1. a)What is the empirical formula of a compound that has 55.3% K, 14.6% P, and

Question

1. a)What is the empirical formula of a compound that has 55.3% K, 14.6% P, and 30.1% O.

b) What is the molecular formula of a compound with empirical formula CH2 and molar mass 168 g/mol.                        

2. When a 0.0500 L sample of 0.500 M lead (II) nitrate is added to 0.0500 L of 0.500 M calcium sulfate in a coffee cup calorimeter at constant pressure, a temperature increase of 5.52 K is observed.

Pb(NO3)2(aq) + CaSO4(aq)   à   PbSO4(s) + Ca(NO3)2(aq)

3.Methanol (CH3OH) is used as a fuel in race cars. A) write a balanced equation for the combustion of liquid methanol in air. B) Calculate standard enthalpy    change for the reaction, assuming H2O(g) as a product. (Hint: find enthalpy of formation values on appendix C of your textbook). C) Calculate the heat produced by combustion per liter of methanol. The density of methanol is     0.791 g/ml.  

Calculate the Hrxn(in kJ/mol calcium sulfate reacted). The specific heat        for water is Cs= 4.18 J/gK. Assume volumes are additive and density of water        is 1.00 g/ml. (6pts)

Explanation / Answer

1)a)

Therefore, the empirical formula is K3PO4

1)b)Given Empirical formula = CH2

Molar mass = 168g/mol

Empirical formula mass = (1 x 12 + 2 x 1) = 14

Molecular formula = (Empirical fromula)n

n = Molar mass / Empirical formula mass = 168 /14 = 12

So molecular formula is C12H24

Element percentage atomic mass Relative number of atoms simplest ratio simplest whole number ratio Potassium 55.3% 39.1 55.3/39.1=1.4143 1.414/0.4714=3 3 Phosphorous 14.6% 30.97 14.6/30.97=0.4714 0.4714/0.4714=1 1 Oxygen 30.1% 16 30.1/16=1.88125 1.88125/0.4714=4 4

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