Final Examination for CHEM 101L, Fall 2017, Open Book with hints student\'s Name

Question

Final Examination for CHEM 101L, Fall 2017, Open Book with hints student's Name: Cheishaa Cak ignature:nowan 1. If a solution contains 0.50g Sio,, 0.25 g NaCI, and 1.25 g NH,CI, what is the mass percentage of NaCl in the mixture? Give your answer in two significant figures and show your work. 2. A mixture containing SiO,, NaCl, and NH,CI weighs 3.5 g. After subliming away the NH,CI from the mixture, the total weight of the mixture reduced to 2.7 g. What was the mass percentage of the NH,CI in the original mixture? 3. What is the name and chemical formula of the acid present in vinegar? Calculate the weight of HCI in grams needed to make 500 mL of 2M solution of HCL (Hint: Molar mass of HCI- 36.46 8 4. 5. Write the structure of salicylic acid, methyl alcohol and methyl salicylate

Explanation / Answer

1)

Solution contains 0.5 g SiO2 , 0.25 g NaCl , 1.25 g NH4Cl

Mass of the total mixture (solution) =  Mass of SiO2 + Mass of NaCl + Mass of NH4Cl

= 0.5 g + 0.25 g + 1.25 g

  = 2.0 g

Mass % of NaCl = (Mass of NaCl / Total Mass of the solution ) x 100

Mass % of NaCl = (0.25 g / 2.0 g ) x 100 = 25/2 = 12.5 %

2. Mass of the total mixture = 3.5 g

Mass of the mixture after sublimng the NH4Cl = 2.7 g

Mass of NH4Cl sublimed = 3.5 g - 2.7 g = 0.8 g

Mass % of NH4Cl = (Mass of NH4Cl / Total Mass of the solution ) x 100

= ( 0.8 g / 3.5 g)x 100 = 80/3.5 = 22.85 %

3) Vinegar is the liquid consisiting of 5-20% Acetic acid. It formula is CH3COOH.

4) We have to prepare the 500mL of 2 M HCl

Molarity = (mass of solute / mol.wt of the solute) * (1/Volume of solution in L)

2 M = (mass of HCl/36.46g)*(1/0.5 L) [ since 500 mL = 0.5 L]

mass of HCl = 2M * 36.46 g *0.5 L = 36.46 g

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