Chemistry Problems

Assignment-30 points! All work must be shown neatly for full credit.

Titration of Mg and HCl with NaOH

1) If 0.0150 mol of a metal was reacted with 30.0 mL or 4.00 M HCl. Once the reaction completed, some water and 2 drops of phenolthalein were added. The isolution was then titrated with 1.20 M NaOH. It took 25.00 mL of NaOH to reach the pale pink end point. Given above information, answer the following:

a) How many moles of HCl were initially present?

b) How many moles of HCl were in excess?

c) How many moles of HCl reacted with NaOH?

d) Write balanced chemical equation

_____ M (s) + ____ HCl(aq) → ___ MCl__ (aq) + H2(g)

Copper in Brass Analysis

Three standard solutions of CuSO4.5H2O were prepared as follows: Add 1.200 g, 2.400g, and 3.500g CuSO4.5H2O to a 50.0 mL volumetric flask and fill to the mark with distilled water. The absorbance values obtained at 620 nm were 0.105, 0.215, and 0.322 respectively. The unknown brass sample (grams=0.798 g) containing Cu+2 was then placed in spectrophotometer and absorbance value of 0.298 was obtained. Calculate the following:

a) Molarity of all three solutions. The molar mass of CuSO4.5H2O is 249.7 g/mole.

b) Slope and equation of line.

c) Molarity of Cu+2 in an unknown sample.

d) Grams of Cu+2

e) % Cu+2 in Brass sample

Molecular Weight of a Gas Using the Ideal Gas Equation

The unknown sample of volatile liquid was heated to evaporation and vapor collected in an Erlenmeyer flask. The mass of the vapor/gas collected was 0.789 g at 24 degree celcius. The volume of Erlenmeyer flask was 231 mL. The recorded barometric pressure was 753 Torr. Calculate molar mass of the unknown.