Applied Chemistry

Questions & Answers

INTRODUCTION In this experiment, the reaction between magnesium solid and hydrochloric acid will be studied. The rate of reaction and the quantity of reaction will be investigated. The factors that affect each of these will be determined by varying experimental conditions.

Many chemical reactions are known in which two substances react in precise mole ratios to form a known product in virtually 100% yield with no side-reactions or unexpected by-products. Such reactions may be studied conveniently by titration, the carefully-measured addition of a solution of one reactant to a known amount of the second reactant until that point at which the precisely correct mole ratio of the two reactants is reached. This point, called the end-point, may be determined with the use of an indicator. In this experiment we will study three acid-base reactions which fall into the category described above. In the first part, weighed samples of oxalic acid will be titrated with a solution of NaOH of unknown concentration. The end-point will be determined with an indicator which remains colorless so long as excess acid is present, but which turns pink when the first drop of excess NaOH is added. The molarity of NaOH can then be calculated. In the second part, a measured volume of vinegar (a solution of acetic acid) will be titrated with the same NaOH solution. Since the molarity of the NaOH solution is now known, the molarity of acetic acid in the vinegar can be calculated. Given the density of vinegar, the percent composition can also be determined. In the third part, weighed samples of an unknown monoprotic acid will be titrated with the standard NaOH solution. From the data gathered, the molar mass of the unknown acid will be determined.

Q-3 Calculate the minimum mass of air required for complete combustion of 1 kg of a fuel having the composition C = 92%, H₂ = 4%, O₂ = 2% and ash = 2% by weight.

Classify each reaction and give the name of all the chemical formula involved for each number. 1. Na2CO3(s) + SiO2(s) → Na2SiO3(l) + CO2(g) 2. 2 Mg(NO3)2(s) → 2 Mg(NO2)2(s) + O2(g) 3. 3 HNO2(aq) → 2 NO(g) + NO3-(aq) + H3O+(aq) 4. BaCO3(s) → BaO(s) + CO2(g) 5. 2 Eu2+(aq) + 2 H+(aq) → 2 Eu3+(aq) + H2(g) 6. [Ag(NH3)2]+(aq) + 2 CN-(aq) → [Ag(CN)2]-(aq) + 2 NH3(aq) 7. MgO(s) + 2 HCl(aq) → MgCl2(aq) + H2O(l) 8. CaO(s) + SO2(g) → CaSO3(s) 9. 2 NO(g) + O2(g) → 2 NO2(g) 10. N2(g) + 2 O2(g) → 2 NO2(g)

- A compound was analysed and found to contain40 g C, 53.3 g 0, and 6.7 g H. What is the empirical formula of the compound? (Atomic mass: C = 12.01 g/mol, O =16 g/mol, H = 1 g/mol)

1- Choose from the following: Liquid displacement method is used to determine: a- The density of solvent b- The density of liquid c- The volume of an irregular solid d- The volume of solvent

2- The following table shows the masses and densities for different substances. Which of these substance has the least volume?

4- Name the following apparatus: Name the following apparatus:

4. [Crowl 6-13] Liquid heptane is stored in a 100,000-L storage vessel that is vented directly to air. The heptane is stored at 25°C and latm pressure. The liquid is drained from the storage vessel and all that remains in the vessel is the air saturated with heptane vapor. a) Is the vapor in the storage vessel flammable? b) What is the TNT equivalent for the vapor remaining in the vessel? c) If the vapor explodes, what is the overpressure 50m from the vessel? d) What damage can be expected at 50m?

1. Estimate the upper and lower flammable limits of (a) propane, (b) octane, and(c) ethylene oxide. A mixture of 2% propane, 4% octane, and 0.5% ethyleneoxide is prepared. Is this mixture flammable?

3. [Crowl 6-12] The LFL for gasoline is 1.3vol% gasoline vapor in air. Whatevaporation rate of gasoline vapor (in kg/s) will result in a downwindconcentration ¼ of the LFL at 0.1km directly downwind from the release? Assume: Worst-case stability conditions latm and 25°C MW of gasoline vapor: 72g/mol Gasoline liquid specific gravity: 0.72 Lower heating value of gasoline: 44 MJ/kg

2. [Adapted from Crowl 6-9] A barbecue gas cylinder contains 25lb of butane. The cylinder accidentally falls over and ruptures, vaporizing the entire contents of the cylinder. The vapor cloud is ignited, and an explosion occurs. Estimate the overpressure from this explosion 100ft away. Using Table 6-9 in your textbook,what kind of damage is expected. What kind of safeguards could have been implemented in order to prevent this incident?

Q3. A 20 ml of a concentrated solution (A) are diluted to 100 ml. The solution obtained (B)is then diluted again with the same proportions. The concentration of the final solution (C) is c =0.45 g/L What is the concentration of the initial solution (A)?(Ref.1)

Q2. From a solution of concentration c = 80 g / L, how to prepare a 100 mL solution of concentration c = 20 g / L. How much stock solution should I use?(Ref.1)

Q5. True or false:The absorbance of a sample as measured by UV-visible spectrometry is inversely proportional to the concentration of the sample, so that as the concentration increases, the absorbance decreases.(Ref.2)

Q4. When a solution concentration is diluted to half, the absorbance of the diluted solution will:(Ref.2) a- remain constant. b. be duplicated c. be divided by two. d. be divided by four.

Q1. A solution has a mass concentration of 40 g / L. 20 mL of this solution are poured into a250 mL volumetric flask and diluted to 250 ml with water. What is the concentration of the new solution?(Ref.1)

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