1). Calculate the mass of hydrogen peroxide needed to obtain 0.460 L of oxygen gas at STP 2H2O2(aq) → 2H2O(l) + O2(g)

2) 1.Use the reaction shown to calculate the mass of iron that must be used to obtain 0.500 L of hydrogen at STP.
3Fe(s) + 4H2O(l) → Fe3O4(s) + 4H2(g)

1) 1.39 grams H2O2

2) 0.933 grams Fe

Explanation:

Step 1: Data given

Volume of oxygen = 0.460 L

STP = 1 atm and 273 K

Step 2: The balanced equation

2H2O2(aq) → 2H2O(l) + O2(g)

Step 3: Calculate the number of moles O2

p*V = n*R*T

⇒with p= the pressure = 1 atm

⇒with V = the volume = 0.460 L

⇒with n = the number of moles = TO BE DETERMINED

⇒with R = the gas constant = 0.08206 L*atm/mol*K

⇒with T = the temperature = 273 K

n = (p*V)/(R*T)

n = (1 * 0.460)/ (0.08206*273)

n = 0.0205 moles moles

Step 4: Calculate moles H2O2

For 2 moles H2O we'll have 2 moles H2O and 1 mol O2

For 0.0205 moles O2 we'll need 2*0.0205 = 0.041 moles H2O2

Step 5: Calculate mass H2O2

Mass H2O2 = moles H2O2 * molar mass H2O2

Mass H2O2 = 0.041 moles * 34.01 g/mol

Mass H2O2 = 1.39 grams

Step 1: Data given

Volume of hydrogen = 0.500 L

STP = 1 atm and 273 K

Step 2: The balanced equation

3Fe(s) + 4H2O(l) → Fe3O4(s) + 4H2(g)

Step 3: Calculate the moles of H2

p**V = n*R*T

⇒with p= the pressure = 1 atm

⇒with V = the volume = 0.500 L

⇒with n = the number of moles = TO BE DETERMINED

⇒with R = the gas constant = 0.08206 L*atm/mol*K

⇒with T = the temperature = 273 K

n = (p*V) / '*T)

n = (1 * 0.500) / (0.08206 * 273)

n = 0.0223 moles

Step 4: Calculate moles Fe

For 3 moles Fe we need 4 moles H2O to produce 1 mol Fe3O4 and 4 moles H2

For 0.0223 moles H2 we'll need 0.0223 *3/4 = 0.0167 moles Fe

Step 5: Calculate mass of Fe

Mass Fe = moles Fe * atomic mass Fe

Mass Fe = 0.0167 moles * 55.845 g/mol

Mass Fe = 0.933 grams Fe

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