"A chromium compound contains 28.4% sodium and 32.1% chromium by mass, while the rest is oxygen. What is the empirical formula of this compound?"

Start with the definition of empirical formula so we know what we are trying to work out. Empirical formula is the simplest whole-number ratio of elements in a compound. First, let us work out how much of the compound is oxygen. As a percentage, the compound must contain 39.5% as 100 - 28.4 - 32.1 = 39.5%If we set it out in a table it may be easier to work out: Na Cr OMass 28.4 32.1 39.5Mr 23 52 16Mol 1.2 0.6 2.4 Ratio 2 : 1 : 4Therefore, empirical formula = Na2CrO4First, write out the mass by percentage of each component. In the next row, write each elements molecular weight. To determine the molecular ratio of elements we must find the number of moles of each element. We will do this by using the moles = mass/Mr equation. So for Na, we find the moles by 28.4/23 to get 1.2 moles. The numbers in the third row give the ratio of elements in the compound. However, the empirical formula definition stated that we need it to be a whole-number ratio so we must divide all the numbers by our smallest number. We keep repeating this until we get a whole number ratio. In this case, the empirical formula came to Na2CrO4.

Related Chemistry A Level answers

All answers ▸

When 80.0cm^3 of 0.500 M hydrochloric acid was added to 1.75g of impure CaCO3, not all HCl reacts. The unreacted HCl required 22.4 cm^3 of a 0.500 M solution of NaOH for complete reaction. Calculate percentage by mass of CaCO3 in the impure sample.


How do you calculate the pH of a weak acid?


Explain the dipoles on the following covalent bonds: Cl-Cl, H-Cl


The bond angle in a molecule of ammonia (NH3) is 107 degrees so why, when part of a transition metal complex is the bond angle 109.5 degrees.


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences