# chemistry.

posted by .

A chromium compound 28.4% by mass of sodium 32.1% by mass of chromium, the rest being oxygen. Determine the empirical formula of the compound?...Can any one help me for that?

• chemistry. -

Take a 100 g sample. In that 100 g sample there will be
28.4 g Na
32.1 g Cr
100-(32.1+28.4) = 39.5 g oxygen.

Now convert grams to moles.
moles Na = 28.4/approx 23 = 1.23
moles Cr = 32.1/approx 52 = 0.617
moles O = 39.5/approx 16 = 2.47

You need to look these the atomic masses in the periodic table and use the exact number. I'm just using these from memory.

Now you want to convert these moles to a ratio of small whole numbers. The easiest way to do that is to divide each by the smallest of the group, namely 0.617.
Therefore, ratios
Na = 1.23/0.617 = 1.99
Cr = 0.617/0.617 = 1
O = 2.47/0.617 = 4.00

Now round each to a whole number which gives Na = 2, Cr = 1, O = 4 so the empirical formula is
Na2CrO4.

• chemistry. -

How did you get 23,52, 16?

• chemistry. -

moles = grams/atomic mass.
The atomic mass of Na is 22.9897 which I rounded to 23.
The atomic mass of Cr is 51.99 which I rounded to 52.
The atomic mass of O is 15.999 which I rounded to 16.
Those are the numbers I told you that I used from memory and you should use the exact value as found in the periodic table.

## Similar Questions

1. ### Chemistry

Please check my answers for the following questions. THANK YOU. 1) The empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen is.... ANSWER: N2O 2) empirical formula of a compound that consists of 4.80 grams of carbon, …
2. ### chemistry

last one, i PROMISE A compound containing only C, H, O and Cr was subjected to combustion analysis. A sample of 10.88 mg produced 22.43 mg of CO2 and 4.59 mg of H2O. The chromium in the sample was precipitated as 14.09 mg of Ag2CrO4. …
3. ### ap chemistry

18. Answer the following question that relate to the analysis of chemical compounds. (a) A compound containing the elements C, H, N, and O is analyzed. When a 1.2359g sample is burned in excess oxygen, 2.241g of CO2(g) is formed. The …
4. ### chemistry

1.to calculate the percent by massof an element in a known compound, divide the mass of the element in one mole by the _______and multiply by 100%. A(n) _______formula represents the lowest________ratio of the elements in a compound. …
5. ### chemistry

An analysis of an unknown compound found it contained 40 g potassium, 52 g chromium and 56 g of oxygen. a) What is the empirical formula for this compound?
6. ### Chemistry

I need some help with some of these questions: The action of bacteria on meat and fish produces a poisonous compound called cadaverine. As its name implies, it stinks! It is 58.77 percent carbon, 13.81 percent hydrogen, and 27.40 percent …
7. ### Chemistry

I need some help with some of these questions: The action of bacteria on meat and fish produces a poisonous compound called cadaverine. As its name implies, it stinks! It is 58.77 percent carbon, 13.81 percent hydrogen, and 27.40 percent …
8. ### Chemistry

a compound of nitrogen and oxygen is 30.46% by mass N and 69.54% by mass O. the molar mass if the compound was determined to be 92g/mol. What is the empirical formula of the compound?
9. ### chemisrty

The ionic compound sometimes called uranium yellow is used to produce colored glazes for ceramics. It is 7.252% sodium, 75.084% uranium, and 17.664% oxygen. What is the empirical formula for this compound?
10. ### Chemistry

An unknown compound contains only carbon, hydrogen, and oxygen. Combustion analysis of the compound gives mass percents of 31.57% Carbon and 5.30% H. The molar mass is determined by measuring the freezing-point depression of an aqueous …

More Similar Questions