can you help me w/ this problem please (:?

Question

Find the percentage composition of a compound that contains 1.51 g of chromium, 1.13 g of potassium, and 1.62 g of oxygen in a 4.26-g sample of the compound. Please explain how you did it too (: thanks!!

Answer 1

You need a periodic table (see source below).

The atomic weight is g/mol. (see the periodic table below and click on the element (Cr K O)).

Cr X + K X + O Z

x = 1.51g / 51.9961 g/mol = 0.029 mol

y = 1.13g / 39.0983 g/mol = 0.029 mol

z = 1.62g / 15.9994 g/mol = 0.101 mol

Finally, you just need to find the ratio between these 3 numbers.

As percentage: 0.029 / 0.159* = 18.25% Cr and 18.25% K
0.101 / 0.159 = 63.5% O

*0.159 = sum of x + y + z mol.

From wikipedia:

"The mole is useful in chemistry because it allows different substances to be measured in a comparable way. Using the same number of moles of two substances, both amounts have the same number of molecules or atoms. The mole makes it easier to interpret chemical equations in practical terms. Thus the equation:

2H2 + O2 → 2 H2O

can be understood as "two moles of hydrogen plus one mole of oxygen yields two moles of water."

Answer 2

take the mass of each element and divide by the total mass of the entire compound and multiply by 100%

%Cr = 1.51 g Cr / 4.26 g compound x 100% = 35.4% Cr
%K = 1.13 g K / 4.26 g compound x 100% = 26.5% K
%O = 1.62 g O / 4.26 g compound x 100% = 38.0% O

Answer 3

divide each individual weight by the total weight (4.26 g) then multiply by 100 to get a %.
(1.51/4.26) * 100=35.45% Chromium
(1.13/4.26) * 100=26.53% Potassium
(1.62/4.26) * 100=38.02% Oxygen

thats how you do percent composition by weight

Answer 4

1.51 / 4.26 (x 100) = Cr%
1.13 / 4.26 (x 100) = K%
1.62 / 4.26 (x 100) = O%

In other words, part / whole (x 100) = %