CHEM131_S15_X1_Pract_Ans Montgomery College Takoma Park Silver Spring Campus CHEM1 31 – Spring 2015 Name: _____Answers_____. Exam I Multiple Choice Questions: (3 points each = 30 points) 1) A graduated cylinder is filled with 25.0 mL of water. A solid sample is dropped into the graduated cylinder and the 3 water rises to the 37.6 mL mark. What is the mass of the solid if its density is 2.81 g/cm ? A) 9.79 g B) 106 g C) 0.223 g D) 70.3 g E) 35.4 g ____________________________________________________________________________
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CHAPTER I THE PROBLEM AND ITS SETTTING Introduction Throughout the 20th century‚ plastics have been an essential part of the market industry. Most plastics are a combination of other organic and inorganic compounds; 20% of the content of a plastic is composed of additives. Biodegradable plastics are usually derived from proteins such as those that are present in a potato plant. Polymers are large molecules consisting of many repeating units‚ called monomers. Polymers can be made out of starch
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Discussion 2mol of HCL * V = 50 cm3 * 1 mol 50/2=V V=25 cm3 Volume needed to neutralise 50 cm3 of 1 mol dm-3 of NaOH is 25 cm3 of HCL b) Independent variable: Volume of HCL Dependent variable: Temperature of mixed solution Controlled variables: Volume of alkaline‚ Concentration of acid‚ Concentration of alkaline c) Burette d)Fix the burette into a burette holder securely. Pour HCL into the burette with a funnel until it reaches the 0.0cm3 mark. e)The risk of using plastic cup
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conservation of Mass lab is for me to attempt to verify the Law of Conservation of Mass. Procedure: Acid Base Neutralization 1. Using 2 modified‚ beral pipettes fill pipet an about 1/5 full of white vinegar and pipette B about 1/5 full of 1.0 M NaOh (sodium hydroxide). 2. Place the 2 Pipets on the beam balance and read and record the total mass of the 2 pipets. 3. Carefully telescope the stem of pipet A into the stem of pipette B without spilling any liquid. 4. Mix the solutions
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Hrxn= -55.8 KJ/mol Hrxn=qrxn / nLR qcal=CcalT qcal=-qrxn Ccal=mass x specific heat Hrxn=npHop - nr Hor qcal= [Ccal+ mass solid (ppt.) x specific heat of ppt.] x T RESULTS AND DISCUSSION The reaction of HCl and NaOH for calorimeter calibration brought about a 1°C change in temperature (from 29.5 °C to 30.5 °C). The results of the other groups’ calibration are found in TABLE A of the data sheet. The displacement of one metal by another (1M CuSO4 and 0.5g Zn)
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prepare buffer (grams) | | | Volume of buffer prepared (mL) | 100.0 | 100.0 | Molar concentration of HC2H3O2 in buffer (M) | 0.1 | 1.0 | Initial pH of buffer | | | Volume of 0.5 M NaOH to raise pH by 2 units (mL) | | | Volume of 0.5 M HCl to lower pH by 2 units (mL) | | | Volume of 0.5 M NaOH at equivalence point (mL) | | | Data Analysis 1. Write reaction equations to explain how your acetic acid-acetate buffer reacts with an acid and reacts with a base. 2. Buffer
Free PH Acid dissociation constant Acetic acid
Explain how a phenol can be separated from a mixture of a phenol and a neutral compound using the acid-base extraction method. 3. In this separation experiment‚ you first extract a carboxylic acid with NaHCO3(aq)‚ then extract a phenol with NaOH(aq). Can you reverse the order? Why or why not? 4. You perform each extraction twice‚ first with 1 mL and second with 0.15 mL. Why is the second extraction necessary? 5. What is the purpose of washing an ether solution with saturated NaCl
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(2 points) (c) Calculate the pH of a solution made by combining 40.0 milliliters of 0.14-molar HOCl and 10.0 milliliter of 0.56-molar NaOH. (2 points) (d) How many millimoles of solid NaOH must be added to 50.0 milliliters of 0.20 - molar HOCl to obtain a buffer solution that has a pH of 7.49? Assume that the addition of the solid NaOH results in a negligible change in volume. (2 points) (e) Household bleach is made by dissolving chlorine gas in water‚ as represented
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Analysis of the nitrogen content of lawn fertiliser 1. Aim To find the percentage by mass of available nitrogen‚ present as the ammonium ion‚ in a lawn fertiliser. 2. Materials 1.3g lawn fertiliser‚ finely ground 100ml standard sodium hydroxide solution (0.96M) 100ml standard hydrochloric acid (0.94M) Methyl red indicator 500mL de-ionised water Wash bottle containing de-ionised water Red litmus paper 2 × small funnels 250 mL volumetric flask 3 × 250mL conical flask 20mL pipette
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OH- Data: You will first add 6 drops of Ca( NO3)2 to a watch glass. Then add 6 drops of HCl then add 6 drops of NaOH. Analysis: Ca( NO3)2 ‚a white milky solution‚ 6 drops of an acid such as HCl is added which turns colorless‚ and the Ca2+ becomes less soluble‚ which shifts the equilibrium to the right by removing the OH-. After adding the NaOH to the solution turns back to the milky solution that it once was‚ the Ca2+ becomes more soluble‚ which shifts the equilibrium
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