Question

1. When heated, calcium carbonate gives off CO2 according to the following reaction: CaCO3(s) → CO2(g) + CaO(s) You perform this reaction in lab by heating a test tube containing CaCO3 and collect the CO2 over water for later analysis. You collect 20.3 mL of gas. What mass of CO2 have you collected? Assume the temperature and pressure of your lab is 25 °C and 1.00 atm. The vapor pressure of water at 25 °C is 24.0 Torr. (a) 35.4 mg (b) 36.5 mg (c) 611 mg (d) 877 mg (e) 26.9 g

2. At 25 °C, the Ksp of CaSO4 is 9.1×10–6 . How many of the following procedures will change the value of Ksp for CaSO4? I. presence of Na2SO4 in solution II. changing the temperature of the solution III. changing the amount of water in solution IV. presence of Ca(NO3)2 in solution (a) 0 (b) 1 (c) 2 (d) 3 (e) 4

Answer 1

Solution :-

Q1) volume of CO2 = 20.3 ml * 1 L / 1000 ml = 0.0203 L

Temperature = 25.0 C +273 = 298 K

Pressure of CO2 = 760 torr - 24.0 torr = 736 torr *(1 atm / 760 torr) = 0.9684 atm

Now lets calculate the moles of the CO2

PV= nRT

PV/RT = n

0.9684 atm * 0.0203 L / 0.08206 L atm per mol K * 298K = n

0.0008039 mol = n

So the moles of CO2 = 0.0008039 mol

Mass of CO2 = moles * molar mass

                       = 0.0008039 mol * 44.01 g per mol

                       = 0.0354 g

Lets convert it to mg

0.0534 g * 1000 mg / 1 g = 35.4 mg

So the correct answer is 35.4 mg

So the mass of CO2 produced = 35.4 mg

Q2)

CaSO4 ksp = 9.1*10^-6

How many of the following procedures will change the value of Ksp for CaSO4? I. presence of Na2SO4 in solution II. changing the temperature of the solution III. changing the amount of water in solution IV. presence of Ca(NO3)2 in solution

Na2SO4 contains the SO4^2- common ion therefore it will change the ksp

Changing the temperature causes the change in the solubility of the compounds

Changing the amount of water is also affects the ksp because the solubility is depends on the amount of water.

Ca(NO3)2 will add Ca^2+ ions therefore it can decrease the ksp

So the answer is option e = 4