4.A compund is found to have(by mass)48.38% carbon,8.12% hydrogen and the rest oxygen.(What % is missing to make the sum 100 %?) That is,figure % oxygen.What is its empirical formula?

Take a 100 g sample which will give you

43.38 g Carbon
8.12 g hydrogen
and 100-43.38-8.12 = g oxygen.

Now convert each of the grams to moles.
43.38 g/atomic mass C = moles C.
8.12 g/atomic mass H = moles H.
g oxygen/atomic mass O = moles O.

Now find the ratio of these moles to each other. The easiest way to do this is to divide the smallest number by itself (which of course will give you 1.000), then divide the other number of moles of the other elements by that same small number. The result should be values that are very close to whole numbers. Round them to whole numbers and those are the subscripts for the molecule. Note: Do not round too much; e.g. round 1.05 to 1.00 and 2.15 to 2.00 but 1.5 or 1.4 or 1.6 are rounded to 1.5 (because then you multiply everything by 2 to get rid of the 1/2) and the other numbers become whole numbers, usually, too. Post your work if you get stuck.

To find the missing percentage and calculate the empirical formula, we need to follow these steps:

1. Calculate the percentage of oxygen in the compound:
The mass percentages of carbon and hydrogen sum up to 48.38% + 8.12% = 56.5%. Since the total mass percentage should be 100%, we can calculate the percentage of oxygen by subtracting 56.5% from 100%:
Oxygen % = 100% - 56.5% = 43.5%

2. Determine the empirical formula:
The empirical formula represents the simplest whole number ratio of atoms in a compound. To determine it, we need to find the ratio between the different elements.

Divide the mass percentages of each element by their atomic masses to get the number of moles:
Moles of carbon = (48.38% / atomic mass of carbon)
Moles of hydrogen = (8.12% / atomic mass of hydrogen)
Moles of oxygen = (43.5% / atomic mass of oxygen)

Next, find the simplest whole number ratio by dividing the moles of each element by the smallest number of moles calculated. Round the ratio to the nearest whole number.

3. Write the empirical formula using the ratios obtained:
The empirical formula is written using the element symbols and the mole ratio. For example, if the ratio is 2:4:1, the formula would be C2H4O.

Note: To provide the specific empirical formula, we would need the atomic masses for carbon, hydrogen, and oxygen.