbing substances in the sample - The thickness of the sample - The chemical characteristics of the absorbing species - When the sample is in solution, the relationship btw. these factors is expressed using Beer's Law.
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What factors does the amount of light of a specific wavelength absorbed by a sample depend on? What is used to express the relationship between these factors?
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A solution is a homogenous mixture of two or more substances. The two components are a solute and a solvent
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What is a solution and what are its two components?
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When the amount of solute is expressed in moles and the amount of solution in liters, the concentration term is molarity (M): moles of solute/liter of solution
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Molarity
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mass of solute/total solution mass
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Mass percent
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moles of solute/kilograms of solvent
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Molality (m)
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moles of component/total moles all components
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Mole fraction
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A standard solution is a solution for which the concentration is known exactly
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What is a standard solution?
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An alum is a hydrated double sulfate salt.
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What is an alum?
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Molality expresses the concentration as moles of solute per kilogram of solvent, while molarity expresses the concentration as moles of solute per liter of solution.
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What is the significant difference between molality (m) and molarity (M)?
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M2(SO4)3X2SO4 • 24H2O - Where M is aluminum or a different trivalent metal, and X is an group I metal, or some other monovalent metal.
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What is the general formula for alum?
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The water molecules are more strongly hydrated to the trivalent cation. This is because the trivalent cation has a higher-charge and the higher the charge the stronger the attraction.
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In an alum, are the water molecules more strongly hydrated to the monovalent cation or the trivalent cation? Explain
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First the water would evaporate, then salts would form, then it would completely evaporate.
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What might you expect to happen to the alum if it were heated to a high temperature?
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Fold paper into quarters, put in funnel for gravity and wet slightly
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What is the technique for securing a piece of filter paper into a funnel for gravity filtration?
