Question

76

What is the total sample size (in grams) for a sample of ethanol (CH₃CH₂OH) which contains 2.51 g of oxygen?

77.

What is the total sample size (in grams) for a sample of sodium nitrite which contains 3.54 g of oxygen?

Answer 1

First we have to calculate the molecualr weight of the compounds:

MW(CH3CH2OH) = 46g/mole

MW(NaNO2)= 69g/mole

Atomic weight of the oxygen is 16g/mole, that means

1mole of O -------- weights------16g

X --------------------------------------- 2,51g

X=2,51g*1mole/16g= 0,16 mole of O

In the compound 1 mole of CH3CH2OH we have 1 mole of Oxygen, so if i have 0,16mole of O we will have 0,16mole of CH3CH2OH. Now, with the molecular weigth of the compound we make the cahnge to grams.

1mole of CH3CH2OH ---------weights------- 46g

0,16mole---------------------------------------------X

X= 7,36g

So the weight of the complete sample of CH3CH2OH will be 7,36g.

In the case of NaNO2.

We have 3,54g of oxygen with the atomic weight we change it to moles.

1 mole of O -------- 16g

X ---------------------- 3,54g

X= 0,22 mole

1 mole of NaNO2 -------conteins-------- 2moles of Oxygen

X -------------------------------------------------- 0,22mole

X= 0,11mole of NaNO2

1 mole of NaNO2 --------weights------69g

0,11mole ------------------------------------ X

X=7,63g

So we will have a 7,63g of NaNO2.