Calculations Flashcards
What is relative atomic mass?
The elements mass number shown in the periodic table
Usually the biggest number
What is the molar mass of an element?
It’s relative formula mass in grams
What is molar mass measured in?
g/mol
What is one mole of any substance?
It’s relative formula mass
eg. Carbon has a relative mass of 12 so that equals 1 mole
24 would be 2 moles
How do you calculate the % of element in a compound?
Mass of that element divided by the mass of the whole compound then multiply it by 100
What is the steps to working out the empirical formula?
1) change percentages to grams
2) divide each by their relative masses
3) put the new numbers in a ratio
4) divide by the smallest number in ratio and write the new ratio
5) put it into your formula
What are 3 important steps to calculate the mass of a substance when it’s given?
- write out the balanced equation
- work out relative masses for the things you need
- divide by that number to 1g, then multiply by the number to get to the substance you need
How can you work out percentage of yield?
Actual yield / predicted yield X 100
What does a 100% yield mean?
You got all the product you expected to get
What does 0% yield mean?
No reactants were converted into product
A reversible reaction is where…?
The products of the reaction can react themselves to produce the original reactants
What can you use to separate artificial colours?
Use paper chromatography
How does paper chromatography work?
- extract colour and add a few drops of solvent
- put spots of coloured solution on the base line above level of solvent, then roll up sheet and put in beaker with solvent
- the solvent will then seep up the paper taking the dyes with it
What are the advantages of using machines to analyse unknown substances?
- sensitive
- very fast
- very accurate
What else can be used to identify substances?
Gas chromatography
What can gas chromatography separate out?
A mixture of compounds and helps identify the substances present
How does gas chromatography work?
- A gas is used to carry substances through column with solid material, travel at different speeds so are separated
- time taken to reach detector which identifies the substances is called the retention time
What can a gas chromatography column be linked to?
A mass spectrometer - known as GC-MS which can identify the substances leavening accurately
