# Question #500f0

##### 1 Answer

#### Explanation:

The first thing to do is to convert the total pressure of the mixture from *atmospheres* to *torr* by using the conversion factor

#color(blue)(ul(color(black)("1 atm " = " 760 torr")))#

As you can see, the total pressure of the mixture will be equal to

#P_"total" = "760 torr"#

Now, **Dalton's Law of Partial Pressures** states that the total pressure of a gas mixture is equal to the **sum** of the individual partial pressures of the gases that make up the mixture.

In other words, the partial pressures of the three gases must amount to the total pressure of the mixture.

#P_"total" = P_ ("CO"_ 2) + P_ ("N"_ 2) + P_( "O"_ 2)#

You can thus say that the aprtial pressure of oxygen gas will be equal to

#P_( "O"_ 2) = P_"total" - (P_ ("CO"_ 2) + P_ ("N"_ 2))#

In your case, you will have

#P_ ("CO"_ 2) + P_ ("N"_ 2) = "593.425 torr" + "0.055 torr" = "593.480 torr"#

Keep in mind that the value must be rounded to **three decimal places**.

The partial pressure of oxygengas will thus be

#color(darkgreen)(ul(color(black)(P_ ("O"_ 2) = "760 torr" - "593.480 torr" = "166.520 torr")))#

The answer must also be rounded to **three decimal places** because **constant**, meaning that we defined

Thsi implies that you can use *as many decimal palces* with this value as you have for your actual data.

In other words, you have

#color(darkgreen)(ul(color(black)(P_ ("O"_ 2) = "760.000 torr" - "593.480 torr" = "166.520 torr")))#

We can use

Finally, keep in mind that when working with **addition or subtraction**, like we are doing here, the number of *significant figures* is always given by the number of value with the **least number of decimal places**.

#"593.425 torr " -># sixsig figs,threedecimal places#"0.055 torr " -># twosig figs,threedecimal places

This is why the answer must be rounded to **three decimal places**, not to two significant figures.