Quantitative Analysis

Question 1

What is the formula for mass (using Mr and Moles)?

Answer 1

Mass = Moles x Relative formula mass

Question 2

What is the formula for Percentage Yield?

Answer 2

Percentage Yield = (Actual Yield/Theoretical Yield) x 100

Question 3

What is the formula for concentration?

Answer 3

Concentration = moles/volume

Question 4

What are the steps to calculating maximum mass?

Answer 4

1. Work out the relative formula masses for the two substances
2. Divide the Relative Formula Mass of the compound you WANT by the other one
3. Take the number you get and multiply by the mass you are given in the question

Question 5

What are the steps to calculating the empirical formula?

Answer 5

1. First you find out the moles of each substance by dividing the mass (in grams) by the Ar of the substance
2. Then you divide the moles of each substance by the smallest amount of moles

Question 6

What are the steps to calculating the molecular formula of a compound?

Answer 6

1. First calculate the empirical formula
2. Then work out the molar mass of the empirical formula
3. Use molecular formula molar mass/empirical formula molar mass (molecular formula molar mass is given in the question)
4. multiply the number that you got from molecular formula molar mass/empirical formula molar mass by the subscripts of the empirical formula

Question 7

Why is it not always possible to achieve 100% yield in a chemical reaction?

Answer 7

• Some of the product may be lost when it is seperated from the reactant mixture
• Some of the reactants may react in different ways to the expected reaction so we do not get the product we expected
• Reversible reactions may not go to completion

Question 8

What are the steps to calculating the percentage mass of an element in a compound?

Answer 8

1. First calculate the atomic mass of each element
2. Then you use Mass Percent = (Mr of element you want to find out/ Mr of compound) x 100