1.2- Amounts of substances

Question 1

Give the definition of the mole

Answer 1

Amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12

Question 2

Give the definition of RAM

Answer 2

RAM is the average mass of one atom compared to one twelfth of the mass of one atom of carbon 12

Question 3

Give the definition of molecular mass

Answer 3

Molecular mass is the average mass of a molecule compared to one twelfth of the mass of one atom of carnon 12

Question 4

Give the 3 calculations equations containing moles for the 3 states of matter

Answer 4

Solids- Moles = Mass/Mr
Gases- PV =nRT
Liquids- moles = concentration x volume

Question 5

Give the formula for density

Answer 5

Density = mass/volume

Question 6

Give the definition of empirical formula

Answer 6

An emiprical formula is the simplest ratio of atoms of each element in the compound

Question 7

What is the general method for calculating empirical formula

Answer 7

. Divide each mass by the percentage of the atomic mass of the element
. For each of the answers divide the each by the smallest one
. Sometimes the numbers you will then calculate need to be multiplied to give whole numbers
. The whole numbers are the empirical formula

Question 8

What is a hydrated salt

Answer 8

A hydrated salt contains water of crystallisation

Question 9

Outine the method of heating in a crucible for hydrated calcium sulfate

Answer 9

.Weigh an empty clean dry crucible and lid
. Add 2g of hydrated calcium sulfate to the crucible and weigh again
. Heat strongly with a bunsen burner
. Weigh crucible and the contents again
. Heat cruibile and reweigh until you reach a consant mass

You should not use large amounts as decomposition is likely to be incomplete, the crucible needs to be dry otherwise a wet crucible would give an inaccurate result

Question 10

Give the formula for mass concentration

Answer 10

Mass concentration = mass/volume

Question 11

Outline the method for making a standard solution

Answer 11

. Weigh the sample bottle containing the required mass of solid on a 2dp balance

. Transfer to beaker and reweight sample bottle

. Record the difference in mass

. Add 100 cm3 of distilled water to the beaker , use a glass rod to stir and help dissolve the solid

. Can also heat gently to dissolve all the contents

. Pour solution into a 250cm3 flash via funnel

. Rinse beaker and funnel and add washing from the beaker and the glass rod to the volumetric flask

. Make up to the mark distilled water using a dropping pipette for last few drops

. Invert the flask several times to ensure uniform solution

Question 12

Outline the method for diluting a solution

Answer 12

. Pippete 25cm3 of original solution into a 250cm3 volumetric flask
. Make up to the mark with distilled water using a dropping pipette for the last few drops
. Invert flask several times to ensure uniform solution

Question 13

What is the formula for calculating a dillution

Answer 13

New diluted concentraton = original conc x orignal vol/ new diluted vol

Question 14

What are the safety and hazards for, irritants, corrosives, flammables, toxins and oxidising

Answer 14

Irritant- Dilute acids and alkalis, wear goggles
Corrosives- Stronger acids and alkalis, wear goggles
Flammable- Keep away from naked flame
Toxic- Wear gloves, avoid skin contact and wash hands after use
Oxidising- Keep away from flammable, easily oxidised materials

Question 15

What are limiting and excess reactants

Answer 15

Limiting reacants are the reactant which is given a fixed volume when reacting, and an excess reactant is used in excess with a volume greater than the experimental amount needed to react

Question 16

Give the formula for percentage yield and atom economy

Answer 16

Percentage yield = actual yield/ theoretical yield x 100

Percentage atom economy = Mass of useful products/ Mass of all reactants x 100

Question 17

Outline the method for carrying out a titration

Answer 17

. Rinse all of the equipment with the suitable solution
. Pippete 25cm3 of the alkali into the conical flask
. Touch the surface of alkali with the pippete to ensure the correct amount is added
. Add acid solution to the burette
.Make sure that the jet space is filled with acid
.Add a few drops on indicator
. Phenolphtalein goes from pink to colourless
.Methyl orange goes from yellow to red
. Add acid to the alkali while swirling the mixture and add dropwise at end point
.Note buretter reading
.Repeat titration until you get at least 2 concordant results, readings that are 0.1 within eachother
.Plot all of the results into a table

Question 18

Give the formula for the percentage uncertainty

Answer 18

Uncertainty%= 100 x uncertainty/ measurement made on apparatus