1) Determine the grams of the cation present in each of the following compounds.

Question

1) Determine the grams of the cation present in each of the following compounds. Show all work and place your answers in the space provided. i)

(1) 3.45 grams of Ca3(PO4)2

(2) 28.2 grams of Sr(OH)2

(3) 142.1 grams of NH4NO3

(2) Calculate the density (in g/L) of NO2 (g) at -38.1°C and 719. torr. Assume that the gas is acting ideal and

report your answer in the space provided.

(3) If 2.34 grams of ethane (C2H6) is combusted with 85.8 grams of molecular oxygen (O2), how many

grams of water will be produced? Report your answer using the correct number of sig figs in the

space provided.

(4) How many grams of sodium hydroxide need to be added to 15.0 milliliters of a 1.24 molar sodium

hydroxide solution in order to produce a 15.0 milliliters of a 2.34 molar sodium hydroxide solution?

Assume that the volume of the added sodium hydroxide is negligible and report your answer with the

correct sig figs in the space provided.

(5) A sample of copper(II) sulfate pentahydrate (CuSO4 5H2O, MM = 249.71 g/mol) contains 3.59 * 1024

oxygen atoms. Determine how many grams of copper(II) sulfate pentahydrate are present in the

sample and report your answer in decimal notation using the correct number of sig figs in the space

provided.

(6) The combustion of butene (C4H8 , MM = 56.12 g/mol) in the presence of molecular oxygen (O2, MM =

32.00 g/mol) produces carbon dioxide (CO2 , MM = 44.01 g/mol) and water (H2O, MM 18.02 g/mol)

according to the following balanced equation:

C4H8(g) + 6 O2(g) 4 CO2(g) + 4 H2O(l)

If 38.5 grams of butene are burned with excess molecular oxygen, what is the percent yield of the

reaction if 113 grams of carbon dioxide are collected in lab? Write your answer using the correct

number of sig figs in the box provided.

Please do it all of them hear ((DO NOT WRITE IN A PAPER))

Explanation / Answer

1. molar mass of Ca3(PO4)2 = 310 g/mol ; no of moles = 3.45/310 = 0.011 mol

1 mole contains avagadro number of molecules atoms or ions

Total no of cations = 3 x 6.022 x 10^23 x 0.011 = 1.987 x 10^22 cations

molar mass of Sr(OH)2 = 121 ; no of moles = 28.2/121 =0.233 mol

1 mole contains avagadro number of molecules atoms or ions

Total no of cations = 1 x 6.022 x 10^23 x 0.233 = 1.403 x 10^23 cations

molar mass of NH4NO3 = 80 ; no of moles = 140/80 =1.75 mol

1 mole contains avagadro number of molecules atoms or ions

Total no of cations = 1 x 6.022 x 10^23 x 1.75 = 1.053 x 10^24 cations

2. d = P x MW / (R x T) (MW is the molecular wt)

719 torr = 0.946 atm and T = 273-38.1 = 234.9 K R =0.0821atm.l/(mol k) MW = 46

d= 0.946x46/(0.0821x234.9) g/L = 2.256 g/L

3. C2H6 + 2O2 ====> 2CO2 + 3H2O

mol of ethane = 2.34/30 = 0.078 mol of oxygen = 85.8/32 = 2.68

Clearly ethane is the limiting reagent : 1 mol of ethane gives 3 moles of water

0.078 moles of ethane gives 0.234 moles of water ; wt = 0.234 x 18 = 4.212 g

4. Molarity = no of moles / volume of water in L = wt / (mol wt x vol in L)

1.24 = wt/(40 x 0.015 L) ; wt of NaOH = 1.24 x 40 x 0.015 = 0.744 g

2.34 = wt / (40 x 0.015) ; wt of NaOH = 2.34 x 40 x 0.015 = 1.404 g

5. 1 mol contains avagadro number of atoms

No. of moles = 3.59 x 10^24/6.022 x 10^23 = 5.96 mol

MM = 249.71 g/mol ; wt = 5.96 x 249.71 g = 1488.271 g

6. C4H8(g) + 6O2(g) ==> 4CO2(g) + 4H2O(g)

38.5 g of butene = 38.5/52 mol = 0.74 mol

1 mol of butene produces 4 mol of carbondioxide

0.74 mol produces 4x0.74 = 2.96 mol of CO2 = 130.24 g of CO2 theoritically

collected in lab = 113 g

Percent yield = actual / theoritical x 100 = 113/130.24 x 100 = 86.76 %

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