1) **Answer:**

**moles of oxygen (n) = 1.86 moles**

**Explanation:**

according to Boyle's law the formula to solve this problem is:

**PV=nRt**

when P is the pressure which equal 1.25 atm

and V is the volume which equal 37.5 L

n is the number of moles which we need to calculate it

R is constant which equal 0.082

t is the temperature in kelvin

By substitution:

1.25*37.5 = n * 0.082 * 307

**So n = 1.86 moles**

**2) Answer:**

**the volume of oxygen gas = 34 L**

**Explanation:**

at standard temperature and pressure (STP) 1 mole of gas will equal = 22.4L

So when we have 1.5 moles of oxygen at standard temperature and pressure (STP) so we will estimate it like that

1.5 moles *22.4 L/ 1 mole = approximately **34 L**

**3) Answer:**

The volume of H2 = **2.29 L**

**Explanation:**

according to the Balanced equation we can see that the molar ratio between Zn and H2 1 : 1

so to know the number of moles of H2 we will get it for Zn first :

number of moles Zn = mass of Zn / molar mass Zn

= 5.98 / 65.39 =0.0914 moles

so number of moles H2 = 0.09 moles

by substitution in the following formula:

**PV = nRT**

0.978 * V = 0.09 * 0.082 * 298

so The volume of H2 = **2.29 L**

**4) Answer:**

Volume of O2 = ** 1.4 L**

**Explanation:**

first we have to balance the equation:

**2Na2O2 +2CO2 → 2Na2CO3 + O2**

**2 mole CO2 give 1 mole of O2 so **the molar ratio is 2:1

at S**TP **1 mole of gas will equal = 22.4 L

??? moles of CO2 = 2.8

n CO2 = 0.125 moles so n O2 = 0.125 /2 = 0.0625 moles

so when 1 mole of as = 22.4

0.0625 moles O2 = ???

Volume of O2 =0.0625 moles * 22.4 L/ 1 mole

=** 1.4 L**

**5) Answer:**

the initial quantity of sodium metal used** = 17.2 **gram

**Explanation:**

at S**TP **1 mole of gas will equal = 22.4 L

so moles of H2 equal ?? when 8.40 liters of H2 gas were produced

so moles of H2 = 8.4/22.4 =0.375 moles

**and according to the balanced equation the molar ratio between H2 ans Na is 1 : 2 **

so number of moles for Na = 0.375 *2 = 0.75 moles

to get the initial quantity of sodium metal (mass Na) = number of moles * molar mass

mass Na = 0.75 moles * 23 gm/mole**= 17.25 **

**6) Answer:**

**False**

**Explanation:**

**because **STP means standard temperature and pressure. and the Standard temperature must be 273 K and the standard pressure must be 1 atm but in the question the temperature is 298 K not 273 K so , It is not a standard temperature

**7) Answer:**

**22.4 liters**

**Explanation:**

1 mole of gas will equal = 22.4 L

because at the Standard temperature must be 273 K and the standard pressure must be 1 atm

so V = nRT/P

=1 mole * 0.082 * 273 K / 1 aTm

**= 22.4 liters**